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RTP header-compression over PPPoE and VoIP

Hi there,

I have a 1750 in one of my branches that is accessing my core site over the internet via a DSL line. The DSL line is connected to a DSL Modem provided by the ISP and I am using PPPoE on the 1750 to access the internet. I have configured the ip rtp header-compression on the dialer interface but I don't see any stats for ip rtp when I issue the sho ip rtp header-compression command.

The quality of the VoIP is OK until someone browses the internet or any other traffic is introduced on the DSL.

I think my problem is that on my core site, the router (3660) is behind my firewall and the traffic having to go thru my PIX to get to the DSL line that I am using to get on the internet. I know that RTP is not supported on the Ethernet interface on the cisco 3660, my question is: should I get an ADSL wic for the 3660 in the core site and have my voice traffic going out on it. Also, should I replace the Ethernet WIC in the 1750 in the remote site with an ADSL WIC?

Any help is appreciated.


Fadi Bayeh


Re: RTP header-compression over PPPoE and VoIP

The suggestion that you are making is not going to help you. RTP header compression only helps you to save some bandwidth. It does not guarantee any voice quality. If you want preferential treatment for voice over data, you must consider some QoS mechanisms like LLQ on your end boxes. Of course, the QoS will not be honoured when it travels through internet, but you will have some control at the entry points.