One document matched: draft-ietf-sipclf-problem-statement-04.xml
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<front>
<title abbrev="SIP CLF">The Common Log Format (CLF) for the Session
Initiation Protocol (SIP)</title>
<author fullname="Vijay K. Gurbani" initials="V." surname="Gurbani"
role="editor">
<organization>Bell Laboratories, Alcatel-Lucent</organization>
<address>
<postal>
<street>1960 Lucent Lane</street>
<city>Naperville</city>
<region>IL</region>
<code>60566</code>
<country>USA</country>
</postal>
<email>vkg@bell-labs.com</email>
</address>
</author>
<author fullname="Eric W. Burger" initials="E.W." surname="Burger"
role="editor">
<organization>Georgetown University</organization>
<address>
<postal>
<street></street>
<city></city>
<region></region>
<code></code>
<country>USA</country>
</postal>
<email>eburger@standardstrack.com</email>
<uri>http://www.standardstrack.com</uri>
</address>
</author>
<author fullname="Tricha Anjali" initials="T." surname="Anjali">
<organization>Illinois Institute of Technology</organization>
<address>
<postal>
<street>316 Siegel Hall</street>
<city>Chicago</city>
<region>IL</region>
<code>60616</code>
<country>USA</country>
</postal>
<email>tricha@ece.iit.edu</email>
</address>
</author>
<author fullname="Humberto Abdelnur" initials="H." surname="Abdelnur">
<organization>INRIA</organization>
<address>
<postal>
<street>INRIA - Nancy Grant Est</street>
<street>Campus Scientifique</street>
<street>54506, Vandoeuvre-lès-Nancy Cedex</street>
<country>France</country>
</postal>
<email>Humberto.Abdelnur@loria.fr</email>
</address>
</author>
<author fullname="Olivier Festor" initials="O." surname="Festor">
<organization>INRIA</organization>
<address>
<postal>
<street>INRIA - Nancy Grant Est</street>
<street>Campus Scientifique</street>
<street>54506, Vandoeuvre-lès-Nancy Cedex</street>
<country>France</country>
</postal>
<email>Olivier.Festor@loria.fr</email>
</address>
</author>
<date year="2010" />
<area>RAI</area>
<workgroup>SIPCLF</workgroup>
<abstract>
<t>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
proxies, registrars, redirect servers as well as back-to-back user
agents.</t>
</abstract>
</front>
<middle>
<section title="Terminology">
<t>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 <xref
target="RFC2119">RFC 2119</xref>.</t>
<t><xref target="RFC3261">RFC 3261</xref> 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".</t>
<t>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.</t>
</section>
<section anchor="intro" title="Introduction">
<t>Servers executing on Internet hosts produce log records as part of
their normal operations. A log record is, 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.</t>
<t>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: </t>
<figure>
<artwork><![CDATA[
%h %l %u %t \"%r\" %s %b
remotehost rfc931 authuser [date] request status bytes
]]></artwork>
</figure>
<t><list style="hanging">
<t hangText="remotehost:">Remote hostname (or IP number if DNS
hostname is not available, or if DNSLookup is Off.</t>
<t></t>
<t hangText="rfc931:">The remote logname of the user.</t>
<t></t>
<t hangText="authuser:">The username by which the user has
authenticated himself.</t>
<t></t>
<t hangText="[date]:">Date and time of the request.</t>
<t></t>
<t hangText="request:">The request line exactly as it came from the
client.</t>
<t></t>
<t hangText="status:">The HTTP status code returned to the
client.</t>
<t></t>
<t hangText="bytes:">The content-length of the document
transferred.</t>
<t></t>
</list></t>
<t>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 <xref target="challenges"/>).
The SIP CLF needs to do considerably more.</t>
</section>
<section title="Problem statement" anchor="p-s">
<t>The <xref target="RFC3261">Session Initiation Protocol</xref>(SIP) is
an Internet multimedia session signaling protocol that is increasingly
used for other services besides session establishment. 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.</t>
<t>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.</t>
</section> <!-- problem-statement -->
<section title="What SIP CLF is and what it is not"
anchor="2B-not-2B">
<t>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.</t>
<t>The SIP CLF is amenable to quick parsing (i.e., well-delimited
fields) and it is platform and operating system neutral.</t>
<t>The SIP CLF is amenable to easy parsing and lends itself
well to creating other innovative tools.</t>
<t>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.</t>
<t>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.</t>
</section> <!-- 2B-not-2B -->
<section anchor="approaches"
title="Alternative approaches to SIP CLF">
<t>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.</t>
<section anchor="clf-cdr" title="SIP CLF and CDRs">
<!--
SIP CDR information is taken from 3GPP TS 32.260, Section 6.1.3,
http://www.3gpp.org/ftp/Specs/archive/32_series/32.260/32260-610.zip.
