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New Member

RTP header compression

Is there a way to specific a range of udp port for the rtp compression? It seens to me that Cisco IOS only compress the rtp header when the udp port, both source and destination is in the range 16384 - 32767. I have a Mediatrix APA III-4fxs, and a Vegastream Vega50 talk with a 3COM SIP gateway, and running Cisco 3640 router in the middle. I can not change the port on the mediatrix. For the Vega50, it has a function that let you change the udp port to the 16384 range, but not the 3COM. When I make the test call, it only does one way compression, 3COM to Vega50 with the destination port being 16388. But not vise verse.

4 REPLIES
Cisco Employee

Re: RTP header compression

There isn't any way to change the port numbers. It is not a negotiated protocol, so if we are compressing it, we have no control over the other side. make sure you try ip header-compression iphc-format, which follows the standard (can't remember the RFC#, 2508 maybe?).

New Member

Re: RTP header compression

What mean was that the IOS only compress rtp if the udp port range is fall into 16384 - 32767. I found out I was able to change the range in the 3COM Total Control gateway as well as the ATA 186 and Vegastream 50, but not the Mediatrix box. We have a large number of those Mediatrix SIP box, and the vendor said there box is hard coded to start at 5004. IP rtp header-compression iphc-format doesn't work under frame-relay encapsulation.

New Member

Re: RTP header compression

Actually, using frame-relay traffic shaping and a map class you can define the udp port range starting as low as 2000. But you won't have the same range of ports. ie 2000 + 16383 = ports 2000 to 18383. So you would have to make sure ALL of your equipment is using only this port range.

Cisco Employee

Re: RTP header compression

When I said IOS i meant that only do it on a router not on callmanager. I am sorry for any confusion I may have caused.

Thank you,

-Mckee

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