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3.1.5.19 Interpretation of o= line in the SDP

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The o= line of an SDP message, as specified in [RFC4566], specifies the session originator and session identifiers that include the session identifier, session version, network type, address type, and unicast address. ABNF notation, as described in [RFC5234], of the o= line is as follows:

O=<username> <sess-id> <sess-version> <nettype> <addrtype> <unicast-address>

  • The sess-id parameter MUST be ignored on a receive.

  • The sess-version parameter MUST be a numeric value but the value MUST be ignored on a receive. This parameter is not incremented in subsequent SDP offers or SDP answers<32>.

  • The nettype parameter MUST be "IN".

  • The addrtype parameter MUST be either "IP4" or "IP6"<33>.

    • If the addrtype is "IP4" the unicast-address parameter MUST be the dotted-decimal representation of the IP version 4 address.

    • If the addrtype is "IP6" the unicast-address parameter MUST be the textual representation of the IP version 6 address.

  • Changes to the unicast-address parameter in subsequent SDP offers or SDP answers MUST be ignored.