SIP Invite

SIP Invite^†

INVITE sip:bob@biloxi.com SIP/2.0
Via: SIP/2.0/UDP pc33.atlanta.com:5060;branch=z9hG4bK776asdhds
To: Bob <sip:bob@biloxi.com>
From: Alice <sip:alice@atlanta.com>;tag=1928301774
Call-ID: a84b4c76e66710
CSeq: 314159 INVITE
Contact: <sip:alice@pc33.atlanta.com>
Content-Type: application/sdp
Content-Length: 142
(Alice’s SDP not shown)

SIP is a text-based protocol and uses ISO 10646 character set in UTF-8 encoding (RFC 2279). The message body uses MIME and can use S/MIME for security.

The generic form of a message is:

generic-message = start-line
message-header* CRLF
[ message-body ]

^† Example adapted from draft-ietf-sip-rfc2543bis-06.ps

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Transcript

[slide127] Here is what an INVITE actually looks like. It says, INVITE the method, the SIP URI and now SIP/2.0 for version 2 we have a via header, a To, blah, blah, and then we'll have Alice's SDP. It's encoded with ISO 10646 characters, with UTF-8 encoding, and the body of this message, which is application/sdp, which has some length to it, can be MIME encoded, and we can even use S/MIME encoding, so we can basically encrypt it. So, that means that only Bob can decode the S/MIME, and know which media streams, what ports, et cetera, Alice wants to use. It's just like an HTTP message, it has a start line, the message header, the carriage return line feed, and then the message body. You can write this trivially, it's really easy.