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This article describes how issues related to the RTP Packetization interval can be solved in the case of conference calls on VoipNow servers. The recommended solution is to make sure that all parties involved in that call have the packetization interval set to 20ms during conference calls on VoipNow servers. Otherwise, when channels are bridged, voice breaks, missing or dropped syllables, unexplained clicks or noises may occur.

Overview

Voice breaks, missing or dropped syllables, unexplained clicks or noises are triggered by different values of the ptime parameter when channels are bridged. According to the RFC3551 for packetized audio, the default packetization interval must be 20 ms or one frame, whichever is longer, unless required otherwise. However, a receiver should be able to accept packages with a packetization interval between 0 and 200ms.

Good to

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know

If autoframing=yes is set in sip.conf within the global section, all calls will try to set the packetization based on the preferences of the remote end point.

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Ptime and

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different devices

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Aastra 6751i

• To set the RTP packetization interval on Aastra 6751i, you need to go to the Advanced Settings->Global SIP->Codec Preference List;
• Valid values: 5 to 90, in increments of 5 milliseconds;
• To use this phone registered on a VoipNow server, you need to set the Packetization interval to 20ms;

Grandstream Gxp2020

Web Interface

Go to Advanced Settings -> iLBC frame size and select a framesize of 30ms.

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# iLBC Frame Size. 0 - 20ms(default), 1 - 30ms.
P97 = 1

Yealink T20P

The ptime parameter can be set via provisioning templates.

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[ account ]
path=/config/voip/sipAccount0.cfg
<yealink t20p configuration parameters>
  
ptime = 20
  
[ account ]
path=/config/voip/sipAccount1.cfg
<yealink t20p configuration parameters>
  
ptime = 20

Some Linksys devices, such as PAP2 or SPA2102, have the RTP Packet Size parameter set to 30ms by default.

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Siemens Speedstream 3610

To set the RTP packetization interval on Siemens Speedstream 3610, you need to go to the Voice Setup -> Advanced Setting.

If you are using this device registered on a VoipNow server, please set the RTP Packetization period to 20ms.Valid values: in increments of 10ms.

Resources

Asterisk Documentation

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