Network Configurations

This is the real meat of your network design because it includes the specifications for your network topology, cabling, and, to some extent, choice of network adapters. Ethernet networks (10Base-5, 10Base-2, and 10Base-T) all use a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) algorithm to send data across the wire. In this algorithm, the network adapter is required to listen (carrier sense) before sending data. If two or more computers (multiple access) send data at the same time, a data collision occurs, and this is detected by the computer (collision detection). When a collision occurs, the computers will pause for a random time before retransmitting the data. Token ring networks use a token passing algorithm. Only one computer will have a token, which permits that computer to send data on the network. Once the data has been sent, the token is released for the next computer to use to send data. Each network configuration has unique strengths and weakness that need to be explored before you make your final determination as to which one you will implement. There are basically seven different network configurations available, which include:

•  Thick Ethernet (10Base-5)—Thick Ethernet networks use a bus topology with a maximum segment length of 500 meters, a maximum of 100 workstations per segment, and a minimum distance of 2.5 meters between workstations. Thick Ethernet workstations utilize a drop cable with a maximum length of 50 meters to attach to the network trunk. Thick Ethernet networks operate at speeds up to 10Mb/sec.

•  Thin Ethernet (10Base-2)—Thin Ethernet implementation also uses a bus topology with a maximum segment length of 185 meters, a maximum of 30 workstations per segment, and a minimum .5 meter distance between workstations. Unlike a thick Ethernet network, thin Ethernet networks do not use a drop cable. Instead, the network trunk is brought right up to the workstation and is connected to a T-connector via a bayonet nut connector. The T-connector then attaches directly to the network adapter. Thin Ethernet networks operate at speeds up to 10Mb/sec.

•  Ethernet (10Base-T)—This is the most common network implementation in use today. It utilizes UTP/STP cables configured in a star topology with a maximum segment length of 100 meters. You can continue to add workstations to your network by adding additional hubs and routers. The network performance will be the limiting factor to the number of workstations you can add to a single segment. Ethernet networks operate at speeds up to 10Mb/sec.
I find that more than 30 workstations on a single segment causes network congestion in a day-to-day work environment, so I recommend that you break your segments up with a router or switching hub when you reach this limit. You may also want to break up your segments whenever you reach 50 to 60 percent of your network bandwidth.

•  Token Ring—Token ring networks use a ring topology and are generally used in IBM shops because it is the easiest network to connect to IBM mainframes. Token ring networks can operate at either 4Mb/sec. or 16Mb/sec. One very important item here is that you cannot mix and match transmission rates in a single ring. A ring must be all 4Mb/sec. or all 16Mb/sec. Mixing transmission speeds in a single ring can bring the entire ring down.
A single MAU can support up to 260 workstations with a maximum 100 meter length between the MAU and workstation when utilizing STP cable. When you use UTP cable, this drops to 72 workstations with a maximum length of 45 meters between the MAU and workstation. You should consider breaking up your segments whenever you reach 60 to 80 percent of your network bandwidth.

•  100Mb Options—If you are looking at implementing multimedia or video conferencing in your network, you will need a high-performance media to accomplish this goal. This means either fiber optics or fast Ethernet. But there are a few items to consider before you make the move to either of these, including:

•  Fiber Optics—A fiber-optic network requires that you completely redesign your network. You will have to replace all of your current network cables with fiber optics, which can be a costly proposition. You will also have to replace all of your hubs and routers. This is not something I recommend unless you really need the electrical isolation provided by fiber optics.

•  Fast Ethernet—This is a good alternative to replacing your network cables with fiber-optic cables because you have two choices, depending on your network cables. If you are using Level 3 UTP cabling and are not using the additional 2 pairs of wires for voice (never a recommended choice), you can use the 100Base-VG fast Ethernet adapters. These adapters provide 100Mb/sec. transmission speeds by utilizing all 4 pairs of wires in the standard RJ-45 cables. If you have Level 5 UTP (the recommended choice), you can use the 100Base-TX network adapters. These network adapters use the same 2 pairs of wires in your UTP cable, but provide 100Mb throughput.

Once you have made your decision as to which configuration to use for your local area network (LAN), you can actually implemented it to build your physical network. Once you have put together two or more LANs, you will most likely find yourself with the dilemma of joining these two networks into a single physical network. If the networks are in the same basic area, you can probably just string additional network cabling and use a router to hook them together. But if these two LANs are separated by a few miles, you need to come up with another method. This method, called a WAN, is described in the following section.