GarrettCom DS 880 - Manual (Page 25)

Magnum DS880 Dual-Speed Stackable Hubs Installation and User Guide (05/01)
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Packet Source Destination Address Table Filter/Forward
Source Address Address Maintenance Action
10 Mb
Not in table Not in table Add source to table Forward
10 Mb Not in table In table Add source to table Filter
10 Mb In table Not in table None Forward
10 Mb In table In table None Filter
100 Mb Not in table Not in table Add source to table Forward
100 Mb Not in table In table Add source to table Filter
100 Mb In table Not in table None Forward
100 Mb In table In table None Filter
Table 4.1: DS880 Dual-Speed Hub Functionality
1. Address Learning (Address Table Maintenance)
The Magnum DS880-B bridge module is a state machine design which has a total
address table capacity of 8K addresses. With a large address table, a Magnum DS880 can serve
the needs of a medium-sized to large network. Table 4.1 shows what filter / forward action the
Magnum DS880-B will take in each packet-processing situation, and when a new node address
will be added to the internal Address Table. When a new node-address packet comes into a port
for the first time, then the new source address is “learned” at the same time that the packet is
forwarded. After learning, subsequent packets from the same node address are routinely
processed. The address tables are flushed periodically to update the network status and to purge
any inactive stations from the tables of both domains.
2. Throughput Increase
By selectively forwarding packets from each domain to the other domain based on its
switching (bridging) logic, the Magnum DS880-B increases the available bandwidth for the
users on both sides of the network. As shown in Figure 4.1, it keeps the local traffic on each side
contained, preventing unnecessary packets and bad packets from traveling to the other domain
and using up bandwidth needlessly over there. This results in more available network
bandwidth on both sides and a throughput increase on for all users on both domains.
1.1 Software Transparency
4.1.1 The Magnum DS880-A and -B Dual-Speed Hubs need no software set-up and are
transparent to system and application software, including network management
software.