Allied Telesis Rapier Switch - Manual (Page 52)

52 Rapier Switch Software Reference
Software Release 2.5.1
C613-02025-00 REV B
■ control of the egress scheduling algorithm
■ priority relabelling of frames, at Layer 2, by replacing the VLAN tag User
Priority field
■ class of service relabelling of frames, at Layer 3, by replacing the DSCP
(DiffServ Code Point) or the TOS precedence value in the IP header’s Type
of Service (TOS) field
Spanning Tree Protocol (STP)
The Spanning Tree Protocol (STP) makes it possible to automatically disable
redundant paths in a network to avoid loops, and enable them when a fault in
the network means they are needed to keep traffic flowing. A sequence of
LANs and switches may be connected together in an arbitrary physical
topology resulting in more than one path between any two switches. If a loop
exists, frames transmitted onto the extended LAN would circulate around the
loop indefinitely, decreasing the performance of the extended LAN. On the
other hand, multiple paths through the extended LAN provide the opportunity
for redundancy and backup in the event of a bridge experiencing a fatal error
condition.
Table 15: The different QoS-type controls available on the switch.
Command set Use for Do not use for
QoS Bandwidth limiting of classified traffic flows.
Priority queueing of classified traffic flows.
Replacing TOS or DSCP byte of IP header.
Replacing User Priority in VLAN tag header.
Providing a coordinated QoS solution for a port or
ports, using the QoS policy model.
Configuring a DiffServ domain.
Limiting total bandwidth on a port, unless
other QoS controls are also required.
Hardware packet filters Priority queueing of classified traffic flows.
Replacing TOS or DSCP byte of IP header.
Replacing User Priority in VLAN tag header.
Forwarding a flow that is marked to be dropped (for
example, because bandwidth allocation is exceeded).
Specifying actions for packets which match the ingress
and egress ports of a classifier (if set), but do not match
the classifier’s other parameters.
Configuring a simple DiffServ domain.
Bandwidth limiting.
Configuring most DiffServ domains.
Layer 3 switch filters Priority queueing of up to 16 distinctly different types
of traffic flow.
Replacing TOS or DSCP byte of IP header.
Replacing User Priority in VLAN tag header.
QoS for non-IP traffic (e.g. IPX).
QoS based on VLANs.
Bandwidth limiting.
SET SWITCH PORT Limiting total ingress and/or egress bandwidth on
ports. Limiting bandwidth of particular types of
traffic.
Limiting egress bandwidth if priority
queueing is also required.