HP Survivable Branch Communication zl Module powered by Microsoft Lync Planning and Design Guide 2011-02

2-30
Design Considerations
Planning for High Availability
On an HP E5400 zl Series switch, you can install redundant power supplies.
The SBM itself connects to the HP zl switch on an internal port, which is highly
reliable.
Behavior During a WAN Outage
If your branch office’s WAN link fails, the SBM continues to provide voice
services. Aware that the main-office Lync servers cannot be reached, the SBM
routes all non-local Lync calls (both those to PSTN users and those to Lync
users at other sites) through its PSTN connections.
Although the SBM supports voice services during the failover situation, some
advanced functionality will not be available until the WAN link is restored.
The table indicates which Lync features do and do not fail over. After the WAN
connection is restored, full functionality should return within 15 minutes.
Note During the WAN outage, all calls except ones between local branch users are
routed through the PSTN connection. The SBM might support fewer total calls
because calls to Lync users at other sites must use a PSTN channel. See
“Considerations for Local PSTN Calls and Planning Your Telephony Cards” on
page 2-5 for guidelines for determining the number of PSTN calls supported
by your SBM.
Table 2-19. Features That Fail Over
Feature Supported in Normal
Operation
Supported during
WAN Outage
Branch users can call other Lync users at
the branch.
X X
Branch users can log in and register to
place and receive calls.
XX
Non-branch users at the branch can log in
and register to place and receive calls.
X
Branch users can place PSTN calls. X X
Branch users can send instant messages
(IMs) to other Lync users at the branch.
XX
Outside callers can call local branch users
through the PSTN.
XX