SIPCLF V. Gurbani, Ed.
Internet-Draft Bell Laboratories, Alcatel-Lucent
Intended status: Informational E. Burger, Ed.
Expires: May 17, 2012 Georgetown University
T. Anjali
Illinois Institute of Technology
H. Abdelnur
O. Festor
INRIA
November 14, 2011
The Common Log Format (CLF) for the Session Initiation Protocol (SIP)
draft-ietf-sipclf-problem-statement-08
Abstract
Well-known web servers such as Apache and web proxies like Squid
support event logging using a common log format. The logs produced
using these de-facto standard formats are invaluable to system
administrators for trouble-shooting a server and tool writers to
craft tools that mine the log files and produce reports and trends.
Furthermore, these log files can also be used to train anomaly
detection systems and feed events into a security event management
system. The Session Initiation Protocol does not have a common log
format, and as a result, each server supports a distinct log format
that makes it unnecessarily complex to produce tools to do trend
analysis and security detection. We propose a common log file format
for SIP servers that can be used uniformly by user agents, proxies,
registrars, redirect servers as well as back-to-back user agents.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 17, 2012.
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Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem statement . . . . . . . . . . . . . . . . . . . . . . 4
4. What SIP CLF is and what it is not . . . . . . . . . . . . . . 4
5. Alternative approaches to SIP CLF . . . . . . . . . . . . . . 5
5.1. SIP CLF and CDRs . . . . . . . . . . . . . . . . . . . . . 5
5.2. SIP CLF and Wireshark packet capture . . . . . . . . . . . 6
6. Motivation and use cases . . . . . . . . . . . . . . . . . . . 6
7. Challenges in establishing a SIP CLF . . . . . . . . . . . . . 8
8. Data model . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. SIP CLF mandatory fields . . . . . . . . . . . . . . . . . 10
8.2. Mandatory fields and SIP entities . . . . . . . . . . . . 12
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. UAC registration . . . . . . . . . . . . . . . . . . . . . 13
9.2. Direct call between Alice and Bob . . . . . . . . . . . . 15
9.3. Single downstream branch call . . . . . . . . . . . . . . 16
9.4. Forked call . . . . . . . . . . . . . . . . . . . . . . . 22
10. Security Considerations . . . . . . . . . . . . . . . . . . . 30
11. Operational guidance . . . . . . . . . . . . . . . . . . . . . 31
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 32
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
14.1. Normative References . . . . . . . . . . . . . . . . . . . 32
14.2. Informative References . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33
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1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
RFC 3261 [RFC3261] defines additional terms used in this document
that are specific to the SIP domain such as "proxy"; "registrar";
"redirect server"; "user agent server" or "UAS"; "user agent client"
or "UAC"; "back-to-back user agent" or "B2BUA"; "dialog";
"transaction"; "server transaction".
This document uses the term "SIP Server" that is defined to include
the following SIP entities: user agent server, registrar, redirect
server, a SIP proxy in the role of user agent server, and a B2BUA in
the role of a user agent server.
2. Introduction
Servers executing on Internet hosts produce log records as part of
their normal operations. Some log records are, in essence, a summary
of an application layer protocol data unit (PDU), that captures in
precise terms an event that was processed by the server. These log
records serve many purposes, including analysis and troubleshooting.
Well-known web servers such as Apache and Squid support event logging
using a Common Log Format (CLF), the common structure for logging
requests and responses serviced by the web server. It can be argued
that a good part of the success of Apache has been its CLF because it
allowed third parties to produce tools that analyzed the data and
generated traffic reports and trends. The Apache CLF has been so
successful that not only did it become the de-facto standard in
producing logging data for web servers, but also many commercial web
servers can be configured to produce logs in this format. An example
of Apache CLF is depicted next:
%h %l %u %t \"%r\" %s %b
remotehost rfc931 authuser [date] request status bytes
remotehost: Remote hostname (or IP number if DNS hostname is not
available, or if DNSLookup is Off.
rfc931: The remote logname of the user.
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authuser: The username by which the user has authenticated himself.
[date]: Date and time of the request.
request: The request line exactly as it came from the client.
status: The HTTP status code returned to the client.
bytes: The content-length of the document transferred.
The inspiration for the SIP CLF is the Apache CLF. However, the
state machinery for a HTTP transaction is much simpler than that of
the SIP transaction (as evidenced in Section 7). The SIP CLF needs
to do considerably more.
3. Problem statement
The Session Initiation Protocol [RFC3261](SIP) is an Internet
multimedia session signaling protocol. A typical deployment of SIP
in an enterprise will consist of SIP entities from multiple vendors.
Currently, if these entities are capable of producing a log file of
the transactions being handled by them, the log files are produced in
a proprietary format. The result of multiplicity of the log file
formats is the inability of the support staff to easily trace a call
from one entity to another, or even to craft common tools that will
perform trend analysis, debugging and troubleshooting problems
uniformly across the SIP entities of multiple vendors.
SIP does not currently have a CLF format and this document serves to
provide the rationale to establish a SIP CLF and identifies the
required minimal information that must appear in any SIP CLF record.
4. What SIP CLF is and what it is not
The SIP CLF is a standardized manner of producing a log file. This
format can be used by SIP clients, SIP Servers, proxies, and B2BUAs.
The SIP CLF is simply an easily digestible log of currently occurring
events and past transactions. It contains enough information to
allow humans and automata to derive relationships between discrete
transactions handled at a SIP entity or to search for a certain
dialog or a related set of transactions.
