DISPATCH Working Group J.J. Garcia Aranda
J. Perez Lajo
Internet Draft L.M. Diaz Vizcaino
Intended status: Standards Track Alcatel-Lucent
Expires: July 2011 C. Barcenilla
J. Salvachua
J. Quemada
Univ. Politecnica de Madrid
January 25, 2011
The Quality for Service Protocol
draft-aranda-dispatch-q4s-00.txt
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on July 25, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
Garcia Aranda Expires July 25, 2011 [Page 1]
Internet-Draft The Quality for Services Protocol January 2011
carefully, as they describe your rights and restrictions with
respect to this document.
Abstract
This memo describes an application level protocol for the standard
communication of e2e QoS compliance information using a protocol
based on Hypertext Transfer Protocol (HTTP), which forms the basis
for the World Wide Web, and Session Description Protocol (SDP).
Quality HTTP (Q4S) provides a mechanism for latency, jitter,
bandwidth an packet loss negotiation and monitoring, alerting
whenever one of the negotiated conditions is violated.
Implementation details on the actions to be triggered upon
reception/detection of QoS alerts exchanged by the protocol are out
of scope of this draft, it is application dependant (e.g. increase
quality, reduce bit-rate) or even network dependant (e.g. change
connection's quality profile).
Table of Contents
1. Introduction......................................... 4
1.1. Motivation...................................... 5
1.2. Summary of Features............................... 6
2. Terminology ......................................... 7
3. Overview of Operation................................. 7
3.1. Protocol Phases.................................. 8
3.1.1. Handshake Phase.............................. 9
3.1.1.1. Description of Quality parameters inside SDP. 12
3.1.2. Quality negotiation phase..................... 16
3.1.2.1. Stage 0: Measurement of latencies and jitters 17
3.1.2.1.1. Round Trip Time calculation........... 19
3.1.2.1.2. Jitter calculation.................. 19
3.1.2.1.3. Packet loss calculation.............. 20
3.1.2.1.4. Communication of results............. 20
3.1.2.1.5. Constraints not reached.............. 22
3.1.2.1.6. Constraints not reached with Policy server
involved ................................... 25
3.1.2.1.7. Constraints reached ................. 26
3.1.2.2. Stage 1: Measurement of bandwidth and packet loss
............................................. 29
3.1.2.2.1. Constraints not reached.............. 32
3.1.2.2.2. Constraints not reached with Policy server
involved ................................... 36
Garcia Aranda Expires July 25, 2011 [Page 2]
Internet-Draft The Quality for Services Protocol January 2011
3.1.2.2.3. Constraints reached ................. 36
3.1.2.3. QoS Level out of range................... 37
3.1.2.4. QoS Level increments without changes in network
behaviour..................................... 39
3.1.2.5. Trigger an application in combination with HTTP39
3.1.3. Continuity phase............................ 40
3.1.3.1. Normal mode............................ 41
3.1.3.2. Sliding window mode...................... 43
3.2. Dynamic constraints and flows...................... 45
3.3. Qos-level downgrade operation...................... 46
3.4. Sanity check of Quality sessions................... 47
4. Q4S messages........................................ 48
4.1. Requests....................................... 48
4.2. Responses...................................... 49
4.3. Header Fields................................... 51
4.3.1. Specific Q4S Request Header Fields............. 51
4.3.2. Specific Q4S Response Header Fields ............ 52
4.4. Bodies ........................................ 53
4.4.1. Encoding................................... 53
5. General User Agent behavior. .......................... 54
5.1. Roles......................................... 54
5.2. Multiple Quality sessions in parallel............... 54
5.3. General client behavior .......................... 55
5.3.1. Generating requests.......................... 56
5.4. General server behavior .......................... 56
6. Q4S method definitions ............................... 58
6.1. BEGIN......................................... 58
6.2. GET........................................... 58
6.3. READY......................................... 59
6.4. PING.......................................... 59
6.5. DATA.......................................... 59
6.6. QOS-ALERT...................................... 60
6.7. CANCEL ........................................ 60
7. Response codes...................................... 61
7.1. 100 Trying..................................... 61
7.2. 200 OK ........................................ 61
7.3. Redirection 3xx................................. 61
7.4. Request Failure 4xx.............................. 61
7.4.1. 400 Bad Request............................. 61
7.4.2. 404 Not Found............................... 61
7.4.3. 405 Method Not Allowed....................... 62
7.4.4. 406 Not Acceptable .......................... 62
7.4.5. 408 Request Timeout.......................... 62
7.4.6. 412 A precondition has not been met ............ 62
7.4.7. 413 Request Entity Too Large.................. 62
7.4.8. 414 Request-URI Too Long...................... 62
7.4.9. 415 Unsupported Media Type.................... 62
Garcia Aranda Expires July 25, 2011 [Page 3]
Internet-Draft The Quality for Services Protocol January 2011
7.4.10. 416 Unsupported URI Scheme................... 63
7.5. Server Failure 5xx............................... 63
7.5.1. 500 Server Internal Error..................... 63
7.5.2. 501 Not Implemented.......................... 63
7.5.3. 503 Service Unavailable...................... 63
7.5.4. 504 Server Time-out.......................... 63
7.5.5. 505 Version Not Supported..................... 64
7.5.6. 513 Message Too Large........................ 64
7.6. Global Failures 6xx.............................. 64
7.6.1. 600 session not exist........................ 64
7.6.2. 601 quality level not allowed ................. 64
7.6.3. 603 Session not allowed...................... 64
7.6.4. 604 authorization not allowed ................. 64
8. Implementation Recommendations......................... 64
8.1. Default client constraints........................ 64
8.2. Bandwidth measurements........................... 65
8.3. Packet loss measurement resolution ................. 65
8.4. Measurements and reactions........................ 65
8.5. Scenarios...................................... 66
8.5.1. Client to ACP............................... 66
8.5.2. Client to client............................ 67
9. Security Considerations............................... 67
10. IANA Considerations................................. 68
11. Conclusions........................................ 71
12. References ........................................ 72
12.1. Normative References............................ 72
12.2. Informative References .......................... 73
13. Acknowledgments.................................... 74
14. Authors' Addresses.................................. 75
1. Introduction
The World Wide Web (WWW) is a distributed hypermedia system which
has gained widespread acceptance among Internet users. Although WWW
browsers support other, preexisting Internet application protocols,
the native and primary protocol used between WWW clients and servers
is the HyperText Transfer Protocol (HTTP) (RFC 2616 [1]). The ease
of use of the Web has prompted its widespread employment as a
client/server architecture for many applications. Many of such
applications require the client and the server to be able to
communicate each other and exchange information with certain quality
constraints.
Quality in communications at application level consists of four
measurable parameters:
Garcia Aranda Expires July 25, 2011 [Page 4]
Internet-Draft The Quality for Services Protocol January 2011
o Latency: The time a message takes to travel from source to
destination. It may be approximated to RTT/2 (Round trip time),
assuming the networks are symmetrical.
o Jitter: latency variation. There are some formulas to calculate
Jitter, and in this context we will consider the statistical
variance formula.
o Bandwidth: To assure the quality, a protocol MUST assure the
availability of bandwidth needed by the application.
o Packet loss: The percentage of packet loss is closely related
to bandwidth and jitter. Affects bandwidth because a high
packet loss implies sometimes retransmissions that also
consumes extra bandwidth, other times the retransmissions are
not achieved ( for example in video streaming over UDP) and the
information received is less than the required bandwidth. In
terms of jitter, a packet loss sometimes is seen by the
destination like a larger time between arrivals, causing a
jitter growth.
Q4S provides a mechanism for quality monitoring and it is based on
HTTP and SDP in order to be easily integrated in WWW, but it may be
used by any type of application, not only those based on HTTP.
Quality requirements may be needed by any type of application that
communicates using any kind of protocol, especially those which have
real-time constraints.
Q4S is an application level Client/Server protocol which tries to
measure continuously session quality for a given flow (or set of
flows), end-to-end and in real-time; raising an alert if quality
parameters are below a given threshold. The thresholds of each
application are different, depending on the nature of each
application. Q4S does not describe either the actions carried out to
deal with the alert or how to implement them.
Q4S is session-independent from the application flows, in order to
minimize the impact on them. To perform the measurements, two
control flows are created on either direction (forward and reverse).
1.1. Motivation
Monitoring quality of service (QoS) in computer networks is useful
for several reasons:
o Enable real-time services and applications to verify whether
network resources achieve a certain QoS level.
Garcia Aranda Expires July 25, 2011 [Page 5]
Internet-Draft The Quality for Services Protocol January 2011
o Monitoring helps real-time services and applications to run
through the Internet, allowing the existence of Application
Content providers (ACPs) which offer guaranteed real-time
services to the final users.
o Monitoring also applies to Peer to Peer (P2P) real-time
applications
o Enable ISPs to offer QoS to any ACP or final user application
in an accountable way
o Enable e2e negotiation of QoS parameters, from any ISP to any
ISP.
A protocol to monitor QoS must address the following issues:
o Must be ready to be used in conjunction with current standard
protocols and applications, without forcing a change on them.
o Must have a formal and compact way to specify quality
constraints of the desired application to run.
o Must have measurement mechanisms avoiding application
disruption.
o Must have specific messages to alert about the violation of
quality constraints in different directions (forward and
reverse), because network routing may not be symmetrical, and
of course, quality constraints may not be symmetrical.
o Must Protect the data (constrains, measurements, QoS levels
asked to the network) in order to avoid the injection of
malicious data in the measurements.
1.2. Summary of Features
Quality for Service is a message-oriented communication protocol
that can be used in conjunction with any other application-level
protocol.
The benefits in quality enhancement provided by Q4S can be used by
any type of application that uses any type of protocol for data
transport. It provides a quality monitoring scheme to any
communication that takes place between the client and the server,
not only the Q4S communication itself.
Garcia Aranda Expires July 25, 2011 [Page 6]
Internet-Draft The Quality for Services Protocol January 2011
Q4S does not establish multimedia sessions and it does not transport
application data. The type of use and kind of protocol of this
quality communication is application dependant and can be whatever.
Q4S doesn't force any particular protocol or way of using of the
quality connection.
Q4S session lifetime is composed of four phases with different
purposes, and inside each phase a negotiated measurement procedure
is used. Different measurement procedures can be used inside Q4S
(although for compatibility reasons a default measurement mechanism
is defined). Basically, Q4S only defines how to transport SLA
information and measurement results as well as providing some
mechanisms for alerting.
Q4S MUST be executed just before starting a client-server
application which needs a quality connection in terms of latency,
jitter, bandwidth and packet loss. Once client and server have
succeeded in establishing communication under quality constraints,
the application can start, and Q4S continues measuring and alerting.
During the lifetime of the quality session, the protocol stays in a
special state in which it periodically renews the session and alerts
if the measurements of quality parameters do not meet the negotiated
application requirements.
The quality parameters can be suggested by the client in the first
message, but the server can accept these parameter values or force
others. The server is in charge of deciding the final values of
quality connection.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119 [3].
3. Overview of Operation
This section introduces the basic operation of Q4S using simple
examples. This section is of tutorial nature and does not contain
any normative statements.
Garcia Aranda Expires July 25, 2011 [Page 7]
Internet-Draft The Quality for Services Protocol January 2011
3.1. Protocol Phases
All elements of the IP network contribute to the quality in terms
of latency, jitter, bandwidth and packet loss. All these elements
have their own quality policies in terms of priorities, traffic
mode, etc. and each element has its own way to manage the quality.
The purpose of a quality connection is to establish an end-to-end
communication with enough quality for the application.
To monitor negotiated SLA compliance, four phases are defined
o Handshake phase: in which the server is contacted by the client
and in the answer message the quality constraints for the
application is communicated.
o Negotiation phase: in which the quality of the connection is
measured in both directions (latency, jitter, bandwidth and
packet loss), and Q4S messages are sent in order to alert when
the quality does not match the constraints. This phase is
iterative until quality constraints are reached or the session
is cancelled after checking that the quality constraints are
impossible to reach. Just after reaching the quality
requirements, Q4S provides a simple optional mechanism to start
the application which will benefit from quality connection,
using HTTP.
o Continuity phase: in which quality is continuously measured. If
quality becomes degraded, an alert shall be released. New
measurements may follow up to a negotiated maximum before
moving to Termination phase. In this phase the measurements
MUST avoid disturbing application by consuming network
resources.
o Termination phase: in which the session is terminated.
Garcia Aranda Expires July 25, 2011 [Page 8]
Internet-Draft The Quality for Services Protocol January 2011
+---------------------------------------------------------------+
| constraints not reached |
| +------------------+ |
| | | |
| Handshake ---> Negotiation +--> Continuity -+-+-> Termination |
| A | | A | |
| | | | | | |
| +--+ | +----------+ |
| | |
| +->Application |
| starts |
| |
+---------------------------------------------------------------+
Figure 1 Session lifetime phases.
3.1.1. Handshake Phase
The first phase consists of a Q4S BEGIN method issued from the
client to the server.
