Internet Engineering Task Force (IETF)                      G. Salgueiro
Request for Comments: 6873                                 Cisco Systems
Category: Standards Track                                     V. Gurbani
ISSN: 2070-1721                                Bell Labs, Alcatel-Lucent
                                                             A. B. Roach
                                                                 Mozilla
                                                           February 2013

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

Abstract

   The SIPCLF working group has defined a Common Log Format (CLF)
   framework for Session Initiation Protocol (SIP) servers.  This CLF
   mimics the successful event logging format found in well-known web
   servers like Apache and web proxies like Squid.  This document
   proposes an indexed text encoding format for the SIP CLF that retains
   the key advantages of a text-based format while significantly
   increasing processing performance over a purely text-based
   implementation.  This file format adheres to the SIP CLF information
   model and provides an effective encoding scheme for all mandatory and
   optional fields that appear in a SIP CLF record.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6873.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   1. Introduction ....................................................3
   2. Terminology .....................................................3
   3. Document Conventions ............................................4
   4. Format ..........................................................5
      4.1. Index Pointers .............................................8
      4.2. Mandatory Fields ..........................................10
      4.3. SIP CLF Encoding and Character Escaping Requirements ......13
      4.4. Optional Fields ...........................................14
   5. Example SIP CLF Record .........................................22
   6. Text Tool Considerations .......................................24
   7. Security Considerations ........................................24
   8. Operational Guidance ...........................................25
   9. IANA Considerations ............................................25
      9.1. SIP CLF Version ...........................................25
      9.2. SIP CLF Transport Flag ....................................26
   10. Acknowledgments ...............................................26
   11. References ....................................................27
      11.1. Normative References .....................................27
      11.2. Informative References ...................................27

1. Introduction

   The extensive list of benefits and the widespread adoption of the
   Apache Common Log Format (CLF) has prompted the development of an
   analogous event logging mechanism for the Session Initiation Protocol
   (SIP) [RFC3261].  Implementing a logging scheme for SIP is a
   considerable challenge.  In part, this is due to the fact that the
   behavior of a SIP entity is more complex as compared to an HTTP
   entity.  Additionally, there are shortcomings to the purely text-
   based HTTP CLF that need to be addressed in order to allow for real-
   time inspection of SIP log files [RFC6872].  Experience with Apache
   CLF has shown that dealing with large quantities of log data can be
   very processor intensive, as doing so necessarily requires reading
   and parsing every byte in the log file(s) of interest.

   An implementation-independent framework for the SIP CLF has been
   defined in [RFC6872].  This memo describes an indexed text file
   format for logging SIP messages received and sent by SIP clients,
   servers, and proxies that adheres to the information model presented
   in Section 8 of [RFC6872].  This document defines a format that is no
   more difficult to generate by logging entities than standard (i.e.,
   non-indexed) text log formats, while being radically faster to
   process.  In particular, the format is optimized for both rapidly
   scanning through log records and quickly locating commonly accessed
   data fields.

   Further, the format proposed by this document retains the key
   advantage of being human readable and able to be processed using the
   various Unix text processing tools, such as sed, awk, perl, cut, and
   grep.

2. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   "SHOULD", "SHOULD NOT", "RECOMMENDED", and "NOT RECOMMENDED" are
   appropriate when valid exceptions to a general requirement are known
   to exist or appear to exist, and it is infeasible or impractical to
   enumerate all of them.  However, they should not be interpreted as
   permitting implementers to fail to implement the general requirement
   when such failure would result in interoperability failure.

   [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.

   The reader is expected to be familiar with the terminology and
   concepts defined in [RFC6872].

3. Document Conventions

   This document defines the logging syntax for the SIP CLF.  This
   syntax is demonstrated through the use of various examples.  The
   formatting described here does not permit these examples to be
   unambiguously rendered due to the constraints imposed by the
   formatting rules for RFCs.  To avoid ambiguity and to meet the RFC
   layout requirements, this document uses the <allOneLine/> markup
   convention established in [RFC4475].

   For the sake of clarity and completeness, the entire text defining
   this markup convention from Section 2.1 of [RFC4475] is quoted below:

      Several of these examples contain unfolded lines longer than 72
      characters.  These are captured between <allOneLine/> tags.  The
      single unfolded line is reconstructed by directly concatenating
      all lines appearing between the tags (discarding any line feeds or
      carriage returns).  There will be no whitespace at the end of
      lines.  Any whitespace appearing at a fold-point will appear at
      the beginning of a line.

      The following represent the same string of bits:

         Header-name: first value, reallylongsecondvalue, third value

         <allOneLine>
         Header-name: first value,
          reallylongsecondvalue
         , third value
         </allOneLine>

         <allOneLine>
         Header-name: first value,
          reallylong
         second
         value,
          third value
         </allOneLine>

      Note that this is NOT SIP header-line folding, where different
      strings of bits have equivalent meaning.

   The IP addresses used in the examples in this document correspond to
   the documentation address block 192.0.2.0/24 (TEST-NET-1) as
   described in [RFC5737].

4. Format

   The CLF for the Session Initiation Protocol [RFC6872] defines an
   information model to which this logging format adheres, and Section
   8.1 of that document defines all the mandatory information model
   elements.

