Polycom SOUNDPOINT SIP 2.2.0 User Manual

Page 83

Configuring Your System

4 - 35

DNS SIP Server Name Resolution

If a DNS name is given for a proxy/registrar address, the IP address(es)

associated with that name will be discovered as specified in RFC 3263. If a port

is given, the only lookup will be an A record. If no port is given, NAPTR and

SRV records will be tried, before falling back on A records if NAPTR and SRV

records return no results. If no port is given, and none is found through DNS,

5060 will be used.
Refer to

for an example.

Behavior When the Primary Server Connection Fails

For Outgoing Calls (INVITE Fallback)
When the user initiates a call, the phone will go through the following steps to

connect the call:

Try to make the call using the working server.

If the working server does not respond correctly to the INVITE, then try

and make a call using the next server in the list (even if there is no current

registration with these servers). This could be the case if the Internet

connection has gone down, but the registration to the working server has

not yet expired.

If the second server is also unavailable, the phone will try all possible

servers (even those not currently registered) until it either succeeds in

making a call or exhausts the list at which point the call will fail.

At the start of a call, server availability is determined by SIP signaling failure.

SIP signaling failure depends on the SIP protocol being used as described

below:

• If TCP is used, then the signaling fails if the connection fails or the Send

fails.

• If UDP is used, then the signaling fails if ICMP is detected or if the signal

times out. If the signaling has been attempted through all servers in the list

and this is the last server, then the signaling fails after the complete UDP

timeout defined in RFC 3261. If it is not the last server in the list, the

maximum number of retries using the configurable retry timeout is used.

For more information, refer to

and

on page

Note

Failure to resolve a DNS name is treated as signalling failure that will cause a
failover.