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SIP Body

The SDP information in the SIP body includes IP addresses the ALG uses to create channels for the media stream. Translation of the SDP section also allocates resources, that is, port numbers to send and receive the media.

The following excerpt from a sample SDP section shows the fields that are translated for resource allocation.



o=user 2344234 55234434 IN IP4 10.150.20.3

c=IN IP4 10.150.20.3

m=audio 43249 RTP/AVP 0

SIP messages can contain more than one media stream. The concept is similar to attaching multiple files to an e-mail message. For example, an INVITE message sent from a SIP client to a SIP server might have the following fields:



c=IN IP4 10.123.33.4

m=audio 33445 RTP/AVP 0
c=IN IP4 10.123.33.4

m=audio 33447 RTP/AVP 0
c=IN IP4 10.123.33.4

m=audio 33449 RTP/AVP 0

J-series devices support up to 6 SDP channels negotiated for each direction, for a total of 12 channels per call. For more information, see SDP Session Descriptions.

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