   This document defines the format of SIP CLF records as follows:

     0          7 8        15 16       23 24         31
     +-----------+-----------+-----------+-----------+
     |  Version  |           Record Length           | 0 - 3
     +-----------+-----------+-----------+-----------+
     |       Record Length (cont)        |    0x2C   | 4 - 7
     +-----------+-----------+-----------+-----------+
     |              CSeq Pointer (Hex)               | 8 - 11
     +-----------+-----------+-----------+-----------+
     |      Response Status-Code Pointer (Hex)       | 12 - 15
     +-----------+-----------+-----------+-----------+
     |              R-URI Pointer (Hex)              | 16 - 19
     +-----------+-----------+-----------+-----------+
     |   Destination IP address:port Pointer (Hex)   | 20 - 23
     +-----------+-----------+-----------+-----------+
     |     Source IP address:port Pointer (Hex)      | 24 - 27
     +-----------+-----------+-----------+-----------+
     |             To URI Pointer (Hex)              | 28 - 31
     +-----------+-----------+-----------+-----------+
     |             To Tag Pointer (Hex)              | 32 - 35
     +-----------+-----------+-----------+-----------+
     |            From URI Pointer (Hex)             | 36 - 39
     +-----------+-----------+-----------+-----------+
     |            From Tag Pointer (Hex)             | 40 - 43
     +-----------+-----------+-----------+-----------+

     |             Call-Id Pointer (Hex)             | 44 - 47
     +-----------+-----------+-----------+-----------+
     |           Server-Txn Pointer (Hex)            | 48 - 51
     +-----------+-----------+-----------+-----------+
     |           Client-Txn Pointer (Hex)            | 52 - 55
     +-----------+-----------+-----------+-----------+
     |      Optional Fields Start Pointer (Hex)      | 56 - 59
     +-----------+-----------+-----------+-----------+
     |    0x0A   |                                   | 60 - 63
     +-----------+                                   +
     |                   Timestamp                   | 64 - 67
     +                                   +-----------+
     |                                   |    0x2E   | 68 - 71
     +-----------+-----------+-----------+-----------+
     |         Fractional Seconds        |    0x09   | 72 - 75
     +-----------+-----------+-----------+-----------+
     |                  Flags Field                  | 76 - 79
     +-----------+-----------+-----------+-----------+
     |Flag (cont)|    0x09   |                       | 80 - 83
     |-----------+-----------+                       |
     |                                               |
     |                                               |
     |      Mandatory Fields (variable length)       |
     |                                               |
     |                                               |
     +-----------+-----------+-----------+-----------+
     |    0x09   |          Tag          |    0x40   |\
     +-----------+-----------+-----------+-----------+ \
     |                   Vendor-ID                   |  \
     +-----------+-----------+-----------+-----------+   \
     |                Vendor-ID (cont)               |    \   Repeated
     +-----------+-----------+-----------+-----------+     \  as many
     |     0x2C  |            Length (Hex)           |      > times as
     +-----------+-----------+-----------+-----------+     /  necessary
     | Len (cont)|    0x2C   |    BEB    |    0x2C   |    /
     +-----------+-----------+-----------------------|   /
     |                                               |  /
     |            Value (variable length)            | /
     |                                               |/
     +-----------+-----------+-----------+-----------+
     |    0x0A   |
     +-----------+

                      Figure 1: SIP Common Log Format

   The format presented in Figure 1 is for a single SIP CLF log entry.
   While there is no actual subdivision in practice, this format can be
   logically subdivided into the following three distinct components:

   1.  Index Pointers: The first 60 bytes of this format.  This portion
       is metadata, primarily composed of a list of pointers that
       indicate the beginning of both the variable-length mandatory and
       optional fields that are logged as part of this record.  These
       pointers are implemented as a mechanism to improve processing of
       these records and to allow a reader to expeditiously skip
       directly to the desired field without unnecessarily going through
       the entire record.  This logical subdivision within the SIP CLF
       format will be referenced in this document with the
       <IndexPointers> tag.  A 0x0A (LF character) delimits
       <IndexPointers> from the next logical grouping.

   2.  Mandatory Fields: The next logical grouping in this format is a
       Tab-delimited (0x09) listing of the mandatory fields as described
       in Section 8.1 of [RFC6872] and in the order listed in
       <IndexPointers>.  This logical subdivision within the SIP CLF
       format will be referenced in this document with the
       <MandatoryFields> tag.

   3.  Optional Fields: The last logical component MAY be present as it
       is an OPTIONAL extension to the SIP CLF format.  Its purpose is
       to provide flexibility to the developer of this SIP CLF to log
       any desired fields not included in <MandatoryFields>.  This
       includes SIP bodies and any vendor-specific extensions.  This
       logical subdivision within the SIP CLF format will be referenced
       in this document with the <OptionalFields> tag.

   This logical structure of the SIP CLF record format can be
   graphically represented as shown in Figure 2 below:

                                 <IndexPointers>
                                 <MandatoryFields>
                                 <OptionalFields>

             Figure 2: Logical Structure of the SIP CLF Record

   Note that Figures 1 and 2 plus the terminating line-feed (0x0A) at
   the end of the SIP CLF record are different representations of the
   same format but are functionally equivalent.  The representation of
   this format is a two-line record where the <IndexPointers> metadata
   is on one line and the actual data like <MandatoryFields> and
   <OptionalFields> (if present) is on another.

   In the following sections note that indications of "hexadecimal
   encoded" indicate values that are always unsigned and are to be
   written out in human-readable base-16 numbers using the UTF-8
   characters 0x30 through 0x39 ('0' through '9') and 0x41 through 0x46
   ('A' through 'F').  Similarly, indications of "decimal encoded"

   indicate that the value is to be written out in human-readable
   base-10 numbers using the UTF-8 characters 0x30 through 0x39 ('0'
   through '9').  In both encodings, numbers always take up the number
   of bytes indicated and are padded on the left with UTF-8 '0' (zero)
   characters to fill the entire space.

4.1. Index Pointers

   The <IndexPointers> portion of the SIP CLF record (shown in Figure 3)
   is a 60-byte header that indicates metadata about the record.

