1 / 21

Managing TCP Connections in Dynamic Spectrum Access Based Wireless LANs

Managing TCP Connections in Dynamic Spectrum Access Based Wireless LANs. Ashwini Kumar Prof. Kang G. Shin. Overview. Introduction Motivation & Challenges Main Contribution: DSASync DSASync at Link Layer (DSASync_LL) DSASync at TCP Layer (DSASync_TCP) Evaluation Future Work .

garson
Download Presentation

Managing TCP Connections in Dynamic Spectrum Access Based Wireless LANs

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Managing TCP Connections in Dynamic Spectrum Access Based Wireless LANs • AshwiniKumar • Prof. Kang G. Shin

  2. Overview • Introduction • Motivation & Challenges • Main Contribution: DSASync • DSASync at Link Layer (DSASync_LL) • DSASync at TCP Layer (DSASync_TCP) • Evaluation • Future Work

  3. Dynamic Spectrum Access • Communication increasingly becoming wireless and mobile, but • Wireless spectrum is a limited and shared resource • Side-effects: overcrowding, interference increase • Dynamic Spectrum Access (DSA): Opportunistic wireless communication on licensed bands • Aims to solve spectrum-usage inefficiency& shortage • Still evolving

  4. Why DSA Can Be Effective? [[Source: Shared Spectrum Company] [[Source: New America Foundation]

  5. Motivation • WLANs mainly deployed as edge networks • Connections are from wireless client to cloud • DSA is an inherently disruptive technology: blackout period (TFP) Sensing PU Access Channel-switch Capacity change B1 Raw Capacity • DSA contributes tocapacity & delay fluctuations • Device-centric QoS provisioning insufficient for end-to-end connections B2 Time T1 T2 T3 T4 T5 T6 T7 T8

  6. Challenges • Efficient monitoring/response mechanism to mitigate effect of DSA-related events • Transparent to ongoing connections • End-to-end semantics of TCP must not be violated • Ease of configuration/deployment • No changes must be introduced in wired cloud • No need to recompile/re-link of existing protocols

  7. DSASync Overview • No restrictions on the DSA protocol • Centralized operation at BS • Key concepts: caching + traffic-shaping Corresponding Host (CH) DSAN Base Station (BS) DSASync Wired Network (WN) Spectrum-agile Host (SH)

  8. DSASync Architecture • Logically a link layer component • But affects the transport layer, executes at BS • Key Advantage: TCP semantics maintained, no protocol modification necessary - uses only existing TCP hooks Application DSASync_TCP Transport Routing DSASync_LL Link/MAC DSASync Module Physical

  9. DSASync at Link Layer (DSASync_LL) • Passive monitoring & estimation unit for DSA parameters • E.g., fsense(i), tsense(i), fsense(DSAN), tswitch(DSAN), gON(PU), etc • Uses MAC/PHY events or historical averages • Establishes if Transmission Freeze Period (TFP) is active • Needed by DSASync_TCP component • In implementation, usually encapsulated within the MAC

  10. DSASync at TCP Layer (DSASync_TCP) • Sniffs incoming/outgoing packets • Maintains per connection state, e.g., seq. nos. & last ACK seen CH-SH (Ingress) traffic manager SH-CH (Egress) traffic manager DSASync_TCP Capacity change manager

  11. CH-SH (Ingress) Traffic Manager (DSASync_TCP_CH-SH) Start Packet p received? No Advt. 0 rwin for conn. Yes Yes Conn. rwin filling up? TFP going on? No No Put p to transmit queue Yes Buffer < thresh? Yes Buffer p Advt. 0 rwin to all CHs No

  12. SH-CH (Egress) Traffic Manager DSASync_TCP_SH-CH • Smoothens outgoing flow to mask DSA disruptions • Estimate outgoing data-rate D(i) • α(i) = 1-(TFPavg/ΔT), β(i) = max(α(i), αmin) • Effective data rate, Deff(i) = β(i)D(i) • Algorithm to empty queue at “smoothed rate” • Further optimization, from O(N) to O(1) FCFS dequeue scheme

  13. Capacity Change Manager (DSASync_TCP_CAP) • Exploits built-in TCP congestion control • Executed when existing traffic suddenly unsustainable • Force timeout or trigger fast retransmit (recovery) by sending duplicate ACKs to CHs

  14. Evaluation • Implementation: Basic DSA protocol in 802.11 (MadWifi), PU emulation using MadWifi+Click • DSASync kernel module runs at the router • Metrics: goodput, delay, jitter • Testbed: infrastructure edge WLAN (6 clients) • Channel = 36, def. PHY capacity = 24Mbps, buffer capacity = 500MB • TCP Reno: initial TCP send & recv. window is 256KB • αmin = 0.5, Bhigh = 500MB, Blow = 400MB • Def. PU utilization = 20%, sensing overhead = 5%

  15. Results: Overhead • Overhead characterization: • Compare overhead with 802.11 (no DSA overhead) • Avg. 1.9% reduction in throughput • End-to-end delay increase around 1.1ms

  16. Microbenchmarks • CH-SH (ingress) traffic benefitted most: 74% improvement, low retrans. overhead (0.018Mbps) • SH-CH (egress) traffic improvement 10%

  17. Microbenchmarks • End-to-end delay variation lower for SH-CH (egress) traffic • DSASync makes SH-CH connection resilient

  18. Microbenchmarks • PHY capacity reduced by 50% at 5s • Distributed DSASync agents useful?

  19. Macrobenchmarks • 4 TCP streams on each client – total 24 concurrent connections • Trends similar to microbenchmarks • Improvements even greater: 102% for CH-SH (ingress) direction

  20. Future Work • Evaluation on a large scale testbed • Extend DSASync for UDP • Motivation: UDP streams carry most of the QoS-sensitive multimedia traffic today • Challenge: stateless protocol implies no built-in hooks to control the connection

  21. Questions?

More Related