CPSC 441: Multimedia Networking1 Outline r Scalable Streaming Techniques r Content Distribution Networks

CPSC 441: Multimedia Networking2 Streaming Popular Content r Consider a popular media file m Playback rate: 1 Mbps m Duration: 90 minutes m Request rate: once every minute r How can a video server handle such high loads? m Approach 1: Start a new “stream” for each request m Allocate server and disk I/O bandwidth for each request m Bandwidth required at server= 1 Mbps x 90

CPSC 441: Multimedia Networking3 Streaming Popular Content using Batching r Approach 2: Leverage the multipoint delivery capability of modern networks r Playback rate = 1 Mbps, duration = 90 minutes r Group requests in non-overlapping intervals of 30 minutes: m Max. start-up delay = 30 minutes m Bandwidth required = 3 channels = 3 Mbps Time (minutes) Channel 1 Channel 2 Channel 3

CPSC 441: Multimedia Networking4 Batching Issues r Bandwidth increases linearly with decrease in start-up delays r Can we reduce or eliminate “start-up” delays? m Periodic Broadcast Protocols m Stream Merging Protocols

CPSC 441: Multimedia Networking5 Periodic Broadcast Example r Partition the media file into 2 segments with relative sizes {1, 2}. For a 90 min. movie: m Segment 1 = 30 minutes, Segment 2 = 60 minutes r Advantage: m Max. start-up delay = 30 minutes m Bandwidth required = 2 channels = 2 Mbps r Disadvantage: Requires increased client capabilities Time (minutes) Channel 1 Channel 2

CPSC 441: Multimedia Networking6 Skyscraper Broadcasts (SB) r Divide the file into K segments of increasing size m Segment size progression: 1, 2, 2, 5, 5, 12, 12, 25, … r Multicast each segment on a separate channel at the playback rate r Aggregate rate to clients: 2 x playback rate [Hua & Sheu 1997]

CPSC 441: Multimedia Networking7 Comparing Batching and SB Server Bandwidth Start-up Delay BatchingSB 1 Mbps90 minutes 2 Mbps45 minutes30 minutes 6 Mbps15 minutes3 minutes 10 Mbps9 minutes30 seconds r Playback rate = 1 Mbps, duration = 90 minutes r Limitations of Skyscraper: m Ad hoc segment size progress m Does not work for low client data rates

CPSC 441: Multimedia Networking8 Reliable Periodic Broadcasts (RPB) r Optimized PB protocols (no packet loss recovery) m client fully downloads each segment before playing m required server bandwidth near minimal m Segment size progression is not ad hoc m Works for client data rates < 2 x playback rate [Mahanti et al. 2001, 2003, 2004]

CPSC 441: Multimedia Networking9 Reliable Periodic Broadcasts (RPB) r Optimized PB protocols (no packet loss recovery) m client fully downloads each segment before playing m required server bandwidth near minimal m Segment size progression is not ad hoc m Works for client data rates < 2 x playback rate r extend for packet loss recovery r extend for “bursty” packet loss r extend for client heterogeneity [Mahanti et al. 2001, 2003, 2004]

CPSC 441: Multimedia Networking10 Optimized Periodic Broadcasts r r = segment streaming rate = 1 r s = maximum # streams client listens to concurrently = 2 r b = client data rate = s x r = 2 r length of first s segments: r length of segment k  s:

CPSC 441: Multimedia Networking11 Outline r Scalable Streaming Techniques r Content Distribution Networks

CPSC 441: Multimedia Networking12 Content distribution networks (CDNs) Content replication r Challenging to stream large files (e.g., video) from single origin server in real time r Solution: replicate content at hundreds of servers throughout Internet m content downloaded to CDN servers ahead of time m placing content “close” to user avoids impairments (loss, delay) of sending content over long paths m CDN server typically in edge/access network origin server in North America CDN distribution node CDN server in S. America CDN server in Europe CDN server in Asia

CPSC 441: Multimedia Networking13 Content distribution networks (CDNs) Content replication r CDN (e.g., Akamai, Limewire) customer is the content provider (e.g., CNN, YouTube) r CDN replicates customers’ content in CDN servers. When provider updates content, CDN updates servers origin server in North America CDN distribution node CDN server in S. America CDN server in Europe CDN server in Asia

CPSC 441: Multimedia Networking14 CDN example origin server ( r distributes HTML r replaces: with h ttp:// HTTP request for DNS query for HTTP request for Origin server CDNs authoritative DNS server Nearby CDN server CDN company (cdn.com) r distributes gif files r uses its authoritative DNS server to route redirect requests

CPSC 441: Multimedia Networking15 More about CDNs routing requests r CDN creates a “map”, indicating distances from leaf ISPs and CDN nodes r when query arrives at authoritative DNS server: m server determines ISP from which query originates m uses “map” to determine best CDN server r CDN nodes create application-layer overlay network