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

The Common Log Format for the Session Initiation Protocol defines an information model to which this logging format 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: times as +-----------+-----------+-----------+-----------+ / necessary | Len (cont)| 0x2C | BEB | 0x2C | / +-----------+-----------+-----------------------| / | | / | Value (variable length) | / | |/ +-----------+-----------+-----------+-----------+ | 0x0A | +-----------+ ]]> The format presented in 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 (0x09) delimited listing of the mandatory fields as described in Section 8.1 of 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 below: ]]> Note that and 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 number 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.

The <IndexPointers> portion of the SIP CLF record (shown in ) is a 60-byte header that indicates metadata about the record. The fields that make up <IndexPointers> are described below: 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 () via the Standards Action method as described in . 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. 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 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 . 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.

The <MandatoryFields> portion of the SIP CLF record is shown below: 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. 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). 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 are separated by a "." (UTF-8 character 0x2E) from the number of seconds. Request/Response Flag Retransmission Flag Sent/Received Flag Transport Flag The Transport Flag values are IANA-assigned () via the IETF Review method as described in . Currently registered values are: Encryption Flag After the "Timestamp", "Fractional Seconds" and the "Flags" fields are the values for the mandatory fields specified in Section 8.1 of , which are described below: The Command Sequence header field, including the CSeq number and method name. Set to the value of the SIP response status code for responses. Set to a single UTF-8 dash (0x2D) for requests. The Request-URI in the start line (mandatory in request), including any URI parameters. 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 . IPv6 addresses are represented using the hexadecimal notation detailed in Section 4 of (or the special-case mixed hexadecimal and decimal notation detailed in Section 5 of ) 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 . IPv6 addresses are represented using the hexadecimal notation detailed in Section 4 of (or the special-case mixed hexadecimal and decimal notation detailed in Section 5 of ) and enclosed in square brackets ('[' and ']'). Value of the URI in the To header field. Value of the tag parameter (if present) in the To header field. Value of the URI in the From header field. Value of the tag parameter (if present) in the From header field. The value of the Call-ID header field. 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. (See Section 9 of for usage.) Client transaction identification code - this field is used to associate client transactions with a server transaction for forking proxies or B2BUAs. Upon forking, implementations can reuse the value they inserted into the topmost Via header's branch parameter, or they can generate a unique identification string for the client transaction. (See Section 9 of for usage.) Note: The definitions of the Server-Txn and Client-Txn are taken directly from and are provided here only as a convenience to the implementer. The definitions specified in 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 .

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. And 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 when optionally logging either the entire message (Tag=02) or simply a SIP body (Tag=01) as described in . 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 and specified in Section 8.1 of ) 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.

The <OptionalFields> portion of the SIP CLF record is shown below: times as +-----------+-----------+-----------+-----------+ / necessary | Len (cont)| 0x2C | BEB | 0x2C | / +-----------+-----------+-----------------------| / | | / | Value (variable length) | / | |/ +-----------+-----------+-----------+-----------+ ]]> Optional fields are those SIP message elements that are not a part of the mandatory fields list detailed in Section 8.1 of . After the <MandatoryFields> section, there is an OPTIONAL <OptionalFields> group (shown in ) 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 . Logging any optional SIP elements MUST be done according to the format shown in . 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 , 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 (Note: this is the second format detailed in Section 6.3.2 of ). It makes use of the Private Enterprise Number (PEN), which provides an identifier through a globally unique name space . 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 the optional element being logged is Base64 encoded or not. 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 which do not form a valid UTF-8 sequence, as specified by . 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: 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 . The following Tag values are used to identify which of these optional elements are being logged: 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 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 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):

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. 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 . 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. 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 . 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. 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 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: 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 are also defined below: Indicates the length of only the "Value" field of this optionally logged element (as shown in ), hexadecimal encoded. This length corresponds to the length of the "Value" field only and MUST NOT include any of the other elements shown in . Indicates whether the subsequent Value Field of the optionally logged element is Base64 encoded or not. 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. 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. Contact header field logged as an optional field:

Via: SIP/2.0/UDP host.example.com; branch=z9hG4bKnashds8;received=192.0.2.1 To: Bob ;tag=a6c85cf From: Alice ;tag=1928301774 Call-ID: a84b4c76e66710 Contact: CSeq: 314159 INVITE Content-Length: 0 ]]> The Contact header field would be logged as an optional field in the following manner:

]]> Reason-Phrase logged as an optional field:

SDP body to be logged as an optional field:

This body has a Content-Type of application/sdp and is of 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:

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 ]]> 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. binary body to be logged as an optional field:

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 ]]> 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. Codec information from the SDP body logged as an optional field:

From: Alice ;tag=1928301774 Call-ID: a84b4c76e66710 CSeq: 314159 INVITE Max-Forwards: 70 Date: Thu, 21 Feb 2002 13:02:03 GMT Contact: 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:

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

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 .