Internet DRAFT - draft-gurbani-sipclf-problem-statement


SIPPING                                                  V. Gurbani, Ed.
Internet-Draft                         Bell Laboratories, Alcatel-Lucent
Intended status: Informational                            E. Burger, Ed.
Expires: July 19, 2010                                     Neustar, Inc.
                                                               T. Anjali
                                        Illinois Institute of Technology
                                                             H. Abdelnur
                                                               O. Festor
                                                        January 15, 2010

 The Common Log Format (CLF) for the Session Initiation Protocol (SIP)


   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.

Status of this Memo

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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.  SIP CLF fields . . . . . . . . . . . . . . . . . . . . . . . .  9
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   10. Operational guidance . . . . . . . . . . . . . . . . . . . . . 12
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 12
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 12
     13.2. Informative References . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13

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1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [1].

   RFC 3261 [2] 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.  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.

   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.

3.  Problem statement

   The Session Initiation Protocol [2](SIP) is an Internet multimedia
   session signaling protocol that is increasingly used for other
   services besides session establishment.  A typical delpoyment 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 text 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.  For example, a SIP
   administrator should be able to issue a concise command to discover
   relationships between transactions or to search a certain dialog or

      Note: The exact form of the "concise command" is left unspecified
      until the working group agrees to one or more formats for encoding
      the fields.

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   The SIP CLF is amenable to quick parsing (i.e., well-delimited
   fields) and it is platform and operating system neutral.

   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 mutil-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

   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

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   dialog through a sequence of CDR records.

   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).

   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

   First, while the Wireshark format saves bulk of the information
   needed to create transaction and dialog state, the Wireshark format
   is a binary format that does not lend itself very well to being
   manipulated by text-based tools.  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

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 servers from multiple vendors participating in routing
      requests.  Absent a CLF format, each server 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

   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 [3].  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 server (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 9)
      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 server 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

   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 [2] 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.  SIP CLF fields

   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.

   Accordingly, the following SIP CLF fields are defined as mininal
   information that must appear in any SIP CLF record:

   date:  Date and time of the request or response represented as the
      number of seconds and milliseconds since the Unix epoch.

   remotehost:  The DNS name or IP address of the upstream client.

   authuser:  The user name by which the user has been authenticated.
      If the user name is unknown or when a request is challenged, the
      value in this field must be "-"

   method:  The upper-case name of the SIP method.

   request-uri:  The Request-URI, including any URI parameters.

   from:  The From URI, including the tag.  Whilst one may question the
      value of the From URI in light of RFC4744 [4], 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.

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   to:  The To URI, including tag.

   callid:  The Call-ID.

   status:  The SIP response status code returned upstream.

   contactlist:  Contact URIs in the response, if any.  A "-" field
      value may be used if there aren't any Contact URIs.

   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.

   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.  A more detailed explanation of why it is
      needed is provided next.

   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.

      To best demonstrate the correlation directives "server-txn" and
      "client-txn", some examples are necessary.  In order to do so, it
      helps to use a canonical representation for the SIP CLF.  The most
      expedient way to do so is to use an ASCII representation for
      illustration purposes only, but to be safe, the working group
      should okay this since a specific SIP CLF format has not been
      defined yet.  To get a gist of how these correlation directives
      help, please see Section 6 of a predecessor [5] to this draft.

   Finally, the SIP CLF should be extensible such that future SIP
   methods, headers and bodies can be represented as well.

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      Note: Not sure what else to say here since the specific format
      used to encode the CLF has some bearing on extensibility.  A type-
      length-value (TLV) format or a PCAP format has advantages over an
      ASCII format.  All three formats -- the ASCII, binary TLV format,
      and the PCAP format -- are available in Gurbani et al. [5], Roach
      [6], and Kaplan [7], respectively.

9.  Security Considerations

   A log file by its nature reveals the 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.  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 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.  While transporting SIP CLF files is out of scope in the
   current working group charter, it seems worth drawing attention to
   the fact that if the file is transported using unencrypted FTP or
   email, intermediaries and adversaries may have access to the raw SIP
   CLF records.  Accordingly, if the SIP CLF file is to be moved from
   the generating host, secure FTP or secure email must be used instead.

   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.  However, where to draw a judicial line regarding the
   inclusion of non-mandatory headers can be challenging.  Clearly, the
   more information a SIP server 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.

   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.

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10.  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.

11.  IANA Considerations

   This document does not require any considerations from IANA.

12.  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, David Harrington, Christer
   Holmberg, Hadriel Kaplan, Atsushi Kobayashi, Jiri Kuthan, Scott
   Lawrence, Simon Perreault, Adam Roach, Dan Romascanu, Robert Sparks,
   Brian Trammell, Dale Worley, Theo Zourzouvillys and others that we
   have undoubtedly, but inadvertently, missed.

   Adam Roach proposed and documented the binary TLV-format and Hadriel
   Kaplan proposed and documented the PCAP-based format as alternative
   SIP CLF representations.

13.  References

13.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [2]   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.

13.2.  Informative References

   [3]   Rieck, K., Wahl, S., Laskov, P., Domschitz, P., and K-R.
         Muller, "A Self-learning System for Detection of Anomalous SIP
         Messages",  Principles, Systems and Applications of IP

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         Telecommunications  Services and Security for Next Generation
         Networks (IPTComm),  LNCS 5310, pp. 90-106, 2008.

   [4]   Peterson, J. and C. Jennings, "Enhancements for Authenticated
         Identity Management in the Session Initiation Protocol (SIP)",
         RFC 4474, August 2006.

   [5]   Gurbani, V., Burger, E., Anjali, T., Abdelnur, H., and O.
         Festor, "The Common Log File (CLF) format for the Session
         Initiation Protocol (SIP)", draft-gurbani-sipping-clf-01 (work
         in progress), March 2009.

   [6]   Roach, A., "Binary Syntax for SIP Common Log Format",
         draft-roach-sipping-clf-syntax-01 (work in progress), May 2009.

   [7]   Kaplan, H., "PCAP-compatible Binary Syntax for SIP Common Log
         File Format", draft-kaplan-sipping-clf-pcap-00 (work in
         progress), June 2009.

   [8]   Debar, H., Curry, D., and B. Feinstein, "The Intrusion
         Detection Message Exchange Format (IDMEF)", RFC 4765,
         March 2007.

   [9]   Claise, B., "Specification of the IP Flow Information Export
         (IPFIX) Protocol for the Exchange of IP Traffic Flow
         Information", RFC 5101, January 2008.

   [10]  Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009.

Authors' Addresses

   Vijay K. Gurbani (editor)
   Bell Laboratories, Alcatel-Lucent
   1960 Lucent Lane
   Naperville, IL  60566


   Eric W. Burger (editor)
   Neustar, Inc.


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   Tricha Anjali
   Illinois Institute of Technology
   316 Siegel Hall
   Chicago, IL  60616


   Humberto Abdelnur
   INRIA - Nancy Grant Est
   Campus Scientifique
   54506, Vandoeuvre-les-Nancy Cedex


   Olivier Festor
   INRIA - Nancy Grant Est
   Campus Scientifique
   54506, Vandoeuvre-les-Nancy Cedex


Gurbani, et al.           Expires July 19, 2010                [Page 15]