The ISDN Solution

An ISDN connection can offer the best performance when compared to either an X.25 or modem connection. This is because ISDN is a digital-based connection. Therefore, the quality of the connection is superior to your average modem connection and much faster than an X.25 connection. However, ISDN utilizes a proprietary phone connection and is therefore not acceptable for mobile computer users. It does perform well for sites where your local phone company supports ISDN phone lines. An ISDN connection can support one or two 64Kbps (some phone companies utilize 8Kbps as overhead, so you may only get 56K) connections. In theory, this can give you up to a 128Kbps (possibly only 112Kbps) data transfer rate. With compression, you can achieve a 512Kbps transmission speed.

Like an X.25 connection, you will also require a proprietary adapter, which will increase your WAN expense. You will also have to consider the monthly and per-minute access fees when considering your budget. These fees vary from state to state, and ISDN service, in general, is not available in every state. You should check with your local phone company first before deciding to use this alternative.

Using Routers To Increase Performance

A router or bridge can be used to provide a major benefit that a RAS connection cannot perform for you. This benefit is the ability to dial up and connect to a remote network node based on user demand. A RAS connection must either be user-initiated or permanent. A router or bridge (depending on the manufacturer) can automatically dial up a remote node when it detects a request for an external server in its internal database. This can decrease your phone bill quite a bit over a dedicated connection to your remote server.

Some routers can use either a regular phone line or a digital-leased line. Regular phone lines, of course, offer a limited bandwidth and increased cost based on whether you dial local or long distance phone numbers. For a constant communication linkage, I recommend a leased line. Leased lines vary in cost from location to location, so you should check with your phone company for the specific costs associated with connecting your sites. Leased lines also come in various types and speeds, as you can see in Table 8.1.

Another advantage a router or bridge has over a RAS connection is that almost all RAS devices (modems) are asynchronous. This means that the modem does not operate at its full potential all of the time. Instead, it must pause while data is transferred to or from the UART. These pauses lower the effective throughput quite a bit. On the other hand, a synchronous device, such as a router or bridge, uses its full bandwidth all the time.

If you are going to use the Internet as your WAN backbone, you really should spend some time considering the security issues. The Internet is not a secure environment. It is possible for an Internet hacker to trap TCP/IP packets on the Internet and use the information obtained in these packets to hack his or her way into your network. It’s a remote possibility, but a very real one. For these reasons, you may want to consider using a firewall, a proxy server, or both on your network.

Firewalls And Proxy Servers

The first question you probably have is, what do firewalls and proxy servers have to do with designing and building a network? The answer, of course, depends on whether you plan to use one in the first place. If you plan on connecting to the Internet or using the Internet Information Services to publish data on the Internet, a firewall or proxy server should be one of those must-have items. Both of these products can protect your network from potential security breaches. After all, if the whole world can access your network, there may come a time when someone will decide to try and access more than the information you are making freely available to the public. Preventing an external user from accessing unauthorized areas on your computer (or your entire network) or preventing your internal network clients from accessing external resources (such as Internet resources) is where you will enter the realm of firewalls, proxy servers, and other alternatives. Unlike firewalls, proxy servers can also be used to cache intranet or Internet requests and improve performance.

These topics will be discussed in the following sections; however, the aim is not to be an all-inclusive reference, because there is just too much material to fit into a single chapter. Instead, the discussion is a general reference that describes the technologies involved in limiting access to your network. There is one sure statement I can make about this entire process of limiting access to your network—there is no guarantee that you can prevent an expert from working his or her way into your system from the Internet. At best, you can be aware of an intrusion. At worst, the intruder could bypass all your safeguards and do whatever is desired. These are unlikely propositions, but the longer you are connected to the Internet, the more likely your chance of running into these situations will become.

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TIP:  There is one other safeguard you can use that has absolutely nothing to do with limiting access to your computers. It’s pretty simple but, nonetheless, very important. Just make daily, weekly, and monthly backups of your server and your network client computers. At least if you have a backup, you can restore your previous configuration.

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