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This chapter provides cabling guidelines for determining how to build networks using FastHubs.
The IEEE 802.3u standard defines two different classes of 100BaseT repeaters, Class I and Class II. Class I repeaters limit a network to having a single repeater. Class II repeaters allow networks to be built with more than one repeater. In addition, Class II repeaters allow longer cable distances in single repeater configurations than do Class I repeaters. The FastHub 100 series, FastHub 216T, and FastHub 300 series are Class II repeaters. Moreover, the FastHub 116T, FastHub 216T, and the FastHub 300 series exceed the specifications for Class II repeaters, allowing the use of longer cable lengths than standard Class II repeaters.
 | Caution Many switches have "built-in" repeaters or plug-in repeater modules. In these devices, the switch is actually attached to a port on the internal repeater. When connecting to a switch, determine if the port is a repeater port or not, and, if so, what type of repeater is present. If it is not a repeater port, the switch is treated as an ordinary end-station. If the port is a Class I repeater port, do not connect the FastHub or any other repeater to the port. If it is a Class II repeater port, refer to the "FastHubs in Extended and Multivendor Configurations" section in this chapter for configuration guidelines. |
The FastHub 116T can be connected to other FastHub 116T units as well as to other Class II repeaters, such as the FastHub 100 series, FastHub 216T, and FastHub 300 series.
FastHubs can be cascaded using the standard 100BaseTX ports on the front of each FastHub. When one FastHub is cascaded to another FastHub, using Category 5 UTP cable and the 100BaseTX ports, the two FastHubs appear to the rest of the network and to the management consoles as two logical repeaters. Figure 2-1 shows how cascading two FastHubs results in a maximum of 30 stations on the same segment.
You can build networks with two or more Class II repeaters in a single collision domain. With two Class II repeaters, you can have a short segment connecting the repeaters while maintaining 100-meter Category 5 UTP connections to the attached stations. Using more than two repeaters in a single collision domain requires considerably shorter connections to attached stations. Figure 2-2 shows the connection of two FastHubs to form a collision domain with up to 30 ports.
This section provides two simple network configurations, as specified in the IEEE 802.3u standard, using the FastHub. These configurations were designed to satisfy the requirements of most networks that are built to the EIA/TIA-568 wiring standard. This standard specifies 100-meter Category 5 UTP connections from wiring closets to desktops. If your network requirements cannot be met with one of these configurations, or if you are building networks mixing FastHub units with other Class II repeaters, see the "FastHubs in Extended and Multivendor Configurations" section in this chapter.
With only Category 5 UTP cable segments, the maximum length for any cable segment is 100 meters, as shown in Figure 2-3.
The maximum Category 5 UTP cable segment length is 100 meters. When stations are connected to the FastHubs with 100-meter Category 5 UTP cable segments, the Category 5 UTP cable connecting the two FastHubs is limited to a distance of 23 meters, as illustrated in Figure 2-4.
If all of the Category 5 UTP cable segments connecting stations to one or both of the FastHubs are less than 100 meters, the length of the Category 5 UTP cable segment connecting the two FastHubs can be increased. See the "FastHubs in Extended and Multivendor Configurations" section for more information.
The previous cabling examples applied to configurations of one or two FastHub units with Category 5 UTP segments assumed to be at their worst-case distance, 100 meters. When the maximum Category 5 UTP segment length is less than 100 meters, longer inter-repeater links or more repeaters can be deployed. On the other hand, when FastHubs are deployed with the FastHub 100 series or standard Class II repeaters (Class II repeaters that meet but do not exceed the IEEE 802.3u specification), the maximum span is decreased.
A specific calculation of maximum cable length is required in the following cases:
Allowable repeater configurations are determined by the longest path between any two stations. This path constraint is determined by cable segment lengths, cable types, number of repeaters, and repeater types. The arithmetic underlying this determination can be reduced to a constraint on the sum of the segment lengths between the two furthest stations. The constraint is expressed in total meters and assumes that all segments are Category 5 UTP.
Step 1 Confirm that no Category 5 UTP segment is greater than 100 meters.
Step 2 Confirm that the sum of the Category 5 UTP-equivalent segment lengths between any two end-stations (including bridges, switches, or routers) is less than the maximum value specified in Table 2-1. For multirepeater networks, it is critical to evaluate not just the paths passing through the most repeaters but also the station-to-station paths (if applicable) passing through one, two, or three repeaters.
| Number and Type of Repeaters in the Path | Maximum Total Cable Distance in Path (Category 5 UTP Equivalents, in Meters) |
|---|---|
| 1 FastHub | 200 |
| 1 other Class II repeater | 200 |
| 2 FastHubs | 223 |
| 1 FastHub and 1 other Class II repeater | 214 |
| 3 FastHubs | 149 |
| 2 FastHubs and 1 other Class II repeater | 140 |
| 1 FastHub and 2 other Class II repeaters | 131 |
It is possible to add a third FastHub in the same collision domain to increase the total number of connected stations to 48. Using Table 2-1, we see that the maximum Category 5 UTP equivalent distance between any two stations connected by three FastHubs is
149 meters.
In the following example, all three FastHubs are in the same wiring closet, separated by
1-meter Category 5 UTP cable segments. Substituting this information into the formula shown in Figure 2-5, we see that B + D = 2 meters, A + (2 meters) + E < 149 meters, and therefore A + E < 147 meters. If A is 60 meters, then E would be 87 meters.
Note that after assigning cable lengths to A and E, we must check to see if the configuration rules for stations separated by two FastHubs have been violated. That is,
A + B + C < 223 meters and C + D + E < 223 meters. For the first configuration,
we get: A (60 meters) + B (1 meter) + C < 223. In this case, C must be < 162. For the
second configuration (C + D + E < 223) we get: D (1 meter) + E (87 meters) + C < 223.
In this case, C must be < 135.
To satisfy both paths (A, B, C and C, D, E), C must be less than or equal to 135 meters. Note that these are Category 5 UTP equivalent meters.
It is possible to build networks combining FastHubs with other Class II repeaters from Cisco or other vendors (see Figure 2-6).
Using Table 2-1, we see that A + B + C < 214 meters. Note that these are Category 5 UTP equivalent meters.
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