1. ISCC Antalya, 2003WTRP1 UC Berkeley WOW Wireless Token Ring Protocol (WTRP) Performance Comparison with IEEE 802.11 Mustafa Ergen, Duke Lee, Raja Sengupta, Pravin Variaya

2. ISCC Antalya, 2003WTRP2 UC Berkeley WOW Automated Vehicle Platoon Real-time safety critical control over ad-hoc network Vehicles transmit control data in round robin every 20 ms Wireless Quality of Service

3. ISCC Antalya, 2003WTRP3 UC Berkeley WOW Motivations for WTRP Quality of service (real time applications) Distributed solution (robust against a single node failure) Flexible topology (token ring can be created with Pico cells) Safety critical applications (need fast recovery from failure) No need for clock synchronization (compared to TDMA) Partial connectivity (hidden terminal problem)

4. ISCC Antalya, 2003WTRP4 UC Berkeley WOW Motivations for WTRP Quality of service (real time applications) Distributed solution (robust against a single node failure) Flexible topology (token ring can be created with Pico cells) Safety critical applications (need fast recovery from failure) No need for clock synchronization (compared to TDMA) Works on partial connectivity (no hidden terminal problem)

5. ISCC Antalya, 2003WTRP5 UC Berkeley WOW Motivations for WTRP Quality of service (real time applications) Distributed solution (robust against a single node failure) Flexible topology (token ring can be created with Pico cells) Safety critical applications (need fast recovery from failure) No need for clock synchronization (compared to TDMA) Works on partial connectivity (no hidden terminal problem) centralized (802.11 PCF, Bluetooth)distributed (token ring)

6. ISCC Antalya, 2003WTRP6 UC Berkeley WOW Motivations for WTRP Quality of service (real time applications) Distributed solution (robust against a single node failure) Flexible topology (token ring can be created with Pico cells) Safety critical applications (need fast recovery from failure) No need for clock synchronization (compared to TDMA) Works on partial connectivity (no hidden terminal problem) 14312 TDMA

7. ISCC Antalya, 2003WTRP7 UC Berkeley WOW Motivations for WTRP Quality of service (real time applications) Distributed solution (robust against a single node failure) Flexible topology (token ring can be created with Pico cells) Safety critical applications (need fast recovery from failure) No need for clock synchronization (compared to TDMA) Works on partial connectivity (no hidden terminal problem)

8. ISCC Antalya, 2003WTRP8 UC Berkeley WOW Additional Challenges From Wireless Medium Partial connectivity (unable to hear all nodes in a ring) Support for multiple rings Self-managed admission control Frequent packet loss, corruption

9. ISCC Antalya, 2003WTRP9 UC Berkeley WOW The Wireless Token Ring Protocol (WTRP) is a medium access control protocol for wireless networks in mission critical systems. It supports quality of service in terms of bounded latency and reserved bandwidth. The token passing defines the transmission order, and each token is forced to give up the token after a specified amount of time. Each ring has unique ring id based on unique MAC address of one of the stations of the ring. (The station is called the owner of the ring). When owner leaves the ring, another station elects itself to be the owner of the ring.

10. ISCC Antalya, 2003WTRP10 UC Berkeley WOW Connectivity Table Each node builds and updates connectivity table that contains information of all stations in its reception range, and transmission order of the nodes in its ring

11. ISCC Antalya, 2003WTRP11 UC Berkeley WOW Unique Priority of Token Based on ring address and generation sequence number pair. Station only accept token that has higher priority than the last token that the station has accepted. ring addressgeneration sequence … Implicit ACK ACK is thought to be received when the successor initiates a transmission or token.

12. ISCC Antalya, 2003WTRP12 UC Berkeley WOW Descriptions (Operations) Joining : Stations periodically invite other nodes to join the ring by broadcasting the available resources left in the medium Leaving: When B wants to leave, it requests A to connect to its successor, C. If A does not have connection with C, then it connects to the next node in terms of the transmission order of the ring. A B C D E F 1. SET_SUC C 2. SET_PRED A Invite Contend Token

13. ISCC Antalya, 2003WTRP13 UC Berkeley WOW Descriptions (Management) Ring Recovery Able to recover quickly by keeping information about topology of the ring, recovers from multiple simultaneous faults by taking increasingly drastic actions AB C D E F 2. SET_PRED A 1. Retransmit TOKEN Token Recovery Multiple token is deleted using unique priority of token based on generation sequence number and token ring address pair. 2 2 6 6 6 2 6 6 2 2 6 6 6 2 6

14. ISCC Antalya, 2003WTRP14 UC Berkeley WOW WTRP

15. ISCC Antalya, 2003WTRP15 UC Berkeley WOW IEEE 802.11

16. ISCC Antalya, 2003WTRP16 UC Berkeley WOW A B A B A B 1 3 2 Token Rotation Time C C C

17. ISCC Antalya, 2003WTRP17 UC Berkeley WOW Robustness

18. ISCC Antalya, 2003WTRP18 UC Berkeley WOW Fairness

19. ISCC Antalya, 2003WTRP19 UC Berkeley WOW Throughput

20. ISCC Antalya, 2003WTRP20 UC Berkeley WOW Conclusions The wireless token ring protocol (WTRP) is a medium access control protocol for wireless networks in mission critical systems. It supports quality of service in terms of bounded latency and reserved bandwidth. WTRP is efficient in the sense that it reduces the number of retransmissions due to collisions. It is fair in the sense that each station takes a turn to transmit and is forced to give up the right to transmit after transmitting for a specified amount of time. It is a distributed protocol that supports many topologies since not all stations need to be connected to each other or to a central station. It can be used with an admission control agent for bandwidth or latency reservations. WTRP is robust against single node failure. WTRP is designed to recover gracefully from multiple simultaneous faults.