Introduction to Data Communications
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45l. Ring Calculations

Maximum Ring Length

The ring length of a Token Ring network is based on the length of the cable used in concentrator-to-concentrator connections, and in the longest concentrator-to-node connection. It is based on Type 1 cabling.




		Ring Speed		Maximum Ring Length

		4 Mbps			1200 ft/ 360 m

		16 Mbps			550 ft/ 168 m

Ring Length Calculations

The following ring has Type 1 cabling, 4 passive concentrators and the lobe with the Maximum Lobe Length (MLL) indicated. The cable length for this ring is calculated by adding all the cable lengths between the passive concentrator's Ring In and Ring Out connectors together plus the Maximum Lobe Length (MLL).

Total Cable Length = MML + RI/RO cable lengths

Total Cable Length = 40 ft + 6 ft + 75 ft + 230 ft + 80 ft = 431 ft

The passive concentrators (MSAUs) will have an effect on the ring length also. Each passive concentrators will appear as 25 ft of Type 1 cable. The Ring Length has to be adjusted for the presence of each of the MSAUs:

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

Ring Length = 431 ft + 4 x 25 ft = 531 ft

If you check the maximum ring length parameters mentioned earlier, you will see that this ring would function within the specifications for both a 4 Mbps and a 16 Mbps Token Ring.

Mixing Cable Types and Ring Length

The Ring Length is always calculated based on Type 1 cable. All other types of cable used in the network are converted to Type 1 cable first before determining the Ring Length. The conversion factors for other cable types is indicated in the following table:


	Cable Type		Conversion Factor



	Type 1, 1A or 2 STP		1.0	(this is the reference)

	Type 6 STP			1.3

	Cat 5 UTP			1.7

	Cat 3 UTP			3.0

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