            0          7 8        15 16       23 24         31
            +-----------+-----------+-----------+-----------+
            |  Version  |           Record Length           | 0 - 3
            +-----------+-----------+-----------+-----------+
            |       Record Length (cont)        |    0x2C   | 4 - 7
            +-----------+-----------+-----------+-----------+
            |              CSeq Pointer (Hex)               | 8 - 11
            +-----------+-----------+-----------+-----------+
            |      Response Status-Code Pointer (Hex)       | 12 - 15
            +-----------+-----------+-----------+-----------+
            |              R-URI Pointer (Hex)              | 16 - 19
            +-----------+-----------+-----------+-----------+
            |   Destination IP address:port Pointer (Hex)   | 20 - 23
            +-----------+-----------+-----------+-----------+
            |     Source IP address:port Pointer (Hex)      | 24 - 27
            +-----------+-----------+-----------+-----------+
            |             To URI Pointer (Hex)              | 28 - 31
            +-----------+-----------+-----------+-----------+
            |             To Tag Pointer (Hex)              | 32 - 35
            +-----------+-----------+-----------+-----------+
            |            From URI Pointer (Hex)             | 36 - 39
            +-----------+-----------+-----------+-----------+
            |            From Tag Pointer (Hex)             | 40 - 43
            +-----------+-----------+-----------+-----------+
            |             Call-Id Pointer (Hex)             | 44 - 47
            +-----------+-----------+-----------+-----------+
            |           Server-Txn Pointer (Hex)            | 48 - 51
            +-----------+-----------+-----------+-----------+
            |           Client-Txn Pointer (Hex)            | 52 - 55
            +-----------+-----------+-----------+-----------+
            |      Optional Fields Start Pointer (Hex)      | 56 - 59
            +-----------+-----------+-----------+-----------+

                         Figure 3: Index Pointers

   The fields that make up <IndexPointers> are described below:

   Version (1 byte):  UTF-8 encoded version for the SIP CLF record.
      Range of valid values for the Version is from 'A' (0x41) to 'Z'
      (0x5A).  This document uses a Version value of "0x41" ('A').

      The value of the SIP CLF Version MUST be incremented for any new
      SIP CLF specification that changes any part of the SIP CLF record
      format.  The SIP CLF Version values are IANA-assigned
      (Section 9.1) via the Standards Action method described in
      [RFC5226].

      Since the version is specified per record, it is possible that a
      SIP CLF log file could contain records with different versions.
      Under normal operating conditions, this is an unlikely occurrence
      and SHOULD be avoided if possible.

   Record Length (6 bytes):  Hexadecimal encoded total length of this
      log record, beginning with the "Version" octet and ending with the
      terminating line-feed.

   Bytes 8 through 55 contain hexadecimal encoded pointers that point to
   the starting location of each of the variable-length mandatory
   fields.  Bytes 56 through 59 contain a hexadecimal encoded pointer
   that points to the starting location of the optional fields portion
   of the SIP CLF record.  Note that there are no delimiters between
   these pointer values -- they are packed together as a single, 52-
   character hexadecimal encoded string.  The "Pointer" fields indicate
   absolute byte values within the record, and are therefore >=82.  They
   point to the start of the corresponding value within the
   <MandatoryFields> portion.  A description of each of the mandatory
   fields that these pointer values point to can be found in
   Section 4.2.

   Optional Fields Start Pointer:  This final pointer indicates the
      location within the SIP CLF record where the OPTIONAL group of
      <OptionalFields> begin, if present.  The "Optional Fields Start
      Pointer" points to the UTF-8 Tab (0x09) character for the first
      entry in the <OptionalFields> portion.  If the OPTIONAL group of
      <OptionalFields> are not implemented, then the "Optional Fields
      Start Pointer" field MUST point to the terminating line-feed
      (0x0A) at the end of the SIP CLF record.

4.2. Mandatory Fields

   The <MandatoryFields> portion of the SIP CLF record is shown below:

            0          7 8        15 16       23 24         31
            +-----------+-----------+-----------+-----------+
            |    0x0A   |                                   | 60 - 63
            +-----------+                                   +
            |                   Timestamp                   | 64 - 67
            +                                   +-----------+
            |                                   |    0x2E   | 68 - 71
            +-----------+-----------+-----------+-----------+
            |         Fractional Seconds        |    0x09   | 72 - 75
            +-----------+-----------+-----------+-----------+
            |                  Flags Field                  | 76 - 79
            +-----------+-----------+-----------+-----------+
            |Flag (cont)|    0x09   |                       | 80 - 83
            |-----------+-----------+                       |
            |                                               |
            |                                               |
            |      Mandatory Fields (variable length)       |
            |                                               |
            |                                               |
            +-----------+-----------+-----------+-----------+

                        Figure 4: Mandatory Fields

   Following the pointers in <IndexPointers>, two fixed-length fields
   are encoded to specify the exact time of the log entry.  As before,
   all fields are completely filled, pre-pending values with '0'
   characters as necessary.

   Timestamp (10 bytes):  Decimal encoded date and time of the request
      or response represented as the number of seconds since the Unix
      epoch (i.e., seconds since midnight, January 1st, 1970, GMT).

   Fractional Seconds (3 bytes):  Decimal encoded fractional seconds
      portion of the Timestamp field to millisecond accuracy.

      The combined Timestamp and Fractional Seconds fields are
      represented in the log file as a UTF-8 encoded string representing
      the date and time of the request or response represented as the
      number of seconds and milliseconds since the Unix epoch.  The
      number of milliseconds is separated by a "."  (UTF-8 character
      0x2E) from the number of seconds.

   Flags Field (5 bytes):

      byte 1 -   Request/Response Flag

         R = Request
         r = Response

      byte 2 -   Retransmission Flag

         O = Original transmission
         D = Duplicate transmission
         S = Server is stateless [i.e., retransmissions are not
            detected]

      byte 3 -   Sent/Received Flag

         S = Sent message
         R = Received message

      byte 4 -   Transport Flag

         The Transport Flag values are IANA-assigned (Section 9.2) via
         the IETF Review method described in [RFC5226].  Currently,
         registered values are:

         U = UDP
         T = TCP
         S = SCTP

      byte 5 -   Encryption Flag

         E = Encrypted message (TLS, DTLS, etc.)
         U = Unencrypted message

   After the "Timestamp", "Fractional Seconds", and the "Flags" fields
   are the values for the mandatory fields specified in Section 8.1 of
   [RFC6872], which are described below:

   CSeq:  The Command Sequence header field, including the CSeq number
      and method name.

   Response Status-Code:  Set to the value of the SIP response status
      code for responses.  Set to a single UTF-8 dash (0x2D) for
      requests.

   R-URI:  The Request-URI in the start line (mandatory in request),
      including any URI parameters.

