Leased Lines are a dedicated communication channel between two or more nodes. Usually, it is a pre-established WAN connection from the customer premises to the service provider network. The lines are usually leased from a service provider; therefore it is called a leased line. The leased lines work as a dedicated tunnel from one point to another point. It is guaranteed bandwidth for network traffic between locations for a fixed rent. Generally, these lines are used for Internet services. T1 lines are the example of leased lines, which have the same data rate as symmetric DSL.
Physically these lines are not dedicated, but it is the reserved circuit between two different points. The lease lines are mostly run on fiber optic cables to provide large bandwidth and speed. Due to large bandwidth, reserved circuits, and enhanced security these lines are quite expensive, so large companies can afford these lines. The lease lines are also known as leased circuits, serial link, serial line, point-to-point link, and T1/E1 or T3/E3 lines. Leased lines are present different capacities, based on the cost and bandwidth required including the distance between the two connected points.
The standards usually used for the leased lines are T1, E1, T3, E3, OC, and STM. T1 link supports 1.544 Mb/s, E1 links support 2.048 Mb/s, T3 supports 43.7 Mb/s, E3 connection supports 34.368 Mb/s. Optical Carrier (OC) transmission rates are different levels, The basic level of OC is OC1 with 51.84 Mbps. The STM is also different levels; the basic level of STM is STM-1, which is support data rate up to 155.52 Mbps. VPN virtual private network is an alternative type of leased line. Using VPNs allow to create a virtual and secure connection between different locations.
Point-to-point links require minimal skills to install and maintain links. Point-to-point links generally present high-quality services. Due to a dedicated link generally, there is no latency or jitter between the endpoints even the bandwidth is slow. Constant availability is necessary for large companies; therefore Point-to-point communication links provide permanent, dedicated capacity.
The leased lines are generally dedicated Point-to-point links, which is the most costly type of WAN connection. The cost becomes considerably when an organization needs to connect many sites over long distances. Leased lines have a fixed capacity so that the bandwidth of the line seldom matches the need exactly. Any change to the leased line generally requires a site visit by ISP personnel to adjust capacity.