The first Q4S message MUST have a special URI (RFC 3986 [4]), which
forces the use of the Q4S protocol if it is implemented in a
standard web browser.
This URI, named "Contact URI", is used to request the start of a
session. Its scheme MUST be:
"q4s:" "//" host [":" port] [path["?" query]
Optionally, the client can send the desired quality parameters
(enclosed in the body of the message as an SDP document) and the
server can take them into account when it builds the answer with the
final values, following an offer / answer schema (RFC 3464 [5]). The
description of these quality parameters are attached in an SDP
document.
If the request is accepted, the server MUST answer with a Q4S 200 OK
message, and in the body of the answer message, an SDP document MUST
be included (RFC 4566 [2]), with information about the required
quality constraints. Q4S responses should use the protocol
designator "Q4S/1.0".
After these two messages are exchanged, the first phase is
completed. The quality parameters have been sent to the client. Next
Garcia Aranda Expires July 25, 2011 [Page 9]
Internet-Draft The Quality for Services Protocol January 2011
step is to measure the quality of the communication path between the
client and the server and alert if the SLA is being violated.
+------------------------------------------------+
| |
| Client Server |
| |
| ------- Q4S BEGIN ------------> |
| |
| <------ Q4S 200 OK ------------ |
| |
| |
+------------------------------------------------+
Figure 2 Regular handshake phase.
Example of Client Request and server answer:
Client Request:
=========================
BEGIN q4s://www.example.com Q4S/1.0
Content-Type: application/sdp
User-Agent: q4s-ua-experimental-1.0
Content-Length: 142
(SDP not shown)
=========================
Server Answer:
=========================
Q4S/1.0 200 OK
Date: Mon, 10 Jun 2010 10:00:01 GMT
Content-Type: application/sdp
Expires: 3000
Q4S-Resource-Server:
q4s://www.example.com/example/util/agent?num=666
Q4S-Policy-Server: q4s://www.qosmanager.com/agent
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Length: 131
(SDP not shown)
=========================
The "Expires" header purpose is to provide a sanity check and
enables the server to close inactive sessions. If the client does
Garcia Aranda Expires July 25, 2011 [Page 10]
Internet-Draft The Quality for Services Protocol January 2011
not send a new request before the expiration time, the server can
close the session.
The "Signature" header contains a digital signature that can be used
by the network to validate the SDP, preventing security attacks.
The signature is an optional header generated by the server using a
hash and encryption method such as MD5 (RFC 1321 [6]) and RSA (RFC
2437 [7]), but it depends on the certificate used by the server.
This certificate is supposed to be delivered by a Certification
Authority (CA) or policy owner to the server. The signature is
applied to the SDP body.
Signature= RSA ( MD5 (<sdp>), <certificate> )
If the signature is not present, other validation mechanism may be
implemented in order to provide assured quality with security and
control.
The optional response header "Q4S-Resource-Server" contains the
Session URI, which is in charge of this session. This URI MUST be
invoked by the client in all later requests. Example:
Q4S-Resource-server:
q4s://www.example.com/example/util/agent?num=666
If this header is not present, the client will continue sending all
requests to the original Contact URI, but if it is present, its use
is mandatory.
The last optional response header is "Q4S-Policy-Server" which
contains the "Policy Server URI" towards which client MUST send the
later QOS-ALERT messages. This header will be explained later on. In
case this header is present, the Q4S-Resource-server header is
mandatory.
During the next phases of the protocol, the client role will perform
a mix of client and server role. Hence, the client can specify a
"Q4S-Resource-Client" header in the BEGIN request, indicating the
Resource Client URI, a relative URI in charge of the server requests
when client receives requests from the server. Example:
Q4S-Resource-Client: /example/useragent
This URI MUST be relative because user agents may not have an
associated domain, or its IP address is unknown.
Garcia Aranda Expires July 25, 2011 [Page 11]
Internet-Draft The Quality for Services Protocol January 2011
3.1.1.1. Description of Quality parameters inside SDP
The original goal of SDP was to announce necessary information for
the participants and multicast MBONE (Multicast Backbone)
applications. Right now, its use has been extended to the
announcement and the negotiation of multimedia sessions. The purpose
of SDP in the Q4S context is different because no media parameters
are set, therefore the number of media attributes ("m") is always
zero. This is because Q4S purpose is not to establish media stream
sessions, but to monitor a quality connection, and this quality
connection can be used to establish media sessions by other
protocols, or for any other purpose.
The SDP embedded in the messages is the container of the quality
parameters. The included information can comprise all or some of the
following parameters, by means of optional session-level attributes:
o QoS level for uplink and downlink: specified in the "qos-level"
attribute. Default values are 0 for both directions. The
meaning of each level is out of scope of Q4S, but, in general,
a higher level should correspond to a better service quality.
o Maximum latency tolerance for uplink and downlink: specified in
the "latency" attribute, expressed in milliseconds.
o Maximum jitter tolerance for uplink and downlink: specified in
the "jitter" attribute, expressed in milliseconds.
o Minimum bandwidth for uplink and downlink: specified in the
"bandwidth" attribute, expressed in kbps.
o Maximum packet loss tolerance for uplink and downlink:
specified in the "packetloss" attribute expressed in
percentage.
o Flows (protocol, source IP, source Port + destination IP,
destination port) of data over TCP and UDP ports to be used in
uplink and downlink: specified in the "flow" attribute.
o Measurement procedure and results of quality measurements:
specified in the "measurement" attribute.
This is an example of SDP for Q4S usage. For each attribute two
values separated by "/" are involved. These values represent the
uplink and downlink values: <uplink> / <downlink>. When one or both
Garcia Aranda Expires July 25, 2011 [Page 12]
Internet-Draft The Quality for Services Protocol January 2011
of these values are empty, it means that there is no constraint on
this parameter.
v=0
o=q4s-UA 53655765 2353687637 IN IP4 192.0.2.33
s=Q4S
i=Q4S parameters
t=0 0
a=qos-level:0/0
a=latency:40/35
a=jitter:10/10
a=bandwidth:20/6000
a=packetloss:5/5
a=flow:data downlink TCP/10000-20000
a=flow:control downlink UDP/55000
a=flow:control downlink TCP/55001
a=flow:data uplink TCP/56000
a=flow:control uplink UDP/56000
a=flow:control uplink TCP/56001
a=measurement:procedure default,50/50,75/75,,0
a=measurement:latency 10000/10000
a=measurement:jitter 10000/10000
a=measurement:bandwidth 0/0
a=measurement:packetloss 0/0
Inside the constraints, several "flow" attributes can be defined.
The goal is to monitor each flow to verify that the quality
constraints are met. These flows include the type (uplink or
downlink), the protocol (TCP or UDP) (RFC 761 [8] and RFC 768 [9])
and the ports that are going to be used by the application data and,
of course, by the control (for quality measurements), because the
quality measurements MUST be achieved over the same quality session
for each direction. All defined flows will be considered within the
same quality profile, which is determined by the qos-level attribute
in each direction.
During negotiation phase control ports will be used for Q4S
messages, and this is the reason to separate application data ports
from Q4S control ports, otherwise they could collide.
The control should involve two UDP flows (one for uplink and other
for downlink) and two TCP flows (one for uplink and other for
downlink), but application data could involve many flows, depending
on the nature of the application. The handshake phase takes place
through the Contact URI, using TCP port 80 for example. However, the
Garcia Aranda Expires July 25, 2011 [Page 13]
Internet-Draft The Quality for Services Protocol January 2011
negotiation phase will take place on the specified control ports
(UDP and TCP) using the Session URI.
A "downlink port" is a port in which the client listens for server
requests (and MUST be used as origin port of client responses),
while an "uplink port" is a port in which server is listening
incoming messages from the client (and MUST be used as origin port
of server responses).
Server's SDP information on "downlink" ports is informational for
the client (it could even be a null value meaning that they could be
choosen randomly as per OS standard rules). "Downlink" ports inside
the SDP must always be matched against actual received port values
on the server side in order deal with NAT/NATP devices. Example:
a=flow:control downlink TCP/0
+------------------------------------------------+
| |
| Client Server |
| |
| downlink port uplink port |
| A | |
| | | |
| +-----------------------------+ |
| |
| |
+------------------------------------------------+
Figure 3 Downlink flow.
+------------------------------------------------+
| |
| Client Server |
| |
| downlink port uplink port |
| | A |
| | | |
| +-----------------------------+ |
| |
| |
+------------------------------------------------+
Figure 4 Uplink flow.
Garcia Aranda Expires July 25, 2011 [Page 14]
Internet-Draft The Quality for Services Protocol January 2011
In addition, measurement parameters are included using the session
attribute "measurement". The first measurement parameter is the
procedure. By default, Q4S provides a "default" procedure for
measurement, but others like RTP/RTCP might be used. In the initial
client request a set of measurement procedures can be sent to the
server for negotiation (one line MUST be included in SDP for each
one). The server will answer with only one line with the chosen
procedure.
For each procedure, a set of values of parameters can be included in
the same attribute line, as in the following example:
a=measurement:procedure default,50/50,75/75,5000,0
Where the procedure name is "default" and one parameter is included
separated by ",". The meaning of each value depends on the
procedure. In the procedure "default", the meaning of these
parameters are:
o The first parameter is the interval of time (in milliseconds)
between PING requests during the negotiation phase. Forward and
reverse values from the client's point of view are separated by
"/". This allows having different responsiveness values
depending on the control resources used in each direction.
o The second parameter is the interval of time (in milliseconds)
between PING requests during the continuity phase. Forward and
reverse values are separated by "/". This allows having two
different responsiveness values depending on the control
resources used in each direction.
o The third parameter is the time used to measure bandwidth
during the negotiation phase. If not present, a default value
of 5000 ms will be assumed. Forward and reverse values are
separated by "/".
o The fourth parameter indicates the mode for continuity phase (0
means "normal" and 1 means "sliding window"). If not present,
normal mode (default value of 0) will be assumed.
Quality parameters read by the procedure provide a snapshot of the
quality level reached in each stage.
Since the handshake phase does not make any measurement, this
section could be empty or filled with dummy values, except
procedure, which is mandatory to start the next protocol phase.
Garcia Aranda Expires July 25, 2011 [Page 15]
Internet-Draft The Quality for Services Protocol January 2011
3.1.2. Quality negotiation phase
This phase depends on the chosen procedure. The following
description corresponds to "default" procedure.
The negotiation phase involves iterations of sequences of messages
until the quality session is compliant with the minimum quality
constraints or until the quality session is terminated due to the
impossibility to meet the constraints.
In order to measure the quality parameters, the client and server
can use different mechanisms. This document only describes the
"default" mechanism, but others can be used, like RTP/RTCP (RFC 3550
[10]). Measurement of latency and jitter is done calculating the
differences in arrival times of packets. This measurement can be
achieved with little bandwidth consumption, whereas bandwidth
measurement involves higher bandwidth consumption in both directions
(uplink and downlink).
Therefore the measurements involve two stages:
o Stage 0: Measurement of latencies, jitters and packet loss
o Stage 1: Measurement of bandwidths and packet loss
Notice that packet loss can be measured in both parts, because the
messages used for measure latencies can also be used for packet loss
measurement.
These two parts are executed sequentially in order to save network
resources. If the required latencies and jitters can not be reached,
it makes no sense to waste network resources measuring bandwidth. In
addition, if the achievement of the required latency and jitter
implies upgrading the quality session level, the chance of
succeeding in bandwidth measurement without retries is higher,
saving network traffic.
The client starts the negotiation phase sending a READY request
using the TCP control ports defined in the SDP. This READY request
includes an "Stage" header that indicates the measurement stage.
The motivation for this READY message is to synchronize negotiation
phases in multiple quality sessions (see 4.2) enabling the
possibility to repeat a successful stage.
Garcia Aranda Expires July 25, 2011 [Page 16]
Internet-Draft The Quality for Services Protocol January 2011
If either jitter or latency are specified, the negotiation phase
begins with the measurement of latencies and jitters (stage 0). If
none of those attributes are specified, stage 0 is skipped.
3.1.2.1. Stage 0: Measurement of latencies and jitters
+------------------------------------------------+
| |
| Client Server |
| |
| ------- Q4S READY -----------> |
| |
| <----- Q4S 200 OK ----------- |
| |
| |
+------------------------------------------------+
Figure 5 Beginning of the Negotiation phase.
Client Request:
=========================
READY q4s://www.example.com Q4S/1.0
Stage: 0
Session-Id: 53655765
User-Agent: q4s-ua-experimental-1.0
Content-Length: 0
=========================
Server Response:
=========================
Q4S/1.0 200 OK
Session-Id: 53655765
Stage:0
Content-Length: 0
=========================
Following this, the client and the server start exchanging a number
of PING requests and responses that will lead to the calculation of
RTT, jitter and packet loss.
The server MUST send its PING requests using the UDP control flow
ports defined in the SDP negotiated during the handshake phase. The
downlink port is set as destination and the uplink port is set as
origin (according to the example, from client UDP port 56000 to
server UDP port 55000).
