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www.softarmor.com/wgdb/docs/draft-ashir-simple-message-guideline-00.txt

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Posted by crouse

A Request Message:

A request is a message sent from the client to the server. Following is a sample request message:

INVITE sip:tpu@hp.com SIP/2.0
Via: SIP/2.0/UDP local.hp.com
From: OC
To: TPU
Subject: Confcall
Call-ID: 132059753@local.hp.com
Content-Type: application/sdp
CSeq: 1 INVITE
Contact:
Content-Length: 187

v=0
o=user1 51633745 1348648134 IN IP4 16.188.155.140
s=Interactive Conference
c=IN IP4 224.2.4.4/127
t=0 0
m=audio 3456 RTP/AVP 0 22
a=rtpmap:22 application/g723.1
The following are the different parts of a request:

First Line:

Contains the method name, such as INVITE.
Via:

Indicates the transport used for transaction and contains the address at which the caller is expecting responses to the request.

From:

Contains a display name, and a SIP or secure SIP (SIPS) uniform resource identifier (URI) that indicates the originator of the request.

To:

Contains the display name (TPU) and a SIP or a SIPS URI towards which the request was originally directed.

Subject:

Contains the subject line for the call

Call ID:

Contains a globally unique identifier for this call generated by the combination of a random string
and the end point’s host name or IP address.

Content-Type:

Contains a description of the message body.

Command sequence (CSeq):

Contains an integer and a method name.

Contact:

Contains a SIP or SIPS URI that represents a direct route to contact the end point. Contact usually
contains a username that is a fully qualified domain name.

Content-Length:

Contains an octet (byte) count of the message body.

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Posted by sagitraz

Start Line: Method • UAS Address • SIP Version
To:
From:
Call-ID
Cseq:
VIA:
Record Route:
Max Forwards: Expires:
Contact:
Supported: Require:
Subject:
Content Type
Content Length
Blank Line
Message Body
SDP Data during Invite

• To: Identifies the intended recipient. If a server needs to redirect the message, it will change the Request URI. The To: header retains the original destination address. To: can use any URI scheme in RFC 2806
• From: Identifies the originator. Must not contain an IP address. May contain a display name. Similar to the address in the Start Line but should not be overwritten by SIP Servers
• Call-ID: Uniquely identifies all messages related to one call. It helps prevent duplicate messages
• C_Seguence Number: Relates each Request with its corresponding Response. Both the Request and Response for a given Invite might have a C_Seq number of “137 Invite”
• VIA: Identifies how each link along the way will communicate. The UAS and each Proxy can add a VIA.
• Record Route – Proxies that want to stay in the path add their URI here
• Max Forwards: Limits the number of hops a message makes. (Default = 70)
• Expires: How long (in minutes) the registration is good for
• Contact: The URI where the UAS would like to receive requests. Must be specific. Used by ACK.
• Supported and Require: Lists extensions to SIP that the UAC supports or needs
Content Type and Body Length: Refer to the Message Body
These are the most common headers. More are defined in RFC3261 and other standards

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Posted by yogendra