When designing a wide area network (WAN), one of the most challenging issues is choosing the correct connection type. You need to consider several factors before implementation can begin—and a solid understanding of all the connection types is critical to making the right choice. Most carriers offer three connection types:
- Circuit-switched connections
- Packet-switched or cell-switched connections
- Dedicated connections
Each type of connection has its advantages and disadvantages. This article will summarize what each connection type has to offer, with consideration given to bandwidth, availability, cost, and ease of management.
Circuit-switched connections are currently the most popular type of WAN connection. Circuit switching transmits data streams and datagrams across dedicated physical circuits. To provide asynchronous dial-in and ISDN services, the telephone companies use circuit switching.
The public switched telephone network (PSTN) uses circuit-switched technology to provide asynchronous services (otherwise known as normal telephone service). Asynchronous dial-in connections offer a low-bandwidth, easily managed, cost-effective solution that is available almost anywhere in the world.
Integrated Services Digital Network (ISDN) is a digital circuit switching technology used to transport voice, data, and video. With speeds up to 1.54 Mbps (T1) in North America and 2.048 Mbps (E1) in Europe, ISDN is a low- to medium-bandwidth solution with relatively low cost. However, availability is somewhat limited and configuration and support are more difficult than for asynchronous communication.
Packet-switched or cell-switched connections
Packet-switched and cell-switched networks are point-to-point connections that travel across a public carrier’s network. While these types of connections are more expensive than asynchronous dial-in and ISDN connections, packet-switched and cell-switched services can provide very high bandwidth solutions at a lower cost than dedicated connections. Examples of packet-switched and cell-switched networks include Frame Relay (packet-switched), X.25 (packet-switched), and Asynchronous Transfer Mode or ATM (cell-switched).
Frame Relay is one of the most popular methods of packet-switched networks. With support for a variety of network protocols, Frame Relay can provide flexible, high-bandwidth solutions for most any network. Frame Relay service charges are usually based on the Committed Information Rate (CIR). The CIR is the amount of bandwidth guaranteed by the service provider. The larger the CIR, the more costly the Frame Relay solution becomes. In addition, designing and supporting Frame Relay networks can be a nightmare. Therefore, a highly skilled network professional is required to install and troubleshoot Frame Relay networks.
X.25 is a legacy, packet-switched, data link layer protocol designed in the 1970s. X.25 was designed to run over noisy analog lines and, therefore, has built-in error-checking mechanisms. The overhead required to perform error checking makes X.25 a low-bandwidth solution by today’s standards. However, if you must deploy a WAN in an environment that contains noisy lines and legacy network equipment, X.25 is still a viable solution.
ATM is quickly becoming the connection method of choice for high-speed communications. ATM is a cell-switching, multiplexing technology, which provides connection-oriented, guaranteed delivery of fixed-length cells. ATM supports speeds of up to OC-192 (that’s 10Gbps), making ATM the solution for high-speed networks supporting voice, video, and data. Of course, all these features come with a price, and when you calculate the monthly carrier fees and the salaries of the highly skilled staff required to support an ATM network, that price can be astronomical.
Dedicated connections are point-to-point serial connections that offer fixed, permanent connections to remote networks. Dedicated links can provide up to T3 (44.736 Mbps) speeds over a public carrier’s network. Since dedicated connections are fixed, permanent connections, there is less overhead required to establish communication between two sites. And because dedicated connections offer low overhead and high-speed transmissions, they’re excellent solutions for companies requiring high-bandwidth, 24/7 WAN connections. However, carrier fees and support costs for dedicated connections are on the high side.
Choosing the best WAN connection
Determining the best WAN connection type for your business can be a difficult task. Properly analyzing WAN traffic patterns and requirements is the key to successfully deploying WAN solutions. For complete information on selecting and configuring your WAN connections using Cisco equipment, check out Cisco IOS 12.0 WAN Solutions.
Warren Heaton Jr., MCSE+I, CCNP, CCDP, is the Cisco program manager for A Technological Advantage in Louisville, KY.If you'd like to share your opinion, please post a comment below or send the editor an e-mail.