The SIP CLF is amenable to quick parsing (i.e., well-delimited
fields) and it is platform and operating system neutral.
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The SIP CLF is amenable to easy parsing and lends itself well to
creating other innovative tools.
The SIP CLF is not a billing tool. It is not expected that
enterprises will bill customers based on SIP CLF. The SIP CLF
records events at the signaling layer only and does not attempt to
correlate the veracity of these events with the media layer. Thus,
it cannot be used to trigger customer billing.
The SIP CLF is not a quality of service (QoS) measurement tool. If
QoS is defined as measuring the mean opinion score (MOS) of the
received media, then SIP CLF does not aid in this task since it does
not summarize events at the media layer.
5. Alternative approaches to SIP CLF
It is perhaps tempting to consider other approaches --- which though
not standardized, are in wide enough use in networks today --- to
determine whether or not a SIP CLF would benefit a SIP network
consisting of multi-vendor products. The two existing approaches
that approximate what SIP CLF does are Call Detail Records (CDRs) and
Wireshark packet sniffing.
5.1. SIP CLF and CDRs
CDRs are used in operator networks widely and with the adoption of
SIP, standardization bodies such as 3GPP have subsequently defined
SIP-related CDRs as well. Today, CDRs are used to implement the
functionality approximated by SIP CLF, however, there are important
differences.
One, SIP CLF operates natively at the transaction layer and maintains
enough information in the information elements being logged that
dialog-related data can be subsequently derived from the transaction
logs. Thus, esoteric SIP fields and parameters like the To header,
including tags; the From header, including tags, the CSeq number,
etc. are logged in SIP CLF. By contrast, a CDR is used mostly for
charging and thus saves information to facilitate that very aspect.
A CDR will most certainly log the public user identification of a
party requesting a service (which may not correspond to the From
header) and the public user identification of the party called party
(which may not correspond to the To header.) Furthermore, the
sequence numbers maintained by the CDR may not correspond to the SIP
CSeq header. Thus it will be hard to piece together the state of a
dialog through a sequence of CDR records.
Two, a CDR record will, in all probability, be generated at a SIP
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entity performing some form of proxy-like functionality of a B2BUA
providing some service. By contrast, SIP CLF is light- weight enough
that it can be generated by a canonical SIP user agent server and
user agent client as well, including those that execute on resource
constrained devices (mobile phones).
Finally, SIP is also being deployed outside of operator- managed VoIP
networks. Universities, research laboratories, and small-to-medium
size companies are deploying SIP-based VoIP solutions on networks
owned and managed by them. Much of the latter constituencies will
not have an interest in generating CDRs, but they will like to have a
concise representation of the messages being handled by the SIP
entities in a common format.
5.2. SIP CLF and Wireshark packet capture
Wireshark is a popular raw packet capture tool. It contains filters
that can understand SIP at the protocol level and break down a
captured message into its individual header components. While
Wireshark is appropriate to capture and view discrete SIP messages,
it does not suffice to serve in the same capacity as SIP CLF for two
reasons.
First, all SIP entities that need to save SIP CLF records would
require a Wireshark library for different operating systems and
configurations to link into. Second, and more importantly, if the
SIP messages are exchanged over a TLS-oriented transport, Wireshark
will be unable to decrypt them and render them as individual SIP
headers.
6. Motivation and use cases
As SIP becomes pervasive in multiple business domains and ubiquitous
in academic and research environments, it is beneficial to establish
a CLF for the following reasons:
Common reference for interpreting events: In a laboratory
environment or an enterprise service offering there will typically
be SIP entities from multiple vendors participating in routing
requests. Absent a CLF format, each entity will produce output
records in a native format making it hard to establish commonality
for tools that operate on the log file.
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Writing common tools: A CLF format allows independent tool providers
to craft tools and applications that interpret the CLF data to
produce insightful trend analysis and detailed traffic reports.
The format should be such that it retains the ability to be read
by humans and processed using traditional Unix text processing
tools.
Session correlation across diverse processing elements: In
operational SIP networks, a request will typically be processed by
more than one SIP server. A SIP CLF will allow the network
operator to trace the progression of the request (or a set of
requests) as they traverse through the different servers to
establish a concise diagnostic trail of a SIP session.
Note that tracing the request through a set of servers is
considerably less challenging if all the servers belong to the
same administrative domain.
Message correlation across transactions: A SIP CLF can enable a
quick lookup of all messages that comprise a transaction (e.g.,
"Find all messages corresponding to server transaction X,
including all forked branches.")
Message correlation across dialogs: A SIP CLF can correlate
transactions that comprise a dialog (e.g., "Find all messages for
dialog created by Call-ID C, From tag F and To tag T.")
Trend analysis: A SIP CLF allows an administrator to collect data
and spot patterns or trends in the information (e.g., "What is the
domain where the most sessions are routed to between 9:00 AM and
12:00 PM?")
Train anomaly detection systems: A SIP CLF will allow for the
training of anomaly detection systems that once trained can
monitor the CLF file to trigger an alarm on the subsequent
deviations from accepted patterns in the data set. Currently,
anomaly detection systems monitor the network and parse raw
packets that comprise a SIP message -- a process that is
unsuitable for anomaly detection systems [rieck2008]. With all
the necessary event data at their disposal, network operations
managers and information technology operation managers are in a
much better position to correlate, aggregate, and prioritize log
data to maintain situational awareness.
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Testing: A SIP CLF allows for automatic testing of SIP equipment by
writing tools that can parse a SIP CLF file to ensure behavior of
a device under test.
