ISCC Antalya, 2003 WTRP 1

UC Berkeley WOWWireless Token Ring Protocol(WTRP)

Performance Comparison with IEEE 802.11

Mustafa Ergen, Duke Lee, Raja Sengupta, Pravin Variaya

ISCC Antalya, 2003 WTRP 2

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

ISCC Antalya, 2003 WTRP 3

UC Berkeley WOW

Motivations for WTRPQuality 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)

ISCC Antalya, 2003 WTRP 4

UC Berkeley WOW

Motivations for WTRPQuality 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)

ISCC Antalya, 2003 WTRP 5

UC Berkeley WOW

Motivations for WTRPQuality 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)

ISCC Antalya, 2003 WTRP 6

UC Berkeley WOW

Motivations for WTRPQuality 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)

1 43 12

TDMA

ISCC Antalya, 2003 WTRP 7

UC Berkeley WOW

Motivations for WTRPQuality 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)

ISCC Antalya, 2003 WTRP 8

UC Berkeley WOW

Additional Challenges From Wireless Medium

Partial connectivity (unable to hear all nodes in a ring)Support for multiple ringsSelf-managed admission controlFrequent packet loss, corruption

ISCC Antalya, 2003 WTRP 9

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.

1

1

77

5

5

44

ISCC Antalya, 2003 WTRP 10

UC Berkeley WOW

Connectivity TableEach 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

ISCC Antalya, 2003 WTRP 11

UC Berkeley WOW

Unique Priority of TokenBased 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 address generation sequence …

Implicit ACKACK is thought to be received when the successor initiates a transmission or token.

ISCC Antalya, 2003 WTRP 12

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

DE

F

1. SET_SUC C

2. SET_PRED A

Invite Contend Token

Token

ISCC Antalya, 2003 WTRP 13

UC Berkeley WOWDescriptions (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

A B C

DE

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.

22

66

6

2

6

62

2

66

6

2

6

ISCC Antalya, 2003 WTRP 14

UC Berkeley WOW

WTRP

ISCC Antalya, 2003 WTRP 15

UC Berkeley WOW

IEEE 802.11

ISCC Antalya, 2003 WTRP 16

UC Berkeley WOW

A

B

A

B

A

B1111 33332222

Token Rotation Time

C CC

ISCC Antalya, 2003 WTRP 17

UC Berkeley WOW

Robustness

ISCC Antalya, 2003 WTRP 18

UC Berkeley WOW

Fairness

ISCC Antalya, 2003 WTRP 19

UC Berkeley WOW

Throughput

ISCC Antalya, 2003 WTRP 20

UC Berkeley WOW

ConclusionsThe 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.