I am sure this is pretty old (circa 2005), but the latest spec is
probably in the same ballpark.
-->
<t>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.</t>
<t>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.</t>
<t>Two, a CDR record will, in all probability, be generated at
a SIP 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).</t>
<t>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.</t>
</section> <!-- clf-cdr -->
<section anchor="clf-pcap" title="SIP CLF and Wireshark packet capture">
<t>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.</t>
<t>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.</t>
</section> <!-- clf-pcap -->
</section> <!-- approaches -->
<section title="Motivation and use cases" anchor="motivation">
<t>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:</t>
<t><list style="hanging">
<t hangText="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.</t>
<t></t>
<t hangText="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.</t>
<t></t>
<t hangText="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.</t>
<t></t>
<t><list style="hanging">
<t>Note that tracing the request through a set of servers is
considerably less challenging if all the servers belong to the
same administrative domain.</t>
</list></t>
<t></t>
<t hangText="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.")</t>
<t></t>
<t hangText="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.")</t>
<t></t>
<t hangText="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?")</t>
<t></t>
<t hangText="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
<xref target="rieck2008"></xref>. 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.</t>
<t></t>
<t hangText="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.</t>
<t></t>
<t hangText="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?")</t>
<t></t>
<t hangText="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 <xref target="sec-cons"/>) to a host with
appropriate computing resources to perform subsequent analysis.</t>
<t></t>
<t hangText="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.</t>
</list></t>
</section> <!-- motivation -->
<section title="Challenges in establishing a SIP CLF"
anchor="challenges">
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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. <xref target="RFC3261">RFC
3261</xref> 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.</t>
<t>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.</t>
</section>
<section title="Data model" anchor="data-model">
<t>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.</t>
<!-- See http://www.ietf.org/mail-archive/web/sip-clf/current/
msg00244.html for WG discussion. -->
<t>OPEN ISSUE: 4K limit for mandatory headers. There has been some
discussion in the WG mailing list (see http://www.ietf.org/mail-archive/
web/sip-clf/current/msg00238.html) to have a limit for headers. 4K
has been mentioned. What are folks thinking here ... is this limit for
URIs only? For all headers that are part of SIP CLF? For each header
that is part of SIP CLF? For the entire SIP CLF record?</t>
<t>The SIP CLF record does not contain any provisions for logging
bodies, whether or not the body appears as part of a SIP message,
separated by a CRLF, or the body appears as the special hname
"body" in a SIP URI. In SIP, bodies can be of arbitrary length and
composition, resulting in unwieldy and overtly verbose SIP CLF records.
