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  1. CUBS: Coordinated Upload Bandwidth Sharing in Residential Networks Enhua Tan1, Lei Guo2, Songqing Chen3, Xiaodong Zhang1 1The Ohio State University 2Yahoo! Inc 3George Mason University ICNP’09, Princeton, NJ

  2. Residential Networks: Broadband Everywhere 93% in 2009 60% in 2005

  3. Residential Networks Bandwidth • Residential networks download / upload bandwidth : asymmetric -- lower upload bandwidth: • Typical DSL: 384 Kbps upload, 1.5 Mbps download • Affected by line quality and distance • Typical Cable: 512 Kbps upload, 7 Mbps download • Cable Network Bandwidth Allocation in U.S. :

  4. Advantages of Limited Upload Bandwidth • Most home users mainly utilize download bandwidth • Residential network physical infrastructure fits limited upload bandwidth: • Cable network: tree structure • Asymmetric bandwidth less attractive to business users: • Servers pay more because of upload traffic (symmetric)

  5. Problems Caused by Limited Upload Bandwidth • Increasingly demanding and dependable P2P-based applications demand equal upload to download bandwidth in principle • Large file download: slow upload peer suffers from slow download due to tit-for-tat incentive • VoIP: demands substantial and stable upload bandwidth to avoid jitters • Internet live streaming: slow upload leads to quality degradation

  6. Case 1: VoIP Performance Deteriorates • Our Internet experiments: computer connects to cable modem • Upload traffic affects ping RTT (round-trip time) from 28ms to 1,000 ms or around: • VoIP demands < 150ms one-way delay: VoIP works poorly! 274 ms jitter! Ping RTT increased by about 1,000 ms!

  7. Case 2: BitTorrent Downloads Slowly • BitTorrent tit-for-tat: download performance constrained by the cap of upload bandwidth • Our Internet experiments show this effect Download time increases when upload cap decreases

  8. Would Upload Bandwidth Increase Effectively Address the Problems? • Observed 25 residential networks for 21 days, we had two main findings: • Upload channel utilization is burstyand unbalanced: < 20% users highly active in cable network • Overall, about 50% - 80% upload bandwidth is idle Simply increasing the upload bandwidth is not a cost-effective solution: more idle upload bandwidth would be underutilized

  9. Our Solution –CUBS: Coordinated Upload Bandwidth Sharing • CUBS monitors availability of upload bandwidth from all members • Utilize idle upload bandwidth from neighboring cable or DSL networks • Bandwidth sharing is fair and flexible Significantly improve performance of upload intensive applications without affecting the performance of neighboring networks

  10. Outline • Problem Statement and Proposal • Internet Measurements • System Design • Evaluation • Conclusion

  11. Residential Upload Bandwidth Measurement • Collected IP addresses using Gnutella crawler • Identified Top-7 ISPs: Charter, Comcast, Cox, Road Runner, Ameritech (AT&T), Pacbell, and Verizon • Scanned 25 subnets by probing from Planet-Lab: up to 78.8% subnet IPs respond • 25 subnets with 2,040 IP addresses for 21 days (during February and March, 2008) • no control on the residential hosts: ICMP ping probing to estimate upload bandwidth • slightly underestimate the available bandwidth: on the conservative side

  12. Measured Results • Cable networks have higher upload capacity than DSL • Average Idle upload bandwidth ratio: Cable higher than DSL Cable 62% - 93% DSL 52% - 83%

  13. Available Upload Bandwidth Distribution < 10% hosts use more than half of upload bandwidth: Unbalanced Cable Varies little along time: Chance to utilize DSL upload bandwidth varies among hosts (due to varied line length) DSL

  14. Feasibilities of CUBS Our measurements show that: • In broadband networks, there exists plenty of unused upload bandwidth: 50% - 80%: • Suggests that CUBS is feasible to utilize the unused bandwidth • Upload channel is utilized in an unbalanced way (less than 20% users fully utilizedtheir upload bandwidth): • CUBS will be feasible to increase upload bandwidth without demanding additional bandwidth supply

  15. Outline • Problem Statement and Proposal • Internet Measurements • System Design • Evaluation • Conclusion

  16. Challenges of CUBS Design • How to share upload bandwidth? • How to discover unused upload bandwidth? • How to encourage users to participate?

