Distributed-Queue%20Access%20for%20Wireless%20Ad%20Hoc%20Networks

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

4-way handshake
9
Introduction to Interframe Space Concept

• DIFS Distributed InterFrame Space
• SIFS Short InterFrame Space

10
Basic Transmission Algorithm
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DQDB (Distributed Queue Dual Bus)

• MAC layer specified in IEEE 802.6 standard used
  in wired MANs.
• Can be 30 miles long with 34155 Mbps
• Composed of 2 bus lines with stations attached to
  both

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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

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

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DQDC scheme
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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

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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.

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Data Channel Access Scheme
20
Control Channel Access Scheme
21
Low-traffic Contention

• AC counting down to 0
• Original counter mechanism doesnt 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 SIFSSIFS following the
  ACK
• AC is gt 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