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CSE 30264 Computer Networks

CSE 30264 Computer Networks. Prof. Aaron Striegel Department of Computer Science & Engineering University of Notre Dame Lecture 20 – March 25, 2010. Today’s Lecture. Project 3 In-Class Exercise Network Issues Quality of Service. Application. Transport. Network. Data. Physical.

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CSE 30264 Computer Networks

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  1. CSE 30264Computer Networks Prof. Aaron Striegel Department of Computer Science & Engineering University of Notre Dame Lecture 20 – March 25, 2010

  2. Today’s Lecture • Project 3 • In-Class Exercise • Network Issues • Quality of Service Application Transport Network Data Physical CSE 30264

  3. Quality of Service Outline Realtime Applications Integrated Services Differentiated Services CSE30264

  4. Sampler, Microphone A D Buffer, D A converter Speaker Realtime Applications • Require “deliver on time” assurances • must come from inside the network • Example application (audio) • sample voice once every 125us • each sample has a playback time • packets experience variable delay in network • add constant factor to playback time: playback point CSE30264

  5. Example Distribution of Delays CSE30264

  6. Integrated Services • Service Classes • guaranteed • controlled-load • Mechanisms • resource reservation (signalling) • admission control • policing • packet scheduling CSE30264

  7. Flowspec • Rspec: describes service requested from network • controlled-load: none • guaranteed: delay target • Tspec: describes flow’s traffic characteristics • average bandwidth + burstiness: token bucket filter • token rate r • bucket depth B • must have a token to send a byte • must have n tokens to send n bytes • start with no tokens • accumulate tokens at rate of r per second • can accumulate no more than B tokens CSE30264

  8. Per-Router Mechanisms • Admission Control • decide if a new flow can be supported • answer depends on service class • not the same as policing • Packet Processing • classification: associate each packet with the appropriate reservation • scheduling: manage queues so each packet receives the requested service CSE30264

  9. Reservation Protocol • Called signalling in ATM • Proposed Internet standard: RSVP • Consistent with robustness of today’s connectionless model • Uses soft state (refresh periodically) • Designed to support multicast • Receiver-oriented • Two messages: PATH and RESV • Source transmits PATH messages every 30 seconds • Destination responds with RESV message • Merge requirements in case of multicast • Can specify number of speakers CSE30264

  10. Sender 1 PATH R Sender 2 R PATH RESV (merged) R RESV Receiver A R RESV R Receiver B RSVP Example CSE30264

  11. RSVP • Associate packet with reservation (classifying): • source address, destination address, protocol number, source port, destination port • Manage packets in queues (scheduling). CSE30264

  12. RSVP versus ATM (Q.2931) • RSVP • receiver generates reservation • soft state (refresh/timeout) • separate from route establishment • QoS can change dynamically • receiver heterogeneity • ATM • sender generates connection request • hard state (explicit delete) • concurrent with route establishment • QoS is static for life of connection • uniform QoS to all receivers CSE30264

  13. Differentiated Services • Problem with IntServ: scalability • Idea: segregate packets into a small number of classes • e.g., premium vs best-effort • Packets marked according to class at edge of network • Core routers implement some per-hop-behavior (PHB) • Example: Expedited Forwarding (EF) • rate-limit EF packets at the edges • PHB implemented with class-based priority queues or WFQ CSE30264

  14. Assured Forwarding (AF) customers sign service agreements with ISPs edge routers mark packets as being “in” or “out” of profile core routers run RIO: RED with in/out DiffServ (cont) CSE30264

  15. Coding • Form into small groups • Twist: Must sit by people who you did not work with on the project Build a simple UDP chat server CSE 30264

  16. Write Threaded Code • UDP Server • Step 1 • Listen on port X (pass in via parameter) • Read message / display on screen CSE 30264

  17. Write Threaded Code • UDP Server • Step 1 • Listen on port X (pass in via parameter) • Read message / display on screen • Step 2 • Keep track of incoming IP / ports • Design • Local vs. global • struct vs. class CSE 30264

  18. Write Main Function • main function • Step 1 • Start up the thread • Loop until input is QUIT! • Step 2 • Send the typed text to all known other clients • Step 3 • Allow adding of IP via syntax • ADDCLIENT 129.74.20.40 8908 • Step 4 • Dump current client list via DUMPSTATUS CSE 30264

  19. Moment of Zen CSE 30264

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