3Com 5112M-TPLS installation and operation guide Fiber Backbone, Twisted Pair To-The-Desk Example

❑You must add a bridge if you exceed four full repeaters. The four-repeater rule for Ethernet limits the number of 10BASE-T modules between any two transceivers. When traffic goes into a port on any repeater-based module and out the backplane, it counts as a 1/2 repeater. When the traffic goes into the module through one port and out another port on the same or a different module, it counts as one full repeater. Therefore, you must add a bridge if the path from one transceiver to another exceeds the four-repeater rule.

❑The equivalent fiber distance for the ONline Ethernet Fiber Modules (see Rule 4) is:

–140 meters for signals that externally enter a Fiber Module port

–50 meters for signals that internally enter a Fiber Module through the ONline Concentrator backplane

❑The equivalent fiber distance for the Security Module (see Rule 4) is:

–420 meters for signals that externally enter a Security Module

–165 meters for signals that internally enter a Security Module through the ONline System Concentrator backplane

For every pair of Security Modules that a signal goes through, deduct a fiber equivalent distance of 585 meters (420 m + 165 m = 585 m) from the overall alllowable network diameter. This is also true if a signal makes a roundtrip through a single Security Module (enters the Security Module through one port and exits another port of the same Security Module). This counts as 585 meters of fiber equivalent distance, and as a full repeater.

Fiber Backbone, Twisted Pair To-The-Desk Example

In the sample configuration shown in Figure 2-1, we determine if the transceivers are within legal Ethernet limits. 22-gauge unshielded twisted pair cable is used to connect 10BASE-T Transceivers to the Security Modules in the concentrators.

2 - 8 ONline 10BASE-T Security Module Installation and Operation Guide