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MAC layer Multicast in Wireless Multihop Networks. Shweta Jain Samir Das. Overview . Motivation. Introduction. Description if IEEE 802.11. Description of various Multicast MAC protocols. Description of Multicast MAC. Performance results. Conclusion. Motivation.

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mac layer multicast in wireless multihop networks

MAC layer Multicast in Wireless Multihop Networks

Shweta Jain

Samir Das

Comsware 2006

overview
Overview
  • Motivation.
  • Introduction.
  • Description if IEEE 802.11.
  • Description of various Multicast MAC protocols.
  • Description of Multicast MAC.
  • Performance results.
  • Conclusion.

Comsware 2006

motivation
Motivation
  • Many applications in wireless multihop networks need one-to- many (multicast) communication.
  • Multicast data may need to be transmitted across various hops before it reaches all multicast receivers.
  • Since wireless links are prone to errors, data may not always be received correctly at the next node along the route.
  • Error recovery in the upper layer can cause large end to end delays in data delivery.
  • An efficient and reliable MAC layer multicast protocol can improve the performance of multicast communication.

Comsware 2006

introduction
Introduction
  • IEEE 802.11 protocol implements positive acknowledgment to provide reliable transmission of unicast data.
  • The same mechanism can be used to provide reliable multicast support at the MAC layer.
  • In this paper we present a reliable multicast MAC protocol.
  • We also evaluate three other Multicast MAC protocols and compare their performance with our approach.
    • Broadcast based multicast
    • Unicast based MAC
    • Multicast MAC.
    • Our approach– Multicast MAC with cliques.

Comsware 2006

description of ieee 802 11 mac
Description of IEEE 802.11 MAC
  • Access Mechanism for unicast data transmission – reliable
  • Access Mechanism for multicast and broadcast data transmission -- unreliable

Comsware 2006

ieee 802 11 unicast transmission
IEEE 802.11– Unicast transmission
  • IEEE 802.11 DCF is the basic access mechanism used for reliable unicast.
  • It uses CSMA/CA and optional Control packet exchange to facilitate medium sharing for unicast data.
  • Requires positive feedback from the receiver to guarantee data delivery.

Comsware 2006

ieee 802 11 ieee 802 11 multicast and broadcast transmission
IEEE 802.11 IEEE 802.11– Multicast and Broadcast transmission
  • IEEE 802.11 access mechanism used for multicast and broadcast transmission.
  • It uses CSMA/CA to facilitate medium sharing for multicast and broadcast data.
  • Does not implement any feedback mechanism, thus there is no data delivery guarantee.

Comsware 2006

mac protocols
MAC protocols
  • Broadcast MAC – Send multicast data as broadcast data (IEEE 802.11 MAC)
      • Disadvantage: Unreliable transmission.
  • Unicast MAC– Send a single multicast data packet as multiple unicast packets to each next hop neighbor.
      • Disadvantage: Large packet delays.
  • Multicast MAC – Perform multicast RTS/CTS exchange with all nexthop neighbors.
      • Disadvantages:
        • Large size of RTS makes it prone to collisions.
        • The RTS/CTS/Data/ACK exchange may take a time longer than the time for which the two hop neighbors set their virtual carrier sensing mechanism.
  • Multicast MAC with cliques – Perform multiple multicast RTS/CTS exchange with each nexthop neighbor group.

Comsware 2006

multicast mac
Multicast MAC
  • Sender:
    • Send a single RTS with multiple nexthop addresses.
    • Wait to receive CTS from each nexthop neighbor.
    • Send data to those neighbors from which CTS was received.
    • Retransmit RTS to those neighbors from which CTS was not received.
  • Receivers:
    • Send CTS after a fixed delay determined by the order in which the receiver’s address appears in the RTS packet.
    • Receive Data and send ACK packets after a fixed delay determined by the address order in the data packet.
  • Others:
    • Invoke the virtual carrier sensing mechanism to allow collision free RTS/CTS/Data/ACK exchange.

Comsware 2006

multicast mac10
Multicast MAC

The wait time for Nth receiver where N is the position index of its address in the RTS

Frame—

N x SIFS + (N-1) x CTS Duration.

Comsware 2006

interference problem
Interference Problem
  • CTS order is Recv 1, Recv 2 and Recv3.
  • Recv 2 does not send CTS because it hears the CTS sent by Recv 1 as noise and invokes its virtual carrier sensing mechanism.
  • Sender has to retransmit RTS to Recv 2.
  • We group the neighbors into groups such that neighbors that can hear each other form a single group called cliques.
  • We perform the RTS/CTS exchange mechanism to send data to each group.

Comsware 2006

multicast mac with cliques
Multicast MAC with Cliques
  • We group neighbors in different cliques and send multicast data to atmost 4 neighbors at a time.
    • Advantage
      • The RTS size is small so it is not prone to collisions
      • The RTS/CTS/Data/ACK exchange completes before the NAV of two hop neighbors and potential interferers expire.

Comsware 2006

clique of neighbors
Clique of neighbors

Comsware 2006

performance evaluation
Performance Evaluation
  • We used network simulator (ns2) version 2.26 for simulation.
  • We experimented with a grid scenario of size 1500x300 with 100 nodes
  • We set up traffic connections for 1 multicast sender and vary the number of receivers -10, 20, 30 and 40 multicast receivers.
  • We run experiments with two-ray ground propagation model and ricean fading models

Comsware 2006

two ray ground propagation model
Two Ray Ground Propagation model
  • Packet delivery fraction for multiple unicast and broadcast MAC fall when the number of multicast receivers is increased.
  • Packet delivery fraction of multicast MAC remain steady with increase in the number of multicast receivers.

Comsware 2006

two ray ground propagation model16
Two Ray Ground Propagation model
  • Average per hop delay rises with the number of multicast receivers for unicast MAC.
  • Delay remains steady for other MAC protocols.
  • Delay is less for broadcast MAC is low due to the absence of retransmissions in broadcast MAC.

Comsware 2006

ricean fading model
Ricean Fading model
  • Packet delivery fraction for all MAC protocols fall when the number of multicast receivers is increased.
  • Packet delivery fraction of multicast MAC fall less steeply than unicast and broadcast MAC protocols.

Comsware 2006

ricean fading model18
Ricean Fading model
  • Average per hop delay rises with the number of multicast receivers for all MAC protocols other than broadcast MAC.
  • Delay remains steady for broadcast MAC protocol due to the absence of retransmissions.
  • Delay is lower for unicast MAC protocol due to lower packet delivery fraction.

Comsware 2006

conclusion
Conclusion
  • We have presented an extension of IEEE 802.11 MAC protocol to provide reliable multicast MAC protocol.
  • We have demonstrated the performance improvement achieved due to our protocol.

Comsware 2006