Most LAN infrastructures continue to use copper-based cable for the desktop and fiber for riser distribution. Placing fiber at the desktop is slowly becoming popular, and with the introduction of RJ-45-style (MT-RJ) connectors, the space required for these installations is not an issue. Designers should be familiar with the certified maximum distances that are permitted for the various media. The specifications incorporated into the physical media standard for each protocol virtually guarantee successful connectivity. While such values are more than rules of thumb, they are easy to incorporate into network designs and insulate the designer from having to understand the detailed electrical criteria involved in twisted-pair wiring and fiber optics. Table 2.1 notes the physical media distance limitations.

	FastEthernet and GigabitEthernet modules are available to span distances over 55 miles.

Cabling design considerations also include terminations and installation. For example, fiber connectors use SC, ST, FC, and other termination types. The choice will impact patch cables, future hardware purchases, and rack space—some connectors may be installed with greater density. For example, MT-RJ is similar to RJ-45 in scale, which requires half the space of ST, FC, or SC connectors.

The installation of the cables will also be an important factor and will affect future modifications to the cable plant and troubleshooting. Some companies require a “home run” from the panel to the station. This type of installation uses a single, continuous wire. In contrast, other organizations install riser cable that terminates to a frame in the closet. These terminations cross-connect to the stations. This type of installation is often cheaper and permits additional flexibility. In either configuration, punch-down work and other maintenance should occur at a single point whenever possible. It is also extremely important to document what is installed.

	Professional cable installers should be used whenever possible. A good cable installer will have both the equipment and training required to adhere to the standards and to properly install and dress the cables. A good cable installation should be capable of service for up to 15 years and is a significant expense.

Routers

Routers are perhaps the most significant tool in the network designer’s repertoire of dealing with broadcasts in the enterprise. As noted in Chapter 1, it would be ideal to reduce the number of broadcasts in the network at the source, but this is not an option under most circumstances.

Unlike Layer 2 devices, routers block broadcasts from leaving the network segment. In other words, routers define the broadcast domain. This is an important consideration, as few protocols will scale beyond 200 nodes per broadcast domain—thus, routers are usually needed in inefficient multi-protocol networks of over 200 nodes.

There are other benefits to routers as well. Routers convert between different media—for example, FDDI and Ethernet. The Catalyst switch (along with most other multiprotocol switches on the market) will also perform this function, but many designers still consider the use of a router to be superior when performing a media conversion. Routers also impose a logical structure on the network, which is frequently necessary when designing large environments. Lastly, routers are very useful for implementing policies regarding access. Access control lists (ACLs) may be used to block access to certain devices in the network or to filter informational packets regarding services (an IPX SAP access list, for example).