Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
csc chp2 flashcards
topics = video streaming and CDNs
| Question | Answer |
|---|---|
| what is stream video traffic | major consumer of internet bandwidth (netflix, youtube, amzon prime - 80% of residential ISP traffic) |
| what's the challenge is there for video streaming | heterogeneity, different users have different capabilities (weird vs mobile / bandwidth rich vs bandwidth poor) |
| what's the solution for heterogeneity | distributed / application-level infrastructure |
| what is multimedia video | a sequence of images displayed at a constant rate (24 images/sec) |
| what is multimedia digital image | array of pixels (pixel represented by bits) |
| what is multimedia coding | uses redundancy within and between images to decrease # bits used to encode image (spatial - within image / temporal - from one image to next) |
| what does CBR stand for | constant bit rate |
| what is CBR | video encoding rate fixed |
| what does VBR stand for | variable bit rate |
| what is VBR | video encoding rate changes as amount of spatial, temporal coding changes |
| what are some examples of multimedia video | MPEG1 (CD-ROM) 1.5Mbps / MPEG2 (DVD) 3-6Mbps / MPEG4 (often used in internet) 64Kbps-12Mbps |
| what are the main challenges regarding streaming a stored video | server to client bandwidth will vary over time, with changing network congestion levels / packet loss and delay due to congestion will delay playout or result in poor video quality |
| how does streaming work | at this time (now), client playing out early part of video, while server still sending later part of the video still to be played |
| what is the main challenges regarding streaming stored video | continuous playout constraint = once client playout begins playback must match original time (but network delays are variable, so will need client-side buffer to match playout requirements) |
| what are some other challenges regarding streaming stored videos | client interactive = pause, fast-forward, rewind, jump through video / video packets may be lost or retransmitted |
| what does client-side buffering and playout delay do | compensate for network-added delay / jitter |
| what does DASH stand for | Dynamic Adaptive Streaming over HTTP |
| what's the purpose of a server when streaming multimedia | divides video file into multiple chunks / each chunk stored, encoded at different rates / manifest file = provides urls for different chunks |
| what's the purpose of a client when streaming multimedia | periodically measures server-to-client bandwidth / consulting manifest, requests one chunk at a time (chooses max coding rate sustainable given current bandwidth / can choose different coding rates at different points in time) |
| using DASH what does a client determine | when to request chunk (so that buffer starvation or overflow doesn't occur) / what encoding rate to request (higher quality when more bandwidth available) / where to request chunk (can request from url server that is close to client) |
| what is the formula for streaming a video | encoding + DASH + playout buffering |
| what does CDN stand for | content distribution networks |
| what is the main challenge for CDN | how to stream content (selected from millions of videos) to hundreds of thousands of simultaneous users |
| what's one option to resolve main challenge for CDN | single point of failure / point of network congestion / long path to distant clients / multiple copies of video sent over outgoing link |
| what's another option to resolve the challenge regarding CDN | store/serve multiple copies of videos at multiple geographically distributed sites |
| define "enter deep" | push CDN servers deep into many access networks (close to users) |
| define "bring home" | smaller number (10's) of larger clusters in POPs near but not within access networks (used by Limelight) |
| what is the purpose of CDN | stores copies of content at CDN nodes (netflix stores copies of madmen) |
| how does a subscribers request content from CDN | retrieve content, directed to nearby copy / may choose different copy if network path congested |
| what does OTT stand for | over the top |
| what are some OTT challenges | coping with a congested internet (from which CDN node to retrieve content / viewer behaviour in presence of congestion / what content to place in which CDN node) |
| END of video streaming and content distribution networks | slide 99 |
Created by:
NtokozoN
Popular Computers sets