NSIS Working Group
Internet Draft Robert Hancock (editor)
Siemens/Roke Manor Research
Ilya Freytsis
Cetacean Networks
Georgios Karagiannis
Ericsson
John Loughney
Nokia
Sven Van den Bosch
Alcatel
Document: draft-ietf-nsis-fw-02.txt
Expires: September 2003 March 2003
Next Steps in Signaling: Framework
Status of this Memo
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Abstract
The Next Steps in Signaling working group is considering protocols
for signaling information about a data flow along its path in the
network. Based on existing work on signaling requirements, this
document proposes an architectural framework for such signaling
protocols.
This document provides a model for the network entities that take
part in such signaling, and the relationship between signaling and
the rest of network operation. We decompose the overall signaling
protocol suite into a generic (lower) layer, with a separate upper
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layers for each specific signaling application. An initial proposal
for the split between these layers is given, describing the overall
functionality of the lower layer, and discussing the ways that upper
layer behavior can be adapted to specific signaling application
requirements.
This framework also considers the general interactions between
signaling and other network layer functions, specifically routing and
mobility. The different routing and mobility events that impact
signaling operation are described, along with how their handling
should be divided between the generic and application-specific
layers. Finally, an example signaling application (for Quality of
Service) is described in more detail.
Conventions used in this document
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 [2].
[Editor's note: if - as is likely - we don't end up using these words
in the framework, this paragraph will disappear.]
Table of Contents
1. Introduction...................................................3
1.1 Definition of the NSIS Signaling Problem ...................3
1.2 Scope and Structure of the NSIS Framework ..................4
2. Terminology....................................................5
3. Overview of Signaling Scenarios and Protocol Structure.........6
3.1 Fundamental Signaling Concepts .............................6
3.1.1 Simple Network and Signaling Topology ..................6
3.1.2 Signaling to Hosts, Networks and Proxies ...............7
3.1.3 Signaling Messages and Network Control State ...........9
3.1.4 Data Flows and Sessions ...............................10
3.2 Layer Model for the Protocol Suite ........................11
3.2.1 Layer Model Overview ..................................11
3.2.2 Layer Split Concept ...................................12
3.2.3 Core NTLP Functionality ...............................13
3.2.4 Path De-Coupled Operation .............................14
3.3 Signaling Application Properties ..........................14
3.3.1 Sender/Receiver Orientation ...........................15
3.3.2 Uni- and Bi-Directional Operation .....................16
3.3.3 Heterogeneous Operation ...............................16
3.3.4 Peer-Peer and End-End Relationships ...................17
3.3.5 Acknowledgements and Notifications ....................17
3.3.6 Security and other AAA Issues .........................18
3.4 Open Layer Model Issues ...................................19
3.4.1 Classical Transport Functionality .....................19
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3.4.2 State Management ......................................20
4. The NSIS Transport Layer Protocol.............................21
4.1 Internal Protocol Components ..............................21
4.2 Addressing ................................................22
4.3 Lower Layer Interfaces ....................................22
4.4 Upper Layer Services ......................................23
4.5 Identity Elements .........................................24
4.5.1 Flow Identification ...................................24
4.5.2 Session Identification ................................24
4.5.3 Signaling Application Identification ..................25
4.6 Security Properties .......................................25
5. Interactions with Other Protocols.............................26
5.1 IP Routing Interactions ...................................26
5.1.1 Load Sharing and Policy-Based Forwarding ..............26
5.1.2 Route Changes .........................................28
5.1.3 Router Redundancy .....................................29
5.2 Mobility Interactions .....................................29
5.2.1 Addressing and Encapsulation ..........................30
5.2.2 Localized Path Repair .................................30
5.2.3 Update on the Unchanged Path ..........................31
5.2.4 Interaction with Mobility Signaling ...................31
5.2.5 Interaction with Context Transfer .....................33
5.3 Interactions with NATs ....................................33
6. Signaling Applications........................................34
6.1 Signaling for Quality of Service ..........................34
6.1.1 Protocol Messages .....................................34
6.1.2 State Management ......................................35
6.1.3 QoS Forwarding ........................................36
6.1.4 Route Changes and QoS Reservations ....................36
6.1.5 Resource Management Interactions ......................38
6.2 Other Signaling Applications ..............................39
7. Security Considerations.......................................39
8. Change History................................................40
8.1 Changes from draft-ietf-nsis-fw-01.txt ....................40
References.......................................................41
Acknowledgments..................................................44
Authors' Addresses...............................................44
Intellectual Property Considerations.............................45
Full Copyright Statement.........................................46
1. Introduction
1.1 Definition of the NSIS Signaling Problem
The NSIS working group is considering protocols for signaling
information about a data flow along its path in the network.
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It is assumed that the path taken by the data flow is already
determined by network configuration and routing protocols,
independent of the signaling itself; that is, signaling to set up the
routes themselves is not considered. Instead, the signaling simply
interacts with nodes along the data flow path. Additional
simplifications are that the actual signaling messages pass directly
through these nodes themselves; this is 'path-coupled' signaling in
the sense described in [3], and that only unicast data flows are
considered.
The signaling problem in this sense is very similar to that addressed
by RSVP [4]. However, there are two generalizations. Firstly, the
intention is that NSIS designs protocols that can be used in
different parts of the Internet, for different needs, without
requiring a complete end-to-end deployment (in particular, the
signaling protocol messages may not need to run all the way between
the data flow endpoints).
Secondly, the signaling is intended for more purposes than just QoS
(resource reservation). The basic mechanism to achieve this
flexibility is to divide the signaling protocol stack into two
layers: a generic (lower) layer, and an upper layer specific to each
signaling application. The scope of NSIS is to define both the
generic protocol, and initially an upper layer suitable for QoS
signaling similar to the corresponding functionality in RSVP. Further
signaling applications may be considered later.
1.2 Scope and Structure of the NSIS Framework
The underlying requirements for signaling in the context of NSIS are
defined in [3]; other related requirements can be found in [5] and
[6]. This framework does not replace or update these requirements.
Discussions about lessons to be learned from existing signaling and
resource protocols are contained in a separate analysis document [7].
The role of this framework is to explain how NSIS signaling should
work within the broader networking context, and how the signaling
protocols should be structured at the overall level. Therefore, it
discusses important protocol considerations, such as routing,
mobility, security, and interactions with network 'resource'
management (in the broadest sense).
The basic framework for NSIS is given in section 3. Section 3.1
describes the fundamental elements of NSIS operation in comparison to
RSVP; in particular, section 3.1.2 describes more general signaling
scenarios, and 3.1.3 defines a broader class of signaling
applications for which the NSIS protocols should be useful. The two-
layer protocol architecture that supports this generality is
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described in section 3.2, and section 3.3 gives examples of the ways
in which particular signaling application properties can be
accommodated within signaling layer protocol behavior.
The overall functionality required from the lower (generic) protocol
layer is described in section 4. This is not intended to define the
protocol detailed design or even design options, although some are
described as examples. The emphasis is on defining the interfaces
between this lower layer protocol and the IP layer and signaling
application protocols, including the identity elements that appear on
these interfaces. Following this, section 5 describes how signaling
applications that use the NSIS protocols can interact sensibly with
network layer operations, specifically routing (and re-routing), IP
mobility, and network address translation.
Section 6 describes particular signaling applications. The example of
signaling for QoS (comparable to core RSVP QoS signaling
functionality) is described in detail in section 6.1, which describes
both the signaling application specific protocol and example modes of
interaction with network resource management and other deployment
aspects. However, note that these examples are included only as
background and for explanation; it is not intended to define an over-
arching architecture for carrying out resource management in the
Internet. Further possible signaling applications are outlined in
section 6.2.
2. Terminology
[Editor's note: it is a matter of taste where we put this.]
Classifier - an entity which selects packets based on their contents
according to defined rules.
[Data] flow - a stream of packets from sender to receiver which is a
distinguishable subset of a packet stream. Each flow is distinguished
by some flow identifier (see section 4.5.1).
Edge node - a (NSIS-capable) node on the boundary of some
administrative domain.
Interior nodes - the set of (NSIS-capable) nodes which form an
administrative domain, excluding the edge nodes.
NSIS Entity (NE) - the function within a node which implements an
NSIS protocol. In the case of path-coupled signaling, the NE will
always be on the data path.
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NSIS Signaling Layer Protocol (NSLP) - generic term for an NSIS
protocol component that supports a specific signaling application.
See also section 3.2.1.
NSIS Transport Layer Protocol (NTLP) - placeholder name for the NSIS
protocol component that will support lower layer (signaling
application independent) functions. See also section 3.2.1.
Path-coupled signaling - a mode of signaling where the signaling
messages follow a path that is tied to the data messages.
Path-decoupled signaling - signaling - signaling for state
manipulation related to data flows, but only loosely coupled to the
data path, e.g. at the AS level.
Peer discovery - the act of locating and/or selecting which NSIS peer
to carry out signaling exchanges with for a specific data flow.
Peer relationship - signaling relationship between two adjacent NSIS
entities (i.e. NEs with no other NEs between them).
Receiver - the node in the network which is receiving the data
packets in a flow.
Sender - the node in the network which is sending the data packets in
a flow.
Session - application layer flow of information for which some
network control state information is to be manipulated or monitored
(see section 4.5.2).
Signaling application - the purpose of the NSIS signaling: a service
could be QoS management, firewall control, and so on. Totally
distinct from any specific user application.
3. Overview of Signaling Scenarios and Protocol Structure
3.1 Fundamental Signaling Concepts
3.1.1 Simple Network and Signaling Topology
The NSIS suite of protocols is envisioned to support various
signaling applications that need to install and/or manipulate state
in the network. This state is related to a data flow and is installed
and maintained on the NSIS Entities (NEs) along the data flow path
through the network; not every node has to contain an NE. The basic
protocol concepts do not depend on the signaling application, but the
details of operation and the information carried do. This section
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discusses the basic entities involved with signaling as well as
interfaces between them.