   Destination IP address:port:  The IP address of the downstream server
      and the port number, separated by a single ':'.  IPv4 addresses
      are represented in "dotted decimal" notation as per [RFC1166].
      IPv6 addresses are represented using the hexadecimal notation
      detailed in Section 4 of [RFC5952] (or the special-case mixed
      hexadecimal and decimal notation detailed in Section 5 of
      [RFC5952]) and enclosed in square brackets ('[' and ']').

   Source IP address:port:  The IP address of the upstream client and
      the port number over which the SIP message was received, separated
      by a single ':'.  IPv4 addresses are represented in "dotted
      decimal" notation as per [RFC1166].  IPv6 addresses are
      represented using the hexadecimal notation detailed in Section 4
      of [RFC5952] (or the special-case mixed hexadecimal and decimal
      notation detailed in Section 5 of [RFC5952]) and enclosed in
      square brackets ('[' and ']').

   To URI:  Value of the URI in the To header field.

   To Tag:  Value of the tag parameter (if present) in the To header
      field.

   From URI:  Value of the URI in the From header field.

   From Tag:  Value of the tag parameter (if present) in the From header
      field.

   Call-Id:  The value of the Call-ID header field.

   Server transaction identification code (Server-Txn):  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 tracking forking.  (See Section 9 of [RFC6872] for
      usage.)

   Client transaction identification code (Client-Txn):  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 of [RFC6872] for usage.)

      Note: The definitions of the Server-Txn and Client-Txn are taken
      directly from [RFC6872] and are provided here only as a
      convenience to the implementer.  The definitions specified in
      [RFC6872] should be considered authoritative in the event of a
      conflict.

   This data MUST appear in the order listed in <IndexPointers>, and
   each field MUST be present.  Fields are subject the maximum SIP CLF
   field size of 4096 bytes as detailed in Section 8 of [RFC6872].

4.3. SIP CLF Encoding and Character Escaping Requirements

   The mandatory fields in a SIP CLF record are separated by a single
   UTF-8 Tab character (0x09).  Any Tab characters present in the data
   to be written will be replaced by a UTF-8 space character (0x20)
   prior to being logged.

   The decision to replace tabs with spaces was based on there being no
   standardized use of tabs in SIP headers to convey any other meaning
   than whitespace.  Tabs may appear in message bodies, and in the event
   that the bodies are logged, the conversion to space may cause
   problems when reconstructing the body from the corresponding log
   entry.  Two consequences of the decision to replace Tab with a space
   character are: (a) it will become impossible to reconstruct a
   signature over the logged field that matches the signature over
   fields in the original SIP message, and (b) any future SIP header
   fields that include tabs with a different semantic meaning than
   simply signifying whitespace will lose this meaning when logged.
   Finally, the tabs-to-spaces substitution MUST occur when logging
   mandatory fields and optional SIP Header Field or Reason-Phrase
   (Tag=00); it MUST also occur when optionally logging either the
   entire message (Tag=02) or simply a SIP body (Tag=01) as described in
   Section 4.4.

   An element will not always have an appropriate value to provide for
   one of these fields, even when the field is required to appear in the
   SIP CLF record.  In such circumstances, when a given mandatory field
   from Section 4.2 and specified in Section 8.1 of [RFC6872]) is not
   present, then that empty field MUST be encoded as a single horizontal
   dash ("-").  In the event that a field failed to parse, it MUST be
   encoded as a single question mark ("?").  If these characters are
   part of a sequence of other characters, then there is no ambiguity.
   If the field being logged contains only one character, and that
   character is the literal "-", the implementation SHOULD insert an
   escaped %2D for that field in the SIP CLF record.  Similarly, if the
   field contains only one character, and that character is the literal
   "?", the implementation SHOULD insert an escaped %3F for that field
   in the SIP CLF record.

   The terminating carriage return line feed (CRLF) after a given header
   field value MUST NOT be logged.  Since a bare CRLF sequence is not
   permitted within a SIP header field value, mandatory fields MUST NOT
   contain a CRLF when logged and consequently no escaping mechanism is
   required for it.

   Clearly, a SIP parser could not possibly successfully parse a SIP CLF
   record in its entirety given the SIP CLF format described in this
   document.  It is possible to parse individual fields in the SIP CLF
   record if they are extracted and given to a SIP parser that would
   normally parse those sequence of strings.  It should be noted that
   any field value that is modified by the escaping mechanisms defined
   in this document before logging ('-','?', and CRLF) is likely no
   longer well-formed SIP and will fail when given to such a parser.

   The intent of logging using SIP CLF is not to faithfully recreate the
   bit-exact SIP message being logged.  In fact, the formatting rules,
   encoding, and character escaping requirements preclude this and may
   introduce information loss relative to the original SIP message.  A
   log reader should never unescape anything in the SIP CLF record since
   they are intended to be machine processed using text tools such as
   grep and awk.  The human user behind the log reader may be required
   to infer more semantics about any differences between the original
   SIP message and its SIP CLF representation.

4.4. Optional Fields

   The <OptionalFields> portion of the SIP CLF record is shown below:

     0          7 8        15 16       23 24         31
     +-----------+-----------+-----------+-----------+
     |    0x09   |          Tag          |    0x40   |\
     +-----------+-----------+-----------+-----------+ \
     |                   Vendor-ID                   |  \
     +-----------+-----------+-----------+-----------+   \
     |                Vendor-ID (cont)               |    \   Repeated
     +-----------+-----------+-----------+-----------+     \  as many
     |     0x2C  |            Length (Hex)           |      > times as
     +-----------+-----------+-----------+-----------+     /  necessary
     | Len (cont)|    0x2C   |    BEB    |    0x2C   |    /
     +-----------+-----------+-----------------------|   /
     |                                               |  /
     |            Value (variable length)            | /
     |                                               |/
     +-----------+-----------+-----------+-----------+

                         Figure 5: Optional Fields

   Optional fields are those SIP message elements that are not a part of
   the mandatory fields list detailed in Section 8.1 of [RFC6872].
   After the <MandatoryFields> section, there is an OPTIONAL
   <OptionalFields> group (shown in Figure 5) that MAY appear zero or
   more times.  This <OptionalFields> group provides extensibility to
   the SIP CLF.  It allows SIP CLF implementers the flexibility to
   extend the logging capability of this indexed text representation
   beyond just the mandatory log elements described in Section 8.1 of
   [RFC6872].

