Wan Link Connection Options


Many options for implementing WAN solutions are currently available. They differ in technology, speed, and cost. Familiarity with these technologies is an important part of network design and evaluation.
WAN connections can be either over a private infrastructure or over a public infrastructure, such as the Internet.
Private WAN Connection Options
Private WAN connections include both dedicated and switched communication link options.
Dedicated communication links
When permanent dedicated connections are required, point-to-point lines are used with various capacities that are limited only by the underlying physical facilities and the willingness of users to pay for these dedicated lines. A point-to-point link provides 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 also called leased lines.
Switched communication links
Switched communication links can be either circuit switched or packet switched.
Circuit-switched communication links-Circuit switching dynamically establishes a dedicated virtual connection for voice or data between a sender and a receiver. Before communication can start, it is necessary to establish the connection through the network of the service provider. Examples of circuit-switched communication links are analog dialup (PSTN) and ISDN.
Packet-switched communication links-Many WAN users do not make efficient use of the fixed bandwidth that is available with dedicated, switched, or permanent circuits because the data flow fluctuates. Communications providers have data networks available to more appropriately service these users. In packet-switched networks, the data is transmitted in labeled frames, cells, or packets. Packet-switched communication links include Frame Relay, ATM, X.25, and Metro Ethernet.
Public WAN Connection Options
Public connections use the global Internet infrastructure. Until recently, the Internet was not a viable networking option for many businesses because of the significant security risks and lack of adequate performance guarantees in an end-to end Internet connection. With the development of VPN technology, however, the Internet is now an inexpensive and secure option for connecting to teleworkers and remote offices where performance guarantees are not critical. Internet WAN connection links are through broadband services such as DSL, cable modem, and broadband wireless, and combined with VPN technology to provide privacy across the Internet.
Dedicated Connection Link Options
Leased Lines
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.

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