The content of this header is the CALL-ID of the call being
returned. It could be used by call distributors and other applications where users want
control over the calls that are accepted and returned. It can also be used by voicemail
systems and other, similar applications where the user misses a call and wants to return
the missed call.
IN-REPLY-TO: 89222@aol.com
Max-Forwards MAX-FORWARDS is used to prevent looping of messages. When a message
is created (either a request or a response), this header is set to 70. As the message
passes through each proxy in the network, the value is decremented by one, until the
value reaches 0. If a proxy receives a message with a MAX-FORWARDS value of 0, the
message is discarded.
74 Chapter 3
This can also be used by systems that are measuring or monitoring the network to
troubleshoot routing of SIP messages. By measuring the value of the MAX-FORWARDS
header at various points in the network, one could derive where looping is occurring
and identify proxies that are causing circular routing.
MAX-FORWARDS: 70
Min-Expires This header identifies the minimum time allowed for the expiration of a
value such as CONTACT within a proxy, such as a registrar (the S-CSCF in the IMS).
The value is a decimal number expressed in seconds.
MIN-EXPIRES: 60
MIME Version This header identifies the version of MIME used within the message
body if there is content provided in MIME format.
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