CSA - CAN/CSA-ISO/IEC-8802-3
Information Technology - Local and Metropolitan Area Networks - Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications
|Publication Date:||1 February 1995|
Basic Concepts. The Carrier Sense Multiple Access with Collision Detection (CSWCD) media access method is the means by which two or more stations share a common transmission medium. To transmit, a station waits (defers) for a quiet period on the medium (that is, no other station is transmitting) and then sends the intended message in bit-serial form. If, after initiating a transmission, the message collides with that of another station, then each transmitting station intentionally sends a few additional bytes to ensure propagation of the collision throughout the system. The station remains silent for a random amount of time (backoff) before attempting to transmit again. Each aspect of this access method process is specified in detail in subsequent sections of this standard.
This is a comprehensive standard for Local Area Networks employing CSWCD as the access method. This standard is intended to encompass several media types and techniques for signal rates of from 1 Mb/s to 20 Mb/s. This edition of the standard provides the necessary specifications for 10 Mb/s baseband and broadband systems, a 1W s ba seband system, and a Repeater Unit.
Architectural Perspectives. There are two important ways to view local area network design corresponding to
(1) Architecture. Emphasizing the logical divisions of the system and how they fit together.
(2) Implementation. Emphasizing actual components, their packaging and interconnection.
This standard is organized along architectural lines, emphasizing the large-scale separation of the system into two parts: the Media Access Control (MAC) sublayer of the Data Link Layer, and the Physical Layer. These layers are intended to correspond closely to the lowest layers of the IS0 Model for Open Systems Interconnection (see Fig 1-1). See IS0 7498:1984 1101 .l The Logical Link Control (LLC) sublayer and MAC sublayer together encompass the functions intended for the Data Link Layer as defined in the OS1 model.