Two NSIS entities that communicate directly are said to be in a 'peer
relationship'. This concept might loosely be described as an 'NSIS
hop'; however, there is no implication that it corresponds to a
single IP hop. Either or both NEs might store some state information
about the other, but there is no assumption that they necessarily
establish a long-term signaling connection between themselves.
It is common to consider a network as composed of various domains,
e.g. for administrative or routing purposes, and the operation of
signaling protocols may be influenced by these domain boundaries.
However, it seems there is no reason to expect that an 'NSIS domain'
should exactly overlap with an IP domain (AS, area) but it is likely
that its boundaries would consist of boundaries (segments) of one or
several IP domains.
Figure 1 shows a diagram of nearly the simplest possible signaling
configuration. A single data flow is running from an application in
the sender to the receiver via routers R1, R2 and R3. Each host and
two of the routers contain NEs which exchange signaling messages -
possibly in both directions - about the flow. This scenario is
essentially the same as that considered by RSVP for QoS signaling;
the main difference is that we make no assumptions here about the
particular sequence of signaling messages that will be invoked.
Sender Receiver
+-----------+ +----+ +----+ +----+ +-----------+
|Application|----->| R1 |----->| R2 |----->| R3 | ---->|Application|
| +--+ | |+--+| |+--+| +----+ | +--+ |
| |NE|====|======||NE||======||NE||==================|===|NE| |
| +--+ | |+--+| |+--+| | +--+ |
+-----------+ +----+ +----+ +-----------+
+--+
|NE| = NSIS ==== = Signaling ---> = Data flow messages
+--+ Entity Messages (unidirectional)
Figure 1: Simple Signaling and Data Flows
3.1.2 Signaling to Hosts, Networks and Proxies
There are different possible triggers for the NSIS signaling. Amongst
them are signaling applications (that are using NSIS signaling
services), other instances of the signaling, network management
actions, some network events, and so on. The variety of possible
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triggers requires that the signaling can be initiated and terminated
in the different parts of the network - hosts, domain boundary nodes
(edge nodes) or interior domain nodes.
NSIS extends the RSVP model to consider this wider variety of
possible signaling exchanges. As well as the basic end-to-end model
already described, examples such as end-to-edge and edge-to-edge can
be considered. The edge-to-edge case might involve the edge nodes
communicating directly, as well as via the interior nodes.
While end-to-edge (host-to-network) scenario requires only intra-
domain signaling, the other cases might need inter-domain NSIS
signaling as well if the signaling endpoints (hosts or network edges)
are connected to different domains. Depending on the trust relation
between concatenated NSIS domains the edge-to-edge scenario might
cover single domain or multiple concatenated NSIS domains. The latter
case assumes the existence of the trust relation between domains.
In some cases it is desired to be able to initiate and/or terminate
NSIS signaling not from the end host that sends/receives the data
flow, but from the some other entities on the network that can be
called signaling proxies. There could be various reasons for this:
signaling on behalf of the end hosts that are not NSIS-aware,
consolidation of the customer accounting (authentication,
authorization) in respect to consumed application and transport
resources, security considerations, limitation of the physical
connection between host and network and so on. This configuration can
be considered as a kind of "on the data path", see Figure 2.
Proxy1 Proxy2
+------+ +----+ +----+ +----+ +----+ +--------+
|Sender|-...->|Appl|---->| R |-.->| R |--->|Appl|-...->|Receiver|
| | |+--+| |+--+| |+--+| +----+ | |
+------+ ||NE||=====||NE||=.==||NE||====||NE|| +--------+
|+--+| |+--+| |+--+| |+--+|
+----+ +----+ +----+ +----+
+--+
|NE| = NSIS ==== = Signaling ---> = Data flow messages
+--+ Entity Messages (unidirectional)
Appl = signaling application
Figure 2: "On path" NSIS proxy
This configuration presents a set of specific challenges to the NSIS
signaling:
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*) The proxy that terminates signaling on behalf of the NSIS-unaware
host (or part of the network) should be able to make determination
that it is a last NSIS aware node along the path.
*) Where a proxy initiates NSIS signaling on behalf of the NSIS
unaware host, interworking with some other "local" technology might
be required, for example to provide QoS reservation from proxy to the
end host in the case of QoS signaling application.
Another possible configuration, shown in Figure 3 is where an NE can
send and receive signaling information off path for and from remote
processing. The NSIS protocols may or may not be suitable for this
remote processing but in any case it is not currently part of the
NSIS problem. This configuration is supported by considering the NE
as a proxy at the signaling application level. This is a natural
implementation approach for some policy control and centralized
control architectures, see also section 6.1.5.
Receiver
+------+ +----+ +----+ +----+ +-----------+
|Sender|----->| PA |----->| R2 |----->| R3 | ---->|Application|
| | |+--+| |+--+| +----+ | +--+ |
+------+ ||NE||======||NE||==================|===|NE| |
|+--+| |+--+| | +--+ |
+-..-+ +----+ +-----------+
..
..
..
..
+-..-+
|Appl|
+----+
Appl = signaling PA = Proxy for signaling
application application
Figure 3: "Off path" NSIS proxy
3.1.3 Signaling Messages and Network Control State
The distinguishing features of the signaling supported by the NSIS
protocols are that it is related to specific flows (rather than to
network operation in general), and that it involves nodes in the
network (rather than running transparently between the end hosts).
Therefore, each signaling application (upper layer) protocol must
carry per-flow information for the aspects of network-internal
operation corresponding to that signaling application. An example for
the case of an RSVP-like QoS signaling application would be state
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data representing resource reservations. However, more generally, the
per-flow information might be related to some other control function
in routers and middleboxes along the path. Indeed, the signaling
might simply be used to gather per-flow information, without
modifying network operation at all.
We call this information generically 'network control state'.
Signaling messages may install, modify, refresh, or simply read this
state from network elements for particular data flows. Usually a
network element will also manage this information at the per-flow
level, although coarser-grained state management is also possible.
3.1.4 Data Flows and Sessions
Formally, a data flow is a (unidirectional) sequence of packets
between the same endpoints which follow a unique path through the
network (determined by IP routing and other network layer
configuration). A flow is defined by a packet classifier (in the
simple cases, just the destination address and topological origin are
needed). In general we assume that when discussing only the data flow
path, we only need to consider 'simple' fixed classifiers (e.g. IPv4
5-tuple or equivalent).
A session is an application layer concept for a (unidirectional) flow
of information between two endpoints, for which some network state is
to be allocated or monitored. (Note that this use of the term
'session' is distinct from the usage in RSVP. It is closer to the
session concept of, for example, the Session Initiation Protocol.)
The simplest service provided by NSIS signaling is network control
state management at the flow level, as described in the previous
subsection. In particular, it is possible to monitor routing updates
as they change the path taken by a flow and, for example, update
network state appropriately. This is no different from the case for
RSVP (local path repair). Where there is a 1:1 flow:session
relationship, this is all that is required.
However, for some more complex scenarios (especially mobility-related
ones, see [3] and [8]) it is desirable to update the flow:session
relationship during the session lifetime. For example, a new flow can
be added, and the old one deleted (and maybe in that order, for a
'make-before-break' handover), effectively transferring the network
control state between data flows to keep it associated with the same
session. Such updates can only be managed by the end systems (because
of the packet classifier change). To enable this, it must be possible
for end systems to relate signaling messages to sessions as well as
data flows.
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3.2 Layer Model for the Protocol Suite
3.2.1 Layer Model Overview
In order to achieve a modular solution for the NSIS requirements, it
is proposed to structure the NSIS protocol suite into 2 layers,
similar to the original proposal in [9]:
*) a 'signaling transport' layer, responsible for moving signaling
messages around, which should be independent of any particular
signaling application; and
*) a 'signaling application' layer, which contains functionality
such as message formats and sequences, specific to a particular
signaling application.
For the purpose of this document, we use the term 'NSIS Transport
Layer Protocol' (NTLP) to refer to the component that will be used in
the transport layer. We also use the term 'NSIS Signaling Layer
Protocol' (NSLP) to refer generically to any protocol component
within the signaling application layer; in the end, there will be
several NSLPs. These relationships are illustrated in Figure 4. Note
that the NTLP may or may not have an interesting internal structure
(e.g. based on the use of existing transport protocols) but that is
not relevant at this level.
^ +-----------------+
| | NSIS Signaling |
| | Layer Protocol |
NSIS | +----------------| for middleboxes |
Signaling | | NSIS Signaling | +-----------------+
Layer | | Layer Protocol +--------| NSIS Signaling |
| | for QoS | | Layer Protocol |
| | | | for something |
| +-----------------+ | else |
V +-----------------+
=============================================
^ +--------------------------------+
NSIS | | |
Transport | | NSIS Transport Layer Protocol |
Layer | | |
V +--------------------------------+
=============================================
+--------------------------------+
| |
. IP and lower layers .
. .
Figure 4: NSIS Protocol Components
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Note that not every generic function has to be located in the NTLP.
Another option would be to have re-usable components within the
signaling application layer. Functionality within the NTLP should be
restricted to that which interacts strongly with other transport and
lower layer operations.
Because NSIS problem includes multiple signaling applications, it is
very likely that a particular NSLP will only be implemented on a
subset of the NSIS-aware nodes on a path, as shown in Figure 5.
Messages for unrecognized NSLPs are forwarded at the NTLP level.
+------+ +------+ +------+ +------+
| NE | | NE | | NE | | NE |
|+----+| | | |+----+| |+----+|
||NSLP|| | | ||NSLP|| ||NSLP||
|| || | | || || || ||
|| 1 || | | || 2 || || 1 ||
|+----+| | | |+----+| |+----+|
| || | | | | | | || |
|+----+| |+----+| |+----+| |+----+|
====||NTLP||====||NTLP||====||NTLP||====||NTLP||====
|+----+| |+----+| |+----+| |+----+|
+------+ +------+ +------+ +------+
Figure 5: Signaling with Heterogeneous NSLPs
3.2.2 Layer Split Concept
This section describes the basic concepts which underlie how the
necessary functionality within the NTLP can be determined. Firstly,
we make a working assumption that the protocol mechanisms of the NTLP
operate only between adjacent NEs (informally, the NTLP is a 'hop-by-
hop' protocol), whereas any larger scope issues (including e2e
aspects) are left to the upper layers.