   Logging any optional SIP elements MUST be done according to the
   format shown in Figure 5.  The location of the start of
   <OptionalFields> within the SIP CLF record is indicated by the
   "Optional Fields Start Pointer" field in <IndexPointers>.  After the
   initial Tab delimiter byte (0x09) shown in Figure 5, the optional
   field being logged is generally represented by the notation:

   Tag@Vendor-ID,Length,BEB,Value

   The optional field identifier (Tag@Vendor-ID) is composed of a two-
   byte Tag and an eight-byte Vendor-ID (both decimal encoded) separated
   by an "@" character (0x40).  This uniquely identifies the optional
   field being logged.  The format for this identifier is loosely
   modeled after the private use option used by the syslog protocol
   [RFC5424] (Note: this is the second format detailed in Section 6.3.2
   of [RFC5424]).  It makes use of the Private Enterprise Number (PEN),
   which provides an identifier through a globally unique name space
   [PEN].  This syntax provides the necessary extensibility to SIP CLF
   to allow logging of any SIP header, body, as well as any vendor-
   specified SIP element.

   The Base64 Encoded Byte (BEB) is a boolean that is used to indicate
   whether or not the optional element being logged is Base64 encoded.
   The Value field for the optional element being logged MUST be Base64
   encoded if it has any characters that are 'unprintable'.  For the
   purposes of this document, we define 'unprintable' to mean a string
   of octets that: (a) contains an octet with a value in the range of 0
   to 31, inclusive; (b) contains an octet with a value of 127; or (c)
   contains any series of octets greater than or equal to 128 that do
   not form a valid UTF-8 sequence, as specified by [UNICODE].  If the
   optional element being logged is Base64 encoded, then BEB=0x01; if it
   is not Base64 encoded, then BEB=0x00.

   Optional fields are logged according to the following two syntax
   rules:

   (1)  Vendor-ID = 00000000

      A Vendor-ID of zero is used to log the entire SIP message, message
      body, Reason-Phrase, or any SIP header fields that are not a part
      of the mandatory fields list detailed in Section 8.1 of [RFC6872].
      The following Tag values are used to identify which of these
      optional elements are being logged:

      Tag = 00 - Log SIP Header Field or Reason-Phrase

         When logging a SIP Header Field (Tag=00), the associated
         "Value" field MUST be populated by the entire header field
         being logged.  That is, the field-name, the associated colon
         (":"), and the field-value.  This mechanism provides the
         capability to optionally log any SIP header field by
         identifying the field being logged within the "Value" field.

         Because the Reason-Phrase in a response is part of the Status-
         Line and is not identified with a field-name, it is a special
         case.  In this instance, the associated "Value" field MUST be
         populated by the name "Reason-Phrase" followed by a colon (":")
         and a single space (SP) between the colon and the logged
         Reason-Phrase value.

         The corresponding "Length" field includes the length of the
         entire "Value" field.  This includes the field-name, the colon,
         and any linear whitespace (LWS) separator.  For Tag=00, the BEB
         is set according to whether the SIP Header Field value contains
         any 'unprintable' characters.  If it does not, the BEB=00; if
         it does, the BEB=01.  If BEB=01, then only the field-value MUST
         be Base64 encoded; the field-name, the associated colon, and
         any LWS separator MUST retain their original encoding.

         If an optional field occurs more than once in a SIP message
         (e.g., Contact, Route, Record-Route, etc.), then each
         occurrence MUST be logged with the same Tag value (i.e.,
         Tag=00) as a distinct optional field entry in the SIP CLF
         record.  These repeated optionally logged header fields MUST
         preserve the ordinal position of the repeated header fields in
         the SIP header.  For example, a SIP header containing two Via
         header fields with the following ordinal positions within the
         SIP header: V1,V2.  If optionally logging these header fields,
         they would occur as the following entries in the SIP CLF

         record.  (Note: For the sake of brevity, this example only
         shows how these optional header fields would be logged and
         omits the remainder of the SIP CLF record):

         00@00000000,len_V1,00,Via: V1     00@00000000,len_V2,00,Via: V2

         The terminating carriage return line feed (CRLF) after a given
         header field value MUST NOT be logged.  Since a bare CRLF
         sequence is not permitted within a SIP header field value,
         optional SIP header fields logged with Tag=00 MUST NOT contain
         a CRLF when logged and consequently no escaping mechanism is
         required for it.

      Tag = 01 - Log message body

         SIP message bodies of all types can be optionally logged using
         Tag=01.  If the message body is logged it MUST adhere to the
         maximum size limitation of 4096 bytes for a SIP CLF field, as
         detailed in Section 8 of [RFC6872].  Unlike with Tag=00, there
         can only be a single entry in the SIP CLF record with Tag=01.
         When optionally logging the message body, if the maximum SIP
         CLF field size of 4096 bytes is exceeded, the message body
         being logged MUST be truncated to meet these size limitations.

         When logging a message body (Tag=01), the associated "Value"
         field is populated with the Content-Type itself plus the SIP
         message body separated with a space.  In this manner,
         everything about the SIP message body is self-described using a
         single tag as compared to enumerating a separate tag for each
         body type.  Additionally, the corresponding "Length" field
         includes the SIP message body, the length of the embedded
         Content-Type, and the space separator between the MIME type and
         the body content.

         For an optionally logged message body (Tag=01), the BEB is set
         according to whether the message body contains any
         'unprintable' characters.  If it does not, the BEB=00; if it
         does, the BEB=01.  If BEB=01, then the message body that
         follows is entirely Base64 encoded except the prepended
         Content-Type as described in the previous paragraph.

         If an optionally logged SIP message body contains any CRLFs,
         they MUST be escaped by using the URI encoded equivalent value
         of "%0D%0A".  This escaping mechanism applies to all body
         types.  So we don't make any distinction in treatment between
         the various possible body types.  If a logged message body has
         BEB=01, then it MUST be Base64 encoded prior to any character
         escaping.  Thus, if a binary body (like an image) is logged, it

         will be Base64 encoded first and that Base64 character stream
         could never include the CRLF escape sequence of "%0D%0A"
         because "%" is not a valid Base64 character.