Garcia Aranda Expires July 25, 2011 [Page 17]
Internet-Draft The Quality for Services Protocol January 2011
At the same time the server must begin to do exactly the same, using
UDP control ports to send PING requests towards the clients.
+------------------------------------------------+
| |
| Client Server |
| |
| --------- Q4S READY -----------> |
| <-------- Q4S 200 OK ----------- |
| |
| --------- Q4S PING ------------> |
| <-------- Q4S 200 OK ----------- |
| <-------- Q4S PING ------------- |
| -------- Q4S 200 OK ----------> |
| --------- Q4S PING ------------> |
| <-------- Q4S PING ------------- |
| --------- Q4S 200 OK ----------> |
| <-------- Q4S 200 OK ----------- |
| ... |
| |
+------------------------------------------------+
Figure 6 Simultaneous exchange of PING request and responses.
This is an example of the message sent from the client and the
server response:
Client Request:
=========================
PING q4s://www.example.com Q4S/1.0
Session-Id: 53655765
Sequence-Number: 0
User-Agent: q4s-ua-experimental-1.0
Content-Length: 0
=========================
Server Response:
=========================
Q4S/1.0 200 OK
Session-Id: 53655765
Sequence-Number: 0
Content-Length: 0
=========================
Garcia Aranda Expires July 25, 2011 [Page 18]
Internet-Draft The Quality for Services Protocol January 2011
The meaning of this method is similar to the ICMP echo request
message. Basically the server MUST answer as soon as it receives the
message.
Both endpoints MUST send Q4S PING messages periodically, using the
same UDP control ports always and do not need to wait for a response
to send the next PING request. They just sends PING messages
periodically with a different "Sequence-Number" header value. This
value is a sequential integer number and MUST start at zero. If this
stage is repeated, the initial Sequence-Number MUST start again at
zero.
Optionally the PING request can include a "Timestamp" header, with
the time in which the message has been sent. In case the header is
present, the server MUST include the header in the response without
changing the value.
During this phase, the interval between PING requests is defined in
the first parameter of the attribute line of SDP where the procedure
is specified. In the example, this value is 50 milliseconds (from
the client to the server) and 60ms (from the server to the client).
a=measurement:procedure default,50/60,50/50,5000,0
A couple of correlated messages (request and response matching the
Sequence-Number) allow calculating each sample of RTT.
3.1.2.1.1. Round Trip Time calculation
Based on the PING exchange the client is able to calculate the RTT.
The RTT is the sum of downlink latency (normally named "reverse
latency") and uplink latency (normally named "forward latency").
This process could take a few seconds, and after this time, at least
100 samples of RTT MUST be taken by the client.
3.1.2.1.2. Jitter calculation
Two jitter values are calculated during this stage: uplink jitter
and downlink jitter. Downlink jitter is calculated by the client
taking into account the PING request messages received from the
server. In the same way, uplink jitter is calculated taking into
account the PIG request messages received by the server. Note that
PING responses are not taken into account when calculating jitter
values.
Garcia Aranda Expires July 25, 2011 [Page 19]
Internet-Draft The Quality for Services Protocol January 2011
Every time a request message is received by an endpoint (either
server or client), the corresponding jitter value is updated using
the Statistical Jitter value which is calculated on the first 100
packets received using the statistical variance formula:
Jitter Statistical = SquareRootOf(SumOf((ElapsedTime[i]-
Average)^2)/(ReceivedPacketCount-1))
Hence an endpoint sends a PING periodically with a fixed interval,
each value of "elapsed time" (ET) should be very close to this
interval. If a PING message is lost, the elapsed time value is
doubled, however, this is not an issue because all PING messages are
labeled with a Sequence-Number header. Therefore the receiver can
discard this elapsed time value. In order to have the first jitter
sample, the receiver needs to have 3 PING requests, because each ET
is the time between two PINGs and a Jitter needs at least two ET.
After 100 samples the client has the values of RTT and downlink
jitter and the server has RTT and uplink jitter.
3.1.2.1.3. Packet loss calculation
Packet loss is measured in both directions. Because Sequence-Number
headers are incremented sequentially, the client knows exactly the
number of messages lost from the server to the client, and the
server knows the number of packets lost from the client to the
server.
3.1.2.1.4. Communication of results
After having calculated RTT, jitters and packet loss, the client
MUST send a GET request to the server using TCP control port
requesting instructions. This message MUST always be sent,
independently of the used measurement procedure being used. An SDP
carrying the updated values of latency, jitter and packet loss is
attached to the body of the request.
As the forward and reverse latencies are unknown, the calculation
will assume that the network is symmetric and will assign RTT/2 for
uplink and downlink latencies.
Garcia Aranda Expires July 25, 2011 [Page 20]
Internet-Draft The Quality for Services Protocol January 2011
Client Request:
=========================
GET q4s://www.example.com Q4S/1.0
Host: www.example.com
User-Agent: q4s-ua-experimental-1.0
Content-Type: application/sdp
Content-Length: 142
v=0
o=q4s-UA 53655765 2353687637 IN IP4 192.0.2.33
s=Q4S
i=Q4S parameters
t=0 0
a=qos-level:0/0
a=latency:40/35
a=jitter:10/10
a=bandwidth:20/6000
a=packetloss:5/5
a=flow:data downlink TCP/10000-20000
a=flow:control downlink UDP/55000
a=flow:control downlink TCP/55001
a=flow:data uplink TCP/56000
a=flow:control uplink UDP/56000
a=flow:control uplink TCP/56001
a=measurement:procedure default,50/50,75/75,5000,0
a=measurement:latency 40/40
a=measurement:jitter 0/10
a=measurement:bandwidth 0/0
a=measurement:packetloss 0/2
=========================
When the server receives this message, it compares the latency value
(RTT/2) with its own measurements, in order to avoid
inconsistencies.
At this point there are two possibilities
o The latency, jitter and packet loss constraints are not reached
o The latency, jitter and packet loss constraints are reached
Garcia Aranda Expires July 25, 2011 [Page 21]
Internet-Draft The Quality for Services Protocol January 2011
3.1.2.1.5. Constraints not reached
If the measurements do not meet the quality constraints, the server
answers with a 412 message (a precondition setting required by the
client or server has not been met).
Server Answer:
=========================
Q4S/1.0 412 latency
Date: Mon, 10 Jun 2010 10:00:01 GMT
Content-Type: application/sdp
Expires: 3000
Cause: downlink_latency
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Length: 131
v=0
o=q4s-UA 53655765 2353687637 IN IP4 192.0.2.33
s=Q4S
i=Q4S parameters
t=0 0
a=qos-level:1/0
a=latency:40/35
a=jitter:10/10
a=bandwidth:20/6000
a=packetloss:5/5
a=flow:data downlink TCP/10000-20000
a=flow:control downlink UDP/55000
a=flow:control downlink TCP/55001
a=flow:data uplink TCP/56000
a=flow:control uplink UDP/56000
a=flow:control uplink TCP/56001
a=measurement:procedure default,50/50,75/75,5000,0
a=measurement:latency 40/40
a=measurement:jitter 20/10
a=measurement:bandwidth 0/0
a=measurement:packetloss 1/2
=========================
In the 412 message, the server may include a different value for
"qos-level" SDP session-level attribute, and the measurements done
by the client. All these information MUST be protected using the
signature header.
Garcia Aranda Expires July 25, 2011 [Page 22]
Internet-Draft The Quality for Services Protocol January 2011
After a 412 message is received by the client, a QOS-ALERT request
is sent by the client to acknowledge the SLA violation (using TCP
control port). The QOS-ALET request does not have to be answered.
Notice that the server signature header is present in the client
request, in order to allow an optional integrity validation.
If the "Q4S-Policy-Server" header was included in the server
response of the handshake phase, this message MUST be sent to the
URI indicated in that header, otherwise the QOS-ALERT request MUST
be sent to the server. This request does not need to be answered.
Client Request:
=========================
QOS-ALERT q4s://www.example.com Q4S/1.0
Host: www.example.com
User-Agent: q4s-ua-experimental-1.0
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Type: application/sdp
Content-Length: 142
(SDP not shown)
=========================
Upon receiving the QOS-ALERT request from the client, the server
will issue a QOS-ALERT request towards the client.
Garcia Aranda Expires July 25, 2011 [Page 23]
Internet-Draft The Quality for Services Protocol January 2011
Server Request:
=========================
QOS-ALERT q4s://www.example.com Q4S/1.0
Date: Mon, 10 Jun 2010 10:00:01 GMT
Content-Type: application/sdp
Expires: 3000
Cause: latency
Guard-time: 5000
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Length: 131
v=0
o=q4s-UA 53655765 2353687637 IN IP4 192.0.2.33
s=Q4S
i=Q4S parameters
t=0 0
a=qos-level:1/0
a=latency:40/35
a=jitter:10/10
a=bandwidth:20/6000
a=packetloss:5/5
a=flow:data downlink TCP/10000-20000
a=flow:control downlink UDP/55000
a=flow:control downlink TCP/55001
a=flow:data uplink TCP/56000
a=flow:control uplink UDP/56000
a=flow:control uplink TCP/56001
a=measurement:procedure default,50/50,75/75,5000,0
a=measurement:latency 40/40
a=measurement:jitter 20/10
a=measurement:bandwidth 0/0
a=measurement:packetloss 1/2
=========================
After the client receives this request, it waits for a while
indicated in the server "Guard-time" header, for example to allow
different actions to be carried out by the server. (5 seconds should
be enough, but this depends on each case) and begins again the
measurement process, starting from the beginning (sending the READY
request). The maximum qos-level is 9/9 and if this value is reached
without reaching the constraints, the quality session is aborted
using the CANCEL method, which is detailed further.
If the client does not obeys the "Guard-time", sending the READY
message quickly, then the server MUST wait and not answer the READY
message until the guard time has elapsed.
Garcia Aranda Expires July 25, 2011 [Page 24]
Internet-Draft The Quality for Services Protocol January 2011
If during the measurement process some interference disturbs or
affect the measurement results, it is better to repeat the process
again rather than alerting of an SLA violation. This is always
possible by sending current values of parameter "qos-level" without
changes, and in this case a header Guard-time can be set to "0". It
is a good practice to repeat the measurements before reporting a
violation.
3.1.2.1.6. Constraints not reached with Policy server involved
If during handshake phase the optional header Q4S-Policy-Server is
included in the server response, the QOS-ALERT request MUST be sent
to the policy server, which should implement all or some of these
features (but not exclusive to):
o Client and server validation in terms of SLA.
o Authentication (Signature validation) and security (block
malicious clients)
o Policy rules ( following rules are only examples):
- Maximum quality level allowed for the ACP
- Time bands allowed for provide quality sessions for the ACP
- Number of simultaneous quality sessions allowed
- Maximum time used by quality sessions allowed
- Etc.
With policy server, the QOS-ALERT message sent by the client MUST
contain the URIs of the server and the client to be contacted later
by the policy server. Therefore the following headers MUST be
included in the client request: "Q4S-Resource-server" and
"Q4S-Resource-client"
Depending on the results of the operations achieved by the policy
server, the client could receive different types of errors or CANCEL
messages.
The flows of messages in this case are in the following figure:
Garcia Aranda Expires July 25, 2011 [Page 25]
Internet-Draft The Quality for Services Protocol January 2011
+------------------------------------------------+
| |
| Client Policy Server |
| Server |
| |
| --- QOS-ALERT -----> |
| <-- 100 trying ----- |
| |
| ---- QOS-ALERT ----> |
| <--- QOS-ALERT ----- |
| <--- QOS-ALERT ----- |
| |
+------------------------------------------------+
Figure 7 Policy server.
If the validation or authentication of the QOS-ALERT operation
fails, the policy server will send a CANCEL request to the client
without contacting the server.
If any of the policy rules fail, the server will send a 6XX error to
the client, indicating the rule that is not satisfied.
Only if the validation, authentication and policy checking are
successful, the server is contacted by the policy server and the
QOS-ALERT message is forwarded to it.
3.1.2.1.7. Constraints reached
When latency and jitter measurements match the constraints, the
server answer should be 200 OK:
Server Answer:
=========================
Q4S/1.0 200 OK
Date: Mon, 10 Jun 2010 10:00:01 GMT
Content-Type: application/sdp
Expires: 3000
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Length: 131
(SDP not shown)
=========================
Garcia Aranda Expires July 25, 2011 [Page 26]
Internet-Draft The Quality for Services Protocol January 2011
It means that the client and the server are ready for bandwidth and
packet loss measurement (stage 1).
If the bandwidth constraints are not empty, the negotiation phase
continues with stage 1. Otherwise that stage is skipped.
