Hardware and Software Factors to Consider for 10BASE-2, 10BASE-T, and 100BASE-T

Obviously, it's the hardware that you'll have to replace when making this kind of upgrade. Network protocols, such as TCP/IP, don't care what the underlying physical network is made up of as long as they can get data segments from one place to another. However, you might still be using older software, and if so, you might want to consider upgrading it in addition to the hardware when you plan for this kind of upgrade. As discussed in other parts of this book, Novell's NetWare has basically lost the LAN environment to Unix and Windows NT/2000 and Windows 2003 servers, much less the Windows XP client XP, and even the most recent versions of NetWare can use IP. For NetWare 6, IP is the main protocol, given the emphasis that Novell now puts on Internet access. For the network that you use, whether it be a built-in technology as with Windows or Unix/Linux or an add-on product such as NetWare, the IP protocol remains an underlying factor.

For a historical overview, 10BASE-2 and 10BASE-T have more differences than just the type of cables they use. Although both of them use the same messaging technique (CSMA/CD), their topologies are basically different: 10BASE-2 uses a bus topology, whereas 10BASE-T (and 100BASE-T) installations use a star topology, implemented by a switch, although you might find an older hub still being used. The distances that can be covered by cable segments are also different. The network adapters transmit signals at different speeds. When preparing for an upgrade, check your network inventory to determine which parts of the hardware you'll have to upgrade in addition to the cabling. The major considerations that need to be researched when upgrading from 10BASE-2 to a twisted-pair network are as follows :

• Network cables ” The fundamental difference between 10BASE-2 and 10BASE-T/100BASE-T is the move from coaxial cable to twisted-pair wiring, usually Category 5 cables, although newer cabling is now being deployed.

  For more about cables and other relevant components, refer to Chapter 6, "Wiring the Network ”Cables, Connectors, Concentrators, and Other Network Components ."

  
  

• Network topology ” You'll be going from a linear bus topology to a star topology. The distances covered by 10BASE-T/100BASET are shorter than those allowed using 10BASE-2. But because of the star topology and the uses of switches, you'll actually find it easier to greatly extend the reach of your network.

• Network adapters ” Older network adapters might have only a BNC connector on them. You'll need cards that provide an RJ-45 jack for 10BASE-T or 100BASE-T. This connector looks much like an ordinary telephone jack, but is slightly larger.

• Network cable connectors ” Instead of BNC connectors, twisted-pair cabling uses RJ-45 connectors.

• Hubs and switches ” Although a 10BASE-2 network allows you to use multiport repeaters, no central wiring devices are actually required . For a 10BASE-T/100BASE-T network, you need (at a minimum) a hub to act as a wiring concentrator. Although a lone hub might suffice for a small network with a limited number of users, you should really consider using switches instead because they enable you to further extend the distances covered by a LAN. And it is very unlikely you'll find a hub for sale today.

To learn more about how hubs and switches function, see "Bridges, Repeaters, and Hubs," on the upgradingandrepairingpcs.com Web site and Chapter 8, "Network Switches."

For example, if you're using a multiport repeater, replacing it with a more functional hub or switch seemed a natural thing to do a few years ago. However, remember that the topology rules for 10BASE-2 and 10BASE-T networks specify different maximum cable segment lengths, so you might have to relocate wiring closets or make other accommodations if your current distances are too long:

• Maximum segment length for 10BASE-2: 185 meters

• Maximum segment length for 10BASE-T/100BASE-T: 100 meters

• Maximum number of devices on a 10BASE-2 hub segment: 30

• Maximum number of devices on a 10BASE-T/100BASE-T hub segment: 2 (but one of these is the hub, so effectively, just 1)

Chapter 14, "Ethernet: The Universal Standard," covers in more detail the different cabling distances you'll need to consider.