Troubleshooting: A SIP CLF can enable cursory trouble shooting of a
SIP entity (e.g., "How long did it take to generate a final
response for the INVITE associated with Call-ID X?")
Offline analysis: A SIP CLF allows for offline analysis of the data
gathered. Once a SIP CLF file has been generated, it can be
transported (subject to the security considerations in Section 10)
to a host with appropriate computing resources to perform
subsequent analysis.
Real-time monitoring: A SIP CLF allows administrators to visually
notice the events occurring at a SIP entity in real-time providing
accurate situational awareness.
7. Challenges in establishing a SIP CLF
Establishing a CLF for SIP is a challenging task. The behavior of a
SIP entity is more complex when compared to the equivalent HTTP
entity.
Base protocol services such as parallel or serial forking elicit
multiple final responses. Ensuing delays between sending a request
and receiving a final response all add complexity when considering
what fields should comprise a CLF and in what manner. Furthermore,
unlike HTTP, SIP groups multiple discrete transactions into a dialog,
and these transactions may arrive at a varying inter-arrival rate at
a proxy. For example, the BYE transaction usually arrives much after
the corresponding INVITE transaction was received, serviced and
expunged from the transaction list. Nonetheless, it is advantageous
to relate these transactions such that automata or a human monitoring
the log file can construct a set consisting of related transactions.
ACK requests in SIP need careful consideration as well. In SIP, an
ACK is a special method that is associated with an INVITE only. It
does not require a response, and furthermore, if it is acknowledging
a non-2xx response, then the ACK is considered part of the original
INVITE transaction. If it is acknowledging a 2xx-class response,
then the ACK is a separate transaction consisting of a request only
(i.e., there is not a response for an ACK request.) CANCEL is
another method that is tied to an INVITE transaction, but unlike ACK,
the CANCEL request elicits a final response.
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While most requests elicit a response immediately, the INVITE request
in SIP can pend at a proxy as it forks branches downstream or at a
user agent server while it alerts the user. RFC 3261 [RFC3261]
instructs the server transaction to send a 1xx-class provisional
response if a final response is delayed for more than 200 ms. A SIP
CLF log file needs to include such provisional responses because they
help train automata associated with anomaly detection systems and
provide some positive feedback for a human observer monitoring the
log file.
Finally, beyond supporting native SIP actors such as proxies,
registrars, redirect servers, and user agent servers (UAS), it is
beneficial to derive a CLF format that supports back-to-back user
agent (B2BUA) behavior, which may vary considerably depending on the
specific nature of the B2BUA.
8. Data model
The minimal SIP CLF fields are defined below. Some of these fields
contain URIs. If the URI contains an escaped character (""%" HEX
HEX" mechanism), the escaped character MUST be logged as received.
The maximum size (in number of bytes) for a SIP CLF field is 4096
bytes. This limit is the same regardless of whether the SIP CLF
field is a meta-field (see "Timestamp" and "Directionality" defined
below) or a normal SIP header. If the body of the SIP message is to
be logged, it MUST conform to this limit as well.
Logging bodies of a SIP message is left optional (and is not shown in
the examples of Section 9). If the body is to be logged, the
specific syntax and semantics used to log bodies MUST be defined by
the specific representation format used to generate the SIP CLF
record.
The data model supports extensibility by providing the capability to
log "optional fields". Optional fields are those SIP header fields
(or field components) that are not mandatory (see Section 8.1 for the
mandatory field list). Optional fields may contain SIP headers or
other elements present in a SIP message (for example, the Reason-
Phrase element from the Status-Line production rule in RFC 3261
[RFC3261]). Optional fields may also contain additional information
that a particular vendor desires to log. The specific syntax and
semantics to be accorded to optional fields MUST be defined by the
specific representation format used to generate the SIP CLF record.
Finally, [I-D.ietf-sipclf-format] is an example of a representation
format draft that provides an ASCII-based encoding scheme.
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8.1. SIP CLF mandatory fields
The following SIP CLF fields are defined as minimal information that
MUST appear in any SIP CLF record:
Timestamp - Date and time of the request or response represented as
the number of seconds and milliseconds since the Unix epoch.
Message type - An indicator on whether the SIP message is a request
or a response. The allowable values for this field are 'R' (for
Request) and 'r' (for response).
Directionality - An indicator on whether the SIP message is received
by the SIP entity or sent by the SIP entity. The allowable values
for this field are 's' (for message sent) and 'r' (for message
received).
Transport - The transport over which a SIP message is sent or
received. The allowable values for the transport are governed by
the "transport" production rule in Section 25.1 of RFC3261
[RFC3261].
Source-address - The IPv4 or IPv6 address of the sender of the SIP
message.
Source-port - The source port number of the sender of the SIP
message.
Destination-address - The IPv4 or IPv6 address of the recipient of
the SIP message.
Destination-port - The port number of the recipient of the SIP
message.
From - The From URI. For the sake of brevity, URI parameters SHOULD
NOT be logged.
From-tag - The tag parameter of the From header.
To - The To URI. For the sake of brevity, URI parameters SHOULD NOT
be logged.
To-tag - The tag parameter of the To header. Note that the tag
parameter will be absent in the initial request that forms a
dialog.
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Callid - The Call-ID.
CSeq-Method - The method from the CSeq header.
CSeq-Number - The number from the CSeq header.
R-URI - The Request-URI, including any URI parameters.
Status - The SIP response status code.
