When permanent dedicated connections are required, a point-to-point link is used to provide a pre-established WAN communications path from the customer premises through the provider network to a remote destination. Point-to-point lines are usually leased from a carrier and are called leased lines. This topic describes how enterprises use leased lines to provide a dedicated WAN connection.
Leased lines are available in different capacities and are generally priced based on the bandwidth required and the distance between the two connected points.
Point-to-point links are usually more expensive than shared services such as Frame Relay. The cost of leased line solutions can become significant when they are used to connect many sites over increasing distances. However, there are times when the benefits outweigh the cost of the leased line. The dedicated capacity removes latency or jitter between the endpoints. Constant availability is essential for some applications such as VoIP or Video over IP.
A router serial port is required for each leased line connection. A CSU/DSU and the actual circuit from the service provider are also required.
Leased lines provide permanent dedicated capacity and are used extensively for building WANs. They have been the traditional connection of choice but have a number of disadvantages. Leased lines have a fixed capacity; however, WAN traffic is often variable leaving some of the capacity unused. In addition, each endpoint needs a separate physical interface on the router, which increases equipment costs. Any changes to the leased line generally require a site visit by the carrier.