7.4.1 Leased lines and satellite links

Leased lines are point-to-point, duplex, dedicated links, which are permanently available, typically at speeds between 64 Kbps and 45 Mbps. Leased lines may be used for both voice or data traffic. Data traffic is normally encapsulated in PPP or HDLC. Leased lines assure privacy, since none of the bandwidth provided is shared with other users. Typically the customer pays an installation cost and a monthly rental (usually based on distance) to the provider. Leased lines are available in both analog and digital formats, at a range of speeds. Typically they require a single interface at each end of the circuit to terminate the connection. Private leased lines and satellite links are a mature, established, reliable technology and have been used for many years in the core of large international and regional backbone networks. They form a natural extension for LAN-LAN internetworking and for many applications still represent a good choice.

If utilized efficiently, leased lines represent a reasonable way to build a small to medium-sized network, and they are particularly good for LAN extension applications. However, wherever there is a lull in traffic you are effectively still paying for use. For large networks this limits scalability, since the central site may require dozens of expensive ports over multiple concentrators. One of the more flexible technologies to emerge is the use of channelized circuits, where high-bandwidth circuits are broken up into increments (typically 64-Kbps chunks) and may terminate at different destinations. In...