McMAC: A Parallel Rendezvous MultiChannel MAC Protocol

1
McMAC A Parallel Rendezvous Multi-Channel MAC
Protocol

• Hoi-Sheung Wilson So
• Jean Walrand
• Jeonghoon Mo

2007 WCNC
2
Outline

• Introduction
• McMAC protocol description
• Network and simulation model
• Performance comparison with other protocols
• Design tradeoffs
• Conclusion

3
Introduction

• Using a multi-channel MAC protocol, different
  devices can transmit in parallel on distinct
  channels.
• Single rendezvous protocols
• Dedicated Control Channel approach 14,15,5
• Split-phase protocols 3,10
• Common-hopping approach 12,13
• Multiple rendezvous protocols
• SSCH 2
• McMAC

4
McMAC protocol description

• A sender must know the channel on which its
  receiver is listening.
• Each node use MAC addr. as a random generator
  seed to generate default sequence.
• If a sender knows the seed, the boundary, the
  current offset into a receivers sequence, it can
  predict the hopping pattern of a receiver.
• The sender must know whether that channel is idle
  or not.
• Use traditional RTS/CTS.
• Listen for carrier after switching channel to
  avoid collision.

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McMAC protocol description (cont.)

• Random Channel Hopping
• Devices hop according to a pseudo-random hopping
  sequence.
• Discovery
• A device discovers its 1-hop neighbors and adds
  to neighbor table.
• Synchronization
• Each node estimates the relative speed of clocks
  of its neighbor to track the hopping boundary
  without global synchronization.
• Rendezvous and Scheduling
• When to change channel

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McMAC protocol description (cont.)

• Random Channel Hopping
• Each device hops over all M available channels in
  a pseudo-random fashion using its own MAC address
  as the seed
• Time is divided into Small Slots(Ts) and Big
  Slots(Tb)
• X(t) 16807 X(t-1) mod (231-1) 7
• X(t) X(t) mod M

Ts shortest carrier sensing time of CSMA
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McMAC protocol description (cont.)

• Discovery
• Every packet sent includes the hopping signature
  of the sender, namely the current time (Ts, Tb)
  and the seed of the sender.
• Initial
• 0s10s A node turn on, it monitors a well-know
  channel
• 10sThe node start following default hopping
  sequence, and beacons once every second with a
  small random delay
• If a node receives any pkt, if the sender is a
  newcomer, the receiver records the hopping
  signature of the sender
• Then the receiver sends a pkt with its own
  hopping signature to speedup mutual discovery.

8
McMAC protocol description (cont.)

• Synchronization
• For supporting multi-channel MAC, only pair-wise
  synchronization between neighbors, rather than
  global synchronization, is necessary
• Every packet includes a 32-bit time stamp
• The neighbors then compare the differences in the
  rate at which the clocks of the sender advances
  versus that of their own.

9
McMAC protocol description (cont.)

• Rendezvous and Scheduling
• Using McMAC, rendezvous can happen on multiple
  channels simultaneously among several pairs of
  senders and receivers.
• Each device keeps one packet queue per
  destination to avoid head-of-line blocking and to
  facilitate scheduling.
• With Pdeviate, it allow to temporary deviate from
  its default hopping sequence
• If it decides to deviate, it will choose among
  the channels for which there is at least one
  receiver

Sender
Receiver
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Network and simulation model

• 802.11b
• 20 devices
• 3 channels with a rate of 2 Mbps each.
• 802.11a
• 40 devices
• 12 channels with a rate of 6 Mbps each.
• In both scenarios
• channel switching time is assumed to be 100µs,
• RTS/CTS time is 200µs and 812µs

11
Performance comparison with other protocols

• Short 1KB
• Long 10KB

12
Design tradeoffs

• LQF vs. Random Scheduling
• 10 nodes
• 3 channel
• Link speed 2Mbps
• Each node have 5
• CBR flow to 5
• neighbor

13
Design tradeoffs (cont.)

• Effects of Pdeviate
• Pdeviate 0.20.8
• Load0.20.8
• Traffic is a mix of 50 CBR flows and 50 random
  short file arrivals.

14
Design tradeoffs (cont.)

• Adaptive Probability of Deviation
• Modify the scheduler to always checks if a
  potential receiver will happen to be on the same
  channel as itself.

2 time
3 time
15
Design tradeoffs (cont.)

• Implementation Results
• Telos sensor network platform running TinyOS
• 802.15.4 radio operating in the 2.4GHz ISM band
• BigSlot 3.9ms
• Switching time300µs
• 4 channels
• They beacon every 3 seconds. Each beacon contains
  a 4-byte time stamp.
• 15 nodes
• McMAC correctly coordinates senders and receivers
  to rendezvous on the right channel about 98 of
  the times.

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Conclusion

• This paper propose a new multi-channel MAC
  protocol allow different node pairs to rendezvous
  concurrently on multiple channel.
• They studied the LQF scheduling policy under
  certain traffic conditions, the relation between
  delay and the deviation probability, and local
  receiver preference can reduces delay.
• They implemented McMAC on the Telos platform to
  prove the feasibility of our proposal.