1. Distributed-Queue Access for Wireless Ad Hoc Networks Authors: V. Baiamonte, C. Casetti, C.-F. Chiasserini Dipartimento di Elettronica, Politecnico di Torino, Torino, Italy From: Energy-Efficient Wireless Communications and Networks (EWCN 2004) Yuhe-yi Wang Jan 3, 2006

2. Outline 802.11 Wireless MAC 802.6 DQDB Proposed Method -DQDC Simulation Result Conclusion

3. 802.11 Wireless MAC- Overview Defines MAC and PHY layers for a LAN with wireless connectivity

4. 802.11 Architecture Can be with/without infrastructure support With A centralized controller for each cell, AP Without Each node is a Station. Each communicates directly with each other. Mobile ad-hoc configuration mode

5. 802.11- Two access control services contention-based DCF – Distributed Coordination Function contention-free access control services PCF -- Point Coordination Function polling principle Centralized MAC algorithm

6. DCF Basic access method of IEEE 802.11 Specifies the use of CSMA with CA CSMA/CA Carrier Senses: Every node senses the carries before transmitting If the node detects carrier then defers transmitting Multiple Access Transmissions by one node are generally “ received ” by all other nodes using the medium

7. CSMA/Collision Avoidance Each node must inform other nodes of an intent to transmit CSMA/CA With RTS/CTS When station A wishes to transmit to station B, it sends a Request-to-Send (RTS) packet to B; Destination + Length of Message If station B hears the RTS, and it is not currently deferring, it immediately replies with a Clear-to-Send(CTS) packet to A

8. CSMA/CA with RTS/CTS Any station overhearing an RTS defers all transmissions until some time after the associated CTS packet world have finished random backoff period NAV (Network Allocation Vector) alerts all others to back off for a duration of the transmission RTS CTS Data ACK 4-way handshake

9. Introduction to Interframe Space Concept DIFS: Distributed InterFrame Space SIFS: Short InterFrame Space

10. Basic Transmission Algorithm Sense the medium (perform physical channel assessment) Medium Idle? NAV=0? Transmit Frame Collision? Random Backoff Time Yes No Yes No Yes

11. DQDB (Distributed Queue Dual Bus) MAC layer specified in IEEE 802.6 standard used in wired MANs. Can be 30 miles long with 34~155 Mbps Composed of 2 bus lines with stations attached to both        slot source slot sink slot sourceBus B Bus A 1 2 3 4   5

12. Function of DQDB Transmitting Data Node acquires slot Sets header Copies data into slot Cells propagate to end of bus (absorbed by sink) Copied by intended destination on way        slot source slot sink slot sourceBus B Bus A 1 2 3 4   5

13. Proposed Method- DQDC Distributed Queue Dual Channel Propose a MAC protocol for wireless ad hoc networks Key idea relies on DCF scheme with DQDB protocol 2 separate channels: a control and a data Objective: to achieve 100% utilization of the data channel, minimizing the collision probability on it. Simulation result by ns-2

14. DQDC Overview Data channel Data frames, and ACKs Control channel STA contend for future access to data channel Successful STA stored into a virtual distributed queue system only switch to data channel when at the top of the queue

15. DQDC scheme

16. DQDC in Detail each STA maintains 2 counters Access Counter (AC) Countdown Counter (CC) Access Counter (AC) a global counter that ++ every time a successful contention on control channel -- each transmission on data channel

17. DQDC in Detail (contd.) Countdown Counter (CC) associated with a single data frame waiting to be transmitted reset to current AC value while winning a control-channel contention. -- when start of a transmission on data channel 1: the station is up next for transmits

18. More Than one Frame to Send How about STA with several frames to send? Allowed to occupy more entries at once in the virtual queue. local vector to store each pending AC. CC will be reset to 0 or set to the value for the next entry.

19. Data Channel Access Scheme

20. Control Channel Access Scheme

21. Low-traffic Contention AC counting down to 0 Original counter mechanism doesn ’ t work for contention Solution: post-backoff phase backoff counter to down count if NO transmission on DATA decrease to 0 allows to transmit

22. Missed Transmission Opportunities What if STA that won the contention is turned off? Can be detected when idle channel more than SIFS+SIFS following the ACK AC is > 0 Solution: Decrement AC, CC as if the transmission had occurred.

23. Simulation Results- Scenario Simple Network Scenario: 4 stations, which communicate in pairs. Ad Hoc Mode All within radio proximity Trans. Rate: Data: 11 Mbps Control: 1 Mbps No multihop trans

24. Simulation Results- Throughput

25. Simulation Results- Packet Delay

26. Simulation Results- Energy per Successful Packet

27. Conclusions Proposed DQDC: bases DCF + DQDB (two buses) key idea Goal: achieving 100% utilization of the data channel, minimizing the collision probability on it. DQDC Performance in throughput, delay, energy better than standard DCF Issue: Simulation needs to consider more complex scenarios