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
Note The values for the service types are the default and recommended values.
However, you can use different values if those values are already used by a
different type of traffic. What is crucial is that the switches map the DSCP
values to the correct 802.1p value and queue.
■ If you want to control all QoS values from the domain rather than from
the network infrastructure, configure the GPO Computer Configuration >
Policies > Administrative Templates > QoS Packet Scheduler > Layer-2 priority
value policy:
•For Guaranteed service type, Enabled with a value of 5 (you might
change this value to 6 for even higher priority)
•For Controlled load service type, Enabled with a value of 4
If you did not choose to set the 802.1p value in a GPO, your network adminis-
trators must complete these tasks on all switches:
■ Configure switches to map the Guaranteed service type DSCP (default 40)
to 802.1p CoS 5 or 6.
■ Enable the minimum number of queues required (balancing the extra
buffer space with fewer queues against the greater granularity for differ-
entiated services with more queues).
If you set the Layer 2 priority value with a GPO, the switch administrator might
not need to configure anything more. However, he or she should ensure that
switches are mapping 802.1p values to queues as expected. You might also
change the number of queues. Finally, on some switches, the switch adminis-
trator might need to configure edge ports to trust DSCP.
SBM. You should also prioritize voice traffic forwarded by the SBM. It is
recommended that the network administrator place the SBM’s internal ports
in the voice VLAN. If this VLAN is associated with a priority, then the traffic
will be prioritized. (This method also prioritizes any management traffic to
and from the SBM; however, this traffic will typically not form a large percent-
age of the total traffic.) You can also use Lync to configure the SBM’s Mediation
Server to mark voice traffic for high priority. See “Verify that QoS is Enabled
for the SBM (Optional)” on page 4-54.
Ensure QoS for VoIP calls over the WAN
Because a WAN link typically provides much less bandwidth than LAN links,
QoS is even more crucial for VoIP traffic carried over the WAN to the data
center.