Bandwidth Aggregation in Heterogeneous Networks

1. Bandwidth Aggregation in Heterogeneous Networks Kameswari Chebrolu, Ramesh Rao Department of ECE University of California, San Diego

2. Introduction • Recent mobile Internet growth spurred deployment of different wireless technologies • e.g. GPRS, CDMA2000, HDR, 802.11, Bluetooth, Iridium etc • End-Users have flexibility regarding Interface choice • Can choose any number of interfaces to best fit application needs • Simultaneous use of multiple interfaces opens interesting possibilities • Bandwidth Aggregation, Mobility Support, Security, Reliability • Problem Statement: • How to effectively aggregate bandwidth across multiple network interfaces?

3. Motivation • Applications will drive next-generation network deployments • Video Applications • Video-on-demand • Interactive video • Video conferencing • Multiplayer games • Bandwidth requirements: 250 Kbps to 2-3 Mbps • Problem: • Wireless interfaces have bandwidth limitations • 50 Kbps – 384 Kbps (GPRS, CDMA2000) • TCP applications can also benefit from bandwidth aggregation

4. Challenges in Bandwidth Aggregation • Use of multiple interfaces  Reordering • Video applications have stringent QoS requirements • Interactive applications • One way latency of 150ms , Max limit 400ms • Frame loss rate < 1% • Video on Demand (with VCR functions): • One way latency of 1-2 sec • Frame loss rate < 1% • Cannot tolerate excess delay due to reordering • TCP applications • More than 3 duplicate acks invokes congestion control • Bandwidth probing issues • Inter arrival between acks does not reflect available bandwidth

5. Related Work • Link-Layer Solutions • Bonding – aggregates circuit switched lines • IMA – ATM technology for aggregating multiple point-to-point links • Multilink PPP • Stripe Protocol • Generic load-sharing protocol based on Surplus Round Robin (SRR) • Minimizes packet processing overhead • SRR similar to WRR • Accounts for variable sized packets • Surplus (unused bandwidth) is carried on to next round

6. Related Work (Contd.) • Transport-Layer Solutions • RMTP • Reliable rate-based transport protocol • Flow and congestion control based on bandwidth estimation • Parallel TCP (pTCP) • Opens multiple TCP connections on each interface • Handles congestion and blackout through data reallocation and redundant striping • Network-Layer Solutions • Based on tunneling • Weighted round-robin based scheduling

7. Outline • Architecture • Scheduling algorithm • Evaluation • Analysis • Trace-based simulation • Ongoing work

8. Outline • Architecture • Scheduling algorithm • Evaluation • Analysis • Trace-based simulation • Ongoing work

9. Architecture for Bandwidth Aggregation • Link-Layer Solutions infeasible • End point is an IP address • Application/Transport Layer Solutions • Need to modify/rewrite code • Ensure compatibility with existing infrastructure • Network Layer solution • IP – a single standard • Application transparency and interoperability • Cleanest Solution

10. Our Architecture

11. Architecture Details • Mobile IP based • Packets pass through Home Agent (HA) • Simultaneous Binding - multiple Care-of-Address registration • Intelligent scheduling of packets to multiple addresses • Radio Access Network Selection Unit (RSU) • Located on Mobile Host (MH) • Selects right interfaces based on app. reqmts. and cost • Update bindings with HA • Traffic Management Unit (TMU) • Located on HA and MH • Processes and schedules the incoming traffic onto multiple paths • Conveys application type and end goal requirements to HA • Scheduling Algorithm in TMU is crucial • Focus on Interactive Real-Time Applications

12. Scheduling Algorithm – Design Considerations • Bandwidth • Interested in WWAN system (CDMA2000, GPRS etc) • Provide only a few hundred kbps • Not interested in WLAN/WPAN systems • Wireless hop is the bottleneck link • Delay/Jitter • Wireline Delay – between HA and Base-Station (BS) • Delay values and variation small • If large, variation may likely be masked at BS as wireless hop is bottleneck • Wireless Delay – between Base-Station and MH • Queuing delay and transmission delay

13. Scheduling Algorithm – Design Considerations • Qos Support • Interested in systems that provide QoS (CDMA2000, UMTS etc not HDR) • Negotiated bandwidth and loss rate guaranteed for duration of session

14. Design Possibility – Weighted Round Robin • Schedules packets based on bandwidths of interfaces • Not suitable for real-time applications • Example: • Three interfaces with bandwidth ratios 5:2:1 • Packets 1-5 sent on IF1, 6-7 sent on IF2, 8 on IF3 • Packet 6 arrives ahead of packets 3,4,5 • Packet 3 suffers excess delay due to reordering • Ideal ordering: IF1 – 1,2,4,5,6; IF2 – 3,7; IF3 – 8 • Variants of WRR – Surplus Round Robin (SRR), Shortest Queue First face similar problems

