These multiservice switches form what is sometimes called an aggregation network. Another set of switches may reside between the aggregation network and the core network. For example, a service provider may use an IP service switch to host a small company's firewall so the customer doesn't have to invest in a firewall's hardware or maintenance. A communications service provider may use IP service switches to provide a VPN so customers can get access to their Intranet or corporate network from outside the company. Not all telecom networks have separate IP service switches.
Some switches combine two or more functions into one chassis.
For example, some multiservice switches can add IP services. Switch manufacturers also combine other functions. A switch may combine an ATM switch with a telecom switch or with a voice gateway. The integrated switches let businesses that already use IP phones make calls over the PSTN, the network that currently carries most phone conversations. An exchange carrier must manage all those bits to ensure data and voice signals arrive at the proper destinations.