A Medium Access Control Protocol with Reliable Multicast Support for Wireless Networks Thesis defense of: Vikram Shankar Advising Committee: Dr. Sandeep

A Medium Access Control Protocol with Reliable Multicast Support for Wireless Networks

Thesis defense of:

Vikram Shankar

Advising Committee:

Dr. Sandeep Gupta

Dr. Arunabha Sen Dr. Joseph Hui

December 2002 Mobile Computing and Wireless Networking Lab Arizona State University

Outline of Presentation

Motivation System Model Related work Overview of IEEE 802.11 IEEE 802.11MX (multicast extension) Performance studies Conclusions


Motivation

Need for reliable multicast Group communication Whiteboard applications

Why reliable multicast support at MAC layer? Utilize broadcast nature of wireless medium Local error recovery reduces end-to-end

delays


System Model

Infrastructure-based as well as ad hoc Each node has two transceivers

One for data channel One for busy tones

Bit errors caused by: Channel noise Packet collisions

We deal with one hop reliability only Assumptions:

Multicast recipients are always within transmission range of sender

Antenna is capable of picking up both data bits as well as tones


Hidden Terminal Problem

Translucent circles indicate transmission range of respective colored nodes

Node Blue

Node Orange

Node Green


Exposed Terminal Problem

Node Blue

Node Purple

Node Green

Node Orange



Use of RTS/CTS

RTS

CTS

XCTS

RTS – Request-To-Send CTS- Clear-To-Send

Node Green

Node Orange

Node Blue


Use of RTS/CTS

RTS

CTS

RTSNode Blue

Node

Orange

Node

Green

Node Purple



Some Related Work…

IEEE 802.11 Leader Based Protocol Probability Based Protocol Delay Based Protocol Parity Based Multicast Dual Busy Tone Multiple Access


Leader Based Protocol

RTS

Leader

Base

Station



Base

Station

Leader

CTS

NCTS



DATA

Leader

Base

Station



Base

Station

Leader

ACK

NAK


Problems with Leader Based Protocol

Leader Mobility reduces throughput “Capture Effect” may hide NCTS and NAK

from distant nodes Incoming nodes may not have heard

RTS/CTS exchange and may cause collision

Sender has to know the multicast group members a priori


IEEE 802.11

Modes of operation: Infrastructure-based Ad hoc

Three access mechanisms: Basic CSMA/CA CSMA with RTS/CTS Polling

Does not support reliable multicast


IEEE 802.11


Dual Busy Tone Multiple Access

Node mobility causes problems In coming nodes may not have heard

RTS/CTS exchange Unaware of current transmission Up to 60% of packets may be lost due to

collision Use Transmit Busy tone while transmitting Use Receive Busy tone while receiving


IEEE 802.11MX

Salient features Multicast extension to IEEE 802.11 Remains compatible with IEEE 802.11 Multicast is NAK-based Use of tones instead of packets for NAK and

NCTS Dual Busy tones to reduce packet collisions


Slot Diagram


State Diagram - Sender


State Diagram - Receiver


Results - Throughput


Results - Reliability


Conclusions

IEEE 802.11MX was proposed as a reliable multicast extension to IEEE 802.11

Multicast is NAK-based NAKs and NCTSs are in the form of tones Provides the same reliability as Leader Based

Protocol Has better throughput compared to Leader

Based Protocol


Future Work

Addition of power saving strategies Currently working on reliable multicast

protocol built over IEEE 802.11MX


References

ANSI/IEEE Standard 802.11 Wireless LAN medium control (MAC) and physical layer (PHY) specifications, In 1999 Edition.

J. Deng, Z. J. Haas, “Dual Busy Tone Multiple Access (DBTMA): A New Medium Access Control for Packet Radio Networks”, In IEEE ICUPC’98, Italy, 1998.

J. Kuri, S. Kasera, “Reliable Multicast in Multi-access Wireless LANs”, In Proceedings of INFOCOM’99, New York, March 99.

Network Simulator – ns-2, Available via http://www.isi.edu/nsnam/ns/, [Accessed on Aug 02]

D. Towsley, J. Kurose, S. Pingali, “A Comparison of Sender-Initiated and Receiver-Initiated Multicast Protocols”, In IEEE Journal on Selected Areas in Communication, April 1997.


Thank You!

Documents

A Medium Access Control Protocol with Reliable Multicast Support for Wireless Networks Thesis defense of: Vikram Shankar Advising Committee: Dr. Sandeep