One of the first decisions in computer environment design is the selection of the network type- a group of products that work together, even if they are manufactured by different companies. Products in the same group each follow the same networking rules, and you can count on them to work together properly. Today's most common network types include Ethernet, token ring, and ATM. Each of these three offers a viable alternative for supporting a LAN, each with its own costs and performance benefits. As we will see, Ethernet stands as the prevailing technology and generally is the most appropriate choice for small business networks. Once you select a network type, the network cards, cabling and network software you choose must be compatible with that group.

Token Ring

Token-ring networks can be found primarily in environments with a significant amount of IBM equipment. This network type uses a token-passing protocol; each computer communicates on the network only when presented with the network token. Computers read incoming data packets and transmit outgoing ones as the token rotates throughout the network. Token-ring networks became popular in organizations using IBM mainframes, and continue to be used to a limited degree. At one time, token-ring networks outperformed Ethernet, but this is no longer the case. Token-ring network cards are significantly more expensive than Ethernet cards, and much harder to find. A quick check of a couple of recent networking product catalogs showed dozens of Ethernet cards and not a single token-ring card. The only reason to consider basing a small business network design on token ring is in deference to some prevailing concern, such as compatibility with a larger organizational network.

ATM

Asynchronous transfer mode (ATM) follows a fundamentally different approach and competes with Ethernet for backbone networks and high-performance LANs. In an ATM network, data are broken into small fixed-size cells and switched in virtual circuits established between computers. Most ATM networks operate at a very respectable 145 Mbps. Today, ATM is most commonly found as the backbone technology for enterprise networks. ATM switches are much more expensive than Ethernet hubs, and they require a significant effort to configure. Like token-ring cards, ATM cards for desktop computers are high-priced and hard to find. A small organization would use an ATM-based LAN only if it required an extremely high-performance network to support data-intensive applications such as large-scale imaging projects.

Ethernet

Almost all small networks will use some type of Ethernet, the most inexpensive and flexible option. Network communications catalogs are stuffed with Ethernet products from a variety of vendors. As a reflection of Ethernet's dominance, most business-class desktop computers come with Ethernet ports built directly onto the motherboard.

Ethernet is associated with a set of networking rules called CSMA/CD (Carrier Sense Multiple Access with Collision Detection), formally specified by IEEE 802.3. These network rules describe how devices on the network communicate with one another. Ethernet is a broadcast network, in which all nodes have access to all datagrams or data packets. Each packet has an origin and destination address, and each computer should open the packet only if the destination address matches its own network address. The network supports multiple devices per segment, and each device can transmit on the network at any time. If devices transmit exactly at the same time, however, a collision occurs and the transmissions are lost. Therefore, each station must check after it transmits to see if a collision occurred and, in the event of a collision, wait a random interval and retransmit.

Most varieties of Ethernet operate at 10 Mbps, and each of the nodes on a segment share this bandwidth. The stations on a segment share the overall available bandwidth and can cause collisions with one another in the process. The amount of overall bandwidth available to each station decreases and the likelihood of excessive collisions goes up as the number of stations per segment increases. The lower the number of stations per segment, the better your network will function. Various options are available to divide networks into multiple segments and to reduce the nodes per active segment.

Past their Prime: Thick and Thinwire Ethernet

There are several types of Ethernet cabling, some of which are obsolete. The original version of Ethernet, 10Base-5, or Thick Ethernet, relied on a rigid cable and required you literally to drill into the cable to install taps for each device on the network. While Thick Ethernet may still be in service in some older networks, it is obsolete and should not be used for new installations. 10Base-2, or Thinwire Ethernet, based on a thin, flexible RG-58 coaxial cable and BNC connectors, was extremely popular for a number of years because it was much easier to use than Thick Ethernet. No communications equipment was required-you just connected the network cards via the cables, and you had a functional network. Communications equipment was necessary only if you had multiple Ethernet segments that needed to be connected. The main problem with Thinwire Ethernet was its linear bus topology, where all the computers on a segment were chained together. If any single connector or cable along the segment had a problem, the entire segment would not function. Thinwire Ethernet also had limitations on the number of computers per segment and on the length of each segment; it, too, should be considered obsolete and avoided for any new network.

