Black Box Mixed-Media Fiber Hubs
Installation and User Guide (4/99)
Segment 1
Segment 2
(Bonus Port)
(Inside of Hub)
11
Packet
Source
Destination
Address Table
Filter/Forward
Source
Address
Address
Maintenance
Action
Seg. 1
Not in table
Not in table
Add source to table
Forward
Seg. 1
Not in table
In table
Add source to table
Filter
Seg. 1
In table
Not in table
None
Forward
Seg. 1
In table
In table
None
Filter
Seg. 2
Not in table
Not in table
Add source to table
Forward
Seg. 2
Not in table
In table
Add source to table
Filter
Seg. 2
In table
Not in table
None
Forward
Seg. 2
In table
In table
None
Filter
Table 2.5: SPM Port Module Functionality
2.
Throughput Increase / Software Transparency
By selectively forwarding packets from the mixed-media hub’s ports (or hub stack’s ports) to
the rear-connector port based on its switching logic, an SPM increases the available bandwidth
for the users on both the hub side and the rear-segment side of the network. As shown in Figure
2.5b, it keeps the local traffic on each side contained, preventing unnecessary packets and bad
packets from traveling to the other segment and using up bandwidth needlessly. This results in
more available network bandwidth on both sides and a throughput increase for all users on both
segments. An SPM needs no software configuring and is transparent to system and application
software, including network management software.
Figure 2.5b: Forwarding vs. Filtering in SPM Modules
Segment 1’s packets are
forwarded
when the destination addresses are
NOT
in its address table.
Segment 2’s packets are
forwarded
when the destination addresses are
NOT
in its address table.
Segment 1’s packets are
filtered
when the destination addresses are
in its address table.
Segment 2’s packets are
filtered
when the destination addresses are
in its address table.
100
1
0
SPM Module
