Upgrading from 10BASE-2 or 10BASE-T

Twisted-pair wiring pretty much replaced 10BASE-2 many years ago and was, for a long time, the networking solution of choice. Hubs allowed for centralization of wiring and switches helped localize errors due to faulty cables or network adapter cards.

100BASE-T and gigabit Ethernet solutions are now the de facto standards for creating a new network. If you're creating a network from scratch, it's best to start with the latest and greatest if your budget allows.

Like 10BASE-2 networks, you should ask yourself why you would even want to operate a 10BASE-T network. If you already have one in place, continuing to add new hubs, switches, and routers may make sense, provided this limited bandwidth (10Mbps) can satisfy the demands of your users/ applications. However, 100BASE-T (also known as Fast Ethernet) has been around for more than 5 years, and is now the most widely used version of Ethernet between the wiring closet and the user desktop.

If you're going to swallow the expense of pulling new cabling to replace older coaxial cabling, there's no reason to go to 10BASE-T today. Category 5 (and above) cabling can handle both, and almost every network adapter card produced today can operate at 10Mbps as well as 100Mbps. After you've upgraded the cable plant, you might as well go for the added bandwidth of 100Mbps instead.

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. 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, and even the most recent versions of NetWare can use IP. For NetWare 6.X, 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.
• 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.

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 10BASE2 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)

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.

Growing Beyond a Small LAN continue...

Segmenting the Network Can Improve Performance

You might need to segment devices on the network for many different reasons. These include the following:

1. Topology limitations—You need to add more nodes to the network but the expansion will break distance limitations or maximum nodes-per-segment rules. This is usually the case only in older Ethernet LANs where the broadcast domain was constrained by the round-trip time.

2. Networking protocol limitations—Address space is fragmented and you need to connect segments that have different network addresses. This can happen when two companies merge and both already have an address space in place for their respective networks. It's much easier to simply place one or more routers between the two networks than it is to reassign network addresses to the many devices on the network. When using DHCP to configure workstations, this might not be a limitation, provided that you have an address space that can accommodate all the devices that will be placed on the larger network.

3. Network bandwidth limitations—When a few high-performance servers or workstations consume too much of the segment's available bandwidth, it's time to segment the LAN (create additional subnets) and thus limit network traffic to smaller segments that contain fewer devices.

4. Security reasons—An Ethernet adapter set to promiscuous mode can intercept all packets that are sent out on a particular segment, for example. You need to place a few high security workstations on their own segment, yet allow some kind of connection to the rest of the network. Keep in mind that in an Ethernet network that uses hubs as a wiring concentrator, every device on the hub (or hubs) can see every network frame that's broadcast on the LAN. It isn't difficult to download a program from an Internet source to read every packet that passes through the network.

Geographically distant connections—It's best to segment each geographic location to ensure that unnecessary traffic isn't being sent across the remote connection and wasting valuable bandwidth. Some routers provide a dial-up function so that a dedicated link isn't necessary, providing an inexpensive way to use routers to connect branch offices.

Depending on which combination of these reasons applies to your situation, a router or switch might be the solution you need to segment the network.

Connecting Remote Locations

When a business expands geographically, you'll find that using bridges to connect remote locations isn't a feasible solution. There are many different technologies from which you can choose today— from simple dedicated lines to ATM and Frame Relay—to connect geographically distant locations.

For these connections, you'll find it necessary to incorporate routers or switches. You'll also find these methods of transport expensive. Today, it isn't unreasonable to consider connecting the local network to the Internet with a router that provides virtual private network (VPN) capabilities. Thus, by using an inexpensive connection to the Internet (far cheaper than using leased dedicated lines), you can still provide a secure channel to remote branch locations.

When to Use a Router

Routers are similar to bridges only in the fact that they can both be used to connect multiple network segments. Whereas bridges make all their decisions based on the MAC address of a particular network packet, routers access the addressing information provided by a higher-level protocol to decide how to best forward a packet. Using the OSI reference model (see Appendix A, "Overview of the OSI Seven-

Layer Networking Reference Model"), you can see that the bridge operates at layer 2, the Data Link layer, whereas routers operate at layer 3, the Network layer. With bridges, the address space is flat: It's simply the MAC addresses associated with nodes on each segment, each one unique. For protocols operating at the Network layer, the address space becomes more complicated because there must be a mechanism for identifying the network as well as the individual node.

When to Use a Switch

Switches are one of the fastest growing categories of network equipment. They can act as a wiring concentrator for a LAN just as a hub does, but they also can make available a much larger bandwidth to clients because they selectively forward traffic from one port to another based on the destination address of each packet. When you use a switch with only one node attached to each port, you are in effect creating a collection of broadcast domains that consist of only two network nodes: the switch and the client node connected to the port. For network adapters and switches that support full-duplex operation, the effective bandwidth is doubled for each client and there is no broadcast domain between the two.