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This guide provides detailed information on how to configure and use server redundancy on Htek IP phones. The information applies to Anchor
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- Failover Server Use DNS-SRV or DNS-NAPTR(FSUSN): In this mode, the full phone system functionality is preserved by having a second equivalent capability call server take over from the one that has gone down or off-line. This mode of operation should be done using the DNS-SRV or DNS-NAPTR from the primary to the secondary server.
- Failover Server Use DNS-A(
Anchor OLE_LINK6 OLE_LINK6 Anchor OLE_LINK7 OLE_LINK7 FSUA): In this mode, a second less featured call server (FSUA) with SIP capability takes over call control to provide basic calling capability, but without some advanced features offered by the working server (for example, shared lines, call recording and MWI). IP phones support configurations of two SIP servers per SIP registration for this purpose.
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4. Phone Function Implementation
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Phone Registration
The IP phone must always register to the primary server first. If this is unsuccessful, the phone will re-register as many times as configured until the registration is successful. When the primary server registration is unavailable, the secondary server will serve as the working server.
Registration methods of the fallback mode include:
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Sip Server Domain Name Resolution
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If a domain name is configured for a SIP server, the IP address(es) associated with that domain name will be resolved through DNS as specified by RFC 3263. The DNS query involves NAPTR, SRV and A queries, which allows the IP phone to adapt to various deployment environments. The IP phone performs NAPTR query for the NAPTR pointer and transport protocol (UDP, TCP and TLS), the SRV query on the record returned from the NAPTR for the target domain name and the port number, and the A query for the IP addresses.
If an explicit port (except 0) is specified and the transport type is set to DNS-NAPTR, A query will be performed only. If a SIP server port is set to 0 and the transport type is set to DNS-NAPTR, NAPTR and SRV queries will be tried before falling to A query. If no port is found through the DNS query, 5060 will be used.
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The following introduces a REGISTER FSUA scenario. We set the Anchor
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The phone has ability to register to a failover server when the Anchor
response to a REGISTER request.
1) The phone sends a REGISTER request to the Primary SIP Server.
2) The phone retries to send REGISTER requests to the Primary SIP server (three times by default).
3) After no response from the Primary SIP server, the phone sends a REGISTER request to the failover server.
4) The phone retries to send REGISTER requests to the Failover SIP server (three times by default).
5) After no response from the Failover SIP server, the phone sends a REGISTER request to the Second Failover server.
6) The Failover server responds with 200 OK to the REGISTER request.
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