The document discusses resolving data collisions in CSMA wireless networks through various protocols. It describes the hidden and exposed station problems that can occur in CSMA networks and several research papers that propose solutions. The RTS-CTS handshake protocol is described as a way to avoid collisions between hidden terminals by having the sender and receiver exchange request-to-send and clear-to-send frames before transmitting data. Variants of this approach were incorporated into the IEEE 802.11 standard.

1. Resolving Data Collision in CSMA via Protocols Presented by: Anurag Pratap Singh CS -64 2912210001

2. Wireless LAN configuration 2

3. 3 The 802.11 CSMA Sublayer Protocol (a) The hidden station problem. (b) The exposed station problem.

4. 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

5. RESEARCH PAPER 2 by HossamHassanein 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

6. RASEARCH PAPER 3 BY Tiantong You AND HossamHassanein An 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).

7. RESEARCH PAPER 4 BY Zhenyu Tang and J. J. Garcia-Luna-Aceves Hop reservation multiple access protocol (HRMA) introduced a 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

9. 10 Solution by RTS-CTS protocol The CSMA protocol. (a) A sending an RTS to B. (b) B responding with a CTS to A.

10. 11 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.

11. 12 CSMA variant: DFWCSMA in IEEE802.11 sender receiver idle idle packet ready to send; RTS data; ACK time-out; RTS RxBusy wait for the right to send RTS; CTS time-out  data; NAK ACK time-out  NAK; RTS CTS; data wait for data wait for ACK RTS; RxBusy ACK: positive acknowledgement NAK: negative acknowledgement RxBusy: receiver busy

12. 13 Examples A C A C CSMA avoids the problem of hidden terminals A and C want to send to B A sends RTS first C waits after receiving CTS from B CSMA avoids the problem of exposed terminals B wants to send to A, C to another terminal now C does not have to wait for it cannot receive CTS from A RTS CTS CTS B RTS RTS CTS B

13. 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. .

14. [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

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16. THANK YOU