Technical data

DATA CENTER and CAMPUS NETWORKS DEPLOYMENT GUIDE
Deploying Brocade Networks with Microsoft Lync Server 2010 22 of 52
• Strict Priority (SP). SP ensures service for high-priority traffic. The software assigns the maximum
weights to each queue, to cause the queuing mechanism to serve as many packets in one queue as
possible before moving to a lower queue. This method biases the queuing mechanism to favor the
higher queues over the lower queues.
For example, strict queuing processes as many packets as possible in QoS p3 before processing any packets in
QoS p2, then processes as many packets as possible in QoS p2 before processing any packets in QoS p1, and
so on.
• Hybrid WRR and SP. Starting with Brocade software release FSX 02.2.00, an additional configurable
queuing mechanism combines both the strict priority and WRR mechanisms. The combined method
enables the Brocade device to give strict priority to delay-sensitive traffic, such as Voice and Video
traffic, and WRR priority to other traffic types.
By default, when you select the combined SP and WRR queuing method, the Brocade device assigns strict
priority to traffic in QoS p7 and QoS p6, and WRR priority to traffic in QoS p0 through QoS p5. Thus, the Brocade
device schedules traffic in queue 7 and queue 6 first, based on the strict priority queuing method. When there is
no traffic in queue 7 and queue 6, the device schedules the other queues in round-robin fashion from the
highest priority queue to the lowest priority queue.
Best Practices QoS
First, you should consult with upper management and get an understanding of how critical voice and video are. In
many cases, voice is very important and needs higher priority than most applications, but not all. One thing to be
sure of is that voice and video get a higher priority than day-to-day data traffic. For example, you want to prevent a
user who is watching YouTube to take up all the bandwidth and cause VOIP calls to be dropped.
Second, once you enable DSCP on the switch, any traffic that is marked with a DSCP value will follow the settings
according to Figure 6. By default all Windows clients use a DSCP value of 40 for voice and 0 for video. There are
three different options to change the DSCP value for the clients: Modify the DSCP value through an Active Directory
Group Policy, changing the registry on each client, or by remarking the packets on the Brocade switch. We
recommend that you change it by using a Group Policy, because you can configure it at one location and it will apply
to all the clients. If you make the change on the switch then it will require you make the same changes on all the
switches that see voice or video traffic. In many cases you can create custom scripts, or you can leverage Brocade
INM to distribute and apply custom QoS ACLs to multiple switches.
Rate Limiting
Each Brocade device supports line-rate rate limiting in hardware. The device creates entries in Content Addressable
Memory (CAM) for the rate limiting policies. The CAM entries enable the device to perform rate limiting in hardware
instead of sending the traffic to the CPU. The device sends the first packet in a given traffic flow to the CPU, which
creates a CAM entry—consisting of traffic source and destination addresses—for the traffic flow. The device uses the
CAM entry for rate limiting all the traffic in the same flow. A rate limiting CAM entry remains in the CAM for two
minutes before timing out.
Fixed rate limiting counts the number of bytes (for Brocade FastIron devices) or kilobits (for Brocade TurboIron
devices) that a port receives, in one-second intervals. If the number exceeds the maximum number that was
specified when the rate was configured, the port drops all further inbound packets for the duration of the one-second
interval. Once the one-second interval is complete, the port clears the counter and re-enables traffic.
To configure rate limiting on a Brocade FastIron port, enter commands such as:
FastIron(config)#interface ethernet 24
FastIron(config-if-e1000-24)#rate input fixed 500000
To configure ACL-based rate limiting, you should create individual traffic policies and then reference the traffic
policies in one or more ACL entries (also called clauses or statements). The traffic policies become effective on ports
to which the ACLs are bound.