10Base-T Ethernet

The primary type of Ethernet in use today is 10Base-T, which operates at 10 Mbps and follows a star topology using unshielded twisted-pair cabling.

10Base-T Ethernet networks are very easy to set up. This flavor of Ethernet relies on hubs. Each computer has a dedicated cable that connects its Ethernet card to a port on the hub. Ethernet hubs are relatively passive and require little or no configuration. In most cases, you can plug in the hub to power, connect the cable and you've got an active network. As we'll see later, there are several features to choose from when buying a hub, but almost all types are essentially plug-and-play devices.

You will need drop cables to connect your computers to the network. Pre-built Ethernet cables are available from local computer stores and mail-order companies. You can also build your own, but it's seldom worth the effort. An Ethernet drop cable must be constructed from Category 5 unshielded twisted-pair cable, and terminated with RJ-45 connectors. These connectors look much like those for a telephone jack, except RJ-45s have eight connectors instead of four.

If you are working in a small space, you may be able to connect all the computers in your network directly to the hub without putting new wiring in the walls. But in most cases you will need to have a new cabling system installed in your building to support your network.

The most common, and least expensive, devices used with 10Base-T are shared media hubs, which represent a logical Ethernet segment. Each device connected to a port on a shared media hub shares the bandwidth of a 10-Mbps Ethernet segment and competes for collisions. Multiple hubs can be cascaded together, so that all the devices on multiple physical devices still form a logical Ethernet segment. Each port on a shared media hub connects via a UTP cable to a 10Base-T interface on a network device such as a computer or printer.

When selecting an Ethernet hub, be sure to consider manageability issues. Large networks require remote management capabilities for all devices on the network; each device must be capable of communicating all aspects of its operation with a central management device through protocols such as SNMP (Simple Network Management Protocol), as well as support common implementations such as MIB-2. Most large networks will have one or more dedicated workstations monitoring the network, with the capability to monitor the status of each device, measure overall network performance and alert a network administrator when a device fails, or when its performance falls below acceptable thresholds. Ethernet hubs are classified as either managed or non-managed. If your network is large and relies on central management, it is important to purchase manageable Ethernet hubs. Managed hubs are a requirement of most enterprise networks. Typically, you can purchase one hub with management capabilities, and cascade stackable units from that hub that can rely on the base unit for management. With smaller networks, you may be able to save considerable expense by purchasing unmanaged hubs. Manageability is a relatively expensive feature. If your environment is small and does not use centralized network management, it is not cost-effective to buy managed hubs; most small office networks will work quite well without managed devices. But if you buy non-managed hubs in a managed environment, you will miss out on the ability to monitor and tune the performance of your network, and to detect and repair many network problems in time to head off a total failure.

Switched Ethernet

As we noted above, a shared media hub, or a group of hubs cascaded together, represent a logical Ethernet segment. One of the advances in Ethernet technology involves the use of switching technology. Switching greatly improves both the overall performance of an Ethernet network and the bandwidth available to each station, and it minimizes the impact of errors. The major difference between a shared media hub and an Ethernet switch is that each port on an Ethernet switch is its own logical segment. A device connected to a port on an Ethernet switch has a full 10-Mbps bandwidth to itself and need not contend with other devices for collisions. No special hardware is needed on the devices that connect to an Ethernet switch. The same network interface used for shared media 10Base-T hubs will work with an Ethernet switch. From that device's perspective, connecting to a switched port is just like being the only computer on the network segment. The main disadvantage of using Ethernet switches is that they can cost several times more than a shared media hub.

One common use for an Ethernet switch is to break a large network into segments. While it is possible to attach a single computer to each port on an Ethernet switch, it is also possible to connect other devices such as a shared media Ethernet hub. If your network is large enough to require multiple Ethernet hubs, you could connect each of those hubs to a switch port so that each hub is a separate Ethernet segment. Remember that if you simply cascade them off each other directly, the combined network is a single logical Ethernet segment.

