ricardorojas123 Tue, 03/10/2009 - 18:58

I don't understand :( . Then I do not need the DSPs so that the four E1 in the Cisco 2821 work. When I need install DSP in the voice Gateway ?


Michael Owuor Tue, 03/10/2009 - 19:20


The HWIC-4T1/E1 is described as a T1/E1 high speed WAN interface card (WIC). As you know, WAN interface cards are used to connect your sites to each other. This is different from VWIC or VIC cards which may be used for voice termination, for example where you have a PRI configured on the router to terminate incoming voice calls from the PSTN. You need DSPs when you are doing voice termination. Voice termination applies to a call that has two call legs, one leg on a time-division multiplexing (TDM) interface and the second leg on a VoIP connection. The TDM leg must be terminated by hardware that performs coding/decoding and packetization of the stream. This termination function is performed by the DSP resources.

You would also need DSPs on the router if you need to configure media resources such as conferencing or transcoding resources on the router.

Hope this helps.



ricardorojas123 Thu, 03/12/2009 - 05:25

Thanks mowuor, There is some Cisco book, ebook or document that explains this. For a greater understanding.

Michael Owuor Thu, 03/12/2009 - 05:54

Hi Ricardo,

Here's some information that may be useful.

Cisco Voice Gateways and Gatekeepers book:


Configuring Enhanced Conferencing and Transcoding for Voice Gateway Routers document on CCO


Media Resources Chapter on the CUCM SRND has some good information:


I hope these help.




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