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CrossFire 8600/8605 Token-Ring Switches v. 1.2, P/N: 710001641 Switch Theory of Operation
conversations, the switch creates 160 Mbps throughput in half-duplex mode, or 320
Mbps throughput in full-duplex mode.
A single segment can be dedicated to a single host or shared by several. To optimize
throughput, high-speed servers can be given dedicated switch ports.
By transporting multiple Token-Ring packets simultaneously, it boosts overall
network throughput.
Low Latency
When operating in cut-through mode, the switch minimizes latency—the time it
takes to forward a packet from one Token-Ring segment to another—by beginning
switching immediately after looking at the first six bytes of the destination address
in the packet. If the packet needs to be switched to another LAN segment, its data
begins flowing through the destination port before the entire packet has been
received. The result: packets can appear at the output port 35 microseconds after
entering the input port. Network devices that use store-and-forward technology
introduce much longer delays because they wait to receive the entire packet before
forwarding it.
By minimizing delay, the switch can move more packets freely throughout the
LAN without degrading performance.
Address Management
At power up, the system address tables do not contain any information. Whenever
a switch receives a packet with an unknown source or destination address, it learns
the new source address and stores its location in coming port in the address table.
If the destination address is unknown it sends the packet to all ports that can receive
data from the incoming port. When the response packet comes back, the switch will
learn the responder’s location and adds it to the address table. Once the address
table entries are created, the switch uses these learned address to switch all
subsequent packets to the port where the destination address is located.
The system address table maintains up to 10,000 entries, and each port address table
maintains 5,500 active Token-Ring addresses (each port address table is shared by
four ports, using the following: 1-4, 5-8, 9-12, 13-, etc.). If an address has not been
active for a configurable aging time, it is removed from the tables. This ensures that
the port’s address table is populated only by the most recently used address.
This capability allows users to transparently connect to high-volume backbone
networks.