SIP Proxies may fork, creating several client transactions that
correlate to a single server transaction. Responses arriving on
these client transactions, or new requests (CANCEL, ACK) sent on the
client transaction need log file entries that correlate with a server
transaction. Similarly, a B2BUA may create one or more client
transactions in response to an incoming request. These transactions
will require correlation as well. The last two data model elements
provide this correlation.
Server-Txn - Server transaction identification code - the
transaction identifier associated with the server transaction.
Implementations can reuse the server transaction identifier (the
topmost branch-id of the incoming request, with or without the
magic cookie), or they could generate a unique identification
string for a server transaction (this identifier needs to be
locally unique to the server only.) This identifier is used to
correlate ACKs and CANCELs to an INVITE transaction; it is also
used to aid in forking as explained later in this section. (See
Section 9 for usage.)
Client-Txn - Client transaction identification code - this field is
used to associate client transactions with a server transaction
for forking proxies or B2BUAs. Upon forking, implementations can
reuse the value they inserted into the topmost Via header's branch
parameter, or they can generate a unique identification string for
the client transaction. (See Section 9 for usage.)
This data model applies to all SIP entities --- a UAC, UAS, Proxy, a
B2BUA, registrar and redirect server. The SIP CLF fields prescribed
for a proxy are equally applicable to the B2BUA. Similarly, the SIP
CLF fields prescribed for a UAS are equally applicable to registrars
and redirect servers.
The next section specifies the individual SIP CLF data model elements
that form a log record for specific instance of a SIP entity. It is
understood that a SIP CLF record is extensible using extension
mechanisms appropriate to the specific representation used to
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generate the SIP CLF record. This document, however, does not
prescribe a specific representation format and it limits the
discussion to the mandatory data elements described above.
8.2. Mandatory fields and SIP entities
Each SIP CLF record MUST consist of all the mandatory data model
elements outlined in Section 8.1. This document does not specify a
representation of a logging format; it is expected that other
documents will do so. Each SIP CLF record MUST contain the mandatory
elements shown below:
Timestamp, Message type, Directionality, CSeq-Method,
CSeq-Number, Transport, R-URI, Destination-address,
Destination-port, Source-address, Source-port, To,
To-tag, From, From-tag, Call-ID, Status, Server-Txn,
Client-Txn
In the following cases, an element will not have an appropriate value
to provide for one of these fields, even though the field itself is
mandatory and must appear in the SIP CLF record. For these cases,
the representation document MUST define how to represent such "not
applicable" values. For example, the R-URI field is not applicable
when logging a response, the Status field is not applicable when
logging a request, the To-tag is not known when a request is first
sent out, etc.
The Client-Txn field is always applicable to a UAC. The Server- Txn
field does not apply to a UAC unless the element is also acting as a
UAS, and the message associated to this log record corresponds to a
message handled by that UAS. For instance, a proxy forwarding a
request will populate both the Client-Txn and Server-Txn fields in
the record corresponding to the forwarded request.
The Server-Txn field is always applicable to a UAS. The Client-Txn
field does not apply to a UAS unless the element is also acting as a
UAC, and the message associated to this log record corresponds to a
message handled by that UAC. For instance, a proxy forwarding a
response will populate both the Server-Txn and Client-Txn fields in
the record corresponding to the forwarded response. However, a proxy
would only populate the Client-Txn field when creating a log record
corresponding to a request.
9. Examples
The examples use only the mandatory data elements defined in
Section 8.1. Extension elements are not considered. When a given
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mandatory field is not applicable to a SIP entity, we use the
horizontal dash ("-") to represent it.
There are five principals in the examples below. They are Alice, the
initiator of requests. Alice's user agent uses IPv4 address
198.51.100.1, port 5060. P1 is a proxy that Alice's request traverse
on their way to Bob, the recipient of the requests. P1 also acts as
a registrar to Alice. P1 uses an IPv4 address of 198.51.100.10, port
5060. Bob has two instances of his user agent running on different
hosts. The first instance uses an IPv4 address of 203.0.113.1, port
5060 and the second instance uses an IPv6 address of 2001:db8::9,
port 5060. P2 is a proxy responsible for Bob's domain. Table 1
summarizes these addresses.
+-------------------+--------------------+-------------------+
| Principal | IP:port | Host/Domain name |
+-------------------+--------------------+-------------------+
| Alice | 198.51.100.1:5060 | alice.example.com |
| P1 | 198.51.100.10:5060 | p1.example.com |
| P2 | 203.0.113.200:5060 | p2.example.net |
| Bob UA instance 1 | 203.0.113.1:5060 | bob1.example.net |
| Bob UA instance 2 | [2001:db8::9]:5060 | bob2.example.net |
+-------------------+--------------------+-------------------+
Principal to IP address asignment
Table 1
Illustrative examples of SIP CLF follow.
9.1. UAC registration
Alice sends a registration registrar P1 and receives a 2xx-class
response. The register requests causes Alice's UAC to produce a log
record shown below.
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Timestamp: 1275930743.699
Message Type: R
Directionality: s
Transport: udp
CSeq-Number: 1
CSeq-Method: REGISTER
R-URI: sip:example.com
Destination-address: 198.51.100.10
Destination-port: 5060
Source-address: 198.51.100.1
Source-port: 5060
To: sip:example.com
To-tag: -
From: sip:alice@example.com
From-tag: 76yhh
Call-ID: f81-d4-f6@example.com
Status: -
Server-Txn: -
Client-Txn: c-tr-1
After some time, Alice's UAC will receive a response from the
registrar. The response causes Alice's agent to produce a log record
shown below.
