SIP Messages
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SIPxNano IP-PBX Getting Started Guide
A • Session Initiation Protocol (SIP)
Message Headers
Each SIP message is accompanied by a header with these required fields:
Sample SIP Message
Here’s an example of the SIP message that is sent when one phone dials another:
Figure 55. Sample SIP Message
Message Flow Examples
To illustrate the sequence and direction in which SIP call control methods and response codes are sent, message
flow examples follow for:
•
Call setup
•
Call teardown
•
Successful transfer (blind)
•
Successful transfer (consultative)
Table 10. Message Headers
Field:
Contains:
From
The address of the session originator, expressed as a SIP URL
To
The address of the session target, expressed as a SIP URL
Call-ID A unique identifier assigned to all of the SIP messages related to a call
Cseq
The SIP call control method and an identifying sequence number