Difference between Silent Call and Mute Call


Hi Team

Do we have an official definition between Silent Call and Mute Call?

Does mute mean that calling party does not hear ringback tone, connect, called party voice, and no disconnect tone?

What are the probable causes of Mute? (if defined as total call silence from ringback, party B voice and connect/disconnect tones).

Multi-vendor End-to-End.
Radio: Nokia

High number of RTP packet loss in UL/DL may lead to call Mute / one way talk.
Call mute if consecutive RTP packet loss in (~5 sec or more) UL/DL.

In Ericsson, DRX profile is important to define correctly.
Ondurationtimer / long / short duration cycle, etc.

There is no official definition of mute or silence call.

Even for RTP packets lost the only way to interrupt a VoLTE call is through radio link failure. You can have a VoLTE call full of glitches, metallic voice and interruption and call is still not released until radio link failure.

In the entire world there is not a single VoLTE call released when GBR cannot be sustained anymore due to strong interference in either UL or DL.

In this case where is the quality of VoLTE call when we see values like T310 = 1000 msec and T311 = 10000 msec for VoLTE qci1.

But in VoLTE mostly RLC UM (Unacknowledged Mode) is there it will lead to drop.
So to avoid we have features rate contol, muting, scheduling, rohc, tti, high users scenario then sps and so on to substain call and quality.

RLC AM (Acknowledged Mode) is used in VoLTE but not a good way, it gives a bad quality and packet loss, it is only a mean of reducing drops giving unnecessary RRC signalling and leading to bad quality and eventually muting, silent call and drop.

This is because there is no option in scheduler to release a GBR when the GBR rate cannot be sustained anymore. In other words a GBR is not excatly a GBR, it is more of a best effort GBR.

Normally when GBR cannot be sustained call should be released due to QoS reasons.

All those features will not help you in strong in terference in UL and DL or when there is no dominance.
This is not an issue of poor RSRP.
This is an issue fo strong interference in UL and DL due to no dominance in LTE (no best server).
In VoLTE there are harq/mac retransmissions but not RLC retransmissions.
In 5G VoNR can be done with RLC in AM.
So in VoNR there are also rlc retransmissions.

RLC is UM in VoLTE but AM can be implemented.
But it is not recommended.
I have not worked with 5G yet, so I am not aware of 5G cases.

VoLTE has a pdb budget of 100 msec.
Any packet that cannot be transmitted within 100 msec will be discarded.

Need to be mentioned important parameter tdiscard timer, part of PDCP profile.
Play with this parameter to improve mute call.

So mute call (short 1-2 seconds voice gaps) is pure radio issue.

Increase value of tdiscard will be good for VoLTE.

And the only way to improve it is to improve radio dominance fo cells and avoid A3 events every half a second or so.
Dominance is crucial in LTE and it is also in 5G as well.

Hi @Benjamin_Ng_aru,
Technically speaking, Volte mute call is when you see RTP packets flowing only in one way on your UE packet capture file,

This might be a short duration mostly linked to radio link failures followed by poor radio quality OR transmission link quality as my most of friends already discussed here.

Mute call could also be a visibly long duration which you can easily identify by looking at SIP BYE cause code “200 RTP timeout” either initiated by UE side or IMS side. Which; if one way RTP packets last for 20 seconds or more.
The cause of these problems might exist on radio, transmission, core.

Hope this helps. Thank You.

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