Timestamp: 1275930744.100
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 1
CSeq-Method: REGISTER
R-URI: -
Destination-address: 198.51.100.1
Destination-port: 5060
Source-address: 198.51.100.10
Source-port: 5060
To: sip:example.com
To-tag: reg-1-xtr
From: sip:alice@example.com
From-tag: 76yhh
Call-ID: f81-d4-f6@example.com
Status: 100
Server-Txn: -
Client-Txn: c-tr-1
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9.2. Direct call between Alice and Bob
In this example, Alice sends a session initiation request directly to
Bob's agent (instance 1.) Bob's agent accepts the session
invitation. We first present the SIP CLF logging from Alice's UAC
point of view. In line 1, Alice's user agent sends out the INVITE.
Shortly, it receives a "180 Ringing" (line 2), followed by a "200 OK"
response (line 3). Upon the receipt of the 2xx-class response,
Alice's user agent sends out an ACK request (line 4).
Timestamp: 1275930743.699
Message Type: R
Directionality: s
Transport: udp
CSeq-Number: 32
CSeq-Method: INVITE
R-URI: sip:bob@bob1.example.net
Destination-address: 203.0.113.1
Destination-port: 5060
Source-address: 198.51.100.1
Source-port: 5060
To: sip:bob@bob1.example.net
To-tag: -
From: sip:alice@example.com
From-tag: 76yhh
Call-ID: f82-d4-f7@example.com
Status: -
Server-Txn: -
Client-Txn: c-1-xt6
Timestamp: 1275930745.002
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 32
CSeq-Method: INVITE
R-URI: -
Destination-address: 198.51.100.1
Destination-port: 5060
Source-address: 203.0.113.1
Source-port: 5060
To: sip:bob@example.net
To-tag: b-in6-iu
From: sip:alice@example.com
From-tag: 76yhh
Call-ID: f82-d4-f7@example.com
Status: 180
Server-Txn: -
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Client-Txn: c-1-xt6
Timestamp: 1275930746.100
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 32
CSeq-Method: INVITE
R-URI: -
Destination-address: 198.51.100.1
Destination-port: 5060
Source-address: 203.0.113.1
Source-port: 5060
To: sip:bob@example.net
To-tag: b-in6-iu
From: sip:alice@example.com
From-tag: 76yhh
Call-ID: f82-d4-f7@example.com
Status: 200
Server-Txn: -
Client-Txn: c-1-xt6
Timestamp: 1275930746.120
Message Type: R
Directionality: s
Transport: udp
CSeq-Number: 32
CSeq-Method: ACK
R-URI: sip:bob@bob1.example.net
Destination-address: 203.0.113.1
Destination-port: 5060
Source-address: 198.51.100.1
Source-port: 5060
To: sip:bob@example.net
To-tag: b-in6-iu
From: sip:alice@example.com
From-tag: 76yhh
Call-ID: f82-d4-f7@example.com
Status: -
Server-Txn: -
Client-Txn: c-1-xt6
9.3. Single downstream branch call
In this example, Alice sends a session invitation request to Bob
through proxy P1, which inserts a Record-Route header causing
subsequent requests between Alice and Bob to traverse the proxy. The
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SIP CLF log records correspond to the viewpoint of P1. The line
numbers below refer to Figure 1
Alice P1 Bob
+---INV--------->| | Line 1
| | |
|<---------100---+ | Line 2
| | |
| +---INV-------->| Line 3
| | |
| |<--------100---+ Line 4
| | |
| |<--------180---+ Line 5
| | |
|<---------180---+ | Line 6
| | |
| |<--------200---+ Line 7
| | |
|<---------200---+ | Line 8
| | |
+---ACK--------->| | Line 9
| | |
| |---ACK-------->| Line 10
Figure 1: Simple proxy-aided call flow
1 Timestamp: 1275930743.699
Message Type: R
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: sip:bob@example.net
Destination-address: 198.51.100.10
Destination-port: 5060
Source-address: 198.51.100.1
Source-port: 5060
To: sip:bob@example.net
To-tag: -
From: sip:alice@example.com
From-tag: al-1
Call-ID: tr-87h@example.com
Status: -
Server-Txn: s-x-tr
Client-Txn: -
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Note that at this point P1 has created a server transaction
identification code and populated the SIP CLF field Server-Txn with
it. P1 has not yet created a client transaction identification code,
thus Client-Txn contains a "-".
2 Timestamp: 1275930744.001
Message Type: r
Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 198.51.100.1
Destination-port: 5060
Source-address: 198.51.100.10
Source-port: 5060
To: sip:bob@example.net
To-tag: -
From: sip:alice@example.com
From-tag: al-1
Call-ID: tr-87h@example.com
Status: 100
Server-Txn: s-x-tr
Client-Txn: -
In line 3 below, P1 has created a client transaction identification
code for the downstream branch and populated the SIP CLF field
Client-Txn.
