Upgrading to Ethernet or Token-Ring

You probably can safely assume that any conversion from ARCnet is going to require replacing network adapter cards, hubs, and, most likely, network cables ”in other words, just about everything but the workstations and servers. You'll have to be sure that any specialized devices, such as industrial machinery that uses a network connection, can also be used with a newer technology. It might be a simple matter of swapping out a component card as you do with a PC, or it might involve upgrading firmware or even the replacement of some machinery. These costs must be taken into consideration when you are creating a budget to justify the upgrade.

If you have used Category 3 or better cables, you might be able to reuse the cables, but you will need to modify the connectors to use the appropriate cable pairs and pin-out specifications for 10BASE-T. Ethernet does not support daisy-chaining using twisted-pair wiring, however, so if you have an existing ARCnet LAN that is composed of multiple segments of this sort , you will have to purchase new cabling for an upgrade. If you currently use hubs, you might get by with rewiring the connectors and replacing the hub with an Ethernet hub or switch. However, because you're going through an upgrade from such an old technology, now might be the time to consider running new Category 5, 6, or better cables. This is especially true if you are installing Fast Ethernet and expect to upgrade this to Gigabit Ethernet in the future. For all practical purposes, any future advances in network bandwidth will not use Category 3 cabling, so it's usually better to bite the bullet and expend the money required to replace cables at the same time.

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If you want to plan for the long run, it might even be a good idea to upgrade your cable plant to fiber-optic cables. Although most network adapter cards that have fiber- optic receptacles operate at gigabit or 10Gb speeds, there are now many on the market that can be used for Fast Ethernet (100Mbps) connections until you have a need to upgrade to faster communications. You can use a search engine online to find these manufacturers, and the price of these cards is not inexpensive ”usually $150 and up. However, pulling network cables is a much more expensive proposition, so adapter cards will probably be the least expensive component in this kind of upgrade. By the time you decide to upgrade to gigabit speeds, the price of those adapters will have come down dramatically. One site you might want to visit online for more information is www.unicomlink.com/products/network_equipment/nic_cards.htm.

Chapter 6, "Wiring the Network ”Cables, Connectors, Concentrators, and Other Network Components ," contains an in-depth discussion about the differences in copper cables and fiber-optic cables, including the different types of each.

If you are replacing ARCnet with Token-Ring equipment, you'll also probably have to use new network wiring. The distances that Token-Ring networks cover vary a little from one vendor's products to another. They also are more expensive than Ethernet components. However, like ARCnet, Token-Ring networks can provide a deterministic, maximum access time for nodes on the network. In the past, if timing was critical in your environment, Token-Ring was probably a good upgrade path . However, modern versions of Ethernet currently operate at much larger bandwidths, and in an environment where timing is critical, Ethernet can meet the challenge today.

Although pulling new wiring (both Ethernet cabling or Token-Ring cabling) is a labor- intensive task, if you opt to install new high-grade cable now, it's an investment that will last for many years .

ARCnet normally is used to create small LANs. A few manufacturers sell bridges that can be used to connect the 255-node LANs into larger configurations. Most ARCnet LANs operate at the standard 2.5Mbps rate. Other versions, such as ARCnet Plus, can be used at up to 20Mbps. To decide which Ethernet technology you want to use, examine the current layout and identify important nodes and the bandwidth you think they will need. Try to locate bottlenecks that occur in the current topology, if any.

Here are some questions to ask yourself:

• Which servers do most nodes in the LAN use?

• Where should devices that require a quick response time be placed in the network?

• Which servers get the heaviest use in terms of network bandwidth? Would you benefit from Fast Ethernet or Gigabit Ethernet switching for these servers?

• Can any groups of users and servers be segmented? Are there any groups of users that should be isolated behind a firewall for security purposes? A firewall is unnecessary unless the servers that connect to automation devices are also connected to a more typical office LAN.

• If this upgrade is the result of merging with another network, what kind of interconnection will be made? Which users on each network will be allowed access on the other network?

ARCnet provides a physical LAN that uses a token to allow access to the network medium. Because no prioritization is built into the protocols used, every node on the LAN must process each packet sent out on the wire. Conversion to a simple Ethernet broadcast domain seems to be a simple task. However, you'll need to look closely at the distances between hubs on the current LAN and those distances between workstations and these hubs.

Because ARCnet allows for up to 2,000 feet between active devices, you'll need to make decisions based on the kind of Ethernet technology to which you're upgrading and whether or not it can span the distance you require. You can use Fast Ethernet or Gigabit Ethernet with fiber links to connect switches at larger distances than is possible using coaxial cable, which is rarely used today, or twisted-pair wiring. If your factory floor is small, you should have no trouble locating switches or hubs to service a large number of network nodes. In a large campus environment, you'll need to set up a router or two and segment your network into subnets. This not only cuts down on local segment network traffic, but also makes it easier to manage the network from an administrative point of view. You could also use a cascade of switches to connect geographically distant devices.

Laying Out the New Network

Ethernet offers many solutions to help build networks that range from 10Mbps to gigabit speeds. What you use depends on the current needs of the network, the projected usage for at least three years, and the distances to be covered.

In a small network, such as an office setting, where there are from two to a few dozen computers, a simple solution is to replace the current ARCnet hubs with one or more Ethernet switches, run new cables to the workstations, and equip each workstation with a new Ethernet network adapter card. This kind of a swap-out can be done easily over a weekend without causing downtime for network users. To facilitate the process in a minimal amount of time, you can do a lot of work in advance, such as installing the new cabling and preparing the faceplate and other hardware at the user 's desk and simply hooking things up when you get some downtime. This type of upgrade can be very useful in a large network, or a network that requires a 24/7 operation schedule.