The way in which the NTLP works can be described as follows: When a
signaling message is ready to be sent from one NE, it is given to the
NTLP along with information about what flow it is for; it is then up
to the NTLP to get it to the next NE along the path (up- or down-
stream), where it is received and the responsibility of the NTLP
ends. Note that there is no assumption here about how the messages
are actually addressed (this is a protocol design issue, and the
options are outlined in section 4.2). The key point is that the NTLP
for a given NE does not use any knowledge about addresses,
capabilities, or status of any NEs other than its direct peers.
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The NTLP in the receiving NE either forwards the message directly,
or, if there is an appropriate signaling application locally, passes
it upwards for further processing; the signaling application can then
generate another message to be sent via the NTLP. In this way, larger
scope (including end-to-end) message delivery can be automatically
achieved.
This definition relates to NTLP operation. It is not intended to
restrict the ability of an NSLP to send messages by other means. For
example, an NE in the middle or end of the signaling path could send
a message directly to the other end as a notification of or
acknowledgement for some signaling application event. However, it
appears that the issues in sending such messages (endpoint discovery,
security, NAT traversal and so on) are so different from the direct
peer-peer case that there is no benefit in extending the scope of the
NTLP to include such non-local functionality; instead, an NSLP which
requires such messages and wants to avoid traversing the path of NEs
should use some other existing transport protocol - for example, UDP
would be a good match for many of the scenarios that have been
proposed. Acknowledgements and notifications of this type are
considered further in section 3.3.5.
One motivation for restricting the NTLP to only peer-relationship
scope is that if there are any options or variants in design approach
- or, worse, in basic functionality - it is easier to manage the
resulting complexity if it only impacts direct peers rather than
potentially the whole network.
3.2.3 Core NTLP Functionality
This section describes the basic functionality to be supported by the
NTLP. Note that the analysis has to be based on considering NSLP and
NTLP operation jointly; for example, we can always assume that an
NSLP is operating above the NTLP and taking care of end-to-end issues
(e.g. recovery of messages after restarts and so on).
Therefore, NTLP functionality is essentially just efficient upstream
and downstream peer-peer message delivery in a wide variety of
network scenarios. Message delivery includes the act of locating
and/or selecting which NTLP peer to carry out signaling exchanges
with for a specific data flow. This discovery might be an active
process (using specific signaling packets) or a passive process (a
side effect of using a particular addressing mode). In addition, it
appears that the NTLP can sensibly carry out most of the functions of
enabling signaling messages to pass through middleboxes, since this
is closely related to the problem of routing the signaling messages
in the first place.
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Two major open issues remain about NTLP functionality, namely what
classical transport capabilities (congestion avoidance,
retransmission and so on) it should have, or whether these functions
can be left entirely to the upper layers; and to what extent the NTLP
should provide a common state management service to the signaling
applications. These questions are discussed in section 3.4.
3.2.4 Path De-Coupled Operation
Path-decoupled signaling is defined as signaling for state
installation along the data path, without the restriction of passing
only through nodes (NEs) that are located on the data path. Signaling
messages can be routed to NEs off the data path, but which are
(presumably) aware of it. This allows a looser coupling between NEs
and data plane nodes, e.g. at the AS level.
The main advantages of path-decoupled signaling are ease of
deployment and support of additional functionality. The ease of
deployment comes from a restriction of the number of impacted nodes
in case of deployment and/or upgrade of an NSLP. It would allow, for
instance, deploying a solution without upgrading any of the routers
in the data plane. Additional functionality that can be supported
includes the use of off-path proxies to support authorization or
accounting architectures.
There are potentially significant differences in the way that the two
signaling paradigms should be analyzed. Using a single centralized
off-path NE may increase the requirements in terms of message
handling. This effect, however, is orthogonal to the NSIS charter,
since path-decoupled signaling is equally applicable to distributed
off-path entities. Failure recovery scenarios need to be analyzed
differently because fate-sharing between data and control plane can
no longer be assumed. Furthermore, the interpretation of
sender/receiver orientation becomes less obvious. With the local
operation of NTLP, the impact of path-decoupled signaling on the
routing of signaling messages is presumably restricted to the problem
of peer determination. The assumption that the off-path NEs are
loosely tied to the data path suggests, however, that peer
determination can still be based on L3 routing information.
3.3 Signaling Application Properties
It is clear that many signaling applications will require specific
protocol behavior in their NSLP. This section outlines some of the
options for NSLP behavior; further work on selecting from these
options would depend on detailed analysis of the application in
question.
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3.3.1 Sender/Receiver Orientation
In some signaling applications, one end of the data flow takes
responsibility for requesting special treatment - such as a resource
reservation - from the network. The appropriate end may depend on the
signaling application, or characteristics of the network deployment.
A sender-initiated approach is when the sender of the data flow
requests and maintains the resource reservation used for that flow.
In a receiver-initiated approach the receiver of the data flow
requests and maintains the resource reservation used for that flow.
The NTLP has no freedom in this area: next peers have to be
discovered in the sender to receiver direction, but after that time
the default assumption is that signaling is possible both upstream
and downstream (unless possibly an application specifically indicates
this is not required). This implies that backward routing state must
be maintained or that backward routing information must be available
in the signaling packet.
The sender and receiver initiated approaches have several differences
in operational characteristics. The main ones are as follows:
*) In a receiver-initiated approach, the signaling messages traveling
from the receiver to the sender must be backward routed such that
they follow exactly the same path as was followed by the signaling
messages belonging to the same flow traveling from the sender to the
receiver. This implies that a backward routing state per flow must be
maintained. When using a sender-initiated approach, provided
acknowledgements and notifications can be securely delivered to the
sending node, backward routing is not necessary, and nodes do not
have to maintain backward routing states.
*) In a sender-initiated approach, a mobile node can initiate a
reservation for its outgoing flows as soon as it has moved to another
roaming subnetwork. In a receiver-initiated approach, a mobile node
has to inform the receiver about its handover procedure, thus
allowing the receiver to initiate a reservation for these flows. For
incoming flows, the reverse argument applies.
*) A sender- (receiver-) initiated approach will allow faster setup
and modification if the sender (receiver) is also authorized to carry
out the operation. A mismatch between authorizing and initiating NEs
will cause additional message exchanges either in the NSLP or in a
protocol executed prior to NSIS invocation. Note that this may
complicate modifications of network control state for existing flows.
*) Where the signaling is looking for the last (nearest to receiver)
NE on the data path, receiver oriented signaling is most efficient;
sender orientation would be possible, but take more messages.
*) In either case, the initiator can generally be informed faster
about reservation failures than the remote end.
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3.3.2 Uni- and Bi-Directional Operation
For some signaling applications and scenarios, signaling may only be
considered for one direction of the data flow. However, in other
cases, there may be interesting relationships between the signaling
for the two directions; an example is QoS for a voice call. In the
basic case, bi-directional signaling can simply use a separate
instance of the same signaling mechanism in each direction. Note that
the path in the two directions may differ due to asymmetric routing.
In constrained topologies where parts of the route are symmetric, it
may be possible to use a more unified approach to bi-directional
signaling, e.g. carrying the two signaling directions in common
messages. This optimization might be used for example to make mobile
QoS signaling more efficient.
In either case, the correlation of the signaling for the two flow
directions is carried out in the NSLP. The NTLP would simply be
enabled to bundle the messages together.
3.3.3 Heterogeneous Operation
It is likely that the appropriate way to describe the state NSIS is
signaling for will vary from one part of the network to another
(depending on signaling application). For example in the QoS case,
resource descriptions that are valid for inter-domain links will
probably be different from those useful for intra-domain operation
(and the latter will differ from one NSIS domain to another).
One way to address this issue is to consider the state description
carried within the NSLP as divided in globally-understood objects
("global objects") and locally-understood objects ("local objects").
The local objects are only applicable for intra-domain signaling,
while the global objects are mainly used in inter-domain signaling.
Note that such local objects are still part of the NSIS protocol and
can be inserted, used and removed by one single domain.
The purpose of this division is to provide additional flexibility in
defining the objects carried by the NSLP such that only those objects
that are applicable in a particular setting are used. An example
approach for reflecting the distinction in the signaling is that
local objects could be put into separate local messages that are
initiated and terminated within one single NSIS domain and/or they
could be "stacked" within the NSLP messages that are used for inter-
domain signaling.
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3.3.4 Peer-Peer and End-End Relationships
The assumption taken in this framework is that the NTLP will operate
'locally', that is, just over the scope of a single peer
relationship. End-to-end operation is built up by simply
concatenating these relationships. Any non-local operation (if any)
will take place only in particular NSLPs.
The peering relations may also have an impact on the required amount
of state at each NSIS entity. When direct interaction with remote
peers is not allowed, it may be required to keep track of the path
that a message has followed through the network. This can be achieved
by keeping per-flow state at the NSIS entities or by maintaining a
record route object in the messages.
Note that, for the reasons discussed in section 3.2.1, NSLP peers are
not inevitably NTLP peers. This has a number of implications for the
relationship between the signaling layers, in that NSLP peers may
depend on the service provided by a concatenation of NTLP peer
relationships rather than a single one, which makes it harder to
exploit fully some NTLP properties (e.g. channel security,
reliability).
3.3.5 Acknowledgements and Notifications
We are assuming that the NTLP provides a simple message transfer
service, and any acknowledgements or notifications it generates are
handled purely internally (and apply within the scope of a single
peer relationship).
However, we expect that some signaling applications will requires
acknowledgements regarding the failure/success of state installation
along the data path, and this will be an NSLP function.
