Resolving Data Collision in CSMA via Protocols

Presented by: Anurag Pratap Singh

CS -64 2912210001

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Wireless LAN configuration

LAN

Server

WirelessLAN

Laptops

Base station/access point

Palmtop

radio obstruction

A B C

DE

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The 802.11 CSMA Sublayer Protocol

(a) The hidden station problem.(b) The exposed station problem.

RESEARCH PAPER 1 By Fouad A. Tobagi & Leonard

A busy tone solution for hidden terminal problem in CSMA.

When a node is ready for transmission, it senses the channel to check whether the busy tone is active.

If not, it turns on the busy tone signal and starts data transmissions

Otherwise, it reschedules the packet for transmission after some random rescheduling delay.

Any other node which senses the carrier on the incoming data channel also transmits the busy tone signal on the control channel, thus, prevent two neighboring nodes from transmitting at the same time.

IEEE802i:http://www.cedt.iisc.ernet.in/WEP

RESEARCH PAPER 2 by Hossam Hassanein and Chi-Hsiang Yeh

It assign priority for packets.it can enable different packets with different

priority to access the media and thus gain QoS.

http://www.isaac.cs.berkeley.edu/isaac/wep-faq.html

RASEARCH PAPER 3 BY Tiantong You AND Hossam HassaneinAn Adaptive Distributed ID Assignment Scheme for

CSMA/IC.Achieving collision free medium access in CSMA/IC

only requires that the nodal ID is unique in its preventing range, while the nodal MAC ID (48 bits long) could guarantee uniqueness in the entire

network.

IEEE 802.15.4. Part 15.4 :Wireless medium access control (MAC) and physical layer (PHY) specifications for low-rate wireless personal area networks (LR-WPANs).

RESEARCH PAPER 4 BY Zhenyu Tang and J. J. Garcia-Luna-Aceves

Hop reservation multiple access protocol (HRMA) introduceda multichannel MAC protocol which is based on half-

duplex, very slow frequency-hopping spread spectrum (FHSS) radios

uses a reservation and handshake mechanism to enable a pair of communicating nodes to reserve a frequency hop, thereby guaranteeing collision-free data transmission.

can be viewed as a time slot reservation protocol where each time slot is assigned a separate frequency channel.

IEEE: http://www.ieee802.org/1/files/public/docs2000/P8021XOverview.PDFORiNOCO security paper v2.2 <6> Copyright© 2003

RESEARCH PAPER 5 BY by J. D. Angelopoulos, N. Leligou, Th. Orphanoudakis, G. Pikrammenos

MACA with Piggy-Backed Reservation (MACA/PR)Provide real-time traffic support in multi-hop

wireless networksBased on the MACAW protocol with non-

persistent CSMA

• http://www.blackhat.com/html/bh-usa-02/bh-usa-02 speakers.html#Bruce%20Potter

Problem domainContinuous checking More wait for low priority dataID assignment deals only with hidden surface

problem.HRMA have problem of low efficiency and

throughput.

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Solution by RTS-CTS protocol

The CSMA protocol. (a) A sending an RTS to B.

(b) B responding with a CTS to A.

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CSMAW

Variants of this method can be found in IEEE 802.11 as DFWCSMA (Distributed Foundation Wireless CSMA),

CSMAW (CSMA for Wireless) is a revision of CSMA.The sender senses the carrier to see and transmits a

RTS (Request To Send) frame if no nearby station transmits a RTS.

The receiver replies with a CTS (Clear To Send) frame.Neighbors

see CTS, then keep quiet. see RTS but not CTS, then keep quiet until the CTS is back to

the sender.The receiver sends an ACK when receiving an frame.

Neighbors keep silent until see ACK.Collisions

There is no collision detection. The senders know collision when they don’t receive CTS. They each wait for the exponential backoff time.

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CSMA variant: DFWCSMA in IEEE802.11

idle

wait for the right to send

wait for ACK

sender receiver

packet ready to send; RTS

time-out; RTS

CTS; data

ACK

RxBusy

idle

wait fordata

RTS; RxBusy

RTS; CTS

data; ACK

time-out data; NAK

ACK: positive acknowledgementNAK: negative acknowledgement

RxBusy: receiver busy

time-out NAK;RTS

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CSMA avoids the problem of hidden terminalsA and C want to

send to BA sends RTS firstC waits after receiving

CTS from B

CSMA avoids the problem of exposed terminalsB wants to send to A, C

to another terminalnow C does not have

to wait for it cannot receive CTS from A

Examples

A B C

RTS

CTSCTS

A B C

RTS

CTS

RTS

References[1] 1st Research Paper:The Institute of Electrical and Electronics

Engineers, Inc. IEEE Std 802.11 - Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications, 1999 edition.

 [2] 2nd Research Paper: B. Leiner, D. Nielson, and F. A. Tobagi, Eds.,Proceedings of IEEE GLOBECOM, Special issue on packet radio

networks

 [3] 3rd Research Paper: T.You, C.-H. Yeh, and H. Hassanein, “CSMA/IC: A New Class of Collision-free MAC Protocols for Ad Hoc Wireless Networks,” Proc. IEEE Int'l Symp Computer Communications (IEEE ISCC'03), June/July 2003

 [4] 4th Research Paper : WINGs for the Internet project and

SPARROW project. http://www.cse.ucsc.edu/research/ccrg/, Santa Cruz, CA, 1998.

 .

[5] 5th Research Paper:; J. D. Angelopoulos, N. I. Lepidas, E. K. Fragoulopoulos, I.S. Venieris,“TDMA multiplexing of ATM cells in a residential access SuperPON”, IEEE Journal on Selected Areas in Comm., Special issue on high capacity optical transport networks, Vol. 16, No. 7, September, 1998

[6]www.google.com/lectures/IEEE 802.11 Media Access Control and Network Layer Standards

[7] Chapter 6 of EE136 textbook: A. Leon-Garcia, I. Widjaja, “Communication Networks,” McGraw Hill.

[8]The IEEE 802.11 specification – posted on my.poly.edu – reference materials

[9]P. Brenner, “A Technical Tutorial on the IEEE 802.11 Protocol,” http://www.sss-mag.com/pdf/802_11tut.pdf

ANY

THANK YOU