3 Timestamp: 1275930744.998
Message Type: R
Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: sip:bob@bob1.example.net
Destination-address: 203.0.113.1
Destination-port: 5060
Source-address: 198.51.100.10
Source-port: 5060
To: sip:bob@example.net
To-tag: -
From: sip:alice@example.com
From-tag: al-1
Call-ID: tr-87h@example.com
Status: -
Server-Txn: s-x-tr
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Client-Txn: c-x-tr
4 Timestamp: 1275930745.200
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 198.51.100.10
Destination-port: 5060
Source-address: 203.0.113.1
Source-port: 5060
To: sip:bob@example.net
To-tag: b1-1
From: sip:alice@example.com
From-tag: al-1
Call-ID: tr-87h@example.com
Status: 100
Server-Txn: s-x-tr
Client-Txn: c-x-tr
5 Timestamp: 1275930745.800
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 198.51.100.10
Destination-port: 5060
Source-address: 203.0.113.1
Source-port: 5060
To: sip:bob@example.net
To-tag: b1-1
From: sip:alice@example.com
From-tag: al-1
Call-ID: tr-87h@example.com
Status: 180
Server-Txn: s-x-tr
Client-Txn: c-x-tr
6 Timestamp: 1275930746.009
Message Type: r
Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
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R-URI: -
Destination-address: 198.51.100.1
Destination-port: 5060
Source-address: 198.51.100.10
Source-port: 5060
To: sip:bob@example.net
To-tag: b1-1
From: sip:alice@example.com
From-tag: al-1
Call-ID: tr-87h@example.com
Status: 180
Server-Txn: s-x-tr
Client-Txn: c-x-tr
7 Timestamp: 1275930747.120
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 198.51.100.10
Destination-port: 5060
Source-address: 203.0.113.1
Source-port: 5060
To: sip:bob@example.net
To-tag: b1-1
From: sip:alice@example.com
From-tag: al-1
Call-ID: tr-87h@example.com
Status: 200
Server-Txn: s-x-tr
Client-Txn: c-x-tr
8 Timestamp: 1275930747.300
Message Type: r
Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 198.51.100.1
Destination-port: 5060
Source-address: 198.51.100.10
Source-port: 5060
To: sip:bob@example.net
To-tag: b1-1
From: sip:alice@example.com
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From-tag: al-1
Call-ID: tr-87h@example.com
Status: 200
Server-Txn: s-x-tr
Client-Txn: c-x-tr
9 Timestamp: 1275930749.100
Message Type: R
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: ACK
R-URI: sip:bob@example.net
Destination-address: 198.51.100.10
Destination-port: 5060
Source-address: 198.51.100.1
Source-port: 5060
To: sip:bob@example.net
To-tag: b1-1
From: sip:alice@example.com
From-tag: al-1
Call-ID: tr-87h@example.com
Status: -
Server-Txn: s-x-tr
Client-Txn: c-x-tr
10 Timestamp: 1275930749.100
Message Type: R
Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: ACK
R-URI: sip:bob@bob1.example.net
Destination-address: 203.0.113.1
Destination-port: 5060
Source-address: 198.51.100.10
Source-port: 5060
To: sip:bob@example.net
To-tag: b1-1
From: sip:alice@example.com
From-tag: al-1
Call-ID: tr-87h@example.com
Status: -
Server-Txn: s-x-tr
Client-Txn: c-x-tr
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9.4. Forked call
In this example, Alice sends a session invitation to Bob's proxy, P2.
P2 forks the session invitation request to two registered endpoints
corresponding to Bob's address-of-record. Both endpoints respond
with provisional responses. Shortly thereafter, one of Bob's user
agent instances accepts the call, causing P2 to send a CANCEL request
to the second user agent. P2 does not Record-Route, therefore the
subsequent ACK request from Alice to Bob's user agent does not
traverse through P2 (and is not shown below.)
Figure 2 depicts the call flow.
Bob Bob
Alice P2 (Instance 1) (Instance 2)
+---INV--->| | | Line 1
| | | |
|<---100---+ | | Line 2
| | | |
| +---INV--->| | Line 3
| | | |
| +---INV----+-------->| Line 4
| | | |
| |<---100---+ | Line 5
| | | |
| |<---------+---100---+ Line 6
| | | |
| |<---180---+---------+ Line 7
| | | |
|<---180---+ | | Line 8
| | | |
| |<---180---+ | Line 9
| | | |
|<---180---+ | | Line 10
| | | |
| |<---200---+ | Line 11
| | | |
|<---200---+ | | Line 12
| | | |
| +---CANCEL-+-------->| Line 13
| | | |
| |<---------+---487---+ Line 14
| | | |
| +---ACK----+-------->| Line 15
| | | |
| |<---------+---200---+ Line 16
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Figure 2: Forked call flow
The SIP CLF log correspond to the viewpoint of P2. The fields logged
are shown below; the line numbers refer to Figure 2.