Acknowledgements can be sent along the sequence of NTLP peer
relationships towards the signaling initiator, which relieves the
requirements on the security associations that need to be maintained
by NEs and can ensure NAT traversal in both directions. (If this
direction is towards the flow sender, it implies maintaining reverse
routing state in the NTLP). In certain circumstances (e.g. trusted
domains), an optimization can be made by sending acknowledgements
directly to the signaling initiator (see section 3.2.2).
The semantics of the acknowledgement messages are of particular
importance. An NE sending a message could assume responsibility for
the entire downstream chain of NEs, indicating for instance the
availability of reserved resources for the entire downstream path.
Alternatively, the message could have a more local meaning,
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indicating for instance that a certain failure or degradation
occurred at a particular point in the network.
Notifications differ from acknowledgements because they are not
(necessarily) generated in response to other signaling messages. This
means that it may not be obvious to determine where the notification
should be sent. Other than that, the same considerations apply as for
acknowledgements. One useful distinction to make would be to
differentiate between notifications that trigger a signaling action
and others that don't. The security requirements for the latter are
less stringent, which means they could be sent directly to the NE
they are destined for (provided this NE can be determined).
3.3.6 Security and other AAA Issues
In some cases it will be possible to achieve the necessary level of
signaling security by using basic 'channel security' mechanisms [10]
at the level of the NTLP, and the possibilities are described in
section 4.6. In other cases, signaling applications may have specific
security requirements, in which case they are free to invoke their
own authentication and key exchange mechanisms and apply 'object
security' to specific fields within the NSLP messages.
In addition to authentication, authorisation (to manipulate network
control state) has to be considered as functionality above the NTLP
level, since it will be entirely application specific. Indeed,
authorisation decisions may be handed off to a third party in the
protocol (e.g. for QoS, the resource management function as described
in section 6.1.5). Many different authorisation models are possible,
and the variations impact
*) what message flows take place - for example, whether authorisation
information is carried along with a control state modification
request, or is sent in the reverse direction in response to it;
*) what administrative relationships are required - for example,
whether authorisation takes place only between peer signaling
applications, or over longer distances.
Because the NTLP operates only between adjacent peers, and places no
constraints on the direction or order in which signaling applications
can send messages, these authorisation aspects are left open to be
defined by each NSLP. Further background discussion of this issue is
contained in [11].
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3.4 Open Layer Model Issues
3.4.1 Classical Transport Functionality
The first major issue is the extent to which the NTLP should include
'traditional' transport like functions, or whether these should be
seen as either fundamentally unnecessary or automatically handled by
the upper layers. The following functions have been identified as
candidates:
1. Local retransmission to improve reliability. The argument in favor
is that the NTLP can recover from congestive loss or corruption much
more rapidly than end-to-end (NSLP) mechanisms; the argument against
is that the additional complexity in the NTLP is not needed for all
signaling applications. (It's assumed that the NTLP is not actually
providing perfect message delivery guarantees or notifications, for
example because NSLP peers may be separated by more than one NTLP
peer relationship. A signaling application that needs peer-peer
acknowledgements of this nature should define them within the NSLP.)
In-order message delivery and duplicate detection are related
functions.
2. Congestion control. Here, the question is whether the NTLP should
include a common mechanism which protects the local portion of the
network from overload, or whether this can be derived from the
behavior of each signaling application.
3. Message fragmentation. For NSLPs that generate large messages, it
will be necessary to fragment and re-assemble them efficiently within
the network, where the use IP fragmentation may lead to reduced
reliability and be incompatible with some addressing schemes. (It's
assumed that the counterpart functionality, of bundling small
messages together, can be provided locally by the NTLP as an option
if desired; it doesn't affect the operation of the network
elsewhere.)
4. Flow control. Here, the question is how a receiving NSLP should be
protected from overload - whether the NTLP should provide a flow
controlled channel, or whether this should be managed using
application layer acknowledgements, for example.
It appears that all these issues don't affect the basic way in which
the NSLP/NTLP layers relate to each other (e.g. in terms of the
semantics of the inter-layer interaction); it is much more a question
of the overall performance/complexity tradeoff implied by placing
certain functions within each layer.
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3.4.2 State Management
It is clear that the NTLP may have to manage some per-flow state to
carry out its message delivery functions (for example, state about
the reverse route for signaling messages, or state needed for route
change detection). How this state is stored and managed is an
internal matter for the NTLP (see section 4), and the details (in
particular, any connection model it might use) is in any case
entirely invisible to the signaling applications.
However, signaling applications are frequently managing network
control state for their own purposes, and it is an open issue how
much the NTLP should provide a common service to do this for them.
The simplest case is that the NTLP simply delivers messages, and any
state-related aspects (lifetimes, message semantics and so on) are
entirely invisible to it, being part of the signaling application
data. This provides the simplest interface between NTLP and NSLP.
The other extreme is where the NTLP provides a complete state
management service, including explicit commands for creation,
modification and deletion of state with known lifetimes in remote
nodes. This service could make it easy to write new signaling
applications, at the cost of increasing the complexity of the
NTLP/NSLP interface; in particular, there would be many more events
and error conditions to generate within the NTLP, and there may be
several different types of state management semantics required by
different signaling applications. The commonality with other parts of
NTLP functionality is not clear.
An intermediate case is where there is particular support for the
refresh messages used for soft-state maintenance. The characteristics
of these messages are that they can be sent and processed without
invoking signaling application specific logic, and that their timing
can be manipulated to fit in with other NTLP requirements (e.g.
jittering to avoid network synchronization, or to allow bundling with
other messages). Therefore, provided this functionality can be
defined simply and universally, there may be benefits in supporting
it within the NTLP itself. The implication would be that some NTLP
messages contain timing and other control information (to allow the
refresh to be handled correctly at intermediate NSLP-unaware nodes).
In addition, the automatic generation and reception of refreshes
could be handled above or below the NSLP/NTLP boundary (this seems to
be mainly an API issue).
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4. The NSIS Transport Layer Protocol
This section describes the overall functionality required from the
NTLP. It mentions possible protocol components within the NTLP layer
and the different possible addressing modes that can be utilized.
The interfaces between NTLP and the layers above and below it are
identified, with a description of the identity elements that appear
on these interfaces.
It is not the intention of this discussion to design the NTLP or even
to discuss design options, although some are described as examples.
The goal is to provide a general discussion of required functionality
and to highlight some of the issues associated with this.
4.1 Internal Protocol Components
The NTLP includes all functionality below the signaling application
layer and above the IP layer. The functionality that is required
within the NTLP is described in section 3.2.
Some NTLP functionality could be provided via components existing as
sublayers within the NTLP design. For example, if specific transport
capabilities are required, such as congestion avoidance,
retransmission, security and so on, then existing protocols, such as
TCP or TLS, could be incorporated into the NTLP. This possibility is
not required or excluded by this framework.
==================== ===========================
^ +------------------+ +-------------------------+
| | | | NSIS Specific Functions |
| | | | .............|
NSIS | | Monolithic | |+----------+. Peer .|
Transport | | Protocol | || Existing |. Discovery .|
Layer | | | || Protocol |. Aspects .|
| | | |+----------+.............|
V +------------------+ +-------------------------+
==================== ===========================
Figure 6: Options for NTLP Structure
If peer-peer addressing (section 4.2) is used for some messages, then
active next-peer discovery functionality will be required within the
NTLP to support the explicit addressing of these messages. (This
could use message exchanges for dynamic peer discovery as a sublayer
within the NTLP; there could also be an interface to external
mechanisms to carry out this function.)
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4.2 Addressing
There are two ways to address a signaling message being transmitted
between NSIS peers:
*) peer-peer, where the message is addressed to a neighboring NSIS
entity that is known to be closer to the destination NE.
*) end-to-end, where the message is addressed to the destination
directly, and intercepted by an intervening NE.
With peer-peer addressing, an NE will determine that address of the
next NE based on the payload of the message (and potentially on the
previous NE). This requires the address of the destination NE to be
derivable from the information present in the payload. This can be
achieved through the availability of a local routing table or through
participation in active peer discovery message exchanges. Peer-peer
addressing inherently supports tunneling of messages between NEs, and
is equally applicable to the path-coupled and path-decoupled cases.
In the case of end-to-end addressing, the message is addressed to the
data flow receiver, and (some of) the NEs along the data path
intercept the messages. The routing of the messages should follow
exactly the same path as the associated data flow (but see section
5.1.1 on this point). Note that securing messages sent this way
raises some interesting security issues (these are discussed in
[12]).
It is not possible at this stage to mandate one addressing mode or
the other. Indeed, each is necessary for some aspects of NTLP
operation: in particular, initial discovery of the next downstream
peer will usually require end-to-end addressing, whereas reverse
routing will always require peer-peer addressing. For other message
types, the choice is a matter of protocol design. The mode used is
not visible to the NSLP, and the information needed in each case is
available from the flow identifier (section 4.5.1) or locally stored
NTLP state.
4.3 Lower Layer Interfaces
The NTLP interacts with 'lower layers' of the protocol stack for the
purposes of sending and receiving signaling messages. This framework
places the lower boundary of the NTLP at the IP layer. The interface
to the lower layer is therefore very simple:
*) The NTLP sends raw IP packets
*) The NTLP receives raw IP packets. In the case of peer-peer
addressing, they have been addressed directly to it. In the case of
end-to-end addressing, this will be achieved by intercepting packets
that have been marked in some special way (by special protocol number
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or by some option interpreted within the IP layer, such as the Router
Alert option [13] and [14]).
*) The NTLP receives indications from the IP layer regarding route
changes and similar events (see section 5.1).
For correct message routing, the NTLP needs to have some information
about link and IP layer configuration of the local networking stack.
For example, it needs to know:
*) [in general] how to select the outgoing interface for a signaling
message, in case this needs to match the interface that will be used
by the corresponding flow. This might be as simple as just allowing
the IP layer to handle the message using its own routing table. There
is no intention to do something different from IP routing (for end-
to-end addressed messages); however, some hosts allow applications to
bypass routing for their data flows, and the NTLP processing must
account for this.
*) [in the case of IPv6] what address scopes are associated with the
interface that messages are sent and received on (to interpret scoped
addresses in flow identification, if these are to be allowed).