Garcia Aranda Expires July 25, 2011 [Page 27]
Internet-Draft The Quality for Services Protocol January 2011
+------------------------------------------------+
| |
| Client Server |
| |
| --------- Q4S READY -----------> |
| <-------- Q4S 200 OK ----------- |
| |
| --------- Q4S PING ------------> |
| <-------- Q4S 200 OK ----------- |
| <-------- Q4S PING ------------- |
| --------- Q4S 200 OK ----------> |
| --------- Q4S PING ------------> |
| <-------- Q4S PING ------------- |
| <-------- Q4S 200 OK ----------- |
| --------- Q4S 200 OK ----------> |
| ... |
| --------- Q4S GET -------------> |
| <-------- Q4S 412 -------------- |
| --------- Q4S QOS-ALERT -------> |
| <-------- Q4S QOS-ALERT -------- |
| (delay) |
| --------- Q4S PING ------------> |
| <-------- Q4S PING ------------- |
| <-------- Q4S 200 OK ----------- |
| --------- Q4S 200 OK ----------> |
| ... |
| --------- Q4S GET -------------> |
| <-------- Q4S 412 -------------- |
| --------- Q4S QOS-ALERT -------> |
| <-------- Q4S QOS-ALERT -------- |
| (delay) |
| --------- Q4S PING ------------> |
| <-------- Q4S PING ------------- |
| <-------- Q4S 200 OK ----------- |
| --------- Q4S 200 OK ----------> |
| ... |
| --------- Q4S GET -------------> |
| <-------- Q4S 200 OK ----------- |
| |
+------------------------------------------------+
Figure 8 Latency and jitter measurements with final success
Garcia Aranda Expires July 25, 2011 [Page 28]
Internet-Draft The Quality for Services Protocol January 2011
3.1.2.2. Stage 1: Measurement of bandwidth and packet loss
This stage begins in the same way as the previous one, sending a
READY request over TCP control ports. This READY message "Stage"
header value is 1.
+------------------------------------------------+
| |
| Client Server |
| |
| --------- Q4S READY -----------> |
| <-------- Q4S 200 OK ----------- |
| |
+------------------------------------------------+
Figure 9 Starting bandwidth and packet loss measurement
Client Request:
=========================
READY q4s://www.example.com Q4S/1.0
User-Agent: q4s-ua-experimental-1.0
Stage: 1
Session-Id: 53655765
Content-Length: 0
=========================
Server Response:
=========================
Q4S/1.0 200 OK
Session-Id: 53655765
Stage: 1
Content-Length: 0
=========================
Just after receiving the 200 OK, both the client and the server MUST
start sending messages simultaneously using the UDP control ports,
at the needed rate to reach the bandwidth constraint in each
direction using messages of 1 Kbyte length. The messages are sent
during a period of time defined in the SDP. This time is the third
parameter of procedure "default", in milliseconds. If this parameter
is not present, a value of 5 seconds will be used by default.
a=measurement:procedure default,50/50,75/75,5000,0
Garcia Aranda Expires July 25, 2011 [Page 29]
Internet-Draft The Quality for Services Protocol January 2011
+------------------------------------------------+
| Rate |
| A |
| | |
|downlink rate-|-------------------+ <-- traffic |
| | | sent by |
| | | server |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| uplink rate-|-------------------+ <-- traffic |
| | | sent by |
| | | client |
| | | |
| | | |
| |---|---|---|---|---|----> time |
| 0 1 2 3 4 5 (sec.) |
| |
+------------------------------------------------+
Figure 10 Bandwidth and packet loss measurements.
The goal of this phase is not to measure the internet connection
bandwidth connection but to determine if the quality constraints can
be reached or not. This is the reason for not sending more bit rate
than needed.
All requests to be sent MUST be 1 kilobyte length (UDP payload
length), and include a Sequence-Number header with a sequential
number starting at 0. If the stage is repeated, the values MUST
start again at zero. Examples:
Garcia Aranda Expires July 25, 2011 [Page 30]
Internet-Draft The Quality for Services Protocol January 2011
Client message:
=========================
DATA q4s://www.example.com Q4S/1.0
User-Agent: q4s-ua-experimental-1.0
Session-Id: 53655765
Sequence-Number: 0
Content-Type: text
Content-Length: XXXX
aaaaaaaaaaaaa ( to complete 1024 bytes UDP payload length)
=========================
The requests MUST NOT be answered, but only sent. The client will
send packets to the server in order to allow server measure client
bandwidth, and the server will do the same towards the client. The
packets have a Sequence-Number to be aware of the packet loss at
reception. The value of Sequence-Number will start at zero and will
be incremented by 1 for each message.
server message:
=========================
DATA q4s://www.example.com Q4S/1.0
Session-Id: 53655765
Sequence-Number: 0
Content-Type: text
Content-Length: 1024
aaaaaaaaaaaaa ( to complete 1024 bytes UDP payload length)
=========================
After a 5 seconds measurements the client has a collection of server
messages and may calculate the packet loss and downlink bandwidth
received. At the other side, the server has the uplink bandwidth and
packet loss.
Client MUST send a GET message to the server using the TCP control
port including the SDP data filled up with the measured downlink
bandwidth and packet loss.
Garcia Aranda Expires July 25, 2011 [Page 31]
Internet-Draft The Quality for Services Protocol January 2011
Client Request:
=========================
GET q4s://www.example.com Q4S/1.0
Host: www.example.com
User-Agent: q4s-ua-experimental-1.0
Session-Id: 53655765
Content-Type: application/sdp
Content-Length: 142
v=0
o=q4s-UA 53655765 2353687637 IN IP4 192.0.2.33
s=Q4S
i=Q4S parameters
t=0 0
a=qos-level:1/1
a=latency:40/35
a=jitter:10/10
a=bandwidth:20/6000
a=packetloss:5/5
a=flow:data downlink TCP/10000-20000
a=flow:control downlink UDP/55000
a=flow:control downlink TCP/55001
a=flow:data uplink TCP/56000
a=flow:control uplink UDP/56000
a=flow:control uplink TCP/56001
a=measurement:procedure default,50/50,50/50,5000,0
a=measurement:latency 30/30
a=measurement:jitter 6/4
a=measurement:bandwidth 0/4000
a=measurement:packetloss 0/3
==============================
At this point there are two possibilities:
o The bandwidth and packet loss constraints are not reached in
one or both directions.
o The bandwidth and packet loss constraints are reached in both
directions.
3.1.2.2.1. Constraints not reached
If the measurements do not reach the quality constraints, the server
answers with a 412 message (a precondition setting required by the
client or server has not been met). Otherwise it returns 200 OK.
Garcia Aranda Expires July 25, 2011 [Page 32]
Internet-Draft The Quality for Services Protocol January 2011
In the 412 message, the server may include a different value for the
"qos-level" SDP session-level attribute, and the measurements of
bandwidth and packet loss in both directions. All these information
MUST be protected using the signature header.
Server Answer:
=========================
Q4S/1.0 412 downlink_bandwidth
Date: Mon, 10 Jun 2010 10:00:01 GMT
Content-Type: application/sdp
Expires: 3000
Cause:downlink_bandwidth
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Length: 131
v=0
o=q4s-UA 53655765 2353687637 IN IP4 192.0.2.33
s=Q4S
i=Q4S parameters
t=0 0
a=qos-level:1/2
a=latency:40/35
a=jitter:10/10
a=bandwidth:20/6000
a=packetloss:5/5
a=flow:data downlink TCP/10000-20000
a=flow:control downlink UDP/55000
a=flow:control downlink TCP/55001
a=flow:data uplink TCP/56000
a=flow:control uplink UDP/56000
a=flow:control uplink TCP/56001
a=measurement:procedure default,50/50,50/50,5000,0
a=measurement:latency 30/30
a=measurement:jitter 6/4
a=measurement:bandwidth 200/4000
a=measurement:packetloss 2/3
=========================
After a 412 message the client MUST send a QOS-ALERT request to
acknowledge the SLA violation (using TCP control port). Notice that
the server signature header is present in the client request, in
order to allow integrity validation.
Garcia Aranda Expires July 25, 2011 [Page 33]
Internet-Draft The Quality for Services Protocol January 2011
Client Request:
=========================
QOS-ALERT q4s://www.example.com Q4S/1.0
Host: www.example.com
User-Agent: q4s-ua-experimental-1.0
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Type: application/sdp
Content-Length: 142
v=0
o=q4s-UA 53655765 2353687637 IN IP4 192.0.2.33
s=Q4S
i=Q4S parameters
t=0 0
a=qos-level:1/2
a=latency:40/35
a=jitter:10/10
a=bandwidth:20/6000
a=packetloss:5/5
a=flow:data downlink TCP/10000-20000
a=flow:control downlink UDP/55000
a=flow:control downlink TCP/55001
a=flow:data uplink TCP/56000
a=flow:control uplink UDP/56000
a=flow:control uplink TCP/56001
a=measurement:procedure default,50/50,50/50,5000,0
a=measurement:latency 30/30
a=measurement:jitter 6/4
a=measurement:bandwidth 200/4000
a=measurement:packetloss 2/3
=========================
Upon receiving the QOS-ALERT request from the client, the server
will issue another QOS-ALERT request towards the client.
Garcia Aranda Expires July 25, 2011 [Page 34]
Internet-Draft The Quality for Services Protocol January 2011
Server Answer:
=========================
QOS-ALERT q4s://www.example.com Q4S/1.0
Date: Mon, 10 Jun 2010 10:00:01 GMT
Content-Type: application/sdp
Expires: 3000
Cause: latency
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Length: 131
v=0
o=q4s-UA 53655765 2353687637 IN IP4 192.0.2.33
s=Q4S
i=Q4S parameters
t=0 0
a=qos-level:1/2
a=latency:40/35
a=jitter:10/10
a=bandwidth:20/6000
a=packetloss:5/5
a=flow:data downlink TCP/10000-20000
a=flow:control downlink UDP/55000
a=flow:control downlink TCP/55001
a=flow:data uplink TCP/56000
a=flow:control uplink UDP/56000
a=flow:control uplink TCP/56001
a=measurement:procedure default,50/50,50/50,5000,0
a=measurement:latency 30/30
a=measurement:jitter 6/4
a=measurement:bandwidth 200/4000
a=measurement:packetloss 2/3
=========================
After the client receives this request, both client and server wait
for a while indicated in the server "Guard-Time" header, for example
to allow different actions to be carried out by the server. (5
seconds should be enough, but this depends on each case) and begins
again the measurement process of this stage (bandwidth and packet
loss), starting from the beginning (sending the READY request). The
maximum qos-level is 9/9 and if this value is reached without
reaching the constraints, the quality session is aborted using the
CANCEL method, which is detailed further in this document.
Garcia Aranda Expires July 25, 2011 [Page 35]
Internet-Draft The Quality for Services Protocol January 2011
3.1.2.2.2. Constraints not reached with Policy server involved
If during the handshake phase the optional header Q4S-policy-server
is included in the server response, the QOS-ALERT message MUST be
sent to the policy server. The involved messages and operations are
described in 2.1.2.1.2
3.1.2.2.3. Constraints reached
When measurements match the constraints, the server answer should be
200 OK, and MUST include the URI for triggering the application
using an optional "Trigger-URI" header.
Server Answer:
=========================
Q4S/1.0 200 OK
Date: Mon, 10 Jun 2010 10:00:01 GMT
Trigger-URI: http://www.example.com/app_start
Expires: 3000
Content-Type: application/sdp
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Length: 131
(SDP not shown)
=========================
It means that client and server are ready to start the application.
Garcia Aranda Expires July 25, 2011 [Page 36]
Internet-Draft The Quality for Services Protocol January 2011
+------------------------------------------------+
| |
| Client Server |
| |
| <-------- (DATA packets) ------------> |
| ... |
| --------- Q4S GET ----------------> |
| <-------- Q4S 412 ----------------- |
| ---- Q4S QOS-ALERT ---------------> |
| <--- Q4S QOS-ALERT ---------------- |
| (delay) |
| --------- Q4S READY --------------> |
| <-------- Q4S 200 OK -------------- |
| <-------- (DATA packets) ------------> |
| ... |
| --------- Q4S GET ----------------> |
| <-------- Q4S 412 ----------------- |
| ---- Q4S QOS-ALERT ---------------> |
| <--- Q4S QOS-ALERT ---------------- |
| (delay) |
| --------- Q4S READY---------------> |
| <-------- Q4S 200 OK -------------- |
| <-------- (DATA packets) ------------> |
| ... |
| --------- Q4S GET ----------------> |
| <-------- Q4S 200 OK--------------- |
| |
| |
| |
+------------------------------------------------+
Figure 11 Bandwidth & packet loss measurement with success.
3.1.2.3. QoS Level out of range
If the qos-level has reached the maximum value for downlink or
uplink without matching the constraints, then a CANCEL request MUST
be sent in order to release the session. This request MUST be sent
by the client using the control TCP port and does not have to be
answered. In reaction to the receipt of the CANCEL request, the
server MUST send a CANCEL request too. If the CANCEL request is not
send to or received, the expiration time cancels the session at
server side.