Today, however, using switching technology to replace hubs is about the only option you have today. As stated earlier, you'll find it difficult, if not impossible , to find a hub on the market today. They are legacy devices. If you're going to upgrade your network, consider a switch to be a hub replacement. That doesn't mean you need to discard hubs in small segments of your LAN if you already have them. Indeed, if you connect a few computers that have minimal bandwidth requirements to your LAN, there's really no need to replace a hub with a switch. It all depends on how your users make use of the network. If no one is complaining with a hub connection (which you'll most likely have connected to a switch upstream), don't worry about replacing it. Today it's usually the applications that drive the need for additional network bandwidth. If it's working now and no one is complaining, don't change it.

The main consideration here is the topology requirements used for earlier Ethernet networks. If the cable doesn't provide the distance or bandwidth requirements you need today, you'll have to replace the cabling to accommodate modern networks. In a small LAN environment, this usually isn't the case. In a larger environment, you might have to replace cabling to reach the distances you need, yet still provide the same bandwidth that older equipment (such as hubs) can give to users.

Network Cables

Because 10BASE-2 uses thinnet coaxial cabling, the first upgrade issue you must address is getting the appropriate network cabling.

This should be the simplest decision you have to make. Although it's quite possible to use Category 3 wiring to construct a 10BASE-T (and even a 100BASE-T) network, the only good reason I can think of to do so would be that you already have the wiring in place and can use it with few modifications. Other than that, if you're going to install a 100BASE-T network to replace a network based on coaxial cables, you would be better served to go ahead and use Category 5 cabling or better. Why? Further down the road you might find yourself upgrading to Gigabit Ethernet or even 10 Gigabit Ethernet.

Both of these technologies require Category 5 cables or higher. Although it might seem like Gigabit Ethernet is something that's far in the future, keep in mind that many network administrators didn't think that video on demand would be a requirement today. It's easy to underestimate the network bandwidth that you'll need for future requirements. And because installing the cabling is one of the most labor- intensive (and thus expensive) components of a network upgrade, I recommend that when you decide to upgrade cabling, you go for the latest to protect your investment farther into the future. Indeed, I'd say that your network backbone should already consist of fiber- optic cabling because Gigabit and the newly ratified standard for 10 Gigabit Ethernet operate best using these cables. Both can use ordinary copper cables, but only for very short distances ”usually in the wiring closet.

The amount of cable you need might work out to be a lot more than you used for the 10BASE-2 network. Remember that in the bus topology that thinnet (coaxial) networks such as 10BASE-2 use, you can daisy chain one workstation to another using a linear bus. A 50-ohm terminator terminates each end of the bus. The total amount of cable needed is simply the sum of all the cables that are daisy chained together. When using a hub or switch, you can have two workstations sitting right next to each other, both having a 100-meter twisted-wire cable going back to the hub. Because of this, the total amount of cabling you'll need is generally a lot more than you did when you installed 10BASE-2 technology. Yet consider that the cost of twisted-pair wiring is now a lot less expensive that it used to be. The economies of scale always provide for this.

If you instead use a multiport repeater on an existing 10BASE-2 network, and if only one computer is attached to each port, you'll find that replacing the cables is a simple matter of stringing Category 5 (or greater) cables through the same route used by the current coaxial cables. Then all you need to do is replace the repeater with a switch. If you have segments on a multiport repeater that have more than one computer attached, you'll have to plug each computer into a separate port on a switch. Another possibility is to place these computers on a separate switch and connect it to the network backbone.

Note

Another consideration is how you originally installed your coaxial cables. Different jurisdictions have laws that state how electrical and network cables can be installed. They're generally encased in a conduit of some sort , such as a metal pipe. Trying to place several hundred Category 5 cables in a small space that originally contained just one or two coaxial cables might be a problem. Consider this when designing the topology of your new network.

