RTP Settings Help

The RTP (Real Time Protocol) Settings page allows to configure codec's packet size and silence suppression for each voice codec, to select the G726 codec standard, to define RTP/RTCP port ranges and to enable the RTCP support. All parameters listed on this page may be modified and submitted.

The table Codec Properties includes a list of codecs with packetization ranges and silence suppression associated to them:

• The Packetization Interval is the time interval between two RTP packets of the same stream. If the interval is increased the overhead is decreased but the voice quality might be deteriorated. If the interval is decreased, the network load is increased and the delay is reduced.
• The Silence Suppression allows disabling RTP packet transmission in the case of no voice activity. This feature helps to avoid extra traffic if the RTP stream contains no voice activity. It is activated after 2 seconds of silence and restarted immediately if any sound appears.

 Edit  opens the page RTP Settings - Edit Entry to modify the codec settings. To operate with Edit, only one codec may be selected, otherwise the "One record should be selected" error message appears.

• The drop down list Packetization Interval contains possible values (in milliseconds) to be configured for a selected codec.
• The checkbox Silence Suppression serves to enable the voice activity detection for the selected codec.

The manipulation buttons G726 Standard are used to select between packaging the G.726 codewords into octets. If you experience problems with the G.726 voice quality when one of these packaging is selected, try a different one.

• When Use ITU_T specification is selected, the ITU I.366.2 ("AAL2 type 2 service specific convergence sublayer for narrow-band services") type packaging of codewords is used, where packing code words into octets starts from the most significant rather than the least significant positions in the octet.
• When Use IETF RFC is selected, the IETF RFC ("RTP Profile for Audio and Video Conferences with Minimal Control") type packaging of codewords is used, where packing codewords starts from the least significant positions in the octet.

RTP/RTCP Port Range:
IP connections from the Quadro FXS lines and from the MGCP gateways attached to the Quadro are built up as RTP (Real time Transport Protocol) sessions. For each parallel IP call, two ports are needed: one (even) port for RTP (Real Time Transport Protocol) and one (odd) port for RTCP (Real Time Transport Control Protocol).

• Min- the RTP/RTCP port specified here must be greater than 1024 and less than the specified maximum port (even numbers only).
• Max- the RTP/RTCP port specified here must be less than 65535 and greater than the specified minimum port (odd numbers only).

Since the specified maximum port must be greater than the minimum port, the error message "Min port number should be less than max port number" will occur if this condition is disobeyed. The port range must consist of digits only, otherwise the error "Incorrect Port Range: only Integer values allowed" will appear. The difference between Max and Min RTP ports should be 100 ports or less (according to the system capabilities) otherwise the corresponding warning will appear. RTP/RTCP Port ranges cannot include the defined SIP UDP ports (see SIP Settings) otherwise an error message will appear.

The Enable RTCP Support checkbox activates the Real Time Control Protocol support and allows RTCP packet transmission. The RTCP protocol is used for monitoring the RTP streams and changing RTP characteristics depending on the network conditions.