Introduction to Media Access Control Protocols Yerang Hur and Jiaxiang Zhou System Design Research Lab. Dept. of Computer and Information Science

Some Examples of MAC Layer Protocols for Control Systems CSMA/CD: Carrier Sense Multiple Access with Collision Detection – Ethernet Token bus –ControlNet CAN : bitwise priority –DeviceNet (Rockwell), SDS (Honeywell) TDMA : Time Division Multiple Access –TTP

Controller Area Network (CAN) protocol mainly used in the automotive industry used for transmitting short messages 1M bps a message with a unique identifier MAC: CSMA with arbitration on message priority simultaneous transmission arbitrated based on the message priority

CAN Message Frame arbitration field Frames do not contain addresses. 11 bits Identifier: the identifier with the smallest value has the highest priority. control field data field 0-8 bytes CRC 16 bits ACKEOF 6 bits SOF 2bits7bits 1bit

CAN Bus Arbitration Bit stream is synchronized on the start bit. A sender waits till the bus is free and then starts to send the identifier bit by bit. A sender listens to the network and if a sender observes a bit different from the one itself sends, it stops transmission and yields to other nodes.

TDMA frame slot