Garcia Aranda Expires July 25, 2011 [Page 37]
Internet-Draft The Quality for Services Protocol January 2011
Client Request:
=========================
CANCEL q4s://www.example.com Q4S/1.0
Host: www.example.com
User-Agent: q4s-ua-experimental-1.0
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Type: application/sdp
Content-Length: 142
(SDP not shown)
=========================
Server Request in reaction to Client Request:
=========================
CANCEL q4s://www.example.com Q4S/1.0
Date: Mon, 10 Jun 2010 10:00:01 GMT
Expires: 0
Content-Type: application/sdp
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Length: 131
(SDP not shown)
=========================
Garcia Aranda Expires July 25, 2011 [Page 38]
Internet-Draft The Quality for Services Protocol January 2011
+------------------------------------------------+
| |
| Client Server |
| |
| <-------- (measurements) ------------> |
| |
| --------- Q4S GET ----------------> |
| <-------- Q4S 412 ----------------- |
| ---- Q4S QOS-ALERT ---------------> |
| <--- Q4S QOS-ALERT --------------- |
| --------- Q4S READY --------------> |
| <-------- Q4S 200 OK -------------- |
| |
| <-------- (measurements) ------------> |
| |
| --------- Q4S GET ----------------> |
| <-------- Q4S 412 ----------------- |
| --------- Q4S CANCEL -------------> |
| <-------- Q4S CANCEL -------------- |
| |
| |
+------------------------------------------------+
Figure 12 Failed negotiation phase.
3.1.2.4. QoS Level increments without changes in network behaviour
If the qos-level has not reached the maximum value (9) but after 3
QOS-ALERT messages (with increments in qos-level) the network
remains with the same quality values, the client and the server MUST
assume that the network can not reach the desired quality and abort
the session in order to save resources (time and traffic). To do
that, the client MUST send a CANCEL request and the server MUST
react to it sending a CANCEL request too.
If the client does not send a CANCEL request but a request using a
different method, the server MUST react to it sending a CANCEL
request.
3.1.2.5. Trigger an application in combination with HTTP
When the negotiation phase is successful, an optional simple
mechanism, based on HTTP, is defined to trigger the application.
The application may be triggered using an URI, by means of an HTTP
request, just after negotiation success. The URI MUST be specified
in the Q4S header "Trigger-URI". Other mechanisms, such as including
Garcia Aranda Expires July 25, 2011 [Page 39]
Internet-Draft The Quality for Services Protocol January 2011
a "Location" header in the Q4S message, to force redirection is not
recommended because these mechanisms are achieved without parsing
the body of the message.
Example of use
+------------------------------------------------+
| |
| Client Server |
| |
| --------- HTTP GET ----------------> |
| <-------- redirect to q4s ---------- |
| |
| ------- Q4S BEGIN ----------------> |
| |
| (Handshake Phase) |
| (Negotiation Phase) |
| |
| <---- Q4S 200 OK with trigger URI-- |
| |
| --------- HTTP GET ----------------> |
| |
| (Application starts) |
| |
+------------------------------------------------+
Figure 13 Trigger the application using HTTP URI
In the example, an integration of HTTP and Q4S is shown. First, the
client contacts the server using HTTP, a redirection to a Q4S URI is
achieved and the User Agent starts the Q4S handshake phase. After
negotiation phase succeeds, the client trigger the application using
the URI indicated in the Q4S 200 OK message.
3.1.3. Continuity phase
During the negotiation phase, latency, jitter, bandwidth and packet
loss can be measured, but during continuity phase bandwidth will not
be measured because bandwidth measurements may disturb application
performance.
This phase is supposed to be executed at the same time as the real
time application is being used.
Garcia Aranda Expires July 25, 2011 [Page 40]
Internet-Draft The Quality for Services Protocol January 2011
In the default measurement procedure, two working modes are defined
for this phase (normal and sliding window). The details of working
modes are procedure dependant, and this draft only covers the
default procedure.
3.1.3.1. Normal mode
The server can force the use of normal mode by setting the fourth
parameter of "procedure" SDP attribute to 0. If this parameter is
not set, the default value is assumed (zero), and normal mode will
be used.
Example:
a=measurement:procedure default,50/50,50/50,5000,0
Considering that network conditions can change, the client may
periodically check network conditions against negotiated
constraints. The maximum interval expected between network testing
is indicated in the Q4S Expires header.
However, the measurements can be carried out periodically in a
smaller period of time than "Expires" header value. Intense
interactive applications, like arcade videogames, the period to
repeat the measurements may be very small (even zero), in order to
measure continuously the quality and assure the best reaction time.
To reach the best reaction time, the use of the sliding window mode
is recommended.
To start the continuity phase, the client sends a Q4S READY method,
using the TCP control port, exactly the same as Negotiation,
indicating the new Stage header value for continuity phase (value
2).
Garcia Aranda Expires July 25, 2011 [Page 41]
Internet-Draft The Quality for Services Protocol January 2011
Client Request:
=========================
READY q4s://www.example.com Q4S/1.0
User-Agent: q4s-ua-experimental-1.0
Stage: 2
Session-Id: 53655765
Content-Length: 0
=========================
Server Response:
=========================
Q4S/1.0 200 OK
Session-Id: 53655765
Stage: 2
Content-Length: 0
=========================
After these messages are exchanged, latency, jitter and packet loss
measurement are started, taking care of bandwidth usage. If the
default measurement method is being used, it is recommended to use a
larger interval for PING messages than the one used in the
negotiation phase, but the same number of samples will be taken to
check quality. The goal of incrementing the interval of PING
messages is to minimize the load of the server which would be
running lots of connections in parallel.
The process is the same as described in the negotiation phase. The
difference is the time between samples, because the bandwidth usage
MUST be protected. The interval used for this phase is indicated in
the second parameter of the attribute line for the procedure. In
this example, the interval is 75 milliseconds.
a=measurement:procedure default,50/50,75/75,5000,0
A value larger than the one used in the negotiation phase is
recommended.
Garcia Aranda Expires July 25, 2011 [Page 42]
Internet-Draft The Quality for Services Protocol January 2011
+------------------------------------------------+
| |
| Client Server |
| |
| |
| --------- Q4S READY -----------> |
| <-------- Q4S 200 OK ----------- |
| --------- Q4S PING ------------> |
| <-------- Q4S 200 OK ----------- |
| <-------- Q4S PING ------------- |
| -------- Q4S 200 OK ----------> |
| --------- Q4S PING ------------> |
| <-------- Q4S PING ------------- |
| --------- Q4S 200 OK ----------> |
| <-------- Q4S 200 OK ----------- |
| ... |
| --------- Q4S GET -------------> |
| <-------- Q4S 412 -------------- |
| --------- Q4S QOS-ALERT -------> |
| <-------- Q4S QOS-ALERT -------- |
| (delay) |
| --------- Q4S READY -----------> |
| <-------- Q4S 200 OK ----------- |
| --------- Q4S PING ------------> |
| <-------- Q4S 200 OK ----------- |
| <-------- Q4S PING ------------- |
| -------- Q4S 200 OK ----------> |
| --------- Q4S PING ------------> |
| <-------- Q4S PING ------------- |
| --------- Q4S 200 OK ----------> |
| <-------- Q4S 200 OK ----------- |
| ... |
| --------- Q4S GET -------------> |
| <-------- Q4S 200 OK ----------- |
| |
+------------------------------------------------+
Figure 14 Continuity.
3.1.3.2. Sliding window mode
In order to improve the reaction time when network conditions
degrade quickly, the server can force the use of the sliding window
mode by setting the fourth parameter of the "procedure" SDP
attribute to 1.
Example:
Garcia Aranda Expires July 25, 2011 [Page 43]
Internet-Draft The Quality for Services Protocol January 2011
a=measurement:procedure default,50/50,50/50,5000,1
The sliding window mode applies a sliding window of 100 samples
instead cycles of 100 samples.
In the sliding window mode, PING requests are sent continuously (in
both directions) and when the Sequence-Number header reaches the
value of 100, the client MUST NOT send a GET message for
instructions, but continues sending PING messages with the Sequence-
Number header starting again at zero. When the server PING Sequence-
Number header reaches 100, it does the same, starting again from
zero.
On the client side, the measured values of downlink jitter, downlink
packet loss and latency are calculated using the last samples,
discarding older ones, in a sliding window schema.
+------------------------------------------------+
| |
| 55 56 57 . . . 98 99 100 0 1 2 . . . 55 56 |
| A A |
| | | |
| +---------------------------------+ |
| |
+------------------------------------------------+
Figure 15 Sliding samples window
Only when the client detects that the measured values (downlink
jitter, downlink packet loss and latency) are not reaching the
constraints, a GET request is sent to the server.
When the server receives the GET request, it stops sending PING
requests and answers the GET request just received. If the response
code is 412, then a QOS-ALERT will be requested by the client,
exactly in the same way as described in normal mode.
On the other hand, if the server detects that the measured values
(uplink jitter, uplink packet loss and latency) are not reaching the
constraints, it MUST choose between the following alternatives:
o The server stops sending PING request to the client. In this
case the client MUST notice this lack of PING requests using a
timeout at reception. If so, the client reacts stopping the
sending of PING requests to the server and sends a GET request
for instructions, exactly in the same way as described in
normal mode.
Garcia Aranda Expires July 25, 2011 [Page 44]
Internet-Draft The Quality for Services Protocol January 2011
o It continues sending PING requests but all of them with
Sequence-Number set to -1 till a client GET request is
received. Then the server stops sending PING messages and
answers the GET request with the corresponding 412 error,
exactly in the same way as described in normal mode. The client
reacts sending this GET request when it receives a PING request
with Sequence-Number header set to -1. This behavior allows the
shortest reaction time under degradation of network conditions.
Both alternatives MUST be implemented by the Q4S client.
3.2. Dynamic constraints and flows
Depending on the nature of the application, the constraints to be
reached may evolve, changing some or all constraint values in any
direction.
The client MUST be able to deal with this possibility. When the
server sends an SDP document attached to a reply (200 OK, or 412,
etc), the client MUST assume all the new received values, overriding
any previous value in use.
The dynamic changes on the constraints can be as a result of two
possibilities:
o The application communicates to the Q4S a change in the
constraints. In this case the application requirements can
evolve and the Q4S server will be aware of them.
o The application uses TCP flows. In that case, in order to
guarantee a constant throughput, the nature of TCP behavior
forces the use of a composite constraint function which depends
on RTT, packet loss and window control mechanism implemented in
each TCP stack.
TCP throughput can be less than actual bandwidth if the
Bandwidth-Delay Product (BDP) is large or if the network suffers
from a high packet loss rate. In both cases, TCP congestion control
algorithms may result in a suboptimal performance.
Different TCP congestion control implementations like Reno [14],
High Speed TCP (RFC 3649 [15]), CUBIC [16], Compound TCP (CTCP
[17]), etc. reach different throughputs under the same network
conditions of RTT and packet loss. In all cases, depending on the
RTT measured value, the Q4S server could change dynamically the
packetloss constraints (defined in SDP) in order to make possible to
Garcia Aranda Expires July 25, 2011 [Page 45]
Internet-Draft The Quality for Services Protocol January 2011
reach a required throughput or viceversa (use packetloss measurement
to change dynamically latency constraints).
A general guideline to calculate the packetloss constraint and RTT
constraint consists in approximating the throughput using a
simplified formula which should take into account the TCP stack
implementation of the receiver, in addition to RTT and packet loss:
Th= Function( RTT, packet loss, ...)
Then, depending on RTT measured values, set dynamically the
packetloss constraint.
It is possible to easily calculate a worst-case boundary for the
Reno algorithm which should ensure for all algorithms that the
target throughput is actually achieved. Except that, high-speed
algorithms will then have even a larger throughput, if more
bandwidth is available.
For the Reno algorithm, the Mathis' formula may be used [15] for the
upper bound on the throughput:
Th <= (MSS/RTT)*(1 / sqrt{p})
In absence of packet loss, a practical limit for the TCP throughput
is the receiver_window_size divided by the round-trip time. However,
if the TCP implementation uses a window scale option, this limit can
reach the available bandwidth value.
3.3. Qos-level downgrade operation
During the continuity phase it might be desirable to downgrade the
current qos-level SDP parameter.
The strategy to carry out downgrades must include the possibility to
exclude specific data flows from SDP dynamically. A Q4S client MUST
allow this kind of SDP modifications by server.
Periodically (every several minutes, depending on the
implementation) the server could force a QOS-ALERT, in which the
level is downgraded for control flows, excluding application data
flows from the embedded SDP of that request. To set the new SDP, the
server MUST include the modified SDP in the 412 error message.
This mechanism allows to measure at lower levels of quality while
application flows continue using a higher qos level value.
Garcia Aranda Expires July 25, 2011 [Page 46]
Internet-Draft The Quality for Services Protocol January 2011
o If the measurements in the lower level meet the constraints,
then a new QOS-ALERT to this lower qos-level can be forced by
the server, in which the SDP includes the application data
flows in addition to control flows.
o If the measurements in the lower level do not meet the
constraints, then a new QOS-ALERT to the previous qos-level
MUST be forced by the server, in which the SDP includes only
the control flows.
