Asynchronous Transfer Mode, or ATM for short, is a cell relay network protocol which encodes data traffic into small fixed-sized (53 byte; 48 bytes of data and 5 bytes of header information) cells instead of variable sized packets (sometimes known as frames) as in packet-switched networks (such as the Internet Protocol or Ethernet). It is a connection-oriented technology, in which a connection is established between the two endpoints before the actual data exchange begins
Digital Subscriber Line, or DSL, is a family of technologies that provide digital data transmission over the wires used in the "last mile" of a local telephone network. Typically, the download speed of DSL ranges from 128 kilobits per second (kbit/s) to 24,000 kbit/s depending on DSL technology and service level implemented
A leased line is a (usually) symmetric
telecommunications line connecting two locations together. Unlike traditional PSTN lines they do not have a telephone number, each side of the line being permanently connected to the other. They can be used for telephone, data or Internet services.
In the U.K., leased lines are usually available at speeds of 64k, 128k, 256k, 512k, 2M and provided to the customer on X.21 presentation. Higher speeds are available on alternative interfaces.