If required, certain aspects of the SIP body can be logged as
extension elements; however, whether or not to do so depends on
the specific logging implementation.</t>
<!-- See http://www.ietf.org/mail-archive/web/sip-clf/current/
msg{00228,00238}.html for WG discussion. -->
<section title="SIP CLF mandatory fields" anchor="candidate-fields">
<t>The following SIP CLF fields are defined as minimal
information that MUST appear in any SIP CLF record:</t>
<t><list style="hanging">
<t hangText="Timestamp -">Date and time of the request or response
represented as the number of seconds and milliseconds since the
Unix epoch.</t>
<t></t>
<t hangText="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).</t>
<t></t>
<t hangText="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).</t>
<t></t>
<t hangText="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
<xref target="RFC3261">RFC3261</xref>.</t>
<t></t>
<t hangText="Source-address -">The DNS name or IP address of the
sender of the SIP message.</t>
<t></t>
<t hangText="Source-port -">The source port number of the sender of
the SIP message.</t>
<t></t>
<t hangText="Destination-address -">The DNS name or IP address of
the recipient of the SIP message.</t>
<t></t>
<t hangText="Destination-port -">The port number of the recipient of
the SIP message.</t>
<t></t>
<t hangText="From -">The From URI. Whilst
one may question the value of the From URI in light of <xref
target="RFC4474">RFC4744</xref>, the From URI, nonetheless,
imparts some information. For one, the From tag is important
and, in the case of a REGISTER request, the From URI can provide
information on whether this was a third-party registration or a
first-party one. It is not necessary to log any URI parameters.</t>
<t></t>
<t hangText="From-tag -">The tag parameter of the From header.</t>
<t></t>
<t hangText="To -">The To URI. It is not necessary to log any URI
parameters.</t>
<t></t>
<t hangText="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.</t>
<t></t>
<t hangText="Callid -">The Call-ID.</t>
<t></t>
<t hangText="CSeq-Method -">The method from the CSeq header.</t>
<t></t>
<t hangText="CSeq-Number -">The number from the CSeq header.</t>
<t></t>
<t hangText="R-URI -">The Request-URI, including any URI parameters.</t>
<t></t>
<t hangText="Status -">The SIP response status code.</t>
</list></t>
<t>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.</t>
<t><list style="hanging">
<t hangText="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 <xref target="examples"/> for usage.)</t>
<t></t>
<t hangText="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 <xref target="examples"/> for usage.)</t>
</list></t>
<t>Finally, the SIP CLF should be extensible such that future
SIP methods, headers and bodies can be represented as well. Besides
the mandatory fields listed above, any other SIP header that needs
to be logged will appear as an ordered pair of header field name and
value.</t>
<t>This data model applies to all SIP entities --- a UAC, UAS, Proxy,
a B2BUA, registrar and redirect server. Note that a B2BUA is a
degenerate case of a proxy and as such the SIP CLF fields
prescribed for a proxy is equally applicable to the B2BUA.
Similarly, registrars and redirect servers are a degenerate case of
a UAS, and as such the SIP CLF fields prescribed for a UAS is
equally applicable to registrars and redirect servers.</t>
<t>The next section specifies the individual SIP CLF data model
elements that form a log record for specific instance of a SIP entity.
We limit our specification to using the minimum data model elements. It
is understood that a SIP CLF record is extensible using extension
mechanisms appropriate to the specific representation used to 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.</t>
</section> <!-- candidate-fields -->
<section title="Mandatory fields and SIP entities"
anchor="sip-clf-fields-summary">
<t>Each SIP CLF record MUST consist of all the mandatory data
model elements outlined in <xref target="candidate-fields"/>.
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:</t>
<figure>
<artwork><![CDATA[
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
]]></artwork>
</figure>
<t><xref target="table-fields"/> summarizes how the mandatory fields
are logged by a UAC, UAS, or UAC-half, UAS-half of a SIP proxy
and B2BUA. In the table below:</t>
<t><list style="hanging">
<t hangText="R:">implies that the field is logged when a request
is handled by that SIP entity.</t>
<t></t>
<t hangText="r:">implies that the field is logged when a response
is handled by that SIP entity.</t>
<t></t>
<t hangText="-:">implies that the field is not applicable to that
SIP entity.</t>
</list></t>
<texttable anchor="table-fields">
<ttcol align="left"></ttcol>
<ttcol align="left">UAC</ttcol>
<ttcol align="left">UAS</ttcol>
<ttcol align="left">UAS-half</ttcol>
<ttcol align="left">UAC-half</ttcol>
<c>Timestamp</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>Message type</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>Directionality</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>Transport</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>CSeq-Method</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>CSeq-Number</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R-URI</c>
<c>R</c>
<c>R</c>
<c>R</c>
<c>R</c>
<c>Destination-address</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>Destination-port</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>Source-address</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>Source-port</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>To</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>To-tag</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>From</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>From-tag</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>Call-ID</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>Status</c>
