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

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Design Considerations
Planning Audio Quality
When you set up QoS for the LAN, you ensured that the Lync clients marked
audio and video traffic with the correct DSCP. Most WAN routers, including
HP routers, can both honor the DSCP and preserve it so that other devices in
the WAN continue to honor it. The administrator in charge of the WAN router
simply needs to enable a QoS mechanism such as weighted fair queuing (WFQ)
and set the mechanism to refer to DSCP.
If you have not already done so, you should also negotiate an SLA with your
service provider to guarantee that you have adequate bandwidth.
Ensure Audio Quality on the PSTN Connection
The SBM’s Media Gateway supports a variety of features that improve audio
quality:
■ Noise suppression
■ Comfort noise
■ Echo cancellation
Typically, the SBM administrator does not need to perform any additional
steps to configure the SBM to take advantage of these features. However, this
administrator should keep a few guidelines in mind to optimize the PSTN
connection for your environment. Give the SBM administrator the information
in the section that follows.
Echo Cancellation
Echo cancellation improves audio quality by removing echoes of the speaker’s
voice returning to the speaker after a delay. The SBM’s Media Gateway
supports echo cancellation with a 128 ms echo tail buffer, which indicates that
the gateway can cancel echoes that occur with up to 128 ms delay (almost all
echoes fall within this range).
The SBM’s Media Gateway uses the first interface on a telephony card to obtain
the clock used for echo cancellation. Therefore, the SBM administrator must
always use the first interface on a card (as counted from the left) to establish
one of the PSTN connections; otherwise, the echo cancellation feature does
not work. You can connect other lines to any of the other interfaces.