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CrossFire 8600/8605 Token-Ring Switches v. 1.2, P/N: 710001641 Switch Theory of Operation
the same segment.
Therefore, the IEEE Spanning-Tree Protocol (STP) must be
enabled
, which will place one port in forward and the other in blocked mode. If
there is a break in the main ring, the STP will place both ports in forward mode, and
all MACs on both segments will be relearned.
If a switch port has been configured to RI/RO mode, it will automatically sense
whether the port has been connected to RI or RO of the MAU.
➽ Note:
It is not possible to automatically verify whether an UTP/STP port has been
connected according to the configuration. Any errors, such as attaching port 19 or
20 to a normal MAU port when the CrossFire 8600 port has been configured for
RI/RO, will cause a complete disruption of the ring to which the port is attached.
Therefore, be careful when using the RI/RO feature.
Transmission Priority Queues
To address the needs of delay-sensitive data, such as multimedia, the Token-Ring
ports of the switch have two transmit queues, a high-priority queue and a low-
priority queue.
The queue for a frame is determined by the value of the priority field in the frame
control (FC) byte. If FC priority is above a configurable level (default 3), the frame
is put into the high-priority queue. If an output port becomes congested, you can
dynamically configure the port to transmit all frames at high priority regardless of
the FC byte contents.
CrossLink Connections
Two switch stacks or switches may be interconnected by a number of parallel
Token-Ring connections (up to 256 Mbps using eight ports). The traffic between
the switches will be shared between the connections.
Spanning Tree Protocol Support
IBM initially supported only Source Route Bridging (SRB) in its bridges, so most
networks were built to use it. The main consideration for SRB implementations in
switches is the spanning-tree algorithm for spanning tree explorers (STEs). IBM
originally implemented a form of the Institute of Electrical and Electronics
Engineers (IEEE) spanning-tree algorithm. This algorithm, commonly referred to
as the IBM spanning tree, limits the STE frames to one copy per destination ring.
Some SRB implementations have also implemented the IEEE Spanning Tree
Protocol to be compatible with SRT bridges. The IEEE Spanning Tree Protocol is
not compatible with the IBM Spanning Tree Protocol.
The switch supports both the IEEE 802.1D and IBM Spanning Tree Protocols.