Introduction to Data Communications
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Active Concentrators and Ring Length

Active concentrators and the cables connecting the Ring In/Ring Out connectors are not counted in determining the Ring Length. Since it retimes and regenerates the data signal it is not used in Ring Length calculations.

In the following 16 Mbps Token Ring, all cable types are Type 1. If the active concentrator is ignored, a quick addition of cable lengths indicates that the ring length is over the maximum allowable ring length for 16 Mbps Token Ring. In fact, the active concentrator allows ring lengths over the maximum allowed ring length by discounting the cables attached to it.

Total Cable Length = MML + RI/RO cable lengths

Total Cable Length = 75 ft + 12 ft + 210 ft = 297 ft

The 165 ft and 95 ft cables are not counted because they are attached to the active concentrator's Ring In/Ring Out connectors.

Ring Length = Cable Length + (number of MSAUs x 25 ft)

Ring Length = 297 ft + 3 x 25 ft = 372 ft

The active concentrator is not counted in the calculation of Ring Length so only 3 MSAUs are used. The ring length appears to be 372 ft which is within the limits of 16 Mbps Token Ring (550 ft). In fact, the use of an active concentrator allows this 16 Mbps to operate with a total cable length that is actually greater than the allowed ring length for 16 Mbps Type 1 cabling.

Introduction to Data Communications
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