<c>r</c>
<c>r</c>
<c>r</c>
<c>r</c>
<c>Server-Txn</c>
<c>-</c>
<c>R,r</c>
<c>R,r</c>
<c>R,r</c>
<c>Client-Txn</c>
<c>R,r</c>
<c>-</c>
<c>r</c>
<c>R,r</c>
<postamble>SIP CLF fields logged per entity</postamble>
</texttable>
</section> <!-- sip-clf-fields-summary -->
</section> <!-- data-model -->
<section title="Examples" anchor="examples">
<t>The examples use only the mandatory data elements defined in
<xref target="candidate-fields"/>. Extension elements are not
considered. The examples below use the template defined in
<xref target="sip-clf-fields-summary"/> when logging a SIP CLF
record. When a given mandatory field is not applicable to a SIP
entity as determined by <xref target="table-fields"/>, we use
the horizontal dash ("-") to represent it.</t>
<t>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. <xref target="table-ip-address"/> summarizes
these addresses.</t>
<texttable anchor="table-ip-address">
<ttcol align="left">Principal</ttcol>
<ttcol align="left">IP:port</ttcol>
<ttcol align="left">Host/Domain name</ttcol>
<c>Alice</c>
<c>198.51.100.1:5060</c>
<c>alice.example.com</c>
<c>P1</c>
<c>198.51.100.10:5060</c>
<c>p1.example.com</c>
<c>P2</c>
<c>203.0.113.200:5060</c>
<c>p2.example.net</c>
<c>Bob UA instance 1</c>
<c>203.0.113.1:5060</c>
<c>bob1.example.net</c>
<c>Bob UA instance 2</c>
<c>[2001:db8::9]:5060</c>
<c>bob2.example.net</c>
<postamble>Principal to IP address asignment</postamble>
</texttable>
<t>Illustrative examples of SIP CLF follow.</t>
<section title="UAC registration" anchor="example-reg">
<t>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. The mandatory data model elements correspond
to those listed in <xref target="table-fields"/>. </t>
<figure><artwork><![CDATA[
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
]]></artwork></figure>
<t>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. The mandatory data elements correspond to
those listed in <xref target="table-fields"/>.</t>
<figure><artwork><![CDATA[
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
]]></artwork></figure>
</section> <!-- example-reg -->
<section title="Direct call between Alice and Bob"
anchor="example-direct">
<t>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).</t>
<figure><artwork><![CDATA[
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@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: 198.51.1.100
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: -
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: 198.51.1.100
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
]]></artwork></figure>
</section> <!-- example-direct -->
<section title="Single downstream branch call"
anchor="example-1-branch">
<t>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 SIP CLF log records correspond to the viewpoint of P1. The
line numbers below refer to
<xref target="figure-example-1-branch"/></t>
<figure anchor="figure-example-1-branch"
title="Simple proxy-aided call flow">
<artwork><![CDATA[
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
]]></artwork>
</figure>
<figure>
<artwork><![CDATA[
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: -
]]></artwork>
</figure>
<t>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 "-".</t>
<figure>
<artwork><![CDATA[
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: -
]]></artwork></figure>
<t>In line 3 below, P1 has created a client transaction
identification code for the downstream branch and populated the
SIP CLF field Client-Txn.</t>
<figure>
<artwork><![CDATA[
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
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
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
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
]]></artwork>
</figure>
</section> <!-- example-1-branch -->
<section title="Forked call" anchor="example-forked">
<t>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.)</t>
<t><xref target="figure-forking"/> depicts the call flow.</t>
<figure anchor="figure-forking"
title="Forked call flow">
<artwork><![CDATA[
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
]]></artwork>
</figure>
<t> The SIP CLF log correspond to the viewpoint of P2.
The fields logged are shown below; the line numbers refer
to <xref target="figure-forking"/>.</t>
<figure>
<artwork><![CDATA[
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
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
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
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
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
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
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
]]></artwork>
</figure>
<t>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. The absence of the ACK request
signifies that the ACK was exchanged end-to-end.</t>
<t>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, 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.</t>
</section> <!-- example-forked -->
</section> <!-- examples -->
<!--
<section title="Relationship to other protocols" anchor="relationship">
<t>During the 75th IETF, there was a substantial amount of discussion on
the interplay of SIP CLF and other existing protocols. The
<xref target="RFC5101">IPFIX</xref> protocol is an encompassing solution to
exporting information elements to a central manager over a multitude of
transports. However, specifying the mechanics of exchanging and
transporting SIP CLF records is out of scope of the current SIPCLF charter.
