DSP Design for Centralized Call Processing

[brian.a.balka]

Are there any recommendations on DSP Planning at the remote sites for Centralized Call Processing? When is it recommended to inclulde DSP's at the remote location for transcoding and conferncing?

[jasyoung]

Any time you want to run the network at two or more codec settings (like g.711 and g.729), transcoding is almost unconditionally required:

- Unity can accept g.729 calls directly, but it is not recommended unless you shift the entire box into g.729 mode (it normally keeps recordings at g.711).

- You will run into trouble when attempting to use software conference bridging between sites.

Unless your deployment is quite large (300 phones or more), hardware conference bridging is probably not a serious need, as the software bridging native to CallManager is usually adequate. However, you will definitely need transcoding resources. How much is dictated by how many simultaneous transcoding sessions you need to support, which is in turn driven by your topology and how you expect codecs and usage to break down.

[pambosch]

as I'm aware of, software conference bridge on callmanager works only for G711 calls. That is, if you have a Remote site which comes in with G729 in the central site, you will not be able to conference unless you have a hardware conference bridge (VG200 with DSP for example).

[lnthompson]

I am going to agree here. The software transcoder is NOT sufficient if you are making plans to use any other codecs besides G711 in a multi-site configuration. Conferencing calls of different codec types is not permitted along with a number of other features.

[marinaibm]

All the recommendations on dsp planning are in the ipt design guide

http://www.cisco.com/application/pdf/en/us/guest/netsol/ns268/c649/ccmigration_09186a00800d6805.pdf

[gshonting]

I would definitely put some DSP resources at the central site. If you have a 6500 and can afford it get the 6608 blade. If the port is not being used as a PRI, it can be configured as a transcoder or a conference bridge. I would probably NOT put DSP at the remote sites, as its primary job will be to convert from 711 to 729 and we want the 729 on the wan so the DSP should be closer to the 711 devices.

I had a situation where the remote sites were all g.729 and they could not conference or get MOH without the hardware transcoders.