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Quick Reference Guide to 100-Mbps Multi-Segment Configuration

14.4 100-Mbps Configuration Guidelines: Model 1

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Transmission System Model 1 of the Ethernet standard provides simplified guidelines. These make up a set of "canned" configuration rules that can be used to evaluate 100BASE-T configurations. The goal of the configuration guidelines is to make sure that the important Ethernet timing requirements are met, so that the medium access control protocol will function correctly.

1. All copper (twisted-pair) segments must each be less than or equal to 100 meters in length.

2. Fiber segments must each be less than or equal to 412 meters in length.

3. MII cables must not exceed 0.5 meters each. When it comes to evaluating network timing, delays attributable to the MII interface do not need to be accounted for separately, since these delays are incorporated into DTE and repeater delays.*1

With these rules in mind, Table 14.1*2 shows the maximum collision domain diameter for segments using Class I and Class II repeaters. The maximum collision domain diameter is the longest distance between any two DTEs in the collision domain.

The first row in the table shows that a DTE-to-DTE (station to station) link with no intervening repeater may be made up of a maximum of 100 meters of copper, or 412 meters of fiber. The next row provides the maximum collision domain diameter when using a Class I repeater, including the case of all twisted-pair cable, all fiber optic cable, or a mix of twisted-pair and fiber. Note that in one case, a mix of T4 copper and FX fiber across a Class I repeater is shown. All other cases of mixed fiber and copper are based on TX and FX segments.

The next row shows the maximum collision domain length with a single Class II repeater in the link. The last row shows the maximum collision domain allowed when two Class II repeaters are used in the link. In this last configuration, the twisted-pair segment length is assumed to be 105 meters on the mixed fiber and twisted-pair segment. Some illustrations of example configurations may be found in Appendix B, "100-Mbps Configuration Examples."

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Quick Reference Guide to 100-Mbps Multi-Segment Configuration - 09 SEP 95

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