also don't scale well as networks expand and more routers are introduced. Managing VLANs, which deal with layer 2 MAC addresses in the midst of routers, which deal with layer 3 subnets and domains (IP, IPX, etc.), is a very complicated issue.
What the industry is working toward is virtual routing, which
lets the network manager view the entire enterprise network as a single routed entity.
FROM HUB TO SWITCH
There is an overwhelming move to gain immediate bandwidth by replacing Ethernet hubs with Ethernet switches. The standard 10BaseT Ethernet hub is a shared-media hub, which means that all users share the total 10Mbps bandwidth. The shared-media hub is actually a multiport repeater, because it sends any input signal to all output ports. It is also called an Ethernet concentrator in order to contrast it with the many highly-sophisticated, intelligent hubs on the market that do multiport repeating, switching, bridging, routing and brew your coffee at the same time.
Now, out goes the shared-media hub and in goes the switch. The switch has a backplane fast enough to cross over one port to another port at full-wire speed. If you have 12 ports on the switch, six pairs of ports can be connected simultaneously at wire speed. Instead of 12 users sharing 10Mbps, each user has a full 10Mbps to another user. For a couple of hundred dollars per port on average, we dramatically increase
Switched Token Ring provides the same advantage, as does switched FDDI. The best thing about implementing LAN switches -- also called frame switches -- is that you don't touch the user's machines or cables. That all stays intact while all the work is done in the wiring closet.
You can get a 10-fold increment by moving from 10BaseT to Fast Ethernet (100BaseT). You may also be able to use the same cables. 100BaseTX uses two pairs of Category 5 unshielded twisted pair, and 100BaseT4 uses four pairs of Category 3. Fast Ethernet is being implemented as a backbone running between 10BaseT Ethernet switches that have 100Mbps links. These switches multiplex the 10Mbps ports into the 100Mbps port. Another approach is wiring the 100Mbps link directly to the server.
For more dramatic speed, a Fast Ethernet switch can boost Fast Ethernet just as an Ethernet switch can boost regular Ethernet. But 100Mbps to a user's machine might be overkill, so instead of wiring each switch port to a single machine, the port can be wired to a shared-media hub that fans out to two or more users that don't need that much "oomph." This mixing and matching of switches and concentrators (hubs) lets you totally customize your bandwidth between clients and servers.
If you are upgrading PCs or purchasing new ones, think seriously about installing Ethernet 10/100 cards. For about $50 to $75 more than a standard 10BaseT card, you've got 100BaseT installed and ready for the future. New 10/100 cards provide auto sensing and can detect which topology is being used, so they can sit patiently waiting for their day.
ATM -- FUTURE BACKBONE OR BACK-BREAKER?
Perhaps nothing in the internetworking business has been hyped more than ATM over the past three years. Considering every major networking vendor has embraced it either by developing its own ATM products or by acquiring or aligning itself with an ATM company, it would appear that ATM is the future.
ATM is a switching technology that uses fixed-length cells that switch much faster than variable-length-packets. In addition, ATM is a connection-oriented system like the telephone. Once the call is set up, a pipe (virtual circuit) is set up from source to destination and the packets are pushed through without examining every last detail about them. Connectionless Ethernet and Token Ring systems, on the other hand, inspect every packet. ATM also provides quality