Fast Ethernet

Though Ethernet traditionally has been a 10 Mbps technology, faster versions are now available. While the 10 Mbps variety continues to be the most widely implemented, 100 Mbps Ethernet is rapidly catching on. To operate at this speed, you need network cards and hubs designed for 100Base-T, both of which are now sold by many vendors. While they cost more than 10Base-T, they make a remarkable difference in performance. You can implement 100Base-T on a small network at a very reasonable cost, especially if you stick with unmanaged, non-switched hubs. Even if you choose to go with 10Base-T hubs, consider purchasing network cards that can operate at either 10 or 100 bps. 10/100Base-T cards cost only a little more than ones that operate at 10 Mbps, and give you much more flexibility for upgrading your network in the future. Most 100Base-T hubs will automatically sense whether the card connected to each port is 10 or 100 Mbps and operate accordingly. For even higher performance, you can purchase 100Base-T switched hubs. You can expect significantly higher performance with such a device, but it will also add to your costs.

Gigabit Ethernet

This emerging fast Ethernet technology operates at 1000 Mbps. Still in its early stages, this variety of Ethernet is more suitable for connections between networks than for connecting PCs and printers on a LAN. Gigabit Ethernet is not suitable for small office networks.

Purchasing Equipment

When you're ready to purchase the equipment you need to build your Ethernet, you will soon see an wide variety of vendors, each one offering a range of products. Fortunately, many of the vendors have product lines that specifically focus on small business customers, such as the OfficeConnect series from 3Com, most of the Netgear products from Bay Networks and Intel's InBusiness products.

Prices for network equipment vary greatly. You can generally purchase components and significant discounts below the manufacturer's suggested retail price. Here are approximate street prices for some of the items that you'll need to build a small office network:

• 10Base-T Ethernet cards: $30-50 each
• 10/100Base-T Ethernet cards: $45-120 each
• Unmanaged Shared Media Ethernet hubs: $10-20 per port
• Switched Ethernet hub (10/100): $100-150 per port
• Fast Ethernet hub: $40-75 per port

You can purchase most of your network components from a local computer retail store, mail-order catalogs or over the Internet. Even if you purchase locally, check manufacturers' Web pages to learn which models offer the features and performance you need, and check online catalog ordering sites such as Data Communications Warehouse (http://www.warehouse.com/datacomm/) for pricing. Online ordering is often the most attractive approach. Pricing is low, the selection and availability of products is good, and most offer next-day delivery options.

Networking without a Backbone

One of the keys to designing a network for a large organization is creating methods for a large number of LANs to connect together to form a coherent enterprisewide network. The ties that bind enterprise networks include components such as hubs, routers and switches. These networks typically have a backbone that interconnects each of the individual LANs scattered throughout the organization. This backbone must be designed to move data through the network efficiently and reliably. The backbone for an enterprise network would likely use fiber-optic cabling with multiple redundant paths interconnecting the individual LANs.

The types of networks that serve small businesses follow a much simpler approach. There's no need for high-end backbone routers and switches, and all the complexity that it takes to implement and manage them. Networks for small business typically can rely on a single Ethernet hub to connect everything. In some cases, multiple hubs may be stacked or cascaded to achieve enough ports if the number of networked devices exceeds the capacity of a single hub.

Summary

After considering the various options, we can make the following recommendations for the small office network:

• Use Ethernet rather than token-ring or ATM unless there is some unusual prevailing circumstance.

• Do not use coaxial Ethernet of either the Thick or Thinwire variety.

• Support for network management generally is not required for small networks.

• Use 100Base-T if performance is the highest priority.

• Use 10Base-T if economy is the highest priority.

• Use switched Ethernet to segment the network or deliver faster performance to the desktop.

• Gigabit Ethernet should not yet be considered an option for the small office network.