  17. Residential Networks: Wi-Fi Everywhere • Jupiter Research: 65% of the U.S. households use Wireless connections in 2006 -- higher usage now • A study in 2006: # of APs (Access Points) detected in residential areas ranges 2-20 Residential Network Wireless Access Point (AP) Wireless Station Cable/DSL Modem

  18. CUBS System Periodically estimate local AP’s idle upload bandwidth Local AP of A Station A Associate with foreign AP Local AP of B Active using upload bandwidth now Station B Associate with another foreign AP CUBS System Local AP of C Station C

  19. CUBS Overlay: Discover Bandwidth • Bootstrap: a tracker to record the local AP-ID and IP address of each node • The local AP-ID: {ESSID, AP MAC address} • Overlay connections: new node queries tracker to connect with nearby nodes • Idle bandwidth discovery:each node measures its local AP’s upload bandwidth usage to compute idle bandwidth, and shares this info on overlay

  20. CUBS Node: Wireless for Sharing • Dual connections: branching node’s upload traffic to • the local AP through one network interface • the foreign AP through another wireless interface • Choose foreign AP for bandwidth sharing: • highest available upload bandwidth • acceptable signal strength • Connection binding (network layer): • modifies the connect system call • binds new connection to one of the available network interfaces based on traffic load (or randomly)

  21. Fair Usage of the Upload Bandwidth • Serves as an incentive mechanism to encourage users to share bandwidth over CUBS • Foreign AP owner is able to fully use upload bandwidth: • Tell other users to refrain from competitions when needed • Other user restrains further usage of the foreign AP, and tries to hand-off to another foreign AP

  22. No Excessive Usage of Download • For a new TCP connection: • If it is upload intensive or bidirectional, the connection can be bound to the foreign AP • Otherwise should be bound to local AP • Requires prediction of a connection’s upload to download traffic ratio

  23. No Excessive Usage of Download: Prediction Evaluation • Trace-driven evaluations: • packet header trace of Dartmouth residential wireless network (2004) • uses the mean of the upload-to-download traffic ratios of the latest n connections to the same host for prediction for more than 80% connections, the prediction difference is less than 20%

  24. Discussions • Overlay-based user authentication: • AP owner controls who can use the AP through AP web service to prevents abusive usage • Multiplexing one wireless interface: • FatVAP (NSDI’08) allows one wireless interface to associate with multiple APs: utilize Power-Saving Mode buffering • Can be useful for CUBS user with only one interface

  25. Discussions (Cont.) • Mesh Networks for Sharing Long Distance APs: • CUBS node currently only connects to neighboring APs to harness available bandwidth • CUBS wireless mesh network can route an upload packet to the Internet via an AP which can be out of the signal range of the originator • Then upload bandwidth can be shared among any nodes in the mesh network

  26. Outline • Problem Statement and Proposal • Internet Measurements • System Design • Evaluation • Conclusion

  27. Evaluation Setup • To emulate the residential network, we use NISTNet to control the Internet connections of the APs • Configure the upload and download capacity to be 500 Kbps and 7 Mbps – typical bandwidth caps for a cable subscription

  28. BitTorrent Experiments on Planet-Lab • Repeatable swarm: 1 seed and 18 peers on Planet-Lab • Download lasts for one hour, w/o and w/ CUBS • The average download throughput is improved by > 30%: • No matter it is load-based or hash-based (remote IP)

  29. Fair Bandwidth Sharing in CUBS AP owner gets full upload bandwidth quickly Utilize foreign AP’s upload bandwidth Idle bandwidth is detected and utilized again

  30. Conclusion • A low upload bandwidth cap in residential networks causes problems to P2P applications • Measurements show the total upload is often underutilized • And the upload channel utilization is bursty and unbalanced • CUBS enables a user to share idle upload bandwidth of its coordinated neighbors: • Improve the performance of delay-sensitive or P2P applications • Without demanding additional bandwidth supply from ISPs or infrastructure support • Flexibly shares idle upload bandwidth while providing fairness guarantees

  31. Thank you!Enhua Tan:etan@cse.ohio-state.edu

  32. Probing Ping RTT Distribution (When Upload Channel is Saturated) • most RTTs are larger than 500ms: • implies that queue lengths of residential networks are very large • VoIP quality will degrade when upload is saturated