Synchronous Data Link Control

Synchronous Data Link Control (SDLC) is a computer communications protocol. It is the layer 2 protocol for IBM's Systems Network Architecture (SNA). SDLC supports multipoint links as well as error correction. It also runs under the assumption that an SNA header is present after the SDLC header. [harv|Odom|2004.] . SDLC was mainly used by IBM mainframe and midrange systems; however, implementations exist on many platforms from many vendors. The use of SDLC (and SNA) is becoming more and more rare, mostly replaced by IP-based protocols or being tunneled through IP (using AnyNet or other technologies).Fact|date=June 2008

In 1975, IBM developed the first bit-oriented protocol, SDLC,Fact|date=June 2008 from work done for IBM in the early 1970s.harv|Friend|1988|p=188.] This de facto standard has been adopted by ISO as High-Level Data Link Control (HDLC) in 1979 and by ANSI as Advanced Data Communication Control Procedures (ADCCP). The latter standards added features such as the Asynchronous Balanced Mode, frame sizes that did not need to be multiples of bit-octets, but also removed some of the procedures and messages (such as the TEST message). [harv|Friend|1988|p=191.]

SDLC operates independently on each communications link, and can operate on point-to-point
multipointor loop facilities, on switched or dedicated, two-wire or four-wire circuits, and with full-duplex and half-duplex operation. [harv|Pooch|1983|p=302.] A unique characterstic of SDLC is its ability to mix half-duplex secondary stations with full-duplex primary stations on four-wire circuits, thus reducing the cost of dedicated facilities. [harv|Pooch|1983|p=303.]

Intel used SDLC as a base protocol for BitBus, still popular in Europe fieldbus and included support in several controllers (i8044/i8344, i80152). The 8044 controller is in production by third party vendors.

Notes

References

*cite book
first=Wendell
last=Odom
title=CCNA INTRO Exam Certification Guide: CCNA Self-study
publisher=Cisco Press
location=Indianapolis, IN
year=2004
isbn=1-58720-094-5
*cite book
last=Friend
first=George E.
coauthors=John L. Fike, H. Charles Baker, John C. Bellamy
title=Understanding Data Communications
edition=2nd Edition
year=1988
publisher=Howard W. Sams & Company
location=Indianapolis
isbn=0-672-27270-9
*cite book
last=Pooch
first=Udo W.
coauthors=William H. Greene, Gary G. Moss
title=Telecommunications and Networking
publisher=Little, Brown and Company
location=Boston
year=1983
isbn=0-316-71498-4

External links

[http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/sdlcetc.htm Cisco page on Synchronous Data Link Control and Derivatives]

[http://www.bitbus.org Bitbus community site.]