Configuration of lower layer operation to handle flows in particular
ways is handled by the signaling application.
4.4 Upper Layer Services
The NTLP offers transport layer services to higher layer signaling
applications for two purposes: sending and receiving signaling
messages, and exchanging control and feedback information.
For sending and receiving messages, two basic control primitives are
required:
*) Send Message, to allow the signaling application to pass data to
the NTLP for transport.
*) Receive Message, to allow the NTLP to pass received data to the
signaling application.
The NTLP and signaling application may also want to exchange other
control information, such as:
*) Signaling application registration/de-registration, so that
particular signaling application instances can register their
presence with the transport layer. This may also require some
identifier to be agreed between the NTLP and signaling application to
allow support the exchange of further control information and to
allow the de-multiplexing of incoming data.
*) NTLP configuration, allowing signaling applications to indicate
what optional NTLP features they want to use, and to configure NTLP
operation, such as controlling what transport layer state should be
maintained.
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*) Error messages, to allow the NTLP to indicate error conditions to
the signaling application and vice versa.
*) Feedback information, such as route change indications so that
the signaling application can decide what action to take.
The exact form of the primitives used across this interface and the
information exchanged by them depends on a decision about what the
responsibility of the layers is either side of the interface, and
where state is managed (see section 3.4.2).
4.5 Identity Elements
4.5.1 Flow Identification
The flow identification is a method of identifying a flow in a unique
way. All packets associated with the same flow will be identified by
the same flow identifier. The key aspect of the flow identifier is
to provide enough information such that the signaling flow receives
the same treatment along the data path as that actual data itself,
i.e. consistent behavior is applied to the signaling and data flows
by a NAT or policy-based forwarding engine.
Information that could be used in flow identification may include:
*) source IP address;
*) destination IP address;
*) protocol identifier and higher layer (port) addressing;
*) flow label (typical for IPv6);
*) SPI field for IPSec encapsulated data;
*) DSCP/TOS field
It is assumed that wildcarding on these identifiers is not needed
(further analysis may be required).
We've assumed here that the flow identification is not hidden within
the NSLP, but is explicitly part of the NTLP. The justification for
this is that it might be valuable to be able to do NSIS processing
even at a node which was unaware of the specific signaling
application (see section 3.2.1): an example scenario would be
messages passing through an addressing boundary where the flow
identification had to be re-written.
4.5.2 Session Identification
There are circumstances where it is important to be able to refer to
signaling application state independently of the underlying flow.
For example, if the address of one of the flow endpoints changes due
to a mobility event, it is desirable to be able to change the flow
identifier without having to install a completely new reservation.
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The session identifier provides a method to correlate the signaling
about the different flows with the same network control state.
The session identifier is essentially a signaling application
concept, since it is only used in non-trivial state management
actions that are application specific. However, we assume here that
it should be visible within the NTLP. This enables it to be used to
control NTLP behavior, for example, by controlling how the transport
layer should forward packets belonging to this session (as opposed to
this signaling application). In addition, the session identifier can
be used by the NTLP to demultiplex received signaling messages
between multiple instances of the same signaling application, if such
an operational scenario is supported (see section 4.5.3 for more
information on signaling application identification).
To be useful for mobility support, the session identifier should be
globally unique, and it should not be modified end-to-end. It is well
known that it is practically impossible to generate identifiers in a
way which guarantees this property; however, using a large random
number makes it highly likely. In any case, the NTLP ascribes no
valuable semantics to the identifier (such as 'session ownership');
this problem is left to the signaling application, which may be able
to secure it to use for this purpose.
4.5.3 Signaling Application Identification
Since the NTLP can be used to support several NSLP types, there is a
need to identify which type a particular signaling message exchange
is being used for. This is to support:
*) processing of incoming messages - the NTLP should be able to
demultiplex these towards the appropriate signaling applications;
*) processing of general messages at an NSIS aware intermediate node
- if the node does not handle the specific signaling application, it
should be able to make a forwarding decision without having to parse
upper layer information.
No position is taken on the form of the signaling application
identifier, or even the structure of the signaling application
'space' - free-standing applications, potentially overlapping groups
of capabilities, etc. These details should not influence the rest of
NTLP design.
4.6 Security Properties
It is assumed that the only security service required within NTLP is
channel security. Channel security requires a security association to
be established between the signaling endpoints, which is carried out
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via some authentication and key management exchange. This
functionality could be provided by reusing a standard protocol.
In order to protect a particular signaling exchange, the NSIS entity
needs to select the security association that it has in place with
the next NSIS entity that will be receiving the signaling message.
The ease of doing this depends on the addressing model in use by the
NTLP (see section 4.2).
Channel security can provide many different types of protection to
signaling exchanges, including integrity and replay protection and
encryption. It is not clear which of these is required at the NTLP
layer, although most channel security mechanisms support them all.
Channel security can also be applied to the signaling messages with
differing granularity, i.e. all or parts of the signaling message may
be protected. For example, if the flow is traversing a NAT, only the
parts of the message that do not need to be processed by the NAT
should be protected. It is an open question as to which parts of the
NTLP messages need protecting, and what type of protection should be
applied to each.
5. Interactions with Other Protocols
5.1 IP Routing Interactions
The NSIS Transport Layer (NTLP) is responsible for discovering the
next node to be visited by the signaling protocol. For path-coupled
signaling, this next node should be the one that will be visited by
the data flow. In practice, this peer discovery will be approximate,
as any node could use any feature of the peer discovery packet to
route it differently than the corresponding data flow packets.
Divergence between data and signaling path can occur due to load
sharing or load balancing (section 5.1.1). An example specific to the
case of QoS is given in section 6.1.1. Route changes cause a
temporary divergence between the data path and the path on which
signaling state has been installed. The occurrence, detection and
impact of route changes is described in section 5.1.2. A description
of this issue in the context of QoS is given in section 6.1.2.
5.1.1 Load Sharing and Policy-Based Forwarding
Load sharing or load balancing is a network optimization technique
that exploits the existence of multiple paths to the same destination
in order to obtain benefits in terms of protection, resource
efficiency or network stability. The significance of load sharing in
the context of NSIS is that, if the load sharing mechanism in use
will forward packets on any basis other than the destination address,
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routing of messages using end-to-end addressing does not guarantee
that the messages will follow the data path. Policy-based forwarding
for data packets - where the outgoing link is selected based on
policy information about fields additional to the packet destination
address - has the same impact.
Signaling and data flow packets may diverge because of these
techniques. In OSPF, load balancing can be used between equal cost
paths [15] or unequal cost paths. An example of the latter approach
is Optimized Multi Path (OMP). OMP discovers multiple paths, not
necessarily equal cost paths, to any destinations in the network, but
based on the load reported from a particular path, it determines
which fraction of the data to direct to the given path. Incoming
packets are subject to a (source, destination address) hash
computation, and effective load sharing is accomplished by means of
adjusting the hash thresholds. BGP [16][17] advertises the routes
chosen by the BGP decision process to other BGP speakers. In the
basic specification, routes with the same Network Layer reachability
information (NLRI) as previously advertised routes implicitly replace
the original advertisement, which means that multiple paths for the
same prefix cannot exist. Recently, however, a new mechanism was
defined that will allow the advertisement of multiple paths for the
same prefix without the new paths implicitly replacing any previous
ones [18]. The essence of the mechanism is that each path is
identified by an arbitrary identifier in addition to its prefix.
If the routing decision is based on both source and destination
address, signaling and data flow packets may still diverge because of
layer 4 load-balancing (based on TCP/UDP or port-based). Such
techniques would, however, constrain the use of proxies. Proxies
would cause ICMP errors to be misdirected to the source of the data
because of source address spoofing.
If the routing decision is based on the complete five-tuple,
divergence may still occur because of the presence of router alert
options. In this case, the same constraint on proxy use applies as
above. Additionally, it becomes difficult for the end systems to
distinguish between data and signaling packets. Finally, QoS routing
techniques (section 6.1.3) may base the routing decision on any field
in the packet header (e.g. DSCP, ...).
Most load-balancing techniques use the first n bytes of the packet
header (including SA, DA and protocol field) in the hashing function.
In this case, the above considerations regarding source/destination
address or five-tuple based forwarding apply.
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5.1.2 Route Changes
In a routed network, each packet is independently routed based on its
header information. Whenever a better route towards the destination
becomes available, this route is installed in the forwarding table
and will be used for all subsequent (data and signaling) packets.
This can cause a divergence between the path along which state has
been installed and the path along which forwarding will actually take
place.
The possibility of route changes requires the presence of three
processes in the signaling protocol
1. route change detection
2. installation of state on the new path
3. teardown of state on the old path
Many route change detections methods can be used, some of which need
explicit protocol support and some of which are implementation-
internal. They differ in their speed of reaction and the types of
change they can detect. In rough order of increasing applicability,
they can be summarized as:
a) monitoring changes in local interface state
b) monitoring network-wide topology changes in a link-state routing
protocol
c) inference from changes in data packet TTL
d) inference from loss of packet stream in a downstream flow-aware
router
e) inference from changes in signalling packet TTL
f) changed route of a PATH-like (end-to-end addressed) signaling
packet
g) changed route of a specific end-to-end addressed probe packet
There are essentially three ways in which detection can happen: based
on network monitoring (method a-b), based on data packet monitoring
(method c-d) and based on monitoring signaling protocol messages
(method e-g). Methods contingent on monitoring signaling messages
become less effective as refresh reduction techniques are used.
When a route change has been detected, it is important that state is
installed as quickly as possible along the new path. It is not
guaranteed that the new path will be able to provide the same
characteristics that were available on the old path. In order to be
able to avoid duplicate state installation or, worse, rejection of
the signaling message because of previously installed state, it is
important to be able to recognize the new signaling message as
belonging to an existing session. In this respect, we distinguish
between route changes with associated change of the flow
specification (e.g. in case of a mobility event when the IP source
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might change) and route changes without change of the flow
specification (e.g. in case of a link failure along the path). The
former case requires an identifier independent from the flow
specification.
