Gearbox: Cache-friendly Congestion Control for DASH

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

Transcript

1. Gearbox Yunfeng He, Varun Singh, Jörg Ott Aalto University
2. Rate  Switching 500kbps 800kbps 1000kbps 1200kbps Time line The clients switch between different representations of the same media content based on bandwidth estimation
3. 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
4. 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
5. 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
6. 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
7. 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
8. 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
9. Basic  Test  (vary  latency  2/2)
11. 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
12. 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
13. 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
14. LFUDA Baseline Gearbox
15. 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.