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A study of Cross layer work of University of Trento folk

A ResiliNet Group Presentation Sarvesh Kumar Varatharajan. A study of Cross layer work of University of Trento folk. A study of Cross layer work of University of Trento folk.

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A study of Cross layer work of University of Trento folk

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  1. A ResiliNet Group Presentation Sarvesh Kumar Varatharajan A study of Cross layer work of University of Trento folk

  2. A study of Cross layer work of University of Trento folk • Cross-Layer Performance Optimization in wireless Local Area Network (Kliazovich's PhD Thesis)‏ • Cross Layer ARQ ( Presented Today)‏ • Cross Layer Congestion Control (Present next week)‏ • The Cross-Layer Paradigm In Next Generation Internet: Open Issues & Future Perspectives( Granelli)‏ (Walk through the foils)‏ • Formal Methods in Cross-Layer Modeling and Optimization of Wireless Networks: State of the Art and Future Directions (Skip!!!Difficult for me to understand :-( )‏

  3. Cross-layer Performance Optimization in wireless Local Area Network • Cross-Layer Performance Optimization in wireless Local Area Network (Kliazovich's PhD Thesis)‏ • Cross Layer ARQ

  4. Cross-layer Performance Optimization in wireless Local Area Network • TCP/IP shows poor performance when extended to wireless network environment • Limitations in terms of bandwidth,latency,channel loss and mobility • Available Enhancement Schemes • Link Layer Solutions • Transport Layer Solutions • Cross-Layer Solutions

  5. Cross-layer Performance Optimization in wireless Local Area Network

  6. Cross-layer Performance Optimization in wireless Local Area Network • Link Layer Solutions • TCP unaware link layer solution • TCP unaware protocols optimize performance by hiding the differences between wired and wireless mediums • Can cause adverse effects eg.) ARQ on TCP RTO‏ • TCP aware link layer solution • Knowledge of transport layer protocol provides certain advantages • eg.) Snoop Protocol • Snoop Agents ( at the BS) caches the TCP packets that are sent to mobile nodes. Retransmissions occur locally • Disadvantages • Increases complexity at BS • No consideration of packet loss delay during hand-off

  7. Cross-layer Performance Optimization in wireless Local Area Network • Transport Layer Solutions • Connection Splitting Solutions • I-TCP (Indirect TCP)‏ • Split the connection into two • One between FH and BS and the other between BS and MH • Conceal the wireless link from the FH • Disadvantages: • End-to-end Schematics lost • Additional overhead during hand-off • Can't operate on encrypted packets‏ • TCP Modifications • eg.) SACK‏ • Disadvantage: • Modification of the ACK procedure both at sender and reciever

  8. Cross-layer Performance Optimization in wireless Local Area Network • Cross-Layer Design • ILC-TCP (Interlayer Collaboration Protocol)‏ • State Manager (SM) in parallel to protocol stack • Each layer reports its state to the SM • SM can signal TCP to stop sending packets if conditions not good • Disadvantage: Additional Layer added to the sender

  9. Cross-layer Performance Optimization in wireless Local Area Network • Analysis of existing schemes under 3 different scenarios • Single-hop wireless connections • Multi-hop wireless scenario • Wireless-cum-wired scenario • Conclusion from the related work • No single best solution for all deployment scenario

  10. Cross-layer Performance Optimization in wireless Local Area Network • TCP with link level ARQ • Link layer is not the only layer which acknowledges packet delivery(TCP ACK's)‏ • “A single TCP data packet is acknowledged three times”( One time at the transport level and two times at the link level)‏ • This along with the fact that the physical layer preamble and header are transmitted at the lowest bit rate penalizes performance at higher bit rate

  11. Cross-layer Performance Optimization in wireless Local Area Network • Optimization of the acknowledgement scheme through interaction between transport and link layer will bring down the medium busy time and will improve the performance • A cross layer Link Layer ARQ Exploitation TCP (LLE-TCP) scheme proposed • The idea is to generate the TCP ACK at the sender instead of sending it through the channel

  12. Cross-layer Performance Optimization in wireless Local Area Network • Cross Layer ARQ Agent • Operates between TCP and MAC • Interfaces both • LLE-TCP is a software module • Goes into the firmware • of the wireless card driver

