Voice quality over 4G backup connection with video disabled

[dhawley00]

Remote sites connected to a CUCM v9 cluster over MPLS fail their connection over to 4G back-up connections in the event of a MPLS connection failure.

Phones remain registered to CUCM and voice calls work fine between on-cluster phones with video enabled even if the video is not active on the call.  However voice is garbled and choppy beyond being understandable if it's a on-cluster to PSTN call, or a call on-cluster with one of the endpoints video disable on the CUCM device page.

The 4G carrier has no QoS.  I first thought this might be due to the 4G carrier handling AF31 different than EF.  I tested tagging all EF as AF31, but no change.

So calls on 4G are ok phone to phone, until video is disabled on the device page, then voice quality is horrible.  Tested iLBC, and g.729 as well with no improvements.  Has anyone encountered this, or does anyone have a solution?  Is there a difference in how audio streams are handled between video enabled and disabled calls beyond the QoS tagging?

Thank you in advance!

Dave

[Mohammed al Baqari]

Hi,

Qos won't matter here as 4G won't take the DSCP markings into account (unless this is a managed link by your provider).

Can you check if the call is using MTP when the video is disabled?
 

[dhawley00]

The call is not using MTP for either scenario.

Thanks!

Dave

[Mohammed al Baqari]

Hi, Did you confirm this from RTMT?

Also, can we get a packet capture using port span from the switch port where one of the phones is connected during degraded voice call.

[dhawley00]

Verified no MTP involved for either video or no video call through RTMT.  Stream stats on the phone page show the remote end is directly to the phone.

I will set up a packet capture to collect a degraded and working phone call.

Thanks,

Dave
 

[Dennis Mink]

Mo,

I'm in Australia and there is no QoS on 4G in any case, not even combined with a managed link. (or at least not with Telstra ;-) )

[Mohammed al Baqari]

Thx for the info. Here in Dubai managed link will provide QoS capabilities :)

[Dennis Mink]

RTP in a Video enabled call is treated the same; it is still RTP in a separate stream. Only difference is the DSCP value, which goes from af31 (video and voice to provide lip sync), to ef for audio only.