1. November 27 th, 2012 CS1652 Jack Lange University of Pittsburgh 1

2. OMET Question r Compared to other Pitt CS classes I learned: r (1) Much Less r (2) Slightly Less r (3) The same amount r (4) Slightly More r (5) A lot more 7: Multimedia Networking 7-2

3. 7: Multimedia Networking 7-3 Multimedia and Quality of Service: What is it? multimedia applications: network audio and video (“continuous media”) network provides application with level of performance needed for application to function. QoS

4. Multimedia Networking Application 4

5. 7: Multimedia Networking 7-5 MM Networking Applications Fundamental characteristics: r typically delay sensitive m end-to-end delay m delay jitter r loss tolerant: infrequent losses cause minor glitches r antithesis of bulk data, which is loss intolerant but delay tolerant. Classes of MM applications: 1) stored streaming 2) live streaming 3) interactive, real-time Jitter is the variability of packet delays within the same packet stream

6. 7: Multimedia Networking 7-6 Streaming Stored Multimedia Stored streaming: r media stored at source r transmitted to client r streaming: client playout begins before all data has arrived r timing constraint for still-to-be transmitted data: in time for playout

7. 7: Multimedia Networking 7-7 Streaming Stored Multimedia: What is it? 1. video recorded 2. video sent 3. video received, played out at client Cumulative data streaming: at this time, client playing out early part of video, while server still sending later part of video network delay time

8. 7: Multimedia Networking 7-8 constant bit rate video transmission Cumulative data time variable network Delay (jitter) client video reception constant bit rate video playout at client client playout delay buffered video Streaming Multimedia: Client Buffering r client-side buffering, playout delay compensate for network-added delay, delay jitter

9. 7: Multimedia Networking 7-9 Streaming Multimedia: Client Buffering r client-side buffering, playout delay compensate for network-added delay, delay jitter buffered video variable fill rate, x(t) constant drain rate, d

10. 7: Multimedia Networking 7-10 Streaming Live Multimedia Examples: r Internet radio talk show r live sporting event Streaming (as with streaming stored multimedia) r playback buffer r playback can lag tens of seconds after transmission r still have timing constraint Interactivity r fast forward impossible r rewind, pause possible

11. 7: Multimedia Networking 7-11 Real-Time Interactive Multimedia r end-end delay requirements: m audio: < 150 msec good, < 400 msec OK includes application-level (packetization) and network delays higher delays noticeable, impair interactivity r session initialization m how does callee advertise its IP address, port number, encoding algorithms? r applications: IP telephony, video conference, distributed interactive worlds

12. 7: Multimedia Networking 7-12 Multimedia Over Today’s Internet TCP/UDP/IP: “best-effort service” r no guarantees on delay, loss Today’s Internet multimedia applications use application-level techniques to mitigate (as best possible) effects of delay, loss But multimedia apps require QoS and level of performance to be effective! ? ? ?? ? ? ? ? ? ? ?

13. 7: Multimedia Networking 7-13 Internet Phone: Packet Loss and Delay r network loss: IP datagram lost due to network congestion (router buffer overflow) r delay loss: IP datagram arrives too late for playout at receiver m delays: processing, queueing in network; end- system (sender, receiver) delays m typical maximum tolerable delay: 400 ms r loss tolerance: depending on voice encoding, losses concealed, packet loss rates between 1% and 10% can be tolerated.

14. 7: Multimedia Networking 7-14 Internet Phone: Fixed Playout Delay r receiver attempts to playout each chunk exactly q msecs after chunk was generated. m chunk has time stamp t: play out chunk at t+q. m chunk arrives after t+q: data arrives too late for playout, data “lost” r tradeoff in choosing q: m large q: less packet loss m small q: better interactive experience

15. 7: Multimedia Networking 7-15 Fixed Playout Delay sender generates packets every 20 msec during talk spurt. first packet received at time r first playout schedule: begins at p second playout schedule: begins at p’

16. 7: Multimedia Networking 7-16 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

17. 7: Multimedia Networking 7-17 Content distribution networks (CDNs) Content replication r CDN (e.g., Akamai) customer is the content provider (e.g., CNN) r CDN replicates customers’ content in CDN servers. r 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

18. 7: Multimedia Networking 7-18 CDN example origin server (www.foo.com) r distributes HTML r replaces: http://www.foo.com/sports.ruth.gif with h ttp://www.cdn.com/www.foo.com/sports/ruth.gif HTTP request for www.foo.com/sports/sports.html DNS query for www.cdn.com HTTP request for www.cdn.com/www.foo.com/sports/ruth.gif 1 2 3 origin server CDN’s authoritative DNS server CDN server near client CDN company (cdn.com) r distributes gif files r uses its authoritative DNS server to route redirect requests client

19. 7: Multimedia Networking 7-19 Summary: Internet Multimedia: bag of tricks r use UDP to avoid TCP congestion control (delays) for time-sensitive traffic r client-side adaptive playout delay: to compensate for delay r server side matches stream bandwidth to available client-to-server path bandwidth m chose among pre-encoded stream rates m dynamic server encoding rate r error recovery (on top of UDP) m FEC, interleaving, error concealment m retransmissions, time permitting r CDN: bring content closer to clients

20. ZeroConf Networking r What: m Non-administered networks m Full Plug-and-Play architecture m No centralized services to configure (DNS, DHCP, etc) r Only need to plug computer into network m Automatically assigns address m Automatically discovers services m Automatically negotiates protocols and connections r For local networks mostly m Not easy to allow external (internet) connectivity 7: Multimedia Networking 7-20

21. Finding an Address r Do not require anyone to provide an address m No network administrator m No DHCP server r Step 1: Select a random address m Special range dedicated to internal zeroconf networks r Step 2: Probe to check if address is already taken m How? r Step 3: Assign address to interface 7: Multimedia Networking 7-21

22. What is multicast r So far we’ve talked about unicast and broadcast r Multicast is “in between” r Each interface has an IP address m But also selectively listens for multicast addresses r Each network device has MAC address m But also selectively listens for multicast addresses r One host can send a packet to anyone who wants to receive it m Mechanism for self defined group communication m TCP doesn’t really work, but UDP is fine 7: Multimedia Networking 7-22

23. Multicast DNS r Dedicated TLD:.local r Dedicated Multicast Address: 224.0.0.251 r Send out a DNS request to a multicast group m If a group member has that name they respond r Example m When you buy a new computer you give it a name E.g. “My Mac Laptop” m The DNS address is now “My Mac Laptop.local” If someone queries for that hostname your laptop responds Sort of like an ARP query 7: Multimedia Networking 7-23

24. Service Discovery r Service Discovery extension to DNS (DNS-SD) m DNS used to identify services (not computers) m Based on Multicast r Special domain name format m Instance.ServiceType.Domain m E.g. My iTunes._daap._tcp.local r Query for ServiceTypes m Enumerate all instances of a service r DNS is based on Multicast! m So we can send a query for _daap._tcp.local to EVERYONE! m If a computer is running a given service they respond with their instance name 7: Multimedia Networking 7-24