      Tag = 02 - Log entire SIP message

         The entire SIP message (i.e., SIP header and message body) can
         be optionally logged using a Tag=02.  Logging the entire SIP
         message MUST conform to the maximum size limitation of 4096
         bytes for a SIP CLF field, as detailed in Section 8 of
         [RFC6872].  Unlike with Tag=00, there can only be a single
         entry in the SIP CLF record with Tag=02.  When optionally
         logging the entire SIP message if the maximum SIP CLF field
         size of 4096 bytes is exceeded the entire SIP message being
         logged MUST be truncated to meet these size limitations.

         When optionally logging an entire SIP message (Tag=02), the BEB
         is set according to whether the message body portion contains
         any 'unprintable' characters.  If it does not, the BEB=00; if
         it does, the BEB=01.  If BEB=01, then the entire SIP message is
         Base64 encoded (not just the message body).  Note that unlike
         the case of Tag=01, when logging an entire SIP message (Tag=02)
         with 'unprintable' characters (BEB=01), the Content-Type would
         not be known prior to decode.

         All instances of CRLFs, whether they appear in the SIP headers
         or the SIP message body, MUST be escaped by using the URI
         encoded equivalent value of "%0D%0A".  If a logged SIP message
         has BEB=01 then it MUST be Base64 encoded prior to any
         character escaping.

   (2)  Vendor-ID = PEN

      A Vendor-ID set to a vendor's own private enterprise number from
      the complete current list of private enterprise numbers maintained
      by IANA [PEN] is used to log any other vendor-specified optional
      element of a SIP header or body.  The value of the Tag is set at
      the discretion of the implementer:

      Tag = Vendor-specified tag

   The definition of the various values of the optional field identifier
   (Tag@Vendor-ID) are the basis of how optional elements are logged in
   the SIP CLF.  For the sake of completeness, the remaining fields in
   the format shown in Figure 5 are also defined below:

   Length Field (4 bytes):  Indicates the length of only the "Value"
      field of this optionally logged element (as shown in Figure 5),

      hexadecimal encoded.  This length corresponds to the length of the
      "Value" field only and MUST NOT include any of the other elements
      shown in Figure 5.

   Base64 Encoded Byte (BEB) Field (1 byte):  Indicates whether or not
      the subsequent Value Field of the optionally logged element is
      Base64 encoded.  The Value field for the optional element being
      logged MUST be Base64 encoded if it contains any character that is
      deemed 'unprintable' according to the definition given previously
      in this section.  If the optional element being logged is Base64
      encoded, then BEB=0x01; if it is not Base64 encoded, then
      BEB=0x00.

   Value Field (0 to 4096 bytes):  Contains the actual value of this
      optional field.  As with the mandatory fields, UTF-8 Tab
      characters (0x09) are replaced with UTF-8 space characters (0x20).

   The following are examples of optionally logged SIP elements using
   the syntax described in this section.  All these examples only show
   the <OptionalFields> portion of the SIP CLF record.  The mandatory
   <IndexPointers> and <MandatoryFields> portions of the SIP CLF are
   intentionally omitted for the sake of brevity.  Note that all of
   these examples of optionally logged fields begin with a leading Tab
   delimiter byte (0x09) that is not apparent here.

   (1)  Contact header field logged as an optional field:

           Consider the SIP response:

           SIP/2.0 180 Ringing
           <allOneLine>
           Via: SIP/2.0/UDP host.example.com;
           branch=z9hG4bKnashds8;received=192.0.2.1
           </allOneLine>
           To: Bob <sip:bob@example.com>;tag=a6c85cf
           From: Alice <sip:alice@example.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           Contact: <sip:bob@192.0.2.4>
           CSeq: 314159 INVITE
           Content-Length: 0

   The Contact header field would be logged as an optional field in the
   following manner:

           00@00000000,001C,00,Contact: <sip:bob@192.0.2.4>

   (2)  Reason-Phrase logged as an optional field:

        For the same SIP response the Reason-Phrase would be logged as
        an optional field in the following manner:

           00@00000000,0016,00,Reason-Phrase: Ringing

   (3)  SDP body to be logged as an optional field:

           v=0
           o=alice 2890844526 2890844526 IN IP4 host.example.com
           s=-
           c=IN IP4 host.example.com
           t=0 0
           m=audio 49170 RTP/AVP 0 8 97

   This body has a Content-Type of application/sdp and has a length of
   123 bytes including all the line-feeds.  When logging this body the
   "Value" field is composed of the Content-Type and the body separated
   by a space, which gives it a combined length of 139 (0x008B) bytes.
   This SIP body would be logged as an optional field in the following
   manner:

         <allOneLine>
         01@00000000,008B,00,application/sdp v=0%0D%0Ao=alice 2890844526
         2890844526 IN IP4 host.example.com%0D%0As=-%0D%0A
         c=IN IP4 host.example.com%0D%0At=0 0%0D%0A
         m=audio 49170 RTP/AVP 0 8 97%0D%0A
         </allOneLine>

   Note that the body is actually logged on a single line and is thus
   captured between <allOneLine/> tags.  The line-feeds are escaped
   using %0D%0A to delimit the various lines in the message body.