Because you must string cable from a central location to each workstation, you need to have a place you can use as a wiring closet to store the switch and any other interconnecting equipment used to join the LAN to a larger network. Again, if you were using a multiport repeater in your 10BASE-2 network, all you need to do after stringing the cables is to replace the multiport repeater with a switch. Also keep in mind that if you're simply upgrading a small office LAN (5 “10 computers), you can use an inexpensive off-the-shelf switch from your local computer store and simply place it out of the way somewhere convenient in the office.

For all practical purposes, consider making backbone connections using fiber-optic cabling. Doing so will give you a much faster connection between LANs today and better prepare you for the future. Keep in mind that the old 80%/20% rule no longer applies. This rule stated that 80% of network traffic remained in the local LAN and 20% was sent to another segment of the LAN. Today, it's more typical to centralize large servers in a computer room and keep LANs separated by switches. Because computers on the LAN need to access these servers, and they might be separated by multiple switches or even routers, you should consider the 80%/20% rule to be reversed . Now 80% of network traffic is directed outside of the local LAN.

Network Adapter Cards

If you had the foresight to purchase the kind of network adapter cards called combo cards , which have connectors compatible with both BNC connectors and RJ-45 connectors (see Figure 57.1), this is one piece of hardware you might not necessarily have to replace. The minimum requirement for the NIC is that it have a receptacle to which you can plug in the RJ-45 connector end of the cable to connect the adapter to a hub. However, if you plan to incorporate switches into the network and want servers to use full-duplex connections, you'll probably have to get a newer card for these computers (most older cards supported only 10Mbps and not 100Mbps). Older combo cards enabled you to upgrade from BNC connectors (used by 10BASE-2) to 10BASE-T. Newer cards use the standard RJ-45 jack and allow for 10/100Mbs communications. And today, most of these cards support auto-negotiation and Wake on LAN (WOL) technologies. So, if you're still using combo cards, you can continue to use them, but will most likely be limited to a 10Mbps bandwidth on the network for the workstations that use them.

Figure 57.1. A combo card contains connectors for both thinnet coaxial cables (BNC connectors) and a receptacle for an RJ-45 jack used with twisted-pair wiring.

To learn about the latest developments in network adapter cards, including technologies such as auto-negotiation, WOL, and even newer stuff such as PC Cards and wireless network adapters, refer to Chapter 7, "Network Interface Cards."

If you're going to have to upgrade a large number of workstations to newer NICs, think carefully about the future when you make this purchase. No matter what your budget is, there's absolutely no reason to buy a 10Mbps network card, if you can still find one. At the bare minimum, a 10/100Mbps card that can support your older network as well as Fast Ethernet is the best choice to make. Why? Because the price of network adapter cards has fallen so low that you can now find 10/100Mbps cards (depending on the features they support) for less than $20 “$30, and for even less at some computer stores and online retailers. If you purchase in quantity from a catalog reseller, you might even find greater reductions in price. Network adapter cards in this range are now commodity items. You can even buy them at department stores such as Wal-Mart.

Network Cable Connectors

As already pointed out earlier in this chapter, a 10BASE-2 network uses a different kind of connector than a 10BASE-T/100BASE-T network does. You should pay attention to the details when ordering connectors (if you plan to make cables yourself) or when ordering ready-made cables that have the connectors attached. When upgrading to twisted-pair wiring, I've already suggested that you use Category 5 cabling (or greater) instead of a less capable variety, such as Category 3. This enables you to use the cabling later when you decide it's time to install 100Mbps segments on part or all or part of the network. Keep in mind that Gigabit Ethernet adapters are already available and the standard for 10 Gigabit Ethernet has just been approved. Although you might not find these speeds required for a workstation connection, they will probably figure into server and backbone connections in just a few years or even less. And because predictions of this sort tend to be conservative, think proactively and investigate the costs of these cards and the switches/routers that support them! Better to pay the more expensive up-front cost now than have to switch out a lot of cards at a lower price in the future.

