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The switch uses the WRR algorithm to determine the frequency at which it
services each priority queue. The traffic classes are mapped to one of the
four egress queues provided for each port. You can assign a weight to each
of these queues (and thereby to the corresponding traffic priorities). This
weight sets the frequency at which each queue is polled for service, and
subsequently affects the response time for software applications assigned a
specific priority value.
Layer 3/4 priorities to CoS values
The switch supports several common methods of prioritizing Layer 3/4 traffic
to meet application requirements. Traffic priorities can be specified in the
IP header of a frame by using the priority bits in the Type of Service (ToS)
octet or the number of the TCP/UDP port. If priority bits are used, the ToS
octet can contain six bits for Differentiated Services Code Point (DSCP)
service. When these services are enabled, the priorities are mapped to
a Class of Service value by the switch, and the traffic is then sent to the
corresponding output queue.
DSCP priority
The DSCP is six bits wide, allowing coding for up to 64 different forwarding
behaviors. The DSCP replaces the ToS bits, and it retains backward
compatibility with the three precedence bits so that non-DSCP compliant,
ToS-enabled devices do not conflict with the DSCP mapping. Based on
network policies, different kinds of traffic can be marked for different kinds of
forwarding. The DSCP default values are defined in the
priority table" (page
to CoS value 0.
Address tables
Switches store the addresses for all known devices. This information is
used to pass traffic directly between the inbound and outbound ports. All the
addresses learned by monitoring traffic are stored in the dynamic address
table. You can also manually configure static addresses that are bound
to a specific port.
Static addresses
A static address can be assigned to a specific interface on the switch. Static
addresses are bound to the assigned interface and do not move. When a
static address is seen on another interface, the address is ignored and
is not written to the address table.
Copyright © 2006, Nortel Networks
.
81). All DSCP values that are not specified are mapped
SMB
Using the Nortel Business Ethernet Switch 50 Series
NN47924-301 01.01 Standard
1.00 October 2006
Address tables 149
"Mapping DSCP
Nortel Networks Confidential
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