+------------------------------------------------+
| |
| qos-level |
| A |
| | |
| 4| |
| | |
| 3| +------+ |
| | | | |
| 2| +----+ +----+ +--- |
| | | | | |
| 1| +----+ +-----+ |
| | | |
| 0+---+---------------------------------> time |
| |
+------------------------------------------------+
Figure 16 Possible evolution of qos-level
This mechanism avoids the risk of disturbing the application, while
the measurements are being run in lower levels. However, this
optimization of resources is optional, and MUST be used carefully.
The chosen period to measure a lower qos level is implementation
dependant. Therefore it is not included as a measurement procedure
parameter. It is recommended to use a large value, such as 20
minutes.
3.4. Sanity check of Quality sessions
A session may finish by several reasons (client shutdown, client
CANCEL request, constraints not reached, etc), and any session
finished MUST release the assigned resources.
In order to release the assigned server resources for the session,
the "Expires" header indicates the maximum interval of time that a
client can wait to repeat the continuity phase (in normal mode).
Garcia Aranda Expires July 25, 2011 [Page 47]
Internet-Draft The Quality for Services Protocol January 2011
4. Q4S messages
Q4S is a text-based protocol and uses the UTF-8 charset (RFC 3629
[11]). A Q4S message is either a request or a response.
Both Request and Response messages use the basic format of Internet
Message Format (RFC 5322 [12]). Both types of messages consist of a
start-line, one or more header fields, an empty line indicating the
end of the header fields, and an optional message-body.
generic-message = start-line
*message-header
CRLF
[ message-body ]
start-line = Request-Line / Status-Line
The start-line, each message-header line, and the empty line MUST be
terminated by a carriage-return line-feed sequence (CRLF). Note
that the empty line MUST be present even if the message-body is not.
Much of Q4S's messages and header field syntax are identical to
HTTP/1.1. However, Q4S is not an extension of HTTP.
4.1. Requests
Q4S requests are distinguished by having a Request-Line for a start-
line. A Request-Line contains a method name, a Request-URI, and the
protocol version separated by a single space (SP) character.
The Request-Line ends with CRLF. No CR or LF are allowed except in
the end-of-line CRLF sequence. No linear whitespace (LWS) is allowed
in any of the elements.
Request-Line = Method SP Request-URI SP Q4S-Version CRLF
Method: This specification defines five methods: GET for getting
information and sending quality reports, PING and DATA for
quality measurements purpose, CANCEL for terminating
Garcia Aranda Expires July 25, 2011 [Page 48]
Internet-Draft The Quality for Services Protocol January 2011
sessions, and QOS-ALERT for querying ISPs for quality
upgrades.
Request-URI: The Request-URI is a Q4S URI (RFC 2396) as described in
2.2.1 It Normally indicates the user or service to which this
request is being addressed to, but in the Q4S context, there
are some methods whose URI only reflects the service on the
server side, but nothing more. This is the case of the QOS-
ALERT method, because the real address of a QoS upgrade
request is the network, and therefore in this case the URI
only reflects the server address. In addition the CANCEL
method has the same treatment, and in the ECHO and DATA
methods invoked by the server to the client the meaning of
the URI is only the URI of the service, but not the
destination of the request. The Request-URI MUST NOT contain
unescaped spaces or control characters and MUST NOT be
enclosed in "<>".
Q4S-Version: Both request and response messages include the version
of Q4S in use. To be compliant with this specification,
applications sending Q4S messages MUST include a Q4S-Version
of "Q4S/1.0". The Q4S-Version string is case-insensitive,
but implementations MUST send upper-case. Unlike HTTP/1.1,
Q4S treats the version number as a literal string. In
practice, this should make no difference.
4.2. Responses
Q4S responses are distinguished from requests by having a Status-
Line as their start-line. A Status-Line consists of the protocol
version followed by a numeric Status-Code and its associated textual
phrase, with each element separated by a single SP character. No CR
or LF is allowed except in the final CRLF sequence.
Status-Line = Q4S-Version SP Status-Code SP Reason-Phrase CRLF
The Status-Code is a 3-digit integer result code that indicates the
outcome of an attempt to understand and satisfy a request. The
Reason-Phrase is intended to give a short textual description of the
Status-Code. The Status-Code is intended for use by automata,
whereas the Reason-Phrase is intended for the human user. A client
is not required to examine or display the Reason-Phrase.
Garcia Aranda Expires July 25, 2011 [Page 49]
Internet-Draft The Quality for Services Protocol January 2011
While this specification suggests specific wording for the reason
phrase, implementations MAY choose other text, for example, in the
language indicated in the Accept-Language header field of the
request.
The first digit of the Status-Code defines the class of response.
The last two digits do not have any categorization role. For this
reason, any response with a status code between 100 and 199 is
referred to as a "1xx response", any response with a status code
between 200 and 299 as a "2xx response", and so on. Q4S/1.0 allows
following values for the first digit:
1xx: Provisional -- request received, continuing to process
the request;
2xx: Success -- the action was successfully received,
understood, and accepted;
3xx: Redirection -- further action needs to be taken in order
to complete the request;
4xx: Client Error -- the request contains bad syntax or cannot
be fulfilled at this server;
5xx: Server Error -- the server failed to fulfill an
apparently
valid request;
6xx: Global Failure -- the request cannot be fulfilled at any
server.
The status codes are the same described in HTTP (RFC 2616 [1]). In
the same way as HTTP, Q4S applications are not required to
understand the meaning of all registered status codes, though such
understanding is obviously desirable. However, applications MUST
understand the class of any status code, as indicated by the first
digit, and treat any unrecognized response as being equivalent to
the x00 status code of that class.
The Q4S-ALERT and CANCEL requests do not have to be responded.
Garcia Aranda Expires July 25, 2011 [Page 50]
Internet-Draft The Quality for Services Protocol January 2011
4.3. Header Fields
Q4S header fields are identical to HTTP header fields in both syntax
and semantics.
Some header fields only make sense in requests or responses. These
are called request header fields and response header fields,
respectively. If a header field appears in a message not matching
its category (such as a request header field in a response), it MUST
be ignored.
4.3.1. Specific Q4S Request Header Fields
In addition to HTTP header fields, these are the specific Q4S
request header fields
o Session-Id: the value for this header is the same session id
used in SDP and is assigned by the server. The messages without
SDP MUST include this header. If a message has and SDP body,
this header is optional. The method of <session id> allocation
is up to the creating tool, but it is suggested that a UTC
timestamp be used to ensure uniqueness.
o Sequence-Number: sequential integer number assigned to PING and
DATA messages.
o Timestamp: this optional header contains the system time (with
the best possible accuracy). Indicates the time in which the
request was sent.
o Signature: this header contains a digital signature that can be
used by the network to validate the SDP. The signature is
always generated by the server. It is optional.
o Q4S-Resource-Client: this optional header contains the relative
URI in charge of this session at the client side. In The case
of being included, it MUST appear in the GET request of
handshake phase. This URI MUST be invoked by the server in all
later requests. It is optional, but it should be present, it
becomes mandatory for the counterpart. This URI MUST be
relative because user agents can not have associated domain, in
addition to ignore their public IP address.
Garcia Aranda Expires July 25, 2011 [Page 51]
Internet-Draft The Quality for Services Protocol January 2011
4.3.2. Specific Q4S Response Header Fields
o Expires: the purpose is to provide a sanity check and allow the
server to close inactive sessions. If the client does not send
a new request before the expiration time, the server can close
the session. The value MUST be an integer and the measurement
unit are milliseconds.
o Guard-time: A time interval in milliseconds left vacant (i.e.,
during which no data is sent) during the quality session. The
guard time provides a safety margin before re-starting each
measurement process when a QOS-ALERT has been raised. This
header is optional in all messages but mandatory in the QOS-
ALERT sent by the server.
o Sequence-Number: same meaning as Request Header Fields
o Timestamp: UTC time in nanoseconds. Indicates the time in which
the request was sent. If the server (or a client) receives a
Timestamp header in a request, MUST include the same header
with the same value in the response. The purpose of this header
is simplify the RTT calculation.
o Signature: same meaning as Request Header Fields
o Q4S-Resource-Server: this optional header contains the URI in
charge of this session (Session URI). In case of being
included, it MUST appear in the response to the BEGIN request
of the handshake phase. This URI MUST be invoked by the client
in all later requests. It is optional, but if present, it
becomes mandatory for the counterpart.
o Q4S-Policy-Server: this optional header contains the URI
towards which the client and MUST send the QOS-ALERT messages
(Policy Server URI). In case this header is present, the Q4S-
Resource-Server header is mandatory, and MUST be included in
the QOS-ALERT messages sent by the client to the policy server.
In addition, the QOS-ALERT sent to the policy server MUST
contain the header Q4S-Resource-client
o Cause: This header field is a comma-separated list which
contains the cause(s) for which the connection constraints were
not reached after measurement process. Current defined values
are:
. Downlink_latency
Garcia Aranda Expires July 25, 2011 [Page 52]
Internet-Draft The Quality for Services Protocol January 2011
. Uplink_latency
. Downlink_jitter
. Uplink_jitter
. Downlink_bw
. Uplink_bw
4.4. Bodies
Requests, including new requests defined in extensions to this
specification, MAY contain message bodies unless otherwise noted.
The interpretation of the body depends on the request method.
For response messages, the request method and the response status
code determine the type and interpretation of any message body. All
responses MAY include a body.
The Internet media type of the message body MUST be given by the
Content-Type header field.
4.4.1. Encoding
The body MUST NOT be compressed. This mechanism is valid for
other protocols such as HTTP and SIP (RFC 3261 [13]), but
a compression/coding scheme will limit certain logical
implementations of the way the request is parsed, thus, making the
protocol concept more implementation dependant. In addition,
bandwidth calculation may not be valid if compression is used.
Therefore, the HTTP request header "Accept-Encoding" can not be used
in Q4S with different values than "identity" and if it is present in
a request, the server MUST ignore it. In addition, the response
header "Content-Encoding" is optional, but if present, the unique
permitted value is "identity".
The body length in bytes is provided by the Content-Length header
field. The "chunked" transfer encoding of HTTP/1.1 MUST NOT be used
for Q4S (Note: The chunked encoding modifies the body of a message
in order to transfer it as a series of chunks, each one with its own
size indicator.)
Garcia Aranda Expires July 25, 2011 [Page 53]
Internet-Draft The Quality for Services Protocol January 2011
5. General User Agent behavior.
5.1. Roles
In order to allow peer to peer applications, a Q4S User Agent (UA)
MUST be able to assume both client and server role. The role assumed
depends on who sends the first message.
In a communication between two UAs, the UA that sends the Q4S BEGIN
request in the first place, for starting the handshake phase, shall
assume the client role.
If both UASs send the BEGIN request at the same time, they will wait
for a random time to restart again.
Otherwise, an UA may be configured to act only as server (e.g.,
content provider's side).
+-----------------------------------------------+
| |
| UA(Client) UA(Server) |
| |
| -------- Q4S BEGIN -------------> |
| <------- Q4S BEGIN -------------- |
| |
| ------- Q4S BEGIN --------------> |
| <------ Q4S 200 OK -------------- |
| |
| |
+-----------------------------------------------+
Figure 17 P2P roles.
5.2. Multiple Quality sessions in parallel
A quality session is intended to be used for a single application
(or application instance). It means that for using the application,
the client MUST establish only one quality session against the
server. Indeed, the relation between Session-Id and application is 1
to 1.
If a user wants to raise several independent quality sessions
simultaneously against different servers (or against the same
server) it can execute multiple Q4S clients to establish separate
quality sessions. However, this is not recommended because:
Garcia Aranda Expires July 25, 2011 [Page 54]
Internet-Draft The Quality for Services Protocol January 2011
o The establishment of a new quality session may affect other
running applications over other quality sessions. Thus, minimum
quality level may not be achieved depending on individual
requirements of each application.
o If the negotiation phase is executed separately before running
any application, the quality requirements could not be assured
when the applications are running in parallel.
o Flow identification (Protocol, SourceIP, Source Port +
Destination IP, Destination Port) must always be unique for
each application/application instance, to ensure that each one
of them is using their QoS constraints.
For running different applications in parallel it is highly
recommended to execute the negotiation phase of all of them
simultaneously, in order to assure the quality constraints of all
applications in parallel. To do that, a single User Agent MUST be
used, and this User Agent MUST be able to launch several quality
session negotiations in parallel, synchronizing the beginning of
each negotiation phase, and running again the negotiation phase of
all applications in parallel until all of them succeed.
In order to repeat the execution of a negotiation phase that has
been succeeded, both, client and server MUST allow using the READY
method with a Stage header value already succeeded.
5.3. General client behavior
A Q4S Client has different behaviors. We will use letters X,Y,Z to
designate each different behavior (follow the letter bullets in the
figure below).
