Scenario Two - Polycom SpectraLink 8020 Deployment Manual

Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009
4.1.3.2

Scenario Two

Scenario Two assumes that handset has roamed to Access Point B and is managed by SVP Server 2
(Figure 9)

Packets to handset (from call server or PBX) are first sent through its Home SVP Server (Server
1), then forwarded to SVP Server 2, and then transmitted by AP B to the handset
 On the return trip the handset communicates back through AP B to its "Home" SVP Server
(Server 1) and back to the call server or PBX
Calls between handset may bypass the call server or PBX and connect directly between SVP Alias IP
addresses. Control messaging will still go to /from the call server or PBX.
As a final note, the wireless telephone learns about all available SVP Servers IP addresses when it
powers up and does the "SRP Check-In" with the Registration SVP Server (identified in DHCP option 151
or set statically). Once the handset are aware of all SVP Servers even if the Registration SVP Server
identified by DHCP option 151 goes down, the handset will still find another SVP Server to use. This is
the SVP self-healing concept in action.
Any new or replacement wireless telephones may fail to Check-In if the SVP Server identified by DHCP
option 151 is down. The new handset has not yet learned the list of all SVP Servers and does not get a
response to its Check-In Request. In this case, check the SVP Server identified by DHCP option 151 for
operational status.
Note that it is not possible to create an IP array of the SVP Servers in the DHCP option as the handset
would not understand this and would instead display "No SVP Response" on the screen. DHCP option
151 is required for the handset when it is operating with an IP protocol but is not required when the
handset is working in a Telephony Gateway environment.
When wireless telephones do the first SRP Check-In Request with the registration SVP Server, the
registration SVP will load balance the handsets across all available SVP Servers. It will tell the wireless
telephone to Check-In with another SVP Server based on a load balancing algorithm. This algorithm does
not guarantee an even distribution of handset across all SVP Servers. The wireless telephone will do an
SRP Check-In with this designated SVP Server.
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LAN
SVP Server 1
call server
or PBX
Figure 9 - Scenario Two
28
Best Practices Guide
SVP Server 2
SpectraLink
AP B
8020/8030