Yealink CP860 [253/417] Outgoing call when the working server connection fails

Configuring Advanced Features

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Parameters are explained in the following table:

Parameter

Description

Priority

Specify preferential treatment for the specific host entry. Lower

priority is MORE preferred.

Weight

When priorities are equal, weight is used to differentiate the

preference. The preference is from highest to lowest. Keep the

same to load balance.

Port

Identify the port number to be used.

Target

Identify the actual host for an A query.

SRV query returns two records. The two SRV records point to different hosts and have

the same priority 0. The weight of the second record is higher than the first one, so the

second record will be picked first. The two records also contain a port “5060”, the IP

phone uses this port. If the Target is not a numeric IP address, the IP phone performs the

A query. So in this case, the IP phone uses “server1.yealink.pbx.com” and

“server2.yealink.pbx.com" for the A query.

A (Host IP Address)

The IP phone performs A query for the IP address of each target host name. Example of

A records:

Server1.yealink.pbx.com IN A 192.168.1.13

Server2.yealink.pbx.com IN A 192.168.1.14

The IP phone picks the IP address “192.168.1.14” first.

Outgoing Call When the Working Server Connection Fails

When a user initiates a call, the IP phone will go through the following steps to connect

the call:

1. Sends the INVITE request to the primary server.

2. If the primary server does not respond correctly to the INVITE, then tries to make

the call using the secondary server.

3. If the secondary server is also unavailable, the IP phone will try the fallback server

until it either succeeds in making a call or exhausts all servers 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 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.