1. 1 Chap. 4 Data link layer 3

2. 2 MAC(medium access control) model MAC  If two nodes are transmitted simultaneously, collision of two frames is occurred.  Hence, for successful transmission, MAC is necessary Master-slave communication model  One node is master, the other node is slave  Master regulates transmission of slaves  Advantage  Simple control  Disadvantage  Failure of master causes failure of transmission  Multi-master model

3. 3 Producer-consumer communication model  If any node wants to transmit a frame, it transmits as producer  At this time, the other nodes are consumer  Need to regulate transmission  To avoid collisions  To avoid hogging

4. 4 MAC method ‘Where’ and ‘How’ Where  Central  Greater control  Simple access logic at station  Avoids problems of co-ordination  Single point of failure  Potential bottleneck  Distributed How  Synchronous  Specific capacity dedicated to connection  TDMA (time division multiplexing access)  Asynchronous  In response to demand  round robin, reservation, contention

5. 5 Synchronous TMDA (time division multiplexing access)  Each node has allocated time slots  Cycle, time slot

6. 6 Round robin  Each nodes has fair transmission opportunity  Polling : central method  Representative master-slave model  Poll as indicator  Data as response  Selection for master’s transmission  Profibus-DP  RS232 or RS485 for implementation of upper layer

7. 7  Token passing : distributed method  Token for transmission opportunity  If any node has token, it transmits data for predefined period  Logical ring with sequence of nodes  Profibus-FMS

8. 8 Reservation  Uses time slot similar to TDMA  World-FIP  Example  Mini slot  If any node wants to transmit, it changes 1 of own mini slot

9. 9 Contention  No control of central method, no token of token passing of distributed method  Contention is perfect contention  Representative method of producer-consumer model  CSMA/CA of IEEE 802.3 Ethernet  CSMA/CA of IEEE 802.11 Wireless LAN  Non-destructive bitwise arbitration of CAN

10. 10 Comparison  Round robin  Good if many stations have data to transmit  Reservation and TDMA  Good for stream traffic  Contention  Good for burst traffic  Simple to implement  Efficient under moderate load  Tend to collapse under heavy load