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Phone switches have been around for decades in one fashion or another. While these switches originally connected analog circuits together, they grew into the digital communications network that we use today. Voice calls, just like data communications, traverse vast networks. Phone numbers on the voice network operate in a manner similar to IP packets over a corporate data network. Phone switches, therefore, form the IP routers of the voice world. But just like core and edge routers, phone switches are segmented into different classifications.

The three main classifications of phone switches are Class 3, Class 4 and Class 5. While most people have heard of Class 5 switches, they may not realize that these are just the beginning of the voice network. Usually located at the central office, Class 5 phone switches connect the home or the office telephone to the rest of the voice network, and can handle approximately 100,000 lines.

Class 4 switches are used to interconnect Class 5 switches and provide the internal switching network for a LEC (local exchange carrier) or RBOC (regional Bell operating company). They can also function as interconnect switches to a Class 3 switch or as Class 5 switches for a LEC.

Long-distance connections come from carriers that use a Class 3 switch to route phone calls across the nation or the globe to the local network containing the destination phone.