   (4)  binary body to be logged as an optional field:

        The second body part of the multipart/mime SIP message shown in
        Section 3.1.1.11 of RFC 4475 is a binary encoded body
        (represented in hex) and if logged would have BEB=01 and would
        require Base64 encoding.  That binary body would produce six
        lines of output after being Base64 encoded.  Subsequent escaping
        of the CRLF characters would produce an optionally logged body
        that would look like the following:

        <allOneLine>
        01@00000000,0216,01,multipart/mixed;boundary=7a9cbec02ceef655 MI
        IBUgYJKoZIhvcNAQcCoIIBQzCCAT8CAQExCTAHBgUrDgMCGjALBgkqhkiG9w0BBw
        ExggEgMIIB%0D%0AHAIBATB8MHAxCzAJBgNVBAYTAlVTMRMwEQYDVQQIEwpDYWxp
        Zm9ybmlhMREwDwYDVQQHEwhTYW4g%0D%0ASm9zZTEOMAwGA1UEChMFc2lwaXQxKT
        AnBgNVBAsTIFNpcGl0IFRlc3QgQ2VydGlmaWNhdGUgQXV0%0D%0AaG9yaXR5AggB
        lQBxAjMBEzAHBgUrDgMCGjANBgkqhkiG9w0BAQEFAASBgI70ZvlI8FIt0uWXjp2V
        %0D%0Aquny/hWgZllxYpLo2iqo2DUKaM7/rjy9K/8Wdd3VZI5ZPdZHKPJiIPfpQX
        SeMw2aFe2r25PRDEIQ%0D%0ALntyidKcwMmuLvvHwM/5Fy87An5PwCfhVG3ktqo6
        uz5mzMtd1sZLg4MUnLjm/xgtlE/le2W8mdAF%0D%0A
        </allOneLine>

   Note that the body is actually logged on a single line and is thus
   captured between <allOneLine/> tags.  The line-feeds are escaped
   using %0D%0A to delimit the various lines in the Base64 encoded
   binary body.

   (5)  Codec information from the SDP body logged as an optional field:

           Consider the SIP message:

           INVITE sip:bob@example.com SIP/2.0
           Via: SIP/2.0/UDP host.example.com;branch=z9hG4bKnashds8
           To: Bob <bob@example.com>
           From: Alice <alice@example.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314159 INVITE
           Max-Forwards: 70
           Date: Thu, 21 Feb 2002 13:02:03 GMT
           Contact: <sip:alice@host.example.com>
           Content-Type: application/sdp
           Content-Length: 147

           v=0
           o=UserA 2890844526 2890844526 IN IP4 example.com
           s=Session SDP
           c=IN IP4 host.example.com
           t=0 0
           m=audio 49172 RTP/AVP 0
           a=rtpmap:0 PCMU/8000

   A vendor may choose to log a SIP message element such as the codec
   information from the SDP body.  This vendor-specified SIP element
   would be logged as an optional field in the following manner:

           03@00032473,0014,00,a=rtpmap:0 PCMU/8000

   (6)  N-th message received from a particular peer logged as an
        optional field:

        Perhaps a vendor wants to log that this message is the n-th
        message received from a peering partner.  To do so for the SIP
        message shown above, the vendor would log this information as:

           07@00032473,0016,00,1877 example.com

   Which would signify that this is the 1,877th message from the peering
   partner example.com.  Note that the previous two examples showing an
   optionally logged vendor-specified SIP element use a Vendor-ID with a
   Private Enterprise Number of 32473.  This value has been reserved by
   IANA to be used as an example PEN in documentation according to
   [RFC5612].

5. Example SIP CLF Record

   The following SIP message is an INVITE request sent by a SIP client:

       INVITE sip:192.0.2.10 SIP/2.0
       To: <sip:192.0.2.10>
       Call-ID: DL70dff590c1-1079051554@example.com
       <allOneLine>
       From: "Alice" <sip:1001@example.com:5060>;
       tag=DL88360fa5fc;epid=0x34619b0
       </allOneLine>
       CSeq: 1 INVITE
       Max-Forwards: 70
       Date: Thu, 21 Feb 2012 15:02:03 GMT
       <allOneLine>
       Via: SIP/2.0/TCP 192.0.2.200:5060;
       branch=z9hG4bK-1f6be070c4-DL
       </allOneLine>
       Contact: "1001" <sip:1001@192.0.2.200:5060>
       Content-Type: application/sdp
       Content-Length: 418

       v=0
       o=1001 1456139204 0 IN IP4 192.0.2.200
       s=Session SDP
       c=IN IP4 192.0.2.200
       b=AS:2048
       t=0 0
       m=audio 13756 RTP/AVP 0 101
       a=rtpmap:0 PCMU/8000

   Shown below is approximately how this message would appear as a
   single record in a SIP CLF logging file if encoded according to the
   syntax described in this document.  Due to RFC conventions, this log
   entry has been split into five lines, instead of the two lines that
   actually appear in a log file; and the Tab characters have been
   padded out using spaces to simulate their appearance in a text
   terminal.

       A000100,0053005C005E006D007D008F009E00A000BA00C700EB00F70100
       <allOneLine>
       1328821153.010    RORUU    1 INVITE    -    sip:192.0.2.10
       192.0.2.10:5060    192.0.2.200:56485    sip:192.0.2.10    -
       sip:1001@example.com:5060    DL88360fa5fc
       DL70dff590c1-1079051554@example.com    S1781761-88    C67651-11
       </allOneLine>

   A bit-exact version of the actual log entry is provided here, Base64
   encoded.

    begin-base64 644 clf_record
    QTAwMDEwMCwwMDUzMDA1QzAwNUUwMDZEMDA3RDAwOEYwMDlFMDBBMDAwQkEwMEM3MDBF
    QjAwRjcwMTAwCjEzMjg4MjExNTMuMDEwCVJPUlVVCTEgSU5WSVRFCS0Jc2lwOjE5Mi4w
    LjIuMTAJMTkyLjAuMi4xMDo1MDYwCTE5Mi4wLjIuMjAwOjU2NDg1CXNpcDoxOTIuMC4y
    LjEwCS0Jc2lwOjEwMDFAZXhhbXBsZS5jb206NTA2MAlETDg4MzYwZmE1ZmMJREw3MGRm
    ZjU5MGMxLTEwNzkwNTE1NTRAZXhhbXBsZS5jb20JUzE3ODE3NjEtODgJQzY3NjUxLTEx
    Cg==
    ====

   To recover the unencoded file, the Base64 text above may be passed as
   input to the following perl script (the output should be redirected
   to a file).

