There are many types of telephone lines that can be used to connect remote computer networks together. Not all type of sevice are available in all areas and the fees charged by the various telephone companies {telco} are far from consistant. Even the name used to describe a type of service can be different between telephone companies. The following is a list of the types of services that may be available in a given area and the pros & cons of using that service. Service Name Speed Comments Dial-up {POTS} up to 33.6Kbps This is plain old telephone service. Can be economical for some uses, pretty slow for heavy network traffic. If you have measured service, install Centrex {GTE calls it Centranet}. This makes the two locations 'extensions' of each other. Telcos charge a flat monthly rate for Centrex service. This way the line is 'up' continuously without added charge. Dry-pair lease-line up to 1.544Mbps This is usually the least expensive and fastest of the services if available. Many of the telcos are not installing this type of service any more. Speed depends on the equipment used, distance between locations, and the condition of the wire. The maximum distance between locations with this service is about 7 miles. DSL up to 1.544Mbps Digital Subscriber Loop is a new service being offered in limited locations. Speed depends on the equipment used, distance, and the condition of the wire. The maximum distance between locations with this service is about 12 miles.  DS0 56/64Kbps Sometimes called DDS, this is a 4 wire digital lease line circuit that is almost universally available. There are no distance limitations. Cost can be from $100 a month on up depending on distance, telco, and location. Speed is 64Kbps although in some areas only 56Kbps service exists. A large percentage of small networks are connected this way. ISDN 64Kbps or 128Kbps Centrex {GTE calls it Centranet} ISDN is an economical option if it is available in your area. Regular ISDN is billed as a measured service. When Centrex is specified, telco 'ties' the ISDN circuits of two locations together. This is then billed at a flat rate. Centrex ISDN is only available when both locations use the same telco. T1 1.544Mbps T1 service is widely available and is the equivalent of 24 channels of DS0 service. The channels can be combined or used separately depending on the need. T1 is usually very expensive and mostly used on large networks or to aggregate many small networks into a single pipeline. FT1 multiples of 64Kbps up to 1.544Mbps Fractional T1 is the combined DS0 channels to create whatever bandwidth desired short of a full T1. New tariffs make FT1 a poor choice now in most instances because the full T1 prices are so close to that of any configuration of FT1. Frame Relay up to 1.544Mbps Frame Relay is a shared circuit. It can be economical in the correct situation. It is usually good for long distance connections. You are billed only for the Commited Information Rate {CIR} you specify. This can be as low as 0bps although most telcos insist on at least 8Kbps. If the circuit is likely loaded, you may get the maximum data rate of your local connection {a T1, FT1, or DS0 circuit} but as traffic increases, your data rate can slow down to the CIR. Many companies pay for only the minimum allowed CIR and then live with the occassional slow downs.