Allied Telesis AT-S63 - Manual (Page 343)

AT-S63 Management Software Menus Interface User’s Guide
Section II: Advanced Operations 343
switch.
3. As packets leave the DiffServ domain, classify them according to the
DSCP values.
ˆ Assign the classifiers to flow groups and the flow groups to traffic
classes, with a different traffic class for each DiffServ code point
grouping within the DiffServ domain.
ˆ Give each traffic class the priority and/or bandwidth limiting
controls required for transmission of that type of packet to its next
destination, in accordance with any Service Level Agreement
(SLA) with the providers of that destination.
ˆ If necessary, assign a different DSCP value to each traffic class, to
be written into the TOS field of the packet header, to match the
DSCP or TOS priority values of the destination network.
Examples
The following examples demonstrate how to implement QoS in three
situations:
ˆ “Voice Applications,” next
ˆ “Video Applications” on page 346
ˆ “Critical Database” on page 348
Voice Applications
Voice applications typically require a small but consistent bandwidth. They
are sensitive to latency (interpacket delay) and jitter (delivery delay). Voice
applications can be set up to have the highest priority.
This example creates two policies that ensure low latency for all traffic sent
by and destined to a voice application located on a node with the IP
address 149.44.44.44. The policies raise the priority level of the packets to
7, the highest level. Policy 6 is for traffic from the application that enter the
switch on port 1. Policy 11 is for traffic arriving on port 8 going to the
application. The components of the policies are shown in Figure 111.