1 Timestamp: 1275930743.699
Message Type: R
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: sip:bob@example.net
Destination-address: 203.0.113.200
Destination-port: 5060
Source-address: 198.51.100.1
Source-port: 5060
To: sip:bob@example.net
To-tag: -
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: -
Server-Txn: s-1-tr
Client-Txn: -
2 Timestamp: 1275930744.001
Message Type: r
Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 198.51.100.1
Destination-port: 5060
Source-address: 203.0.113.200
Source-port: 5060
To: sip:bob@example.net
To-tag: -
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: 100
Server-Txn: s-1-tr
Client-Txn: -
3 Timestamp: 1275930744.998
Message Type: R
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Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: sip:bob@bob1.example.net
Destination-address: 203.0.113.1
Destination-port: 5060
Source-address: 203.0.113.200
Source-port: 5060
To: sip:bob@example.net
To-tag: -
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: -
Server-Txn: s-1-tr
Client-Txn: c-1-tr
4 Timestamp: 1275930745.500
Message Type: R
Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: sip:bob@bob2.example.net
Destination-address: [2001:db8::9]
Destination-port: 5060
Source-address: 203.0.113.200
Source-port: 5060
To: sip:bob@example.net
To-tag: -
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: -
Server-Txn: s-1-tr
Client-Txn: c-2-tr
5 Timestamp: 1275930745.800
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 203.0.113.200
Destination-port: 5060
Source-address: 203.0.113.1
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Source-port: 5060
To: sip:bob@example.net
To-tag: b1=-1
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com 100
Status: 100
Server-Txn: s-1-tr
Client-Txn: c-1-tr
6 Timestamp: 1275930746.100
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 203.0.113.200
Destination-port: udp
Source-address: [2001:db8::9]
Source-port: 5060
To: sip:bob@example.net
To-tag: b2-2
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: 100
Server-Txn: s-1-tr
Client-Txn: c-2-tr
7 Timestamp: 1275930746.700
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 203.0.113.200
Destination-port: udp
Source-address: [2001:db8::9]
Source-port: 5060
To: sip:bob@example.net
To-tag: b2-2
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: 180
Server-Txn: s-1-tr
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Client-Txn: c-2-tr
8 Timestamp: 1275930746.990
Message Type: r
Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 198.51.100.1
Destination-port: 5060
Source-address: 203.0.113.200
Source-port: 5060
To: sip:bob@example.net
To-tag: b2-2
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: 180
Server-Txn: s-1-tr
Client-Txn: c-2-tr
9 Timestamp: 1275930747.100
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 203.0.113.200
Destination-port: 5060
Source-address: 203.0.113.1
Source-port: 5060
To: sip:bob@example.net
To-tag: b1-1
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com 100
Status: 180
Server-Txn: s-1-tr
Client-Txn: c-1-tr
10 Timestamp: 1275930747.300
Message Type: r
Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
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R-URI: -
Destination-address: 198.51.100.1
Destination-port: 5060
Source-address: 203.0.113.200
Source-port: 5060
To: sip:bob@example.net
To-tag: b1-1
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: 180
Server-Txn: s-1-tr
Client-Txn: c-2-tr
11 Timestamp: 1275930747.800
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 203.0.113.200
Destination-port: 5060
Source-address: 203.0.113.1
Source-port: 5060
To: sip:bob@example.net
To-tag: b1-1
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com 100
Status: 200
Server-Txn: s-1-tr
Client-Txn: c-1-tr
12 Timestamp: 1275930748.000
Message Type: r
Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 198.51.100.1
Destination-port: 5060
Source-address: 203.0.113.200
Source-port: 5060
To: sip:bob@example.net
To-tag: b1-1
From: sip:alice@example.com
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From-tag: a1-1
Call-ID: tr-88h@example.com
Status: 200
Server-Txn: s-1-tr
Client-Txn: c-1-tr
13 Timestamp: 1275930748.201
Message Type: R
Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: CANCEL
R-URI: sip:bob@bob2.example.net
Destination-address: [2001:db8::9]
Destination-port: 5060
Source-address: 203.0.113.200
Source-port: 5060
To: sip:bob@example.net
To-tag: b2-2
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: -
Server-Txn: s-1-tr
Client-Txn: c-2-tr
14 Timestamp: 1275930748.991
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: INVITE
R-URI: -
Destination-address: 203.0.113.200
Destination-port: udp
Source-address: [2001:db8::9]
Source-port: 5060
To: sip:bob@example.net
To-tag: b2-2
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: 487
Server-Txn: s-1-tr
Client-Txn: c-2-tr
15 Timestamp: 1275930749.455
Message Type: R
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Directionality: s
Transport: udp
CSeq-Number: 43
CSeq-Method: ACK
R-URI: sip:bob@bob2.example.net
Destination-address: [2001:db8::9]
Destination-port: 5060
Source-address: 203.0.113.200
Source-port: 5060
To: sip:bob@example.net
To-tag: b2-2
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: -
Server-Txn: s-1-tr
Client-Txn: c-2-tr
16 Timestamp: 1275930750.001
Message Type: r
Directionality: r
Transport: udp
CSeq-Number: 43
CSeq-Method: CANCEL
R-URI: -
Destination-address: 203.0.113.200
Destination-port: udp
Source-address: [2001:db8::9]
Source-port: 5060
To: sip:bob@example.net
To-tag: b2-2
From: sip:alice@example.com
From-tag: a1-1
Call-ID: tr-88h@example.com
Status: 200
Server-Txn: s-1-tr
Client-Txn: c-2-tr
The above SIP CLF log makes it easy to search for a specific
transaction or a state of the session. Searching for the string
"c-1-tr" on the log records will readily yield the information that
an INVITE was sent to sip:bob@bob1.example.com, it elicited a 100
followed by a 180 and then a 200. Because the ACK request in this
case would be exchanged end-to-end, this element does not see (and
therefore will not log) the ACK.
Searching on "c-2-tr" yields a more complex scenario of sending an
INVITE to sip:bob@bob2.example.net, receiving 100 and 180. However,
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the log makes it apparent that the request to
sip:bob@bob2.example.net was subsequently CANCEL'ed before a final
response was generated, and that the pending INVITE returned a 487.
The ACK to the final non-2xx response and a 200 to the CANCEL request
complete the exchange on that branch.
