Yealink SIP-T2xP Administration Manual

Also see for Yealink SIP-T28P: User guide Auto provisioning guide User guide User guide User guide

Contents

Yealink SIP-T2xP Administration Manual Manual pdf 77 page image

Configuring Advanced Features65Many SIP servers are deployed in redundant pairs, designated as primary andsecondary servers. The IP phone must always contact the primary server except infailover conditions. Server redundancy is often required in VoIP deployments to ensurecontinuity of phone service, for events where the server needs to be taken offline formaintenance, the server fails, or the connection from the IP phone to the server fails. TheIP phone is able to route to a secondary (or alternate) server in a failure situation, whichrequires the use of DNS SRV query for the resolution of proxy address as specified byRFC 3263.When the IP phone accesses the internet, it sends out a DNS SRV query to the server tolook up the IP address and port, and then waits for a response from the server. The DNSSRV query involves NAPTR, SRV and A queries, which allows the IP phone to adapt tovarious deployment environments. The DNS SRV query is configurable on a per-accountbasis.NAPTR (Naming Authority Pointer)First, the IP phone sends the NAPTR query to get the SRV pointer and service type. As anexample, consider the IP phone wishes to resolve ―sip:user@example.com‖. The IPphone performs a NAPTR query for that domain, and the following NAPTR records maybe returned:order pref flags service regexp replacementIN NAPTR 90 50 "s" "SIP+D2T" "" _sip._tcp.example.comIN NAPTR 100 50 "s" "SIP+D2U" "" _sip._udp.example.comParameters are explained in the following table:Parameter DescriptionorderSpecifies preferential treatment for the specific record.The order is from lowest to highest, lower order is MOREpreferred.prefSpecifies the preference to process multiple NAPTRrecords with the same order value. Lower value is MOREpreferred.flags The flag ―s‖ means to do an SRV lookup.serviceSpecifies the service available for SIP by the followingrules:SIP+D2U: SIP over UDPSIP+D2T: SIP over TCPSIP+D2S: SIP over SCTPSIPS+D2T: SIPS over TCP