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diff --git a/trunk/doc/rtp-packetization.txt b/trunk/doc/rtp-packetization.txt new file mode 100644 index 000000000..c558a538e --- /dev/null +++ b/trunk/doc/rtp-packetization.txt @@ -0,0 +1,75 @@ +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. |