When state has been installed along the new path, the existing state
on the old path needs to be removed. With the soft-state principle,
this will happen automatically because of the lack of refresh
messages. Depending on the refresh timer, however, it may be required
to tear down this state much faster (e.g. because it is tied to an
accounting record). In that case, the teardown message needs to be
able to distinguish between the new path and the old path.
The problem of route changes would not occur if there was a way to do
route pinning. Route pinning refers to the independence of the path
taken by certain data packets from reachability changes caused by
routing updates from an Interior Gateway Protocol (OSPF, IS-IS) or an
Exterior Gateway Protocol (BGP).
5.1.3 Router Redundancy
In some environments, it is desired to provide connectivity and per
flow or per class flow management with high-availability
characteristics, i.e. with rapid transparent recovery even in the
presence of route changes. This may involve interactions with the
basic protocols which are used to manage the routing in this case,
such as VRRP [19]. A future version of this document may consider
interactions between NSIS and such protocols in support of high
availability functionality.
5.2 Mobility Interactions
Mobility, in most cases, causes changes to the data path that packets
take. Assuming that signaling has taken place prior to any mobility
to establish some state along the data path, new signaling may be
needed in order to (re)establish state along the changed data path.
The interactions between mobility and signaling protocols have been
extensively analyzed in recent years, primarily in the context of
RSVP and Mobile IP interaction (e.g. [20]), but also in the context
of other types of network (e.g. [21]). This analysis work has shown
that some difficulties in the interactions are quite deeply rooted in
the detailed design of these protocols; however, the problems and
their possible solutions fall under five broad headings. The main
issues for a resource signaling application are limiting the period
after handovers during for which the resource states are not
available along the path; and avoiding double reservations -
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reservations on both the old path and new path. Similar issues may
apply to other types of signaling application.
5.2.1 Addressing and Encapsulation
A mobility solution typically involves address reallocation on
handover (unless a network supports per host routing) and may involve
special packet formats (e.g. the routing header and Home Address
option of MIPv6). Since NSIS may depend on end system addresses for
forwarding signaling messages and defining flows (section 4.5.1), the
special implications of mobility for addressing need to be
considered. Examples of possible approaches that could be used to
solve the addressing and encapsulation problem are as follows:
* Use a flow identification based on low level IP addresses (e.g. the
Care of Address) and other 'standard' fields in the IP header. This
makes least demands on the packet classification engines within the
network. However, it means that even on a part of the flow path that
is unchanged, the session will need to be modified to reflect the
changed flow identification (see section 5.2.3).
* Use a flow identification that does not change (e.g. based on Home
Address); this is the approach assumed in [22]. This simplifies the
problem of session update, at the likely cost of considerably
complicating the flow identification requirements.
In the first approach, to prevent double reservation, NSIS entities
need to be able to recognize that a session with the new flow
identifier is to be correlated with an existing one. A session
identifier could be used for this purpose. This is why the session
identifier as described in section 4.5.2 has to have end-to-end
semantics.
While the feasibility and performance of this first approach needs to
be assessed, given the high impact of requiring more sophisticated
packet classifiers, it still seems more plausible than the second
approach. This implies that signaling applications should define
flows in terms of real, routable (care of) addresses rather than
virtual (home) addresses.
5.2.2 Localized Path Repair
In any mobility approach, a handover will cause at least some changes
in the path of upstream and downstream packets. At some point along
the joined path, an NSIS entity should be able to recognize this
situation, based upon session identification. New state needs to be
installed on the new path, and removed from the old. Who triggers the
new state may be constrained by which entities are allowed to carry
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out which state manipulations, which is then a signaling application
question.
A critical point here is the signaling that is used to discover the
crossover node. This is a generalization of the problem of finding
next-NSIS peer: it requires extending the new path over several hops
until it intersects the old one. This is easy for the uplink
direction (where the mobile is the sender), but much harder for
downlink without signaling via the correspondent. There is no reason
for the crossover node for uplink and downlink flows to be the same,
even for the same correspondent. The problem is discussed further in
[23].
5.2.3 Update on the Unchanged Path
On the path between the crossover node(s) and the correspondent, it
is necessary to avoid, if possible, double reservations, but rather
to update the network control state to reflect new flow
identification (this is needed, by the default assumption of section
5.2.1). Examples of approaches that could be used to solve this
problem are the following:
*) Use a session state identification that does not change even if
the flow definition changes (see Section 4.5.2). Signaling is still
needed to update a changed flow identification, but it should be
possible to avoid AAA and admission control processing.
*) Use an NSIS-capable crossover router that manages this update
autonomously (more efficiently than the end nodes could), with
similar considerations to the local path repair case.
Note that in the case of an address change, end to end message
exchanges will be required at the application layer anyway, so
signaling to update the flow identifier does not necessarily add to
the handover latency.
5.2.4 Interaction with Mobility Signaling
In existing work on mobility protocol and signaling protocol
interactions, several framework proposals describing the protocol
interactions have been made. Usually they have taken existing
protocols (Mobile IP and RSVP respectively) as the starting point; it
should be noted that an NSIS protocol might operate in quite a
different way. In this section, we provide an overview of how these
proposals would be reflected in framework of NSIS. The mobility
aspects are described using Mobile IP terminology, but are generally
applicable to other network layer mobility solutions. The purpose of
this overview is not to select or prioritise any particular approach,
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but simply to point out how they would fit into our framework and any
major issues with them.
We can consider that two signaling processes are active: mobility
signaling and NSIS signaling. The discussion so far considered how
NSIS signaling should operate. There is still a question of how the
interactions between the NSIS and mobility signaling should be
considered.
The basic case of totally independent specification and
implementation seems likely to lead to ambiguities and even
interoperability problems (see [22]). At least, the addressing and
encapsulation issues for mobility solutions that use virtual links or
their equivalents need to be specified in an implementation-neutral
way.
A type of 'loose' integration is to have independent protocol
definitions, but to define how they trigger each other - in
particular, how the mobility protocol triggers sending of
refresh/modify/tear messages. A pair of implementations could use
these triggers to improve performance, primarily reducing latency.
(Existing RSVP modifications consider the closer interaction of
making the RSVP implementation mobility routing aware, e.g. so it is
able to localize refresh signaling; this would be a self contained
aspect of NSIS.) This information could be developed by analyzing
message flows for various mobility signaling scenarios as was done in
[20].
An even tighter level of integration is to consider a single protocol
carrying both mobility and network control state information.
Logically, there are two cases:
1. Carry mobility routing information (a 'mobility object') in the
signaling messages, as is done in [22]. (The prime purpose in this
approach is to enable crossover router discovery.)
2. Carry signaling in the mobility messages, typically as a new
extension header. This was proposed in [24] and followed up in [25];
[26] also anticipates this approach. In our framework, we could
consider this a special case of NSIS layering, with the mobility
protocol playing the role of the signaling transport.
Other modes of interaction might also be possible. The critical point
with all these models is that the general solutions developed by NSIS
should be independent of mobility protocols. Tight integration would
have major deployment issues especially in interdomain cases.
Therefore, any tightly integrated solution is considered out of scope
of initial NSIS development.
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5.2.5 Interaction with Context Transfer
In the context of mobility between different access routers, it is
common to consider performance optimizations in two areas: selection
of the optimal access router to handover to, and transfer of state
information between the access routers to avoid having to regenerate
it in the new access router after handover. The Seamoby Working Group
is developing solutions for these protocols (CARD [27] and Context
Transfer [28] respectively); alternative approaches with similar
characteristics are also possible.
As these solutions are still underdevelopment, it is premature to
specify details on the interaction. It is thought that Context
Transfer transfers state between access routers based upon changes
caused by mobility. NSIS protocol state may be a candidate for
context transfer. Such work, should it be undertaken, will be done
in the Seamoby working group.
5.3 Interactions with NATs
Because at least some messages will almost inevitably contain address
and possibly higher layer information as payload, we must consider
the interaction with address translation devices (NATs). As well as
'traditional' NATs of various types (as defined in [29]) very similar
considerations would apply to some IPv4/v6 transition mechanisms such
as SIIT [30].
In the simplest case of an NSIS unaware NAT in the signaling path,
payloads will be uncorrected and the signaling will be for the
incorrect flow. Applications could attempt to use STUN [31] or
similar techniques to detect and recover from the presence of the
NAT. Even then, NSIS protocols would have to use a well known
encapsulation (TCP/UDP/ICMP) to avoid being dropped by the more
cautious low-end NAT devices.
A simple 'NSIS-aware' NAT would require flow identification
information to be in the clear and not integrity protected. An
alternative conceptual approach is to consider the NAT functionality
being part of message processing itself, in which case the
translating node can take part natively in any NSIS protocol security
mechanisms. Depending on NSIS protocol layering, it would be possible
for this processing to be done in an NSIS entity which was otherwise
ignorant of any particular signaling applications. This is the
motivation for including basic flow identification information in the
NTLP (section 4.5.1).
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Note that all of this discussion is independent of the use of a
specific NSLP for general control of NATs (and firewalls). This is
considered in section 6.2.
6. Signaling Applications
This section describes NSLPs for particular signaling applications.
The assumption is that the NSLP uses the generic functionality of the
NTLP given earlier; this section describes specific aspects of NSLP
operation.
6.1 Signaling for Quality of Service
In the case of signaling for QoS, all the basic NSIS concepts of
section 3.1 apply. In addition, there is an assumed directionality of
the signaling process, in that one end of the signaling flow takes
responsibility for actually requesting the resource. This leads to
the following definitions:
*) NSIS Initiator (NI): the signaling entity which makes the resource
request, usually as a result of user application request.
*) NSIS Responder (NR): the signaling entity that acts as the
endpoint for the signaling and can optionally interact with
applications as well.
*) NSIS Forwarder (NF): the signaling entity an NI and NR which
propagates NSIS signaling further through the network.
Each of these entities will interact with a resource management
function (RMF) which actually allocates network resources (router
buffers, interface bandwidth and so on).
