7.1.WAN Connection Types
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A WAN connection can generally be classified into one of three categories:
A connection interconnecting two sites. This logical connection might physically connect through a service provider’s facility or a telephone company’s central office (CO).
The expense of a dedicated leased line is typically higher than other WAN technologies offering similar data rates because with a dedicated leased line, a customer does not have to share bandwidth with other customers.
A common Layer 2 protocol that could run over a dedicated leased line is Point-to-Point Protocol (PPP).
A T1 circuit, as shown in Figure below , is an example of a dedicated leased line technology commonly found in North America.
A connection that is brought up on an as-needed basis. In fact, a circuit-switched connection is analogous to a phone call, where you pick up your phone, dial a number, and a connection is established based on the number you dial.
Integrated Services Digital Network (ISDN) can operate as a circuit-switched connection, bringing up a virtual circuit (VC) on demand.
This approach to on-demand bandwidth can be a cost savings for some customers who only need periodic connectivity to a remote site. Figure below illustrates a circuit-switched connection.
Similar to a dedicated leased line because most packet-switched networks are always on.
However, unlike a dedicated leased line, packet-switched connections allow multiple customers to share a service provider’s bandwidth.
Even though bandwidth is being shared among customers, customers can purchase a service-level agreement (SLA), which specifies performance metrics (for example, available bandwidth and maximum delay) guaranteed for a certain percentage of time.
For example, an SLA might guarantee a customer that he has a minimum of 5 Mbps of bandwidth available 80 percent of the time.
Frame Relay, is an example of a packet-switched connection. As shown in Figure below , a Frame Relay network allows multiple customers to connect to a service provider’s network, and virtual circuits (VCs, as indicated with the dashed lines) logically interconnect customer sites.
