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. In the case of audio and video transmissions, bits must also arrive at the right time. A seemingly endless set of protocols brings order to the bits.
Protocols organize data into groups called frames, cells, and packets.
Each contains a header and a payload, and sometimes a trailer. The header holds a destination address and may include the length of the frame or packet and a checksum for error correction. Some headers also contain time-stamp information, which tells the receiver how long the data took to travel over the network. That's important in voice and video transmissions where the timing affects the quality of the delivery. These protocols handle the processing of items such as Web pages, data files, and e-mail, respectively.