Note that there is no constraint on which end of the signaling flow
should take the NSIS Initiator role: with respect to the data flow
direction it could be at the sending or receiving end.
6.1.1 Protocol Messages
The QoS NSLP will include a set of messages to carry out resource
reservations along the signaling path. A message set for the QoS NSLP
is shown below (a very similar set of messages was generated in
[32]). Note that the 'direction' column in the table below only
indicates the 'orientation' of the message. The messages can be
originated and absorbed at NF nodes as well as the NI or NR; an
example might be NFs at the edge of a domain exchanging messages to
set up resources for a flow across a it.
Note the working assumption that responder as well as the initiator
can release a reservation (comparable to rejecting it in the first
place). It is left open if the responder can modify a reservation,
during or after setup. This seems mainly a matter of assumptions
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about authorization, and the possibilities might depend on resource
type specifics.
+-------+---------+---------------------------------------------+
| Name |Direction| Semantics |
+-------+---------+---------------------------------------------+
|Request| I-->R | Create a new reservation for a flow |
+-------+---------+---------------------------------------------+
|Modify | I-->R | Modify an existing reservation |
| |(&R-->I?)| |
+-------+---------+---------------------------------------------+
|Release| I-->R & | Delete (tear down) an existing reservation |
| | R-->I | |
+-------+---------+---------------------------------------------+
|Accept/| R-->I | Confirm (possibly modified?) or reject a |
| Reject| | reservation request |
+-------+---------+---------------------------------------------+
|Notify | I-->R & | Report an event detected within the |
| | R-->I | network |
+-------+---------+---------------------------------------------+
|Refresh| I-->R | State management (see section 4.4) |
+-------+---------+---------------------------------------------+
The table also explicitly includes a refresh message. This does
nothing to a reservation except extend its lifetime, and is one
possible state management mechanism (see next section).
6.1.2 State Management
The prime purpose of NSIS is to manage state information along the
path taken by a data flow. The issues regarding state management
within the NTLP (state related to message transport) are described in
section 4. The QoS NSLP will typically have to handle additional
state related to the desired resource reservation to be made.
There two critical issues to be considered in building a robust NSLP
to handle this problem:
*) The protocol must be scalable. It should allow minimization of the
resource reservation state storage demands that it implies for
intermediate nodes; in particular, storage of state per 'micro' flow
is likely to be impossible except at the very edge of the network. A
QoS signaling application might require per flow or lower granularity
state; examples of each for the case of QoS would be IntServ [33] or
RMD [34] (per 'class' state) respectively.
*) The protocol must be robust against failure and other conditions,
which imply that the stored resource reservation state has to be
moved or removed.
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For resource reservations, typically soft state management is
considered for robustness reasons. It is currently open whether the
soft state protocol aspects should be built into the NSLP for
specific signaling applications, or provided as a generic service by
the NTLP; this issue is discussed in section 3.4.2.
6.1.3 QoS Forwarding
The assumption is that the NTLP works with standard (i.e. best-
effort) layer 3 routing. There are, however, several proposals for
the introduction of QoS awareness in the routing protocols. All of
these essentially lead to the existence of multiple paths (with
different QoS) towards the same destination. As such, they also
contain an inherent risk for a divergence between control plane and
data plane, similar to the load sharing case. Clearly, any QoS NSLP
needs to be able to handle this type of routing.
For intra-domain data flows, the difference in routing may result
from a QoS-aware traffic engineering scheme, that e.g. maps incoming
flows to LSPs based on multi-field classification. In BGP, several
techniques for including QoS information in the routing decision are
currently proposed. A first proposal is based on a newly defined BGP-
4 attribute, the QoS_NLRI attribute [16]. The QoS_NLRI attribute is
an optional transitive attribute that can be used to advertise a QoS
route to a peer or to provide QoS information along with the Network
Layer Reachability Information (NLRI) in a single BGP update. A
second proposal is based on controlled redistribution of AS routes
[17]. It defines a new extended community (the redistribution
extended community) that allows a router to influence how a specific
route should be redistributed towards a specified set of eBGP
speakers. The types of redistribution communities may result in a
specific route not being announced to a specified set of eBGP
speakers, that it should not be exported or that the route should be
prepended n times.
6.1.4 Route Changes and QoS Reservations
In this section, we will explore the expected interworking between a
signaling for resource BGP routing updates, although the same applies
for any source of routing updates. The normal operation of the NSIS
protocol will lead to the situation depicted in Figure 7, where the
reserved resources match the data path.
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reserved +----+ reserved +----+
------->| NF |----------->| NF |
+----+ +----+
=====================================
data path
Figure 7: Normal NSIS protocol operation
A route change (triggered by a BGP routing update for instance) can
occur while such a reservation is in place. In case of RSVP, the
route change will be installed immediately and any data that is sent
will be forwarded on the new path. This situation is depicted Figure
8.
Route update
|
v
reserved +----+ reserved +----+
------->| NF |----------->| NF |
+----+ +----+
========== |
|| | +----+
|| +---------->| NF |
|| +----+
============================
data path
Figure 8: Route Change
Resource reservation on the new path will only be started once the
next control message is routed along the new path. This means that
there is a certain time interval during which resources are not
reserved on (part of) the data path. To minimize this time interval
several techniques could be considered. As an example, RSVP [4] has
the concept of local repair, where the router may be triggered by a
route change. In that case the RSVP node can start sending PATH
messages directly after the route has been changed. Note that this
option may not be available if no per-flow state is kept in the NF.
It is not guaranteed that the new path will be able to provide the
same guarantees that were available on the old path. Therefore, in a
more desirable scenario, the NF should wait until resources have been
reserved on the new path before installing the route change (unless
of course the old path no longer exists). The route change procedure
then consists of the following steps:
1. NF receives a route announcement,
2. Refresh messages are forwarded along the current path,
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3. A copy of the refresh message is re-marked as a request and send
along the new path that was announced,
4. When the NF has been acknowledged about the reservations on the
new path the route will be installed and the data will flow along the
new path.
Another example related to route changes is denoted as severe
congestion and is explained in [34]. This solution adapts to a route
change, when a route change creates a congestion on the new routed
path.
6.1.5 Resource Management Interactions
The QoS NSLP itself is not involved in any specific resource
allocation or management techniques. The definition of an NSLP for
resource reservation with Quality-of-Service, however, implies the
notion of admission control. For a QoS NSLP, the measure of signaling
success will be the ability to reserve resources from the total
resource pool that is provisioned in the network. We define the
function responsible for allocating this resource pool as the
Resource Management Function (RMF). The RMF is responsible for all
resource provisioning, monitoring and assurance functions in the
network.
A QoS NSLP will rely on the RMF to do resource management and to
provide inputs for admission control. In this model, the RMF acts as
a server towards client NSLP(s). It is noted, however, that the RMF
may in turn use another NSLP instance to do the actual resource
provisioning in the network. In this case, the RMF acts as the
initiator (client) of an NSLP.
This essentially corresponds to a multi-level signaling paradigm,
with an 'upper' level handling internetworking QoS signaling,
possibly running end-to-end, and a 'lower' level handling the more
specialised intradomain QoS signaling, running between just the edges
of the network (see [35], [36], and [37] for a discussion of similar
architectures). Given that NSIS signaling is already supposed to be
able to support multiple instances of NSLPs for a given flow, and
limited scope (e.g. edge-to-edge) operation, it is not currently
clear that supporting the multi-level model leads to any new protocol
requirements for the QoS NSLP.
The RMF may or may not be co-located with an NF (note that co-
location with an NI/NR can be handled logically as a combination
between NF and NI/NR). To cater for both cases, we define a (possibly
logical) NF-RMF interface. Over this interface, information may be
provided from the RMF about monitoring, resource availability,
topology, and configuration. In the other direction, the interface
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may be used to trigger requests for resource provisioning. One way to
formalize the interface between the NF and the RMF is via a Service
Level Agreement (SLA). The SLA may be static or it may be dynamically
updated by means of a negotiation protocol. Such a protocol is
outside the scope of NSIS.
There is no assumed restriction on the placement of the RMF. It may
be a centralized RMF per domain, several off-path distributed RMFs,
or an on-path RMF per router. The advantages and disadvantages of
both approaches are well-known. Centralization typically allows
decisions to be taken on more global information with more efficient
resource utilization as a result. It also facilitates deployment or
upgrade of policies. Distribution allows local decision processes and
rapid response to data path changes.
6.2 Other Signaling Applications
As well as the use for 'traditional' QoS signaling, it should be
possible to use develop NSLPs for other signaling applications which
operate on different types of network control state. One specific
case is setting up flow-related state in middleboxes (firewalls,
NATs, and so on). Requirements for such communication are given in
[6], and initial discussions of NSIS-like solutions are contained in
[38], [39] and [40]. Other examples include network monitoring and
testing, and tunnel endpoint discovery.
A future version of this document may contain more details on how to
build NSLPs for these types of signaling application.
7. Security Considerations
This document describes a framework for signaling protocols which
assumes a two-layer decomposition, with a common lower layer (NTLP)
supporting a family of signaling application specific upper layer
protocols (NSLPs). The overall security considerations for the
signaling therefore depend on the joint security properties assumed
or demanded for each layer.
Security for the NTLP is discussed in section 4.6. We have assumed
that the role of the NTLP will be to provide message protection over
the scope of a single peer relationship (between adjacent signaling
entities), and that this can most likely be provided by some kind of
channel security mechanism using an external key management mechanism
based on mutual authentication. In addition, the NTLP should be
resilient against denial of service attacks on the protocol itself.
Security for the NSLPs is entirely dependent on signaling application
requirements. In some cases, no additional protection may be required
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compared to what is provided by the NTLP. In other cases, more
sophisticated object-level protection and the use of public key based
solutions may be required. In addition, the NSLP needs to consider
the authorisation requirements of the signaling application.