X) When it sends messages over TCP (methods GET, QOS-ALERT and
CANCEL) it behaves strictly like a state machine that sends
requests and waits for responses. Depending on the response type
it enters in a new state.
When it sends UDP messages (methods PING and DATA), a Q4S client is
not strictly a state machine that sends messages and waits for
responses because:
Y) At latency, jitter and packet loss measurement, the PING
requests are sent periodically, not after receiving the response
to the previous request. In addition, the client MUST answer the
Garcia Aranda Expires July 25, 2011 [Page 55]
Internet-Draft The Quality for Services Protocol January 2011
PING requests coming from the server, therefore assumes the role
of a server.
Z) At bandwidth and packet loss measurement stage, the client does
not expect to receive responses when sending DATA requests to the
server. In addition, it MUST receive and process all server
messages in order to achieve the downlink measurement.
The QOS-ALERT and CANCEL do not need to be answered. However, these
methods may have a conventional answer if an error is produced.
+-----------+------------------------+-----------+-----------+
| Handshake | Negotiation |Continuity |Termination|
| Phase | Phase | Phase | Phase |
| | | | |
| X ---------> Y --> X --> Z --> X ---> Y --> X ---> X |
| | A | A | | A | | |
| | | | | | | | | | |
| | +-----+ +-----+ | +-----+ | |
| | | | |
+------------------------------------------------+-----------+
Figure 18 Phases & client behaviors.
5.3.1. Generating requests
A valid Q4S request formulated by a Client MUST, at a minimum,
contain the following header fields:
If no SDP is included: This is the case of PING and DATA messages.
The header Session-Id and Sequence-Number are mandatory.
If SDP is included: this is the case of GET, QOS-ALERT and CANCEL
messages. Inside SDP is included Session-Id, therefore the inclusion
of Session-Id header is optional.
5.4. General server behavior
If a server does not understand a header field in a request (that
is, the header field is not defined in this specification or in
any supported extension), the server MUST ignore that header field
and continue processing the message.
Garcia Aranda Expires July 25, 2011 [Page 56]
Internet-Draft The Quality for Services Protocol January 2011
The role of the server is changed at negotiation and continuity
phases, in which server MUST send packets to measure jitter, latency
and bandwidth. Therefore, the different behaviors of server are
(follow the letter bullets in the figure below):
R) When the client sends messages over TCP (methods GET, QOS-
ALERT and CANCEL) it behaves strictly like a state machine that
receives messages and sends responses.
When the client begins to send UDP messages (methods PING and DATA),
a Q4S server is not strictly a state machine that receives messages
and sends responses because:
S) At latency, jitter and packet loss measurement, the PING
requests are sent periodically by the client but also by the
server. In this case the server behaves as a server answering
client requests but also behaves as a client, sending PING
requests toward the client and receiving responses.
T) At bandwidth and packet loss measurement, the server sends
DATA requests to the client. In addition, it MUST receive and
process client messages in order to achieve the uplink
measurement.
The QOS-ALERT and CANCEL do not need to be answered. However, these
methods may have a conventional answer if an error is produced.
+-----------+------------------------+-----------+-----------+
| Handshake | Negotiation |Continuity |Termination|
| Phase | Phase | Phase | Phase |
| | | | |
| R ---------> S --> R --> T --> R ---> S --> R ---> R |
| | A | A | | A | | |
| | | | | | | | | | |
| | +-----+ +-----+ | +-----+ | |
| | | | |
+------------------------------------------------+-----------+
Figure 19 Phases & server behaviours.
Garcia Aranda Expires July 25, 2011 [Page 57]
Internet-Draft The Quality for Services Protocol January 2011
6. Q4S method definitions
The Method token indicates the method to be performed on the
resource identified by the Request-URI. The method is case-
sensitive.
Method = "BEGIN" | "PING" | "DATA" | "GET" | "QOS-ALERT" |
"CANCEL" | "READY" | extension-method
extension-method = token
The list of methods allowed by a resource can be specified in an
"Allow" header field (RFC 2616 [1] section 14.7). The return code of
the response always notifies the client when a method is currently
allowed on a resource, since the set of allowed methods can change
dynamically. Any server application SHOULD return the status code
405 (Method Not Allowed) if the method is known, but not allowed for
the requested resource, and 501 (Not Implemented) if the method is
unrecognized or not implemented by the server.
6.1. BEGIN
The BEGIN method means request information from a resource
identified by a Q4S URI. The semantics of this method is the
starting of a quality session.
This method is only used during the handshake phase to retrieve the
SDP containing all quality parameters for the desired application to
run.
When a BEGIN message is received by the server, any current quality
session is cancelled and a new session should be created.
The response to a Q4S BEGIN request is not cacheable.
6.2. GET
The GET method means retrieve information from a resource identified
by a Q4S URI.
In the negotiation and continuity phases, this method is used to
check if the server considers the quality good enough to execute the
desired application. If the measured quality is not enough, the
server will return a 412 error.
The response to a Q4S GET request is not cacheable.
Garcia Aranda Expires July 25, 2011 [Page 58]
Internet-Draft The Quality for Services Protocol January 2011
6.3. READY
The READY method is used to synchronize the starting time for
sending of PING and DATA messages over UDP between clients and
servers.
In addition, the Stage header included in this method is mandatory
and allows clients to repeat a test, which is needed in scenarios
with multiple quality sessions between one client and different
servers.
This message is only used in negotiation and continuity phases, and
only just before making a measurement. Otherwise (out of this
context), the server MUST ignore this method.
6.4. PING
This message is used during the negotiation and continuity phases to
measure the RTT and jitter of a session. The message MUST be sent
only over UDP control port. If a server receives this message in
another port it MUST ignore it.
The fundamental difference between the PING and DATA requests is
reflected in the different measurements achieved with them. PING is
a short message, and MUST be answered in order to measure RTT,
whereas DATA is a long message (1 Kbyte) and MUST NOT be answered.
PING is a request method that can be originated by client but also
by server. Client MUST answer the server PINGs, assuming a "server
role" for these messages during measurement process.
6.5. DATA
This message is used only during the continuity phase to measure the
bandwidth and packet loss of a session. The message MUST be sent
only over UDP control port. If a server receives this message in
other port it MUST ignore it.
The fundamental difference between the PING and DATA requests is
reflected in the different measurements achieved with them. PING is
a short message, and MUST be answered in order to measure RTT,
whereas DATA is a long message (1 Kbyte) and MUST NOT be answered.
Garcia Aranda Expires July 25, 2011 [Page 59]
Internet-Draft The Quality for Services Protocol January 2011
DATA is a request method that can be originated by the client but
also by server. Both (client and server) MUST NOT answer DATA
messages.
6.6. QOS-ALERT
This is the request message that Q4S generates when the measurements
indicate that quality SLA is being violated. It is used during the
negotiation and continuity phases.
This informative message indicates that the user experience is being
degraded and includes the details of the problem (bandwidth, jitter,
packet loss measurements and the SLA). The QOS-ALERT message does
not contain any detail on the actions to be taken, which depends on
the agreements between all involved parties.
A QOS-ALERT request does not have to be answered unless there is an
error condition. However, after receiving a QOS-ALERT request, the
server sends a QOS-ALERT request to the client.
This method can be initiated by the client only after a 412 error
coming from server, and with enough information to build the
QOS-ALERT message.
If the "Q4S-Policy-Server" header was included in the server
response of the handshake phase, the QOS-ALERT message MUST be sent
to the URI indicated in this header, otherwise the QOS-ALERT message
MUST be sent to the server.
With policy server, the QOS-ALERT message sent by the client MUST
contain the URIs of the server and the client to be contacted later
by the policy server. Therefore the following headers MUST be
included in the client request: "Q4S-Resource-Server" and "Q4S-
Resource-Client".
The response to a Q4S QOS-ALERT request is not cacheable.
6.7. CANCEL
Like QOS-ALERT, this message is used for communication with the
network resources. The semantics in this case is the release of the
special resources assigned to the session.
In the same way as QOS-ALERT, CANCEL does not need to be answered.
However, if the server receives a CANCEL message, it should send a
new CANCEL request towards the client acknowledging the reception.
Garcia Aranda Expires July 25, 2011 [Page 60]
Internet-Draft The Quality for Services Protocol January 2011
7. Response codes
Q4S response codes are used for TCP and UDP. However, in UDP only
the response code 200 is used.
7.1. 100 Trying
This response indicates that the request has been received by the
next-hop server (the policy server) and that some unspecified action
is being taken on behalf of this request (for example, a database is
being consulted). This response, like all other provisional
responses, stops retransmissions of a QOS-ALERT by the client.
7.2. 200 OK
The request has succeeded.
7.3. Redirection 3xx
3xx responses give information about the user's new location, or
about alternative services that might be able to satisfy the
request.
The requesting client SHOULD retry the request at the new
address(es) given by the Location header field.
7.4. Request Failure 4xx
4xx responses are definite failure responses from a particular
server. The client SHOULD NOT retry the same request without
modification (for example, adding appropriate headers or SDP
values). However, the same request to a different server might be
successful.
7.4.1. 400 Bad Request
The request could not be understood due to malformed syntax. The
Reason-Phrase SHOULD identify the syntax problem in more detail, for
example, "Missing Sequence-Number header field".
7.4.2. 404 Not Found
The server has definitive information that the user does not exist
at the domain specified in the Request-URI. This status is also
returned if the domain in the Request-URI does not match any of the
domains handled by the recipient of the request.
Garcia Aranda Expires July 25, 2011 [Page 61]
Internet-Draft The Quality for Services Protocol January 2011
7.4.3. 405 Method Not Allowed
The method specified in the Request-Line is understood, but not
allowed for the address identified by the Request-URI.
The response MUST include an Allow header field containing a list of
valid methods for the indicated address.
7.4.4. 406 Not Acceptable
The resource identified by the request is only able of generating
response entities that have content characteristics not acceptable
according to the Accept header field sent in the request.
7.4.5. 408 Request Timeout
The server could not produce a response within a suitable amount of
time, and the client MAY repeat the request without modifications at
any later time
7.4.6. 412 A precondition has not been met
The server is indicating that the SLA is being violated.
7.4.7. 413 Request Entity Too Large
The server is refusing to process a request because the request
entity-body is larger than the one that the server is willing or
able to process. The server MAY close the connection to prevent the
client from continuing the request.
7.4.8. 414 Request-URI Too Long
The server is refusing to process the request because the Request-
URI is longer than the one that the server accepts.
7.4.9. 415 Unsupported Media Type
The server is refusing to process the request because the message
body of the request is in a format not supported by the server for
the requested method. The server MUST return a list of acceptable
formats using the Accept, Accept-Encoding, or Accept-Language header
field, depending on the specific problem with the content.
Garcia Aranda Expires July 25, 2011 [Page 62]
Internet-Draft The Quality for Services Protocol January 2011
7.4.10. 416 Unsupported URI Scheme
The server cannot process the request because the scheme of the URI
in the Request-URI is unknown to the server.
7.5. Server Failure 5xx
5xx responses are failure responses given when a server itself is
having trouble.
7.5.1. 500 Server Internal Error
The server encountered an unexpected condition that prevented it
from fulfilling the request. The client MAY display the specific
error condition and MAY retry the request after several seconds.
7.5.2. 501 Not Implemented
The server does not support the functionality required to fulfill
the request. This is the appropriate response when a Server does not
recognize the request method and it is not capable of supporting it
for any user.
Note that a 405 (Method Not Allowed) is sent when the server
recognizes the request method, but that method is not allowed or
supported.
7.5.3. 503 Service Unavailable
The server is temporarily unable to process the request due to a
temporary overloading or maintenance of the server. The server MAY
indicate when the client should retry the request in a Retry-After
header field. If no Retry-After is given, the client MUST act as if
it had received a 500 (Server Internal Error) response.
A client receiving a 503 (Service Unavailable) SHOULD attempt to
forward the request to an alternate server. It SHOULD NOT forward
any other requests to that server for the duration specified in the
Retry-After header field, if present.
Servers MAY refuse the connection or drop the request instead of
responding with 503 (Service Unavailable).
7.5.4. 504 Server Time-out
The server did not receive a timely response from an external server
it accessed in attempting to process the request.
Garcia Aranda Expires July 25, 2011 [Page 63]
Internet-Draft The Quality for Services Protocol January 2011
7.5.5. 505 Version Not Supported
The server does not support, or refuses to support, the Q4S protocol
version that was used in the request. The server is indicating that
it is unable or unwilling to complete the request using the same
major version as the client, other than with this error message.
7.5.6. 513 Message Too Large
The server was unable to process the request since the message
length exceeded its capabilities.
7.6. Global Failures 6xx
6xx responses indicate that a server has definitive information
about a particular policy not satisfied for processing the request.
7.6.1. 600 session not exist
The Session-Id is not valid
7.6.2. 601 quality level not allowed
The QOS level requested is not allowed for the pair client/server
7.6.3. 603 Session not allowed
The session is not allowed due to some policy (number of sessions
allowed for the server is exceeded, or the time band of the QOS-
ALERT is not allowed for the pair client/server, etc)
7.6.4. 604 authorization not allowed
The policy server does not authorize the QOS-ALERT operation because
any internal or external reason.
