State of knowledge

August 2022

If the telephone connection is established when using a softphone, but one or both parties cannot hear anything or the voice quality is poor, this is often due to the use of incorrect transmission protocols.

Observe transmission protocols

To connect ProCall Enterprise to the telephone system(s) in use, follow the connection instructions and ensure that the correct codecs and connection protocols are set.

One-Way Audio Connection/One-Way Audio

The audio connection for a call on a SIP softphone subscriber line is negotiated between the estos ProCall UC media server and the telephone system connected to the estos ProCall UCServer via SDP protocol (Session Description Protocol). The exchange in SDP includes source and destination for the audio stream consisting of IP address and port number.

If the estos UC media server receives an audio stream from an unknown IP address or an unknown port, i.e. the audio stream is received by the UC media server on an address not signaled by the telephone system in the SDP, the UC media server will discard this audio stream for security reasons and will not forward it to the estos ProCall Enterprise client for Windows or the estos ProCall mobile app.

If the ProCall client's transmit stream (Tx stream/transmit) is received on the remote side, but the ProCall client does not receive an audio stream from the remote side (Rx stream), please check the network topology between estos UC Media Server and PBX or the information exchanged between these two components in the SDP.

Noise reduction

One way to improve the voice quality can be found in the Audio/Video wizard from ProCall: Here it can be helpful to deactivate the noise reduction under Audio devices for Audio/VideoChat and Softphone.

Further articles

Analysis of softphone behavior