1.1 Remote Access
1.1.2 Dedicated connections
Dedicated connections, referred to as leased lines, provide links that are continuously available; they are effective in environments where a steady flow of traffic must cross the WAN. Leased lines are used primarily to provide full-time WAN connectivity between LANs. These connections are referred to as point-to-point because the source and destination are exclusively tied to each other. The use of leased lines is not cost-effective when the link isn’t used on a full-time basis.

As shown in Figure , a point-to-point dedicated link provides a single, preestablished WAN path from the customer premises, through a carrier network (the telephone company), to a remote network. The established path is permanent and fixed for each remote network that is reached through the carrier facilities. Point-to-point links are reserved full-time by the carrier company for the private use of the customer.

The private nature of a dedicated leased-line connection allows a corporation to maximize its control over the WAN connection. Leased lines also offer high speeds up to T3/E3 levels (45 Mbps (Megabits per second)/34Mbps). They are ideal for high-volume environments with steady-rate traffic patterns. However, because the line is not shared, they tend to be more costly.

As a general rule, leased-line connections are most cost-effective when the following situations occur:

  • Long connect times
  • Shorter distances

Some WAN services, such as T1, provide a fixed fee for local-loop access for both locations, and then provide a distance fee for linking those two locations.

Dedicated leased lines typically require synchronous serial connections. The dedicated connections are made by using the router's synchronous serial ports with bandwidth of up to 34 Mbps on an E3 and 45 Mbps on a T3, available through the use of a channel service unit/data service unit (CSU/DSU). Different encapsulation methods at the data link layer provide flexibility and reliability for user traffic. Typical connections on a dedicated network employ 56 kilobits per second (Kbps), 64 Kbps, T1 (1.544 Mbps), E1 (2.048 Mbps), T3, and E3 technologies.

The synchronous serial standards that are supported on most routers are as follows (EIA/TIA stands for Electronic Industries Association/Telecommunications Industry Association):

  • EIA/TIA-232
  • EIA/TIA-449
  • V.35
  • X.21
  • EIA-530

As shown in Figure , a CSU/DSU is a digital interface device (or sometimes two separate digital devices) that adapts the physical interface on a data terminal equipment (DTE) device (such as a terminal) to the interface of a data communications equipment (DCE) device (such as a switch) in a switched carrier network. The CSU/DSU also provides signal timing for communication between these devices. The graphic shows the placement of the CSU/DSU. Different encapsulation methods at the data link layer provide flexibility and reliability for user traffic.