</t>
<t>The <xref target="RFC5424"> syslog </xref> protocol allows the
conveyance of event notification messages. Because of the frequency and
number of messages that will need to be logged, it is not desirable to
send every SIP CLF event to the syslog daemon. Instead, a judicious use of
syslog could be that only certain events -- those that are pertinent
from a network situational awareness perspective -- are sent to
the syslog daemon preferably over a confidentiality and integrity
protected channel such as TLS or DTLS.</t>
<t>Another protocol, <xref target="RFC4765">IDMEF </xref>, defines data
formats and exchange procedures for sharing information of interest to
intrusion detection and response systems and management systems that may
need to react with them. As was the case with syslog, instead of
transporting every message to a detection system, it seems appropriate to
digest certain high-value records from standard SIP CLF and turn only these
into an IDMEF-expressible syntax.</t>
</section>
-->
<section title="Security Considerations" anchor="sec-cons">
<t>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:</t>
<t><list style="symbols">
<t>An attacker may gain access to view the log file, or may
surreptitiously make a copy of the log file for later viewing;</t>
<t>An attacker may mount a replay attack by modifying existing records
in the log file or inserting new records;</t>
<t>An attacker may delete parts of --- or indeed, the whole ---
file.</t>
</list></t>
<t>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 <xref target="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.</t>
<t>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.</t>
<t>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:</t>
<t><list style="symbols">
<t>An attacker may view the records;</t>
<t>An attacker may modify the records in transit or insert previously
captured records into the stream;</t>
<t>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.</t>
</list></t>
<t>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 <xref target="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.</t>
<t>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 <xref target="candidate-fields"></xref>.
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 <xref target="candidate-fields"></xref>.</t>
<t>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.</t>
</section>
<section title="Operational guidance" anchor="ops-guidance">
<t>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.</t>
<t>Listing such operational guidelines in this document is out of
scope for this work.</t>
<!--
<t>NOTE: Preliminary volume analysis was presented to the working
group mailing list during the Anaheim IETF (please see
http://www.ietf.org/mail-archive/web/sip-clf/current/msg00123.html
for the analysis.) An open question is whether the working group
thinks that this analysis should be put in this document.</t>
-->
</section> <!-- ops-guidance -->
<section title="IANA Considerations">
<t>This document does not require any considerations from IANA.</t>
</section> <!-- IANA Cons. -->
<section title= "Acknowledgments" >
<t>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, Simon Perreault, Adam Roach, Dan Romascanu,
Robert Sparks, Brian Trammell, Dale Worley, Theo Zourzouvillys and
others that we have undoubtedly, but inadvertently, missed.</t>
<t>Rainer Gerhards, David Harrington, Cullen Jennings and Gonzalo
Salgueiro helped tremendously in discussions related to arriving
at the beginnings of a data model.</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc2119;
</references>
<references title="Informative References">
&rfc3261;
&rfc4474;
&rfc4475;
&rfc3552;
<reference anchor="rieck2008">
<front>
<title>A Self-learning System for Detection of Anomalous SIP
Messages</title>
<author fullname="Konrad Rieck" initials="K." surname="Rieck">
<organization></organization>
</author>
<author fullname="Stefan Wahl" initials="S." surname="Wahl">
<organization></organization>
</author>
<author fullname="Pavel Laskov" initials="P." surname="Laskov">
<organization></organization>
</author>
<author fullname="Peter Domschitz" initials="P." surname="Domschitz">
<organization></organization>
</author>
<author fullname="Klaus-Robert Muller" initials="K-R."
surname="Muller">
<organization></organization>
</author>
<date year="2008" />
</front>
<seriesInfo name=""
value="Principles, Systems and Applications of IP Telecommunications
Services and Security for Next Generation Networks (IPTComm),
LNCS 5310, pp. 90-106" />
</reference>
<reference anchor="schneier-1">
<front>
<title>Secure audit logs to support computer forensics</title>
<author fullname="Bruce Schneier" initials="B." surname="Schneier">
<organization></organization>
</author>
<author fullname="John Kelsey" initials="J." surname="Kelsey">
<organization></organization>
</author>
<date month="May" year = "1999"/>
</front>
<seriesInfo name=""
value="ACM Transactions on Information and System Security (TISSEC),
2(2), pp. 159,176"/>
</reference>
</references>
</back>
</rfc>
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