recently I’ve managed a very strange issue with Polycom Trio 8800 when placing a call on hold, following you will find the scenario and, the more important thing, the solution!
Skype for Business on-premise with Enterprise Voice enabled.
Sonus SBC 1000 as Voice Gateway (fw. 6.1.1 build 459)
Polycom Trio 8800 with Visual+ (fw 184.108.40.20676)
If you make a voice call from Trio to PSTN (for example a mobile phone) and you place the call on hold, the call immediately drop.
Instead, if you answer an incoming call from PSTN to Trio, there is no issue placing the call on hold.
There are two causes for this behaviour, the first is well described on James Cussen’s Blog here: POLYCOM VVX HOLD ISSUE WITH SONUS SBC1000/2000 CALLS
Long story short, there is a incompatibility between standard Polycom VVX and Trio settings and Sonus SBC 1000 / 2000 settings.
The Sonus gateway supports a maximum payload sizes of 60ms, but VVX / Trio used a Music on Hold payload of 80ms, so there is no way to find a common payload and the call drops.
Trio and VVX have the same behavior and the same solution.
Second cause is specific to Trio when it is paired with a Visual+, so you will not have this issue on VVX IP Phone.
Trio default call is an “Audio+Video” call. This seems to create some problem to Sonus SBC when you place the call on hold.
Even if you fix the first cause, this behaviour needs a different solution: set the default call as an Audio call.
To solve the first and second causes (in order) you have to set these settings in Trio Provisioning file.
I’ve not found any side-effects and the problem result solved.
feature.moh.payload = 60 video.callMode.default = audio
Same as Scenario #1, but the Voice Gateway is a Sonus SWe Lite (virtual SBC) version 7.0.0
With this configuration, if you try to place on-hold a call with a Polycom Trio/VVX IP-Phone, you will get the same problem above and the call drop.
Tracing the call with the Sonus LX Log Tool, you will find this line at the end of SDP part of INVITE
and after the INVITE a 488 Not Acceptable Here
Reason:SIP;cause=488;text="received ptime is not acceptable;maxptime=40"
Because it seems that Sonus SWe Lite support only MOH maximum payload sizes of 40ms (compared to 60ms of SBC 1000/2000).
Glad to know, latest Polycom Trio/VVX firmware support payload of 40ms, so you can set the feature.moh.payload to 40
feature.moh.payload = 40 video.callMode.default = audio
Remember to update the firmware to the latest version, if not this setting will be ignored.
I hope this could help you.