Another factor is that NTLP security mechanisms operate only locally,
whereas NSLP mechanisms may also need to operate over larger regions
(not just between adjacent peers) especially for authorisation
aspects; this complicates the analysis of basing signaling
application security on NTLP protection. Further work on this and
other security design will depend on a refinement of the NSIS threats
work begun in [12].
8. Change History
8.1 Changes from draft-ietf-nsis-fw-01.txt
This -02 version has been very significantly restructured compared to
the previous version, and a section by section change history is
probably neither possible or useful. Instead, this section lists the
major technical and structural changes.
1. The concept of splitting the protocol suite into two layers is
now introduced much earlier, and the rest of the framework
restructured around it. In general, the content is supposed to be
signaling application independent: possibilities for application
dependent behavior are described in section 3.3, and the specific
case of QoS/resource management is restricted to section 6.1.
2. Sender and receiver orientation is now assumed to be a signaling
application protocol property (section 3.3.1), with the NTLP by
default operating bidirectionally (section 3.2.3). As a
consequence, the initiator, forwarder, and responder concepts
only appear in the later sections.
3. In general, the NTLP is now a 'thinner' layer than previously
envisaged (e.g. without specific reserve/tear messages), and so
the possible inter-layer coupling with the NSLP is much reduced.
However, the option of the NTLP providing some kind of generic
state management service is still an open issue (section 3.4.2).
4. In general, authorisation issues are still handled by the NSLP,
including the question of which network entities are allowed to
modify network state. In particular, the issue of 'session'
(previously 'reservation') ownership (section 3.1.4) is assumed
to be handled by the NSLP level, although session identification
is still visible to the NTLP (section 4.5.2). The implication is
that most key aspects of mobility support (section 5.2) are now
NSLP responsibilities.
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5. Both peer-peer and end-to-end addressing modes are assumed to be
needed for the NTLP, and any choice between them is a protocol
design issue (not visible externally).
References
1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
2 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997
3 Brunner, M., "Requirements for QoS Signaling Protocols", draft-
ietf-nsis-req-05.txt (work in progress), November 2002
4 Braden, R., L. Zhang, S. Berson, S. Herzog, S. Jamin, "Resource
ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification", RFC 2205, September 1997
5 Chaskar, H. (editor), "Requirements of a QoS Solution for Mobile
IP", draft-ietf-mobileip-qos-requirements-03.txt (work in
progress), July 2002
6 Swale, R. P., P. A. Mart, P. Sijben, S. Brim, M. Shore, "Middlebox
Communications (midcom) Protocol Requirements", RFC 3304, August
2002
7 Manner, J. and X. Fu, "Analysis of Existing Quality of Service
Signaling Protocols", draft-ietf-nsis-signalling-analysis-01.txt
(work in progress), February 2003
8 Thomas, M., "Analysis of Mobile IP and RSVP Interactions", draft-
thomas-nsis-rsvp-analysis-00.txt (work in progress), October 2002
9 Braden, R., and B. Lindell, "A Two-Level Architecture for Internet
Signaling", draft-braden-2level-signaling-01.txt (work in
progress), November 2002
10 Rescorla, E. et al., "Guidelines for Writing RFC Text on Security
Considerations", draft-iab-sec-cons-03.txt (work in progress),
January 2003
11 Tschofenig, H., M. Buechli, S. Van den Bosch, H. Schulzrinne,
"NSIS Authentication, Authorization and Accounting Issues", draft-
tschofenig-nsis-aaa-issues-00.txt (work in progress), February
2003
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12 Tschofenig, H. and D. Kroeselberg, "Security Threats for NSIS",
draft-ietf-nsis-threats-01.txt (work in progress), January 2003
13 Katz, D., "IP Router Alert Option", RFC 2113, February 1997
14 Partridge, C., A. Jackson, "IPv6 Router Alert Option", RFC 2711,
October 1999
15 Apostolopoulos, G., D. Williams, S. Kamat, R. Guerin, A. Orda,
T. Przygienda, "QoS Routing Mechanisms and OSPF Extensions", RFC
2676, August 1999
16 Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)", RFC
1771, March 1995
17 Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)",
draft-ietf-idr-bgp4-17.txt (work in progress), January 2002
(expired)
18 Walton, D., D. Cook, A. Retana and J. Scudder, "Advertisement of
Multiple Paths in BGP", draft-walton-bgp-add-paths-01.txt (work in
progress), November 2002
19 Knight, S., D. Weaver, D. Whipple, R. Hinden, D. Mitzel, P. Hunt,
P. Higginson, M. Shand, A. Lindem, "Virtual Router Redundancy
Protocol", RFC2338, April 1998
20 Thomas, M., "Analysis of Mobile IP and RSVP Interactions", draft-
thomas-nsis-rsvp-analysis-00.txt (work in progress), October 2002
21 Partain, D., G. Karagiannis, P. Wallentin, L. Westberg, "Resource
Reservation Issues in Cellular Radio Access Networks", draft-
westberg-rmd-cellular-issues-01.txt (work in progress), June 2002
22 Shen, C. et al., "An Interoperation Framework for Using RSVP in
Mobile IPv6 Networks", draft-shen-rsvp-mobileipv6-interop-00.txt
(work in progress), July 2001 (expired)
23 Manner, J., et al., "Localized RSVP", draft-manner-lrsvp-01.txt
(work in progress), January 2003
24 Chaskar, H. and R. Koodli, "A Framework for QoS Support in Mobile
IPv6", draft-chaskar-mobileip-qos-01.txt (work in progress), March
2001 (expired)
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25 Fu, X., et al, "QoS-Conditionalized Binding Update in Mobile
IPv6", draft-tkn-nsis-qosbinding-mipv6-00.txt (work in progress),
January 2002 (expired)
26 Kan, Z., "Two-plane and Three-tier QoS Framework for Mobile IPv6
Networks", draft-kan-qos-framework-01.txt (work in progress), July
2002
27 Trossen, D., G. Krishnamurthi, H. Chaskar, J. Kempf, "Issues in
candidate access router discovery for seamless IP-level handoffs",
draft-ietf-seamoby-cardiscovery-issues-04.txt (work in progress),
October 2002
28 Kempf, J., "Problem Description: Reasons For Performing Context
Transfers Between Nodes in an IP Access Network", RFC3374,
September 2002
29 Srisuresh, P. and M. Holdrege, "IP Network Address Translator
(NAT) Terminology and Considerations", RFC2663, August 1999
30 Nordmark, E., "Stateless IP/ICMP Translation Algorithm (SIIT)",
RFC2765, February 2000
31 Rosenberg, J., J. Weinberger, C. Huitema, R. Mahy, "STUN - Simple
Traversal of UDP Through Network Address Translators", draft-ietf-
midcom-stun-05.txt (work in progress), December 2002
32 Westberg, L., G. Karagiannis, D. Partain, V. Rexhepi., "Framework
for Edge-to-Edge NSIS Signaling", draft-westberg-nsis-edge-edge-
framework-00.txt (work in progress), May 2002
33 Braden, R., D. Clark, S. Shenker, "Integrated Services in the
Internet Architecture: an Overview", RFC 1633, June 1994
34 Westberg, L., Csaszar, A., Karagiannis, G., Marquetant, A.,
Partain, D., Pop, O., Rexhepi, V., Szabó, R., Takács, A.,
"Resource Management in Diffserv (RMD): A Functionality and
Performance Behavior Overview", Seventh International Workshop on
Protocols for High-Speed networks - PfHSN 2002, 22 - 24 April 2002
35 Ferrari, D., A. Banerjea, H. Zhang, "Network Support for
Multimedia - A Discussion of the Tenet Approach", Berkeley TR-92-
072, November 1992
36 Nichols, K., V. Jacobson, L. Zhang, "A Two-bit Differentiated
Services Architecture for the Internet", RFC 2638, July 1999
Hancock et al. Expires - September 2003 [Page 43]
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37 Baker, F., C. Iturralde, F. Le Faucheur, B. Davie, "Aggregation of
RSVP for IPv4 and IPv6 Reservations", RFC 3175, September 2001
38 Shore, M., "Towards a Network-friendlier Midcom", draft-shore-
friendly-midcom-01.txt (work in progress), June 2002
39 Shore, M., "The TIST (Topology-Insensitive Service Traversal)
Protocol", draft-shore-tist-prot-00.txt (work in progress), May
2002
40 Brunner, M. and M. Stiemerling, "Middlebox Signaling in a NSIS
Framework", draft-brunner-nsis-mbox-fmwk-00.txt (work in
progress), June 2002
Acknowledgments
The authors would like to thank Anders Bergsten, Bob Braden, Maarten
Buchli, Eleanor Hepworth, Melinda Shore and Hannes Tschofenig for
significant contributions in particular areas of this draft. In
addition, the authors would like to acknowledge Cedric Aoun, Marcus
Brunner, Danny Goderis, Cornelia Kappler, Mac McTiffin, Hans De Neve,
David Partain, Vlora Rexhepi, Henning Schulzrinne and Lars Westberg
for insights and inputs during this and previous framework
activities.
Authors' Addresses
Ilya Freytsis
Cetacean Networks Inc.
100 Arboretum Drive
Portsmouth, NH 03801
USA
email: ifreytsis@cetacean.com
Robert Hancock
Roke Manor Research
Old Salisbury Lane
Romsey
Hampshire
SO51 0ZN
United Kingdom
email: robert.hancock@roke.co.uk
Hancock et al. Expires - September 2003 [Page 44]
Next Steps in Signaling: Framework March 2003
Georgios Karagiannis
Ericsson EuroLab Netherlands B.V.
Institutenweg 25
P.O.Box 645
7500 AP Enschede
The Netherlands
email: georgios.karagiannis@eln.ericsson.se
John Loughney
Nokia Research Center
11-13 Italahdenkatu
00180 Helsinki
Finland
email: john.loughney@nokia.com
Sven Van den Bosch
Alcatel
Francis Wellesplein 1
B-2018 Antwerpen
Belgium
email: sven.van_den_bosch@alcatel.be
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Hancock et al. Expires - September 2003 [Page 45]
Next Steps in Signaling: Framework March 2003
Full Copyright Statement
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