   <CODE BEGINS>

   #!/usr/bin/perl
   use strict;
   my $bdata = "";
   use MIME::Base64;
   while(<>)
   {
         if (/begin-base64 644 clf_record/ .. /-- ==== --/)
         {
             if ( m/^\s*[^\s]+\s*$/)
             {
               $bdata = $bdata . $_;
             }
          }
   }
   print decode_base64($bdata);

   <CODE ENDS>

6. Text Tool Considerations

   This format has been designed to allow text tools to easily process
   logs without needing to understand the indexing format.  Index lines
   may be rapidly discarded by checking the first character of the line:
   index lines will always start with an alphabetical character, while
   field lines will start with a numerical character.

   Within a field line, script tools can quickly split fields at the Tab
   characters.  The first 12 fields are positional, and the meaning of
   any subsequent fields can be determined by checking the first four
   characters of the field.  Alternately, these non-positional fields
   can be located using a regular expression.  For example, the "Contact
   value" in a request can be found by searching for the perl regex
   /\t0000,....,([^\t]*)/.

7. Security Considerations

   This document does not introduce any new security considerations
   beyond those discussed in [RFC6872].

   In the interest of protecting the sensitive information contained in
   a SIP CLF file, [RFC6872] notes that values might need to be
   obfuscated for privacy reasons when SIP CLF files are exchanged
   between domains.  If a Base64 encoded string contains the non-
   obfuscated value, then that would also need to be obfuscated before
   Base64 encoding.

8. Operational Guidance

   SIP CLF log files will take up a 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.

9. IANA Considerations

   This specification establishes a new "Session Initiation Protocol
   (SIP) Common Log Format (CLF) Parameters" registry, which contains
   two new sub-registries: "SIP CLF Version Values" and "SIP CLF
   Transport Flag Values".  Initial entries are defined by this
   specification for both sub-registries.  Addition of any new sub-
   registry to the "Session Initiation Protocol (SIP) Common Log Format
   (CLF) Parameters" registry is to be done using the IETF Review
   registration policy detailed in [RFC5226].

9.1. SIP CLF Version

   This document defines the SIP CLF "Version" field in Section 4.1.
   IANA has created a registry of Version values entitled "SIP CLF
   Version Values".  Version numbers MUST be incremented for any new SIP
   CLF protocol specification that changes any part of the SIP CLF
   record format.  Changes include addition or removal of fields or a
   change of syntax or semantics of existing fields.

   Version numbers must be registered via the Standards Action method
   described in [RFC5226].  IANA has registered the Versions shown in
   Table 1 below.

             +------------+----------------------+-----------+
             |   Version  |        FORMAT        | Reference |
             +------------+----------------------+-----------+
             | 0x41 ('A') | Defined in [RFC6873] | [RFC6873] |
             +------------+----------------------+-----------+

              Table 1: IANA-Registered SIP CLF Version Values

9.2. SIP CLF Transport Flag

   This document defines the SIP CLF "Transport Flag" as fourth byte in
   the Flags field of the SIP CLF record.  The format and values of the
   Transport Flag are described in Section 4.2.  IANA has created a
   registry of SIP CLF Transport Flag values titled "SIP CLF Transport
   Flag Values".

   SIP CLF Transport Flag values must be registered via the IETF Review
   method described in [RFC5226].  IANA has registered the Transport
   Flag values shown in Table 2 below.

                +-------+--------------------+-----------+
                | Value | Transport Protocol | Reference |
                +-------+--------------------+-----------+
                |   U   |         UDP        | [RFC6873] |
                |   T   |         TCP        | [RFC6873] |
                |   S   |        SCTP        | [RFC6873] |
                +-------+--------------------+-----------+

              Table 2: IANA-Registered SIP CLF Transport Flag

10. Acknowledgments

   The authors of this document would like to acknowledge and thank
   Peter Musgrave (the chair of the SIPCLF working group) and Robert
   Sparks (the assigned Area Director) for their support, guidance, and
   continued invaluable feedback.

   This work benefited from the discussions and invaluable input by the
   various members of the SIPCLF working group.  These include Brian
   Trammell, Eric Burger, Cullen Jennings, Benoit Claise, Saverio
   Niccolini, and Dan Burnett.  Special thanks to Hadriel Kaplan, Chris
   Lonvick, Paul E. Jones, John Elwell, Claudio Allocchio, and Joe
   Clarke for their constructive comments, suggestions, and reviews that
   were critical to the formulation and refinement of this document.

   Thanks to Anders Nygren for his early implementation, insight, and
   reviews of the SIP CLF format.

11. References

11.1. Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

   [RFC6872]  Gurbani, V., Burger, E., Anjali, T., Abdelnur, H., and O.
              Festor, "The Common Log Format (CLF) for the Session
              Initiation Protocol (SIP): Framework and Information
              Model", RFC 6872, February 2013.

11.2. Informative References

   [PEN]      IANA, "Private Enterprise Numbers", 2009,
              <http://www.iana.org/assignments/enterprise-numbers>.

   [RFC1166]  Kirkpatrick, S., Stahl, M., and M. Recker, "Internet
              numbers", RFC 1166, July 1990.

   [RFC4475]  Sparks, R., Hawrylyshen, A., Johnston, A., Rosenberg, J.,
              and H. Schulzrinne, "Session Initiation Protocol (SIP)
              Torture Test Messages", RFC 4475, May 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009.

   [RFC5612]  Eronen, P. and D. Harrington, "Enterprise Number for
              Documentation Use", RFC 5612, August 2009.

   [RFC5737]  Arkko, J., Cotton, M., and L. Vegoda, "IPv4 Address Blocks
              Reserved for Documentation", RFC 5737, January 2010.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952, August 2010.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard, Version
              6.2.0", (Mountain View, CA: ISBN 978-1-936213-07-8), 2012,
              <http://www.unicode.org/versions/Unicode6.2.0/>.

Authors' Addresses

   Gonzalo Salgueiro
   Cisco Systems
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709
   US

   EMail: gsalguei@cisco.com

   Vijay Gurbani
   Bell Labs, Alcatel-Lucent
   1960 Lucent Lane
   Rm 9C-533
   Naperville, IL  60563
   US

   EMail: vkg@bell-labs.com

   Adam Roach
   Mozilla
   Dallas, TX
   US

   EMail: adam@nostrum.com