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Gearbox: Cache-friendly Congestion Control for ...

Gearbox: Cache-friendly Congestion Control for DASH

Yunfeng He, Varun Singh, Jörg Ott
Aalto University, Paris, ABR Workshop, 19.05.2015

Varun Singh

May 19, 2015
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  1. Rate  Switching 500kbps 800kbps 1000kbps 1200kbps Time line The clients

    switch between different representations of the same media content based on bandwidth estimation
  2. CDN  operation 0 1000 2000 3000 4000 5000 00:00 01:00

    02:00 03:00 04:00 05:00 06:00 07:00 08:00 Bitrate [kbps] CacheHit:Impulse; Miss:Blank DownloadTime Min:Second RepresentationBW ReceiveRate CacheHit
  3. Default  algorithm:  dash.js 0 1000 2000 3000 4000 5000 48:00

    50:00 52:00 54:00 56:00 58:00 00:00 02:00 04:00 Bitrate [kbps] CacheHit:Impulse; Miss:Blank DownloadTime Min:Second RepresentationBW ReceiveRate CacheHit • Caches segments. • May have incomplete representations • Innumerable switches This is the 101th client. 12 minute content. 1-2s chunk
  4. Gearbox • adaptation agility and adaptation accuracy. • network fluctuations

    (3G/LTE) and incomplete cached representations • Rate of change of buffer-fill level. • Relies on 2 main metrics: • buffer-fill level • end-to-end latency measurement
  5. Gearbox • Intuition: if the buffer is filling up •

    slowly, switch to a lower representation, smaller chunk size • quickly, switch to a higher resolution, larger chunk size. • At startup: • Adapt upwards slowly, want to get the content quickly • Representation level is only re-evaluated when drastic buffer-level-change happens. • Number of gears • 3 too few • 6 too many Checks current Gear position Gear-shift Flag boolean value? True No Upon last Segment received, Call Gearbox Signal the HTTP client to download the next segment Gear RSP & Input data COUNTER = CYCLE ? Yes False Evaluates representation ( decide Ri(t)+1 ) Checks the change of buffer-level ∆η & Compare ∆η with ∆g Threshold ∆g breached? Yes Increments COUNTER Checks buffer-level in percentage β Set Gear-shift Flag boolean to False Evaluates representation ( decide Ri(t)+1 ) Gear Boundary Reached? No Yes No Shift Gear & Set Gear-shift Flag boolean to True Reset COUNTER to Zero Output: Ri(t)+1 (representation for Next segment) Algorithm Input: β,∆η,Bc, Ri(t),{Ri|Ri R} ∈ Maintain previous representation level Ri(t)+1 : = Ri(t) Gearbox Algorithm β:real time buffer level ∆η:buffer level change Bc: current Bandwidth Ri(t):last chosen Rep Ri(t)+1: next chosen Rep {Ri|Ri R}: available Reps ∈ RSP: Rep switching policy ∆g: buffer level change threshold Not dive into the algorithm today
  6. Testbed • Content Server: • Nginx/Apache configured to listen several

    ports • Content in several representations and several chunk sizes. • Cache proxy: • LRU and heap LFUDA • Single cache, and cascaded cache • Client: • dash.js • Cache tests with multiple clients request the same content. • Clients have different end-to-end latencies • Poisson arrival • Metrics: • Number of Buffer underruns • Number of switches • Average buffer-fill level • Average bit rate
  7. Basic  Test  (vary  latency  1/2) • Trying to keep up

    buffer as full as possible. 0 20 40 60 80 100 00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 0 1 2 3 4 5 BufferLevel (in %) GearPosition(4 in total) Time Minute:Second Bufferlevel_Gearbox GearPosition_Gearbox Bufferlevel_Baseline
  8. Varying  Packet   loss 0 0.2 0.4 0.6 0.8 1

    0 20 40 60 80 100 CDF Bufferlevel(in %) plr0 plr.01 plr.02 plr.05 Remains at lowest representation
  9. Cascaded  Cache  (LFUDA) 0 1000 2000 3000 4000 5000 00:00

    01:00 02:00 03:00 04:00 05:00 06:00 07:00 Bitrate [kbps] CacheHit:Impulse; Miss:Blank DownloadTime Min:Second RepresentationBW ReceiveRate CacheHit 0 1000 2000 3000 4000 5000 00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 Bitrate [kbps] CacheHit:Impulse; Miss:Blank DownloadTime Min:Second RepresentationBW ReceiveRate CacheHit Baseline Gearbox
  10. Buffer  fill  level 0 20 40 60 80 100 00:00

    01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 0 1 2 3 4 5 BufferLevel (in %) GearPosition(4 in total) Time Minute:Second Bufferlevel_Gearbox GearPosition_Gearbox Bufferlevel_Baseline 0 0.2 0.4 0.6 0.8 1 0 1000 2000 3000 4000 5000 6000 CDF BitRate Baseline Gearbox
  11. Conclusions • Work in progress, need to compare with better

    than baseline (early) algorithms. • We find that LFUDA generates more cache hit for DASH, since LFUDA intend to keep big files in the cache. • Different Cache Replacement Policies can affect the cache hit rate in unique ways.