Token Bus.pptx

Token bus

1. IEEE 802.4 – Token Bus By – SAGAR ADHIKARI ROLL NO. - 129 1

2. IEEE 802.4 – Token Bus Definition: Physically, the token bus is a linear or tree-shaped cable to which the stations are attached . Logically the stations are organized into a Ring . 2

3. Introduction Token Bus is a physical bus that operates as a logical ring in LANs using Tokens . Token Bus (IEEE 802.4) combines the features of Ethernet and Token Ring . IEEE 802.4 token bus networks are constructed with 75-ohm coaxial cable using a bus topology. A token is passed among a stations. If a station wants to send a data, it must wait and capture the token. 3

4. The token is passed from one user to other in a Sequence (clockwise or anticlockwise). A station can only transmit the data when it has the token. The logical ring is formed based on the MAC address of the station in a Decreasing order. n stations takes T sec to send the frame . Station take nT sec to wait . 4

5. Token Bus 5

6. Token Bus Logical Ring Organization When the ring is initialized stations are inserted into it in order of station address from highest to lowest . Whenever a station acquires the token it can transmit frame for a specific amount of time . If a station has no data it passes the token immediately upon receiving it . Only one station can hold the token at a time . Do not occur any collision. 6

7. Each station is internally divided into four substations, one at each priority level  0, 2, 4, and 6 for traffic. When a token comes into the station, it passed internally to the priority 6 substation, which can begin transmitting its frames.  When its time expires, the token is passed to priority 4 substation . This process continues until either the priority 0 substation has sent all its frames or its time expires.  After this the token is passed to the next station in the ring. 7

8. Frame Format of Token Bus Preamble –  It is used for bit synchronization. Start Delimiter –  These bits marks the beginning of frame. Frame Control –  This field specifies the type of frame – data frame and control frames. Destination Address –  This field contains the destination address. Source Address –  This field contains the source address. Data –  If 2 byte addresses are used than the field may be upto 8182 bytes and 8174 bytes in case of 6 byte addresses. Checksum –  This field contains the checksum bits which is used to detect errors in the transmitted data. End Delimiter –  This field marks the end of frame. 8

9. Thank you References:- https://www.geeksforgeeks.org/token-bus-ieee-802-4/ https://www.youtube.com/watch?v=OpdwfKSjhn8&list=LLy17dJ0u9ir5pTs9K9rsZgQ&index=2&t=190s https://ecomputernotes.com/computernetworkingnotes/computer-network/ 9