7.2 Encapsulation techniques

Packet- and cell-switched data are moved over wide area circuits by first encapsulating these data. This encapsulation typically embodies addressing and control information pertinent to the underlying transport media and, optionally, basic error checking. There are several encapsulation techniques of interest, including the following:

• Binary Synchronous Control (BSC or Bisync) developed by IBM in the mid-1960s. A half-duplex, point-to-point or multipoint, character-oriented protocol used for bidirectional transfer of character-oriented data.

• Data Communications Message Protocol (DCMP) similar to BSC, but developed by Digital Equipment Corporation (DEC). A half-duplex or full-duplex, point-to-point or multipoint, synchronous or asynchronous byte-count-oriented protocol.

• Synchronous Data Link Control (SDLC) developed by IBM in the early 1970s. The first true bit-oriented protocol, subsequently modified and adopted by the ISO as the ISO 4335 High-Level Data Link Protocol (HDLC) protocol and by ANSI as the ANSI X3.66 Advanced Data Communications Control Protocol (ADCCP).

• High-Level Data Link Control (HDLC) an international standard based on IBM's SDLC and very widely deployed in various forms. HDLC is a bit-oriented, simple, half-duplex or full-duplex, synchronous protocol for point-to-point or multipoint links.

• Serial Line Protocol (SLIP) the first encapsulation protocol to become widely used on simple dial-up serial lines. A subset of HDLC, now largely displaced by PPP, since it is limited to IP and limited in flexibility.

• Point-to-Point (PPP) based on HDLC and created in 1988 by the IETF and now the most popular encapsulation for point-to-point and dial-up links. PPP offers multiprotocol support and strong peer negotiation capabilities and is widely supported, offering excellent multivendor...