Overview ------- Asterisk currently supports configurable RTP packetization per codec for select RTP-based channels. Channels ------- These channel drivers allow RTP packetization on a user/peer/friend or global level: chan_sip chan_skinny chan_h323 chan_ooh323 (Asterisk-Addons) chan_gtalk chan_jingle Configuration ------- To set a desired packetization interval on a specific codec, append that inteval to the allow= statement. Example: allow=ulaw:30,alaw,g729:60 No packetization is specified in the case of alaw in this example, so the default of 20ms is used. Autoframing ------- In addition, chan_sip has the ability to negotiate the desired framing at call establishment. In sip.conf if autoframing=yes is set in the global section, then all calls will try to set the packetization based on the remote endpoint's preferences. This behaviour depends on the endpoints ability to present the desired packetization (ptime:) in the SDP. If the endpoint does not include a ptime attribute, the call will be established with 20ms packetization. Autoframing can be set at the global level or on a user/peer/friend basis. If it is enabled at the global level, it applies to all users/peers/friends regardless of their prefered codec packetization. Codec framing options ------- The following table lists the minimum and maximum values that are valid per codec, as well as the increment value used for each. Please note that the maximum values here are only recommended maximums, and should not exceed the RTP MTU. Name Min Max Default Increment g723 30 300 30 30 gsm 20 300 20 20 ulaw 10 150 20 10 alaw 10 150 20 10 g726 10 300 20 10 ADPCM 10 300 20 10 SLIN 10 70 20 10 lpc10 20 20 20 20 g729 10 230 20 10 speex 10 60 20 10 ilbc 30 30 30 30 g726_aal2 10 300 20 10 Invalid framing options are handled based on the following rules: 1. If the specified framing is less than the codec's minimum, then the minimum value is used. 2. If the specific framing is greater than the codec's maximum, then the maximum value is used 3. If the specificed framing does not meet the increment requirement, the specified framing is rounded down to the closest valid framing options. example allow=ulaw:33 will set the codec to 30ms framing 4. If no framing is specified in the allow= directive, then the codec default is used.