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Currently, many 24/7 networks use several technologies to attempt to maintain operations with no downtime. For example, using clusters, in which two or more servers operate together, prevents a single server from being a point of failure. Other methods include multiple network cards and other redundancy built into the entire network, from routers to duplicate lines of cabling, and so on. Most of these techniques are covered in various chapters throughout this book.

When the LAN is larger, however, you might need to sit down and think about how users utilize network resources before you decide on a migration plan. For example, ARCnet enables you to place a workstation up to 2,000 feet from an active hub. Ethernet's 10BASE-T allows a maximum distance of only 328 feet. If your network has multiple workstations that are using cables that extend the maximum distance allowed by ARCnet, then you will not be able to perform a simple swap-out and replace ARCnet hubs with Ethernet switches. Instead, you will have to look at the geography of your building and decide on locations for switches that can be used to stay within the 10BASE-T limit of 328 feet. The end result is that you will probably use additional switches to extend the distance covered by Ethernet, or use fiber-optic cabling to connect a series of switches over a greater distance. Again, you can solve this problem with a mix-and-match solution by installing Ethernet switches that connect to a fiber-based Fast or Gigabit Ethernet pipe, while allowing switch ports for 10Mbps and 100Mbps computers.

Figure 55.1 shows an ARCnet LAN that uses two active hubs and one passive hub. On the first active hub you can see that there are five workstations, all of which are placed the maximum distance from the hub, 2,000 feet. The passive hub, however, can be no farther from the active hub than 100 feet, and the workstations connected to it are also bound by this limit.

Figure 55.1. ARCnet allows the LAN to span distances of up to 2,000 feet between hubs.

The workstations in this layout are more than 300 feet from the second active hub, which is within the Ethernet 10BASE-T limit of 328 feet. It is a simple matter here to replace this second active hub with an Ethernet switch, and then replace the cables that connect the workstations to the switch and the network adapters in each workstation.

The first active hub, however, poses a problem because it has workstations that are beyond the distance limitation 10BASE-T/100BASE-T technology imposes (see Figure 55.2). Here, a solution might be to replace the active hub and the passive hub with an Ethernet switch, and connect the printer (and the workstations attached to the passive hub) to the new switch. From here you can run an additional link to another switch that is situated closer to the other workstations.

Figure 55.2. Use additional switches to group workstations that are beyond the maximum allowable distance for 10BASE-T or 100BASE-T.

To connect these three switches, you need to use a fiber-optic link to span the distance. When you are looking at switches to purchase, be sure they have the correct ports needed to connect Category 5 (or greater) cables as well as fiber. Twisted-pair cables, such as those used by 10BASE-T and 100BASE-T, typically use an RJ-45 jack, whereas fiber-optic cables typically use an ST or SC type connector. Be sure that the device you choose for a replacement supports the number and kind of ports needed for these connectors.

The purpose of this example is to show that in addition to swapping out the networking equipment when you upgrade to Ethernet, you must pay close attention to the differences between the current ARCnet topology and that of the technology to which you are upgrading. Pay close attention to the limits imposed and compare them with the current layout of user workstations and servers. You will probably find that additional switches will be needed when the ARCnet network is stretched to its limit and needs to be converted to Ethernet.

The same process is required for conversion to a Token-Ring network. You'll need to get the specifications for the hardware (MSAUs, cabling, network cards, and so on) and lay out a topology that can accommodate the nodes on your current network.

Solving Performance Problems

Another consideration for the upgrade path is what kind of interconnecting devices you need to use. In a very small network, one or more 10/100Mbps hubs or switches will probably suffice and be an easy upgrade. ARCnet is not known for having a large bandwidth (2.5Mbps for the standard ARCnet), so if this speed sufficed before upgrading, it's unlikely that you will have to worry about bandwidth problems afterward. Even if the ARCnet bandwidth usage is becoming saturated (at about 65% of the total possible 2.5Mbps), a simple 10Mbps or 100Mbps Ethernet LAN handling the same number of nodes will probably show dramatic improvement.

Speed is another reason you might choose Ethernet over Token-Ring. Although some vendors sell equipment that can be used to run Token-Ring at very fast speeds, the standards on this technology have pretty much stalled in the past few years, so you shouldn't expect to see a lot of vendors devoting research dollars to come up with faster products. Instead, if performance is a problem, a well-planned network of Fast or Gigabit Ethernet to connect switches with ports dedicated to important network nodes might prove a more viable solution than Token-Ring.

As always, though, you should be looking to the future. For example, it is typical that when upgrading an old LAN you will be upgrading not just the physical infrastructure, but also the end-user applications used on the network. Although a simple word processing program that was marketed 10 years ago might not require a lot of network bandwidth to run from a server, the needs of newer versions might seem gigantic in comparison. If end-user workstations are also being replaced , you might find it easier to install a copy of the application on each workstation, assuming that it has much more hard disk storage space than its predecessor (and the cost of additional licenses doesn't prove prohibitive). If you plan to continue serving applications from an application server, you might find it necessary to use Ethernet switches and possibly a higher-bandwidth technology than 10Mbs Ethernet.

The same goes for factory automation devices, which are a lot more complex today than 20 years ago. Faster processors and more specific tasks mean that network communications on the factory floor is a field that will be growing and evolving rapidly during the next few years.

Switches come in many sizes and support varying numbers of ports and bandwidth. You can learn more about switches, and thus how to deploy them in a network, by reading Chapter 8, "Network Switches."

Connecting servers that need a large amount of bandwidth to a switch, in full-duplex mode, can help in this situation. Whether you need to use a switch port or a hub for each user workstation depends on the current user work habits, along with a projection of network use you expect after you upgrade applications.