15. Our approach:Earliest Delivery First • For each path (between HA and MH), estimate arrival time of a packet at MH • Estimation based on • Bandwidth of the interface • One-way wireline delay (estimated) on the Internet path • Schedule the packet on the path that delivers the packet the earliest • Quick remarks • No need for synchronized clocks (relative one-way delay counts) • EDF is not work conserving • EDF cannot totally eliminate reordering • Multiple applications can be handled by combining EDF with Weighted Fair Queuing (WFQ)

16. EDF Details • Each path l is associated with three quantities • A variable , which is the time the channel becomes available next. • , the one-way wireline delay (estimate) of the path • , the bandwidth negotiated • - the arrival time, - the size of packet i, • Packet i scheduled on path l would be delivered at the MH at • EDF schedules the packet on the path p for which • is updated to

17. Performance of EDF • How well can EDF perform? • Can the application QoS requirements be met? • Is performance as good as having a Single-Link (SL) with the same aggregated bandwidth? • Approach • Analysis • Prove fairness of EDF in distributing bits across different links • Compare EDF with SL in terms of work, delay, jitter and buffering • Simulation • Consider application performance level metrics • Measure sensitivity of the algorithm to bandwidth asymmetry, number of interfaces, delay variation, channel losses

18. Properties of EDF • Notation: • - max packet Size, – number of interfaces, - bandwidth of link l, - weight of link l (normalized bandwidth) • Assumptions: • , and • When packets are of constant size, they arrive in order at the client • For variable sized packets – Given P packets to transmit, the maximum difference in normalized bits allocated to any two pair of links is • For WRR, this amount is a function of P and can be unbounded • For SRR it is

19. Properties of EDF (Contd.) • For any time t, the difference between the total number of bits W serviced by SL and EDF is • The difference in delay experienced by a packet i in SL and EDF is bounded by • The jitter experienced by a packet i without buffering is upper bounded by • The jitter experienced by a packet I with buffering is upper bounded by • The buffer size needed to deliver the packets in order is

20. Experimental Methodology • Trace driven simulation • Server • Video frame traces – office cam (Mpeg4 and H.263) • For MPEG-4, avg – 400kbps, peak - 2Mbps, frame period - 40ms • For H.263, avg – 260kbps, peak – 1.5Mbps, frame period - variable • Maximum packet size assumed is 1400 byte • Home Agent • Employs scheduling algorithm • Base-Station • No cross traffic • Serve packets first-come-first-serve basis

21. Experimental Methodology (Contd.) • Client • Begin video display after a fixed delay – startup latency L • Afterwards, display frames consecutively every t seconds (frame period) • Arrival after playback deadline results in frame loss • Startup latency bounds one-way delay of packets • Internet Path • Packet delay traces collected over different Internet paths • Hosts on UCSD, UCB, Duke, CMU • Wireline delay range used 15ms – 22 ms (one-way) • Algorithms under comparison • Single Link – SL • Surplus Round Robin - SRR

22. Application Performance Metrics • Backlog in the system • Delay experienced by packets • Frame Loss probability - Fraction of packets that miss playback deadline • Glitch Duration: Number of consecutive frames that cannot be displayed • Glitch Rate: Number of glitches/sec

23. Bandwidth Allocation % Bandwidth Needed over SL to achieve 0% frame loss, MPEG-4, BS = 3

24. Backlog • Bandwidth fixed at 600kbps SL EDF SRR Backlog in the system between HA and Client application, MPEG-4

25. Delay Distribution Cumulative Percentage of Delay, Mpeg-4, BS=3

26. Frame Loss probability

27. Sensitivity to Bandwidth Asymmetry

28. Sensitivity to Number of Interfaces

29. Extensions to EDF

30. Other Results • Delay Variation : EDF • Truncated Gaussian with mean 22ms, std. devn. 0-10ms • For a split 5:3:1 at 225ms, • No variation introduces 0.26% frame loss • 5ms variation, 0.27% frame loss • 10ms variation, 0.28% frame loss • Channel Losses • Limited retransmissions help • Other Applications • Non-Interactive Applications • Large tolerance for delay  no big difference in relative perf. • Video-On-Demand Applications • High peak-to-mean rates imply over-provisioning of bandwidth • Choice of scheduling algorithm does not matter

31. Summary • Network-layer architecture to enable multiple communication paths • EDF scheduling algorithm: reduces delay experienced by packets in presence of multi-path. • An analysis of the algorithm shows that it doesn’t differ much from idealized SL • Trace-driven simulations • EDF mimics SL closely • Outperforms by a large margin WRR based approaches

32. Ongoing Work • Bandwidth Aggregation in Best-Effort Systems • Bandwidth Estimation at MH • Work ahead scheduling • TCP • Support TCP applications • Network layer solutions • Ad-hoc Networks • Security