CUCM Video Codec Negotiation

[Theofilos Tzachristas]

Hello all, 

When two endpoints try to establish a voice call, they present a list of the supported codecs. This is normally on CUCM done under  "Audio Codec Preference Lists" 

I am using Jabber and I was wondering how the Jabber clients negotiate their video codecs. I know that there is a field in CUCM that limits the maximum bit rate the clients can use. 

Region	Audio Codec Preference List	Maximum Audio Bit Rate	Maximum Session Bit Rate for Video Calls	Maximum Session Bit Rate for Immersive Video Calls
REGION_A	Use System Default (Factory Default low loss)	64 kbps (G.722, G.711)	384 kbps	2147483647 kbps

Is there a list of Video Codecs supported by Call Manager and what is the bandwidth used? 

Also do the clients always try to negotiate with the highest bit rate possible?

I assume with 384 kbps everyone is using CIF. So if increase this value to 768kbps will all the clients use 4CIF? 

[Jaime Valencia · Accepted solution]

I suggest you review this chapter

https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/collab12/collab12/cac.html

[Theofilos Tzachristas]

Thank you.

On Page 13-10 there is a useful table and there is also a link for Cisco Jabber Deployment and Installation Guide

https://www.cisco.com/c/en/us/support/unified-communications/jabber-windows/products-installation-guides-list.html  

I assume the codec with the highest available bandwidth is selected, but it can be also adjusted based on packet loss (Page 13-15) 

"Rate adaptation, or dynamic bit rate adjustments, adapt the call rate to the variable bandwidth available,

down-speeding or up-speeding the video bit rate based on the packet loss condition"