Polycom 4300T Benutzerhandbuch

User Guide V

2

IU 4300T Converged Network Appliance

3 - 50

If you will be using multiple network based call processing servers then you 

will need to enable server redundancy and specify the time between DNS 

lookups in the V

2

IU appliance.  Enabling redundancy allows a DNS server to 

provide a list of multiple call processing servers to the V

2

IU appliance in the 

answers to SRV lookups.  Each server in the list will be monitored using 

periodic messages by the V

2

IU appliance and the highest priority server that 

is currently reachable will be used for signaling.  The V

2

IU appliance uses the 

reachability settings described in step 2 to determine the status of remote 

servers and remove inoperable servers from the list. 
Triggers can also be used by the V

2

IU appliance to determine when to forward 

call requests to a secondary server in the list. A trigger is set when a configured 

number of resends are received by the V

2

IU appliance from a SIP user agent 

attempting to place a call.  When initiating a call a SIP user agent will send an 

INVITE message to the V

2

IU appliance that will then be forwarded to the 

primary server.  In the event that the primary server fails before a reachability 

alarm has been declared using the heartbeat messages the user agent will 

resend INVITE messages until the trigger condition is met.  At this point the 

V

2

IU appliance will forward the call request on to the secondary server in the 

list.  Please use the following steps to enable redundancy and set triggers:  

Log into the V

2

IU appliance using a Netscape or Internet Explorer web 

browser.

Select System.

Select Survivability.

Enter the Time between DNS lookups (in seconds) in the Softswitch 

Reachability section of the web page.  

Select Enable SIP server redundancy in the Softswitch Redundancy 

Settings section of the web page.