IP Type of Service settings for VoIP channels --------------------------------------------- Asterisk can set the Type of Service (TOS) byte on outgoing IP packets for various protocols. The TOS byte is used by the network to provide some level of Quality of Service (QoS) even if the network is congested with other traffic. * SIP ----- In sip.conf, there are three parameters that control the TOS settings: "tos_sip", "tos_audio", and "tos_video". tos_sip controls what TOS SIP call signalling packets are set to. tos_audio controls what TOS RTP audio packets are set to. tos_video controls what TOS RTP video packets are set to. There is a "tos" parameter that is supported for backwards compatibility. The tos parameter should be avoided in sip.conf because it sets all three tos settings in sip.conf to the same value. * IAX2 ------ In iax.conf, there is a "tos" parameter that sets the global default TOS for IAX packets generated by chan_iax2. Since IAX connections combine signalling, audio, and video into one UDP stream, it is not possible to set the TOS separately for the different types of traffic. In iaxprov.conf, there is a "tos" parameter that tells the IAXy what TOS to set on packets it generates. As with the parameter in iax.conf, IAX packets generated by an IAXy cannot have different TOS settings based upon the type of packet. However different IAXy devices can have different TOS settings. The allowable values for any of the tos* parameters are: CS0, CS1, CS2, CS3, CS4, CS5, CS6, CS7, AF11, AF12, AF13, AF21, AF22, AF23, AF31, AF32, AF33, AF41, AF42, AF43 and ef (expedited forwarding), The tos* parameters also take numeric values. The lowdelay, throughput, reliability, mincost, and none values are deprecated because they set the IP TOS using the outdated "IP precedence" model as defined in RFC 791 and RFC 1349. They still work in this version of Asterisk, but will be removed in future releases. =========================================== Configuration Parameter Recommended File Setting ------------------------------------------- sip.conf tos_sip cs3 sip.conf tos_audio ef sip.conf tos_video af41 ------------------------------------------- iax.conf tos ef ------------------------------------------- iaxprov.conf tos ef =========================================== * REFERENCE ----------- RFC 2474 - "Definition of the Differentiated Services Field (DS field) in the IPv4 and IPv6 Headers", Nichols, K., et al, December 1998. IANA Assignments, DSCP registry Differentiated Services Field Codepoints http://www.iana.org/assignments/dscp-registry To get the most out of setting the TOS on packets generated by Asterisk, you will need to ensure that your network handles packets with a TOS properly. For Cisco devices, see the previously mentioned "Enterprise QoS Solution Reference Network Design Guide". For Linux systems see the "Linux Advanced Routing & Traffic Control HOWTO" at . For more information on Quality of Service for VoIP networks see the "Enterprise QoS Solution Reference Network Design Guide" version 3.3 from Cisco at: