WAN Connection Types

Meeting the connection requirements in an enterprise WAN takes careful planning, and is an ongoing process. To successfully deploy and manage your WAN environment, you must be comfortable with the technology involved.

WAN connections fall into three major categories: dedicated, packet switched, and circuit switched.

It is important to know the benefits and drawbacks of each, why you would use one over another, and how to configure and troubleshoot each.

Dedicated

Dedicated WAN connections, also sometimes referred to as point-to-point or leased lines, are the pinnacles of the WAN hierarchy. A dedicated WAN connection, in a nutshell, is a private line, dedicated to your private use, from one point to another. It is the WAN equivalent of an Ethernet cable from the central site to the branch office. Table 2.1 lists some of the pros and cons of the dedicated connection.

Table 2.1. Dedicated Connections

Pros	Cons
The bandwidth you purchase is dedicated to your exclusive use.	You pay for your bandwidth, regardless of whether you use it.
The connection is already established and ready to use at all times.	Because the provider cannot "oversubscribe" your line, it is usually more expensive.
Typically, it allows for higher connection speeds, even greater than T3.	It is only cost-effective with long connection times or critical data and short distances.

Circuit Switched

A circuit-switched WAN connection uses a dedicated circuit through the underlying network, typically the phone company, for the duration of the session. Circuit-switched technologies include asynchronous modem connections and ISDN. As Table 2.2 shows, circuit-switched connections have some distinct advantages as well as some major disadvantages.

Table 2.2. Circuit-Switched Connections

Advantages	Disadvantages
Circuit-switched connections are readily available almost anywhere.	Circuit-switched connections are usually not as fast as other WAN technologies.
Connections are established on an "as-needed" basis, instead of remaining on.	Suboptimal path selection can result in poor performance for the duration of the call.
Circuit-switched connections are inexpensive to set up and maintain.	The more data that needs to be transmitted, the longer the connection is active.

The single biggest advantage to a circuit-switched WAN connection is that they are typically available wherever there is a phone line. The speed limitation on the circuit-switched connection, which is a result of their wide availability and the underlying technology, is its biggest drawback.

The exception to the availability rule is ISDN. Although ISDN is digital, it is still circuit-switched, and it is not necessarily available everywhere that phone service is available. ISDN still needs a dedicated line run from the CO.

Packet Switched

Packet-switched network connections share a lot of the benefits of both dedicated and circuit-switched networks while minimizing the drawbacks. Like a circuit-switched network, the packet-switched network uses a public, readily available backbone, usually the phone company, for network connectivity. Unlike the circuit-switched network, each packet is switched independently of the others. If the network encounters a problem, resulting in the loss of one or more packets, it can route the rest of the transmission around the problem.

As with a dedicated circuit, a packet-switched circuit makes greater speeds available to you, typically T1 or better. Packet-switched connections have one major advantage over dedicated circuits, however, and that is cost.

Because you are sharing the "backbone" connection with other subscribers, the cost is usually a fraction of what a dedicated connection would be.