  13. Cross-layer Performance Optimization in wireless Local Area Network • Packet delivery diagram

  14. Cross-layer Performance Optimization in wireless Local Area Network • Agent interaction with the Link Layer • Success • Failure • Agent interaction with the transport layer • Sender side • ARQ Agent sniffs the packet generated by the higher layer • Access the TCP headers • On successful reception of the link layer ACK, it prepares the TCP ACK • Upon SUCCESS TCP ACK is released to the Transport layer • On FAILURE three duplicate ACK's are generated triggering the fast retransmit

  15. Cross-layer Performance Optimization in wireless Local Area Network • Agent interaction with the transport layer • Receiver side • Silently drops all the standalone non-duplicate TCP ACK packets • Advantages • Does not interfere with the flow control mechanisms • Reduces the Round Trip Time(RTT)‏

  16. Cross-layer Performance Optimization in wireless Local Area Network • TCP Connection Phases • Connection Establishment (Three Way handshake)‏ • ACK suppression is done only for the third handshake as sequence number synchronization,negotiation of the size of the contention window takes place • Data Exchange • Full ACK suppression • Connection Termination • Full ACK suppression • Bidirectional data exchange • If the incoming packet acknowledges a segment number lower or equal to the already acknowledged one,the ACK flag is cleared

  17. Cross-layer Performance Optimization in wireless Local Area Network • Infrastructure Network Scenario • TCP performs poorly in such environments due to completely different characteristics between fixed and wireless parts

  18. Cross-layer Performance Optimization in wireless Local Area Network • TCP ACK's generated at the BS is delivered to the fixed host • TCP ACK's avoided in the wireless part(bottleneck)‏ • LLE-TCP at BS accesses the rwnd of the ACK header and replaces it with empty buffer space left at the BS. Improves Congestion control • Drawback: Complexity at the BS • Mobile station switches off its LLE-TCP if the BS does not support it

  19. Cross-layer Performance Optimization in wireless Local Area Network • Multi hop Networks

  20. Cross-layer Performance Optimization in wireless Local Area Network • Congestion Control at the sender side • LLE-TCP congestion control module (LLE-TCP_CC)‏ • LLE-TCP_CC buffer stores the packet till it gets the ACK from LHR • rwnd set to 1 packet if LLE-TCP buffer not full • rwnd set to 0 packets if LLE-TCP buffer is full • Send a duplicate ACK for the last transmitted data packet with positive value for the advertised window

  21. Cross-layer Performance Optimization in wireless Local Area Network • Experimental Results • Simulation in ns-2 • Implementation of single-hop scenario in 802.11b testbed( Fedora Core Linux with 802.11b Orinoco Silver Cards)‏ • TCP Reno is chosen for comparison

  22. Cross-layer Performance Optimization in wireless Local Area Network • Single-hop Network (Simulation Results)‏

  23. Cross-layer Performance Optimization in wireless Local Area Network • Single-hop Network ( Implementation Results)‏ • These results are 3% less than simulation results??

  24. Cross-layer Performance Optimization in wireless Local Area Network • Multi hop Scenario (Simulation Results)‏ • TCP Segment size=1000 bytes • 10 % to 20 % improvement for small # of hops

  25. Cross-layer Performance Optimization in wireless Local Area Network • Multi hop Scenario (Simulation Results)‏ • Three hops, static environment

  26. Cross-layer Performance Optimization in wireless Local Area Network • Multi hop Scenario (Simulation Results)‏ • 30 nodes placed randomly in 100*100 m • With node mobility ,AODV,RTS/CTS ON • 1000s simulation • Fewer route errors • Fewer route discovery • messages • Reduced RTT

  27. Cross-layer Performance Optimization in wireless Local Area Network • Infrastructure Network Scenario (Simulation Results)‏ • IEEE 802.11b • Wired link 100Mbps,2ms • Results close to single hop • This is bec ACK is sent • on wired link • Congestion control at BS

  28. A study of Cross layer work of University of Trento folk • Cross-Layer Performance Optimization in wireless Local Area Network (Kliazovich's PhD Thesis)‏ • Cross Layer ARQ ( Presented Today)‏ • Cross Layer Congestion Control (Present next week)‏ • The Cross-Layer Paradigm In Next Generation Internet: Open Issues & Future Perspectives( Granelli)‏ (Walk through the foils)‏ • Formal Methods in Cross-Layer Modeling and Optimization of Wireless Networks: State of the Art and Future Directions (Skip!!!Difficult for me to understand :-( )‏

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