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Session Description Protocol. Bandwidth information AS:84. What AS:84 stand for?

asked 2018-09-28 14:59:04 +0000

josesalazmit gravatar image

updated 2018-10-01 12:14:33 +0000

sindy gravatar image

Hello, I ran a Wireshark for ipphone and I found something I never got before. IN the 200 ok sip message, under the Session Description Protocol. I have bandwidth Information AS:84. What AS:84 stands for? who introduce the setting for 84 kbit I ran the same trace in my lab, using cisco router with ospf between links and I don't get it


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answered 2018-09-28 19:56:04 +0000

Jaap gravatar image

It's the indication of the Application Specific bandwidth, see RFC 4566 for the details.

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thanks, for the answer. Do you know why in this specific trace, this parameter has been capture but normally this info is not present in most of my trace? who tags that application? the router? what kind of configuration of the network could introduce this info? QoS?

Regards, Jose

josesalazmit gravatar imagejosesalazmit ( 2018-09-28 20:14:38 +0000 )edit

As the RFC states: "AS: The bandwidth is interpreted to be application specific (it will be the application's concept of maximum bandwidth)." So that will most likely be the application that adds this to the SDP packet. As for why it does that is a question for the application developers, we can only look at the network traffic.

Jaap gravatar imageJaap ( 2018-09-29 07:19:01 +0000 )edit

The "application" here is most likely the phone or the exchange, but if the SDP is forwarded by a SDP-aware device, it may happen that such device filters it out as it forwards the SDP between call branches. So you'd have to capture at the source of the SDP to be sure that the AS:84 is missing in the SDP already there. And make sure that the end devices in your lab have the same firmware and configuration as in the wild where you've seen the AS:84 to be in the SDP.

The idea behind advertising the bandwidth requirement is to allow for QoS management - if the bandwidth on some link would be exceeded by the stream established by this SDP, it is a better strategy to reject such call than to deteriorate the quality of all calls already using that link.

sindy gravatar imagesindy ( 2018-10-01 12:24:45 +0000 )edit

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Asked: 2018-09-28 14:59:04 +0000

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Last updated: Oct 01 '18