1 / 29

Filipe Abrantes and Manuel Ricardo {fla,mricardo}@inescporto.pt

2007 OCT 22. A Simulation Study of XCP-b Performance in Wireless Multi-Hop Networks. Filipe Abrantes and Manuel Ricardo {fla,mricardo}@inescporto.pt. Overview. Overview TCP limitations & XCP background XCP-b Performance in Wireless Multi-hop Networks Conclusions Future work.

jontae
Download Presentation

Filipe Abrantes and Manuel Ricardo {fla,mricardo}@inescporto.pt

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. 2007 OCT 22 A Simulation Study of XCP-b Performance in Wireless Multi-Hop Networks Filipe Abrantes and Manuel Ricardo {fla,mricardo}@inescporto.pt

  2. Overview • Overview • TCP limitations & XCP background • XCP-b • Performance in Wireless Multi-hop Networks • Conclusions • Future work Local/Evento

  3. TCP limitations • Unstable throughput • Increased queuing delay • Limited fairness • Inefficient in high bandwidth delay product networks Local/Evento

  4. XCP background • eXplicit Control Protocol • Routers tell sources how to adjust sending rate • New layer (L3.5) → host-to-network Local/Evento

  5. XCP algorithm • Efficiency controller (MIMD) → fast adaptation • calculates the aggregated feedback every control interval • BW-allocation controller (AIMD) → fairness • on each packet departure • If (feedback_left > 0) • Delta_Throughput = F/n_flows * pkt_size/flow_throughput • // Additive Increase • else • Delta_Throughput = F * pkt_size/input_bw • // Multiplicative Decrease (bit/s) Local/Evento

  6. No per-flow state needed • Efficient way of measuring the number of flows without keeping connection state!! Inter-packet interval (normalized to the ctrl_itvl) 1/3 1/3 1/3 Flow1 1/2 1/2 Flow2 1/4 1/4 1/4 1/4 Flow3 0 (sec) ctl_itvl (sec) Number of active flows Local/Evento

  7. Assuming an error in the capacity estimate • XCP compensates capacity error with queue build-up • Queue proportional to avg RTT and estimation error • e=0.5Mbit/s, d=100ms -> q=11Kbyte Local/Evento

  8. Why XCP-b • Capacity is hard to measure in shared access media → depends on: • Number of active stations • Collisions • Handshake mechanism • Rates used • MAC idle time • May differ from technology to technology Local/Evento

  9. XCP-Blind • Measure spare bandwidth from queue oscillations • Fixed amount of feedback when queue cannot be measured • Minimize oscillations, by stabilizing queue at positive value and performing late reaction Local/Evento

  10. XCP-blind Parameters • χ – set so that queue never exceeds (Qmax) (d=rtt) • n – set to match half of the period of the queue response frequency to errors • κ – not a general rule, but simulations say that it can be set as low as 3 for reasonable values of bandwidth, nodes... recent developments show that queue variance may be used to set κ Local/Evento

  11. Validation in WMN • Studied and validated in single-hop scenarios • Access point scenario • We extend this validation to Wireless Multi-hop Networks • Differences • More complex – multiple bottleneck • Does it still work? • 802.11 problems are more severe in MH scenarios • Hidden node, medium capture may cause extreme unfairness • Can XCP-b minimize them? Local/Evento

  12. Performance • Results • XCP-b vs TCP • lower queing delay • fairness increases • stable throughput • Multi-hop vs. SingleHop • Queue variance increases – more jitter... • Losses or no-losses • Reacting to losses seems as the wise decision • XCP-b parameter sensitivty • Lower χ usually better for smoother results • K should not be too high • n does not impact much, but shouldn’t be too high Local/Evento

  13. Chain Topology • Throughput • Queuing delay Local/Evento

  14. Mesh Access Network – Dynamics (Seq.No.) • XCP-b BDP variance • TCP NewReno Local/Evento

  15. Mesh Access Network – Delay & Fairness • Queuing Delay • Fairness Index Local/Evento

  16. XCP-b parameter sensitivity • too high -> longer periods under-utilized • too high -> inc. only delay • too high -> just MAC drops increases Local/Evento

  17. Conclusions • XCP-b maintains most of it’s properties in WMN • Pros • Reduces latency • Stable throughput • Increases Fairness • Can minimize 802.11 problems to some extent • Efficiency in high BPD networks (good for next-gen 802.11) • Cons: • Complexity • Comparing to the standard XCP • Extra delay - stabilizing queue above zero • Adaption proportional to Qmax/BDP • Queue peaks may occur / oscillation • Differences to single-hop • Higher variance (in queue, delay, throughput, ...) • XCP reacting to losses achieved better results • Only collision and queue drops were simulated (no transmission error losses) Local/Evento

  18. Future work • Compare with L2-aware approach • MAC idle-time • Collisions • Data rates • Try to apply to other forms of explicit congestion control (RCP, ...) Local/Evento

  19. Thank you Questions? Local/Evento

  20. No per-flow state needed (avoiding the division) • Efficient way of measuring the number of flows without keeping connection state!!... And avoiding per-packet divisions!! Inter-packetinterval 0.3 0.3 0.3 0.5 0.5 0.25 0.25 0.25 0.25 1 (sec) 0 (sec) Local/Evento

  21. Local/Evento

  22. The new age of congestion control • Implicit Feedback • Vegas (‘94) – the old rtt vs. loss dilemma • TFRC (‘98/’03) – stable throughput • SCTP(‘00) – session cong. control • FAST(’03) – vegas part II (faster version) • BIC(’04) – stable and efficient • Explicit feedback • ECN(’01) – loss differentiation • XCP(’02) – shares bandwidth • TCP-QS(’02) – approves requests from hosts • EWA(’02) – shares buffer size Local/Evento

  23. XCP system model • The XCP system model • Proven stability for any bandwidth, delay and number of stations Local/Evento

  24. Bandwidth estimation error • XCP model in the presence of estimation error Local/Evento

  25. XCP-b vs XCP • Basic Dynamics Local/Evento

  26. XCP-b vs XCP • Dynamic bandwidth Local/Evento

  27. XCP-b • Different data rates simultaneously Local/Evento

  28. XCP-b vs. TCP • Queuing delay • Fairness • Utilization • Utilization with mice Local/Evento

  29. Architectural Issues • Processing at input-queues in half-duplex media • Layer 2 equipment needs to “look at” an header between IP and transport layer Local/Evento

More Related