Connectors, like cables, can exhibit different performance characteristics depending on how they're manufactured. Be sure that the RJ-45 connectors you choose are compliant with the specifications for Category 5 cables. Inferior connectors can cause a lot of trouble later (such as noise or near-end cross-talk), causing you to spend a lot of time troubleshooting. When constructing your own cables, be sure that you follow the specifications when attaching the jacks to the cables. Many noisy cables are created simply because too much wire is left exposed at the end of the cable where the cable is attached to the connector.

In Chapter 6, you'll find more information about cables and connectors and the problems you can encounter when they aren't manufactured correctly.

Bridges, Hubs, Repeaters, and Switches

To extend the length of a LAN based on 10BASE-2 technology, the standard technique is to attach multiple segments with a bridge or a multiport repeater. A repeater works similar to a hub: It simply makes one large broadcast domain out of the various cable segments that are connected to it. A bridge connects two segments, but is capable of learning MAC addresses. Therefore, a bridge can reduce traffic by passing on frames to segments only if their destination isn't on the local segment from which they originate.

For more information about bridges and how they operate, see "Bridges, Repeaters, and Hubs" on the upgradingandrepairingpcs.com Web site.

You can use bridges on a 100BASE-T network for the same purposes you would use them in 10BASE-2. They can group similar users on local segments, reduce traffic on individual segments, and extend the length of the local area network. Bridges can perform other functions related to performance as well, such as discarding packets with errors and reducing noise. Newer layer 3 switches accomplish much of the same function by reducing traffic between segments and between specific ports on the switch. Since the previous edition of this book was published, the price of switches has decreased dramatically. Because of this, and its superior performance capabilities on anything but a very small network, I advise using a switch rather than a hub. Hubs should be considered to be legacy devices. You probably won't be able to find hubs on sale anymore because switches have replaced them and offer much better performance.

Network applications are becoming more data intensive than ever before as computers become faster and more memory is added. A switch creates a small collision domain (that is, just the switch and the computer attached to a switch port) and can drastically reduce network congestion.

Note

For more information on how switches work and how they can be used to improve performance in your network, refer to Chapter 8. Hubs are now becoming difficult, if not impossible, to find. Even in small networks, switches are now the wiring concentrator of choice. Hubs share bandwidth among all the network segments attached. Switches limit the collision domain and give the full bandwidth to each computer attached. If you're still using an old hub you bought just a few years ago, you should go ahead and upgrade to a switch.

Also, in anything but a small network, you might need to use more than one switch to connect user workstations to the network. If you're planning ahead for a future migration to 100Mbps networking, you'll find that a multitude of switches operate at both 10Mbps and 100Mbs. Look at the cost difference and decide whether making an investment in a 10/100Mbps device now will save you money in the future. Most switches support both speeds, as well as auto-negotiation to determine what types of devices are attached to each port.

A more important factor to consider when evaluating a switch is to find out whether it comes with management software that's compliant with SNMP and RMON standards. Check to find out whether each port can be set to a different speed. If it can, make sure that you know whether it's autosensing or if you must manually set it to operate at one speed or the other.

The Simple Network Management Protocol (SNMP) and RMON (Remote Monitoring) are discussed in detail in Chapter 53, "Network Testing and Analysis Tools."

If your existing network already uses a router to connect to a larger network, be sure that the hub or switch has a receptacle that can be used for the router connection. Most routers made today accept cables terminated with several different kinds of connectors, even 10BASE-2, so this probably won't be a problem. However, you should check this as you do all aspects of the network when making an upgrade plan. Note also that the connection between the switch and a router might need to provide for a larger bandwidth than the connection from the switch to the user's desktop. Although 10Mbps or 100Mbps might be suitable for some end-user applications, when you aggregate this bandwidth and add up the amount of network traffic that will be needed on the entire network, you might want to consider a switch that can use a faster connection ”such as fiber-optic cables ”when it connects to another hub or a router.

For more information about using routers to join individual network subnets, refer to Chapter 10, "Routers," and Chapter 37, "Routing Protocols."