Accton Technology 12se manual Precise Guidelines for Configuring Multiple Hubs

Fast EtherHub-12se User’s Guide

Precise Guidelines for Configuring Multiple Hubs

A detailed formula for calculating maximum cable length was provided in the section on 3UHFLVH￿&DEOH￿/HQJWK￿%XGJHWLQJ in Chapter 2. This formula stated that the

maximum length of cabling that can be run from end-node to end-node is:

367m ³ S(repeater equivalent length)

+ S(length of category 5 twisted-pair cable)

+ (0.9 * S(length of fiber optic cable1)) 1 - if fiber is used

For the daisy chain of three hubs shown in Figure Chapter 3:-4, communications must

be supported for node pairs AB and AC. In this case, first determine the limitations on cable length found on the longest path (i.e., the path with the longest delay time).

Remember that this Class II device has an inherent repeater delay of 90 bit time or 80 meters of twisted-pair cable. Therefore, if node A and B are linked to repeaters 1 and 3 respectively (each using 50 meters of twisted-pair cable), then the maximum length from node A to B is 367m - (3 x 80m) = 127m and the total inter-hub cabling will be limited to 27 meters (i.e., 127m - 2x50m = 27m). Therefore, if you use 15 meters of twisted-pair cable to connect hubs 1 and 2, then 12 meters of cable can be used to connect hubs 2 and 3.

Moreover, if node A and C are linked to adjacent hubs 1 and 2 in this system, then the maximum length of fiber optic cable that can be used to connect node C to hub 2 is 367m - 2*80m - (50m + 15m) = 0.9 * LengthFX, or 157 meters. However, because this value exceeds the maximum permitted length for fiber optic cable, it must be reduced to 112 meters.

Configuring the Network 3-3