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Connecting Networks That Use Different Cables or Topologies

Because switches, like routers, can be found with different kinds of ports that are used to link them (uplink ports), it's possible that you can incrementally upgrade your network, depending on such factors as the size of the broadcast domain and the number of users on each network segment. For example, you might want to replace one multiport repeater with a hub or switch in one department, while leaving another existing multiport repeater in place for a while.

If you need to maintain backward compatibility by keeping a multiport repeater on the network for a while during the upgrade process, you can use a hub or switch that has a BNC port and connect the two using thinwire Ethernet cables. Or you can connect each of these two devices to separate ports on a router, and create different subnets on your network.

Subnets, and how to calculate subnet addresses and subnet masks, are covered in Chapter 14.

Other Possibilities

This chapter covered the basic components that you need to change when converting a network from 10BASE-2 to 10BASE-T and 100BASE-T, which are the most prevalent network standards in place today. However, in addition to the cables, connectors, network adapters, and other devices, a change such as this one might warrant further research into the larger network to which you're connected. In many cases, the local LAN is in reality part of a much larger network. When you have resources that are frequently accessed and lie outside the local LAN, you might need to look at the big picture when making decisions about the local area network. Consider the following:

Do you need to replace the equipment that has been used to connect to the larger network?
Are you currently using a bridge that can be replaced by a switch to improve performance?
Do you have multiple small LANs that can now be merged into a single larger LAN connected by multiple switches?

Upgrading the Network Backbone to Gigabit Ethernet

Today Gigabit Ethernet has arrived, in a big way. You won't find many people using Gigabit to the desktop yet (although in some high-end environments, such as video production, you just might). But as a backbone transport, Gigabit is an ideal replacement for Fast Ethernet or other protocols used to transfer high-bandwidth traffic.

The initial cost for implementing Gigabit Ethernet as a backbone transport doesn't have to be a large expense. Consider what happens when you replace local switches and network adapter cards ”a large expense can be involved due to the high number of workstations and switch ports required.

However, if you're replacing a switch that consolidates traffic from these existing switches, you have only to replace these switches and possibly the cabling between these switches. Consider the collapsed backbone topology discussed in Chapter 2, "Overview of Network Topologies." You don't replace every departmental LAN switch. Instead, a collapsed backbone means that department level switches all feedback to a single larger switch that controls traffic between each of the departmental switches. So, if the departmental switches satisfy your users' needs, you'd have to replace only the central switch that connects them. Gigabit (and now 10 Gigabit Ethernet) is ideal for network backbone transport. You can use this technology to connect backbone switches to others in different buildings in a campus environment, and further localize network traffic. It will still be a few years before it's used to the desktop.