8. Implementation Recommendations
8.1. Default client constraints
To provide a default configuration, it would be good that the client
had a configurable set of Quality headers in the browser settings
menu. Otherwise these quality headers will not be present in the
first message.
Garcia Aranda Expires July 25, 2011 [Page 64]
Internet-Draft The Quality for Services Protocol January 2011
Different business models (out of scope of this proposal) may be
achieved: depending on who pays for the quality session, the server
can accept certain Client parameters sent in the first message, or
force billing parameters on the server side.
8.2. Bandwidth measurements
In programming languages or Operating Systems with timers or limited
clock resolution, it is recommended to use an approach based on
several intervals to send messages of 1KB, in order to reach the
required bandwidth consumption using a rate as close as possible to
a constant rate.
For example, if the resolution is 1 millisecond, and the bandwidth
to reach is 11Mbps, a good approach consists of sending:
1 message of 1KB every 1 millisecond +
1 message of 1KB every 3 milliseconds +
1 message of 1KB every 23 milliseconds
The number of intervals depends on required bandwidth and accuracy
that the programmer wants to achieve.
8.3. Packet loss measurement resolution
Depending on application nature and network conditions, a packet
loss resolution less than 1% may be needed. In such case, there is
no limit to the number of samples used for this calculation. A
tradeoff between time and resolution should be reached in each case.
For example, in order to have a resolution of 1/10000, the last
10000 samples should be considered in the packetloss measured value.
The problem of this approach is the reliability of old samples. If
the interval used between PING messages is 50ms, then to have a
resolution of 1/1000 it takes 50 seconds and a resolution of 1/10000
takes 500 seconds (more than 8 minutes). The reliability of a packet
loss calculation based on a sliding window of 8 minutes depends on
how fast network conditions evolve.
8.4. Measurements and reactions
Q4S can be used as a mechanism for measure and trigger actions (i.e.
lowering video bit-rate) in real-time in order to reach the
application constraints, addressing measured possible network
degradation.
Garcia Aranda Expires July 25, 2011 [Page 65]
Internet-Draft The Quality for Services Protocol January 2011
The trigger is based on message QOS-ALERT, which is always forced by
the server response 412 error. A server can avoid these QOS-REQUEST
messages sending 200 OK when a GET message is received from server,
independently whether the constraints are met or not.
8.5. Scenarios
Q4S could be used in two scenarios:
o client to ACP (Application content provider)
o client to client.
8.5.1. Client to ACP
In this scenario, the policy server is optional. If it exists, the
QOS-ALERT messages MUST be sent to this policy server which acts as
a proxy for this type of messages and validates them (plus any other
actions out of scope of this document).
In order to avoid useless load on the server, the policy server
could receive the BEGIN messages of handshake phase. For this
purpose, the policy server MUST know the URI of the Q4S servers.
In this scenario a client could send the BEGIN to the policy server,
with an additional parameter in the URI requested, which identifies
the server, like:
Q4s://www.policy.com/listofservers?id=xtiwn28821ho4
Then the Policy Server validates the request and forward the BEGIN
to the Q4S server, adding the Q4S-Resource-Server to the response
for the client in the 200 OK response.
Garcia Aranda Expires July 25, 2011 [Page 66]
Internet-Draft The Quality for Services Protocol January 2011
+------------------------------------------------+
| |
| Client Policy Server |
| Server |
| --- BEGIN ---------> |
| <-- 100 trying ----- |
| |
| --- BEGIN ----------> |
| <--- 200 OK ---------- |
| <--- 200 OK----- --- |
| |
+------------------------------------------------+
Figure 20 Policy server.
In this scenario the client MUST send further messages directly to
the server without passing through policy server.
8.5.2. Client to client
In order to solve the client to client scenario, a Q4S register
function MUST be implemented. This allows clients contact each other
for sending the BEGIN message. In this scenario, the policy server
MUST complete the Q4S-Resource-Server header with the public IP
address of the peer which assumes the server role.
The register function is out of scope of this protocol version,
because different HTTP mechanisms can be used and Q4S MUST NOT force
any.
9. Security Considerations
Different types of attacks can be avoided:
o Spoofing of server IP address can be avoided using the
digital signature mechanism. The network can easily
validate this digital signature using the public key of the
server certificate.
o The client could try to send QOS-ALERT requests constantly,
trying to enter in the negotiation phase continuously. In
this case, the server MUST answer a message "CANCEL", in
order to release the all levels reached and return to plain
access without enhanced quality.
This protocol could be supported over IPSec to increase privacy,
although it is out of scope of this proposal.
Garcia Aranda Expires July 25, 2011 [Page 67]
Internet-Draft The Quality for Services Protocol January 2011
10. IANA Considerations
A specific port for Q4S TCP control flow mechanism could be
assigned. It could simplify the network implementation. Other
possibility is to use any other port (like 80, HTTP). In this case
the network could use the protocol designator "Q4S" as the mark for
distinguish and treat the packets.
Q4S uses SDP as a container for session information, in which
quality attributes have been added as extended "session-level"
attributes. These set of new attributes should be registered (in
order to avoid the prefix "X-"). In this document, this set of
attributes has been presented as registered attributes.
This is the list of attribute field names to register:
Garcia Aranda Expires July 25, 2011 [Page 68]
Internet-Draft The Quality for Services Protocol January 2011
Attribute name: qos-level
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: defines the current QoS profile in uplink
and downlink for the communication between client and server. The
exact meaning of each level is implementation dependant but in
general, a higher qos-level value corresponds to a better quality
network profile.
Appropriate attribute values: [0..9] "/" [0..9]
Attribute name: latency
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: defines the latency constraints in
milliseconds in uplink and downlink for the communication between
client and server. Appropriate attribute values: [0..9999] "/"
[0..9999]
If there is no constraint in some direction (uplink, downlink or
both) the value can be empty in that direction
Attribute name: jitter
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: defines the jitter constraints in
milliseconds in uplink and downlink for the communication between
client and server.
Appropriate attribute values: [0..9999] "/" [0..9999]
Attribute name: bandwidth
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: define the bandwidth constraints in kbps in
uplink and downlink for the communication between client and server.
Appropriate attribute values: [0..99999] "/" [0..99999]
Attribute name: packetloss
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: define the packet loss tolerance constraints
in 100% in uplink and downlink for the communication between client
and server.
Appropriate attribute values: [0..99] "/" [0..99]
Attribute name: flow
Type of attribute: session level
Subject to the charset attribute: NO
Garcia Aranda Expires July 25, 2011 [Page 69]
Internet-Draft The Quality for Services Protocol January 2011
Explanation of purpose: define a flow between a client and a server.
The flow involves purpose (data or control), direction (uplink or
downlink) protocol (UDP or TCP) and port or range or ports
Attribute values:
<"control"|"data"> <"uplink"|"downlink"> <"UDP"|"TCP">
<0..65535>[ "-" [0..65535]]
Attribute name: measurement
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: define the procedure to measure the quality
and the different values for each measurement
Attribute values: "procedure/" <procedure> |
"latency "[0..9999] "/" [0..9999] |
"jitter "[0..9999] "/" [0..9999] |
"bandwidth "[0..99999] "/" [0..99999] |
"packetloss "[0..99] "/" [0..99]
If the attribute value is "procedure", the rest of the line MUST
contain the name of the procedure and optional parameters, separated
by ",".
In the case of procedure "default", the valid values are:
a=measurement:procedure default,[0..999]"/" [0..999] "," [0..999]
"/" [0..999] "," [0..9999] "," [0|1]
where:
o The first parameter is the interval of time (in milliseconds)
between PING messages in the negotiation phase. Forward (client
to server) and reverse (server to client) values separated by
"/".
o The second parameter is the interval of time (in milliseconds)
between PING messages in the continuity phase. Forward (client
to server) and reverse (server to client) values separated by
"/".
o The third parameter is the time used to measure bandwidth
during negotiation phase. In case of not present, a default
value of 5000 ms will be assumed.
o The fourth parameter indicates the mode for continuity phase (0
means "normal" and 1 means "sliding window"). In case of not be
present, normal mode (default value of 0) will be assumed.
Garcia Aranda Expires July 25, 2011 [Page 70]
Internet-Draft The Quality for Services Protocol January 2011
Other procedure names are allowed, but at least "default" procedure
implementation is mandatory in client and servers.
11. Conclusions
Q4S defines four phases with different purposes, and inside these
phases the negotiated measurement procedure is used. Different
measurement procedures can be used (even RTCP itself) inside Q4S.
Basically, Q4S only defines how to transport SLA information and
measurement results as well as providing some mechanisms for
alerting. Q4S does not ask for resources. Q4S only alerts if one (or
some) of SLA quality parameters are being violated. Depends on
server (Application content provider) to do something with this
information and return it back to a SLA-compliant state.
Garcia Aranda Expires July 25, 2011 [Page 71]
Internet-Draft The Quality for Services Protocol January 2011
12. References
12.1. Normative References
[1] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1" RFC 2616, June 1999.
[2] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 4566, July 2006.
[3] Bradner, S., "Key words for use in RFCs to Indicate
RequirementLevels", BCP 14, RFC 2119, March 1997.
[4] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 3986, January
2005.
[5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
SDP", RFC 3264, June 2002.
[6] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
[7] Johnsson, J., B. Kaliski, "Public-Key Cryptography Standards
(PCS) #1: RSA Cryptography Specifications version 2.1", RFC
3447, February 2003.
[8] Postel, J., "DoD Standard Transmission Control Protocol", RFC
761, January 1980.
[9] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
1980.
[10] Schulzrinne, H., Casner, S., Frederick, R., Jacobson, V. "RTP:
A Transport Protocol for Real-Time Applications", RFC 3550,
july 2003.
[11] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
RFC 3629, November 2003.
[12] Resnick, P., "Internet Message Format", RFC 5322, October 2008
Garcia Aranda Expires July 25, 2011 [Page 72]
Internet-Draft The Quality for Services Protocol January 2011
12.2. Informative References
[13] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.
Peterson, J., Sparks, R., Handley, M. and Schooler, E. , "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[14] Mathis, M., Semke, J., Mahdavi, J., Ott, T., "The Macroscopic
Behavior of the TCP Congestion Avoidance Algorithm", Computer
Communications Review, 27(3), July 1997.
[15] Floyd, S., "HighSpeed TCP for a Large Congestion Windows", RFC
3649, December 2003.
[16] Rhee, I., Xu, L., Ha, S., "CUBIC for Fast Long-Distance
Networks", Internet-draft draft-rhee-tcpm-cubic-02, February
2009.
[17] Sridharan, M., Tan, K., Bansal, D., Thaler, D., "Compound TCP:
A New TCP Congestion Control for High-Speed and Long Distance
Networks", Internet-draft draft-sridharan-tcpm-ctcp-02,
November, 2008.
Garcia Aranda Expires July 25, 2011 [Page 73]
Internet-Draft The Quality for Services Protocol January 2011
13. Acknowledgments
Many people have made comments and suggestions contributing to this
document. In particular, we would like to thank:
Sonia Herranz Pablo, Clara Cubillo Pastor, Francisco Duran Pina,
Ignacio Moreno Lopez, Michael Scharf and Jesus Soto Viso.
Garcia Aranda Expires July 25, 2011 [Page 74]
Internet-Draft The Quality for Services Protocol January 2011
14. Authors' Addresses
Jose Javier Garcia Aranda
Alcatel-Lucent
C/Maria Tubau 9
28050 Madrid
Spain
Phone: +34 91 330 4348
Email: Jose_Javier.Garcia_Aranda@alcatel-lucent.com
Jacobo Perez Lajo
Alcatel-Lucent
C/Maria Tubau 9
28050 Madrid
Spain
Phone: +34 91 330 4165
Email: Jose_Javier.Garcia_Aranda@alcatel-lucent.com
Luis Miguel Diaz Vizcaino
Alcatel-Lucent
C/Maria Tubau 9
28050 Madrid
Spain
Phone: +34 91 330 4871
Email: Luismi.Diaz@alcatel-lucent.com
Carlos Barcenilla
Universidad Politecnica de Madrid
Avenida Complutense 30
28040 Madrid
Spain
Phone: +34 91 549 5700 - 3032
Email: barcenilla@dit.upm.es
Joaquin Salvachua
Universidad Politecnica de Madrid
Avenida Complutense 30
28040 Madrid
Spain
Phone: +34 91 549 5700 - 3056
Email: jsr@dit.upm.es
Garcia Aranda Expires July 25, 2011 [Page 75]
Internet-Draft The Quality for Services Protocol January 2011
Juan Quemada
Universidad Politecnica de Madrid
Avenida Complutense 30
28040 Madrid
Spain
Phone: +34 91 336 7331
Email: jquemada@dit.upm.es
Garcia Aranda Expires July 25, 2011 [Page 76]