10. Security Considerations
A log file by its nature reveals both the state of the entity
producing it and the nature of the information being logged. To the
extent that this state should not be publicly accessible and that the
information is to be considered private, appropriate file and
directory permissions attached to the log file should be used. The
following threats may be considered for the log file while it is
stored:
o An attacker may gain access to view the log file, or may
surreptitiously make a copy of the log file for later viewing.
o An attacker who is unable to eavesdrop real-time SIP traffic on
the network but nonetheless can access the log file, is able to
easily mount reply attack or other attacks that result from
channel eavesdropping. Encrypting SIP traffic does not help here
because the SIP entity generating the log file would have
decrypted the message for processing and subsequent logging.
o An attacker may delete parts of --- or indeed, the whole --- file.
It is outside the scope of this document to specify how to protect
the log file while it is stored on disk. However, operators may
consider using common administrative features such as disk encryption
and securing log files [schneier-1]. Operators may also consider
hardening the machine on which the log files are stored by
restricting physical access to the host as well as restricting access
to the files themselves.
In the worst case, public access to the SIP log file provides the
same information that an adversary can gain using network sniffing
tools (assuming that the SIP traffic is in clear text.) If all SIP
traffic on a network segment is encrypted, then as noted above,
special attention must be directed to the file and directory
permissions associated with the log file to preserve privacy such
that only a privileged user can access the contents of the log file.
Transporting SIP CLF files across the network pose special challenges
as well. The following threats may be considered for transferring
log files or while transferring individual log records:
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o An attacker may view the records;
o An attacker may modify the records in transit or insert previously
captured records into the stream;
o An attacker may remove records in transit, or may stage a man- in-
the-middle attack to deliver a partially or entirely falsified log
file.
It is also outside the scope of this document to specify protection
methods for log files or log records that are being transferred
between hosts. However, operators may consider using common security
protocols described in [RFC3552] to transfer log files or individual
records. Alternatively, the log file may be transferred through bulk
methods that also guarantees integrity, or at least detects and
alerts to modification attempts.
The SIP CLF represents the minimum fields that lend themselves to
trend analysis and serve as information that may be deemed useful.
Other formats can be defined that include more headers (and the body)
from Section 8.1. However, where to draw a judicial line regarding
the inclusion of non-mandatory headers can be challenging. Clearly,
the more information a SIP entity logs, the longer time the logging
process will take, the more disk space the log entry will consume,
and the more potentially sensitive information could be breached.
Therefore, adequate tradeoffs should be taken in account when logging
more fields than the ones recommended in Section 8.1.
Implementers need to pay particular attention to buffer handling when
reading or writing log files. SIP CLF entries can be unbounded in
length. It would be reasonable for a full dump of a SIP message to
be thousands of octets long. This is of particular importance to CLF
log parsers, as a SIP CLF log writers may add one or more extension
fields to the message to be logged.
11. Operational guidance
SIP CLF log files will take up substantive amount of disk space
depending on traffic volume at a processing entity and the amount of
information being logged. As such, any enterprise using SIP CLF
should establish operational procedures for file rollovers as
appropriate to the needs of the organization.
Listing such operational guidelines in this document is out of scope
for this work.
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12. IANA Considerations
This document does not require any considerations from IANA.
13. Acknowledgments
Members of the sipping, dispatch, ipfix and syslog working groups
provided invaluable input to the formulation of the draft. These
include Benoit Claise, Spencer Dawkins, John Elwell, David
Harrington, Christer Holmberg, Hadriel Kaplan, Atsushi Kobayashi,
Jiri Kuthan, Scott Lawrence, Chris Lonvick, Peter Musgrave, Simon
Perreault, Adam Roach, Dan Romascanu, Robert Sparks, Brian Trammell,
Dale Worley, Theo Zourzouvillys and others that we have undoubtedly,
but inadvertently, missed.
Rainer Gerhards, David Harrington, Cullen Jennings and Gonzalo
Salgueiro helped tremendously in discussions related to arriving at
the beginnings of a data model.
14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
14.2. Informative References
[I-D.ietf-sipclf-format]
Salgueiro, G., Gurbani, V., and A. Roach, "Format for the
Session Initiation Protocol (SIP) Common Log Format
(CLF)", draft-ietf-sipclf-format-03 (work in progress),
October 2011.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
July 2003.
[rieck2008]
Rieck, K., Wahl, S., Laskov, P., Domschitz, P., and K-R.
Muller, "A Self-learning System for Detection of Anomalous
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SIP Messages", Principles, Systems and Applications of IP
Telecommunications Services and Security for Next
Generation Networks (IPTComm), LNCS 5310, pp. 90-106,
2008.
[schneier-1]
Schneier, B. and J. Kelsey, "Secure audit logs to support
computer forensics", ACM Transactions on Information and
System Security (TISSEC), 2(2), pp. 159,176, May 1999.
Authors' Addresses
Vijay K. Gurbani (editor)
Bell Laboratories, Alcatel-Lucent
1960 Lucent Lane
Naperville, IL 60566
USA
Email: vkg@bell-labs.com
Eric W. Burger (editor)
Georgetown University
USA
Email: eburger@standardstrack.com
URI: http://www.standardstrack.com
Tricha Anjali
Illinois Institute of Technology
316 Siegel Hall
Chicago, IL 60616
USA
Email: tricha@ece.iit.edu
Humberto Abdelnur
INRIA
INRIA - Nancy Grant Est
Campus Scientifique
54506, Vandoeuvre-les-Nancy Cedex
France
Email: Humberto.Abdelnur@loria.fr
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Olivier Festor
INRIA
INRIA - Nancy Grant Est
Campus Scientifique
54506, Vandoeuvre-les-Nancy Cedex
France
Email: Olivier.Festor@loria.fr
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