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Communication Networks

Communication Networks. Recitation 10. Multimedia, QoS & Multicast Routing. QoS. network provides application with level of performance needed for application to function. Quality of Service: What is it?. Multimedia applications: network audio and video. Multimedia QoS Requirements.

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Communication Networks

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  1. Communication Networks Recitation 10 Netcomm 2005

  2. Multimedia, QoS& Multicast Routing Netcomm 2005

  3. QoS network provides application with level of performance needed for application to function. Quality of Service: What is it? Multimedia applications: network audio and video Netcomm 2005

  4. Multimedia QoS Requirements • live sources, stored sources • requirements: deliver data in timely manner • short end-end delay for interactive multimedia • e.g., IP telephony, teleconf., virtual worlds, DIS • in time for “smooth” playout • relaxed reliability • 100% reliablity not always required Netcomm 2005

  5. need session’s input traffic must know app’s traffic demand To provide performance (delay, loss) guarantees: Why is QoS so hard? compute session’s output • scheduling discipline Netcomm 2005

  6. Netcomm 2005

  7. RTP - Real-time Transport Protocol • Ip-based protocol providing • time-reconstruction • loss detection • security • content identification • Designed primarily for multicast of real-time data Netcomm 2005

  8. General View • and the result… Netcomm 2005

  9. RTCP – Real-time Control Protocol • Designed to work together with RTP • In an RTP session the participants periodically send RTCP packet to give feedback on the quailty of the data • Comparable to flow and congestion control of other transport protocols • RTP produces sender and receivers reports; statistics and packet counts Netcomm 2005

  10. RTSP – Real-time Streaming Protocol • Client-server multimedia presentation protocol to enable controlled delivery. • Provides ”vcr”-style remote control • RTSP is an application-level protocol designed to work with RTP (and RSVP) to provide a complete streaming service over internet Netcomm 2005

  11. RTSP Cont. Multimedia Stream RTSP RTP UDP IP Ethernet IP header UDP header RTP header RTSP header Ethernet header Multimedia Data IP Packet Netcomm 2005

  12. HTTP GET presentation description (sdp) web server client SETUP media servers PLAY RTP audio/video RTCP TEARDOWN Example: Media on Demand Netcomm 2005

  13. Resource reservation call setup, signaling (RSVP) traffic, QoS declaration admission control • QoS-sensitive scheduling (e.g., WFQ) Intserv: QoS guarantees request/ reply Netcomm 2005

  14. RSVP –Reservation Protocol • Reservation is done in one direction • Receiver-initiated • The sender sends QoS wanted to the receiver which sends an RSVP message back to the sender • The sender does not need to know the capabilities along the path or at the receiver Netcomm 2005

  15. Guaranteed service: worst case traffic arrival: leaky-bucket-policed source simple bound on delay token rate, r bucket size, b per-flow rate, R WFQ D = b/R max Intserv QoS: Service Models Controlled load service: • "a quality of service closely approximating the QoS that same flow would receive from an unloaded network element." arriving traffic Netcomm 2005

  16. edge routers: profile of allowable user traffic packet marking: in-profile out-of-profile “stateless” core routers: • no notion of sessions • forwarding: in-profile have “priority” over out-of-profile Differentiated Services Netcomm 2005

  17. Complexity (per-flow state) at network edge leaky bucket marking High-speed, stateless core routers 1-bit determines forwarding behavior Over-provisioned bandwidth: for in-profile traffic used for out-profile, best effort traffic Differentiated Services Cont. Netcomm 2005

  18. D B H J E I F QoS Routing C K A • QoS Routing = Multiple parameter routing subject to constraints • Link metrics are vectors • NP-complete (good heuristics needed) delay: 10 ms bandwidth :100 Mb/s cell loss ratio: 1.0e-6 G Netcomm 2005

  19. The Problem Traditional unicast model does not scale • Millions of clients • Server and network meltdown Netcomm 2005

  20. Solution: IP Multicast • Source sends single stream • Routers split stream towards all clients • Guarantee only one copy in each link Netcomm 2005

  21. Multicast Routing Tree Multicast Routing Protocol On tree relay router Router with directly attached group members IGMP Netcomm 2005

  22. Internet Group Management Protocol (IGMP) • Used by routers to learn about Multicast Group Memberships on their directly attached subnets • Implemented over IP • Designated Router • Each network has one Querier • All routers begin as Queriers • Mrouter with the lowest IP address chosen Netcomm 2005

  23. How IGMP Works one router is elected the “querier” querier periodically sends a Membership Query messageto the all-systems group (224.0.0.1), with TTL = 1 on receipt, hosts start random timers (between 0 and 10 seconds) for each multicast group to which they belong routers: Q hosts: Netcomm 2005

  24. How IGMP Works (cont.) when a host’s timer for group G expires, it sends a Membership Report to group G, with TTL = 1 other members of G hear the report and stop their timers routers hear all reports, and time out non-responding groups Q G G G G Netcomm 2005

  25. Type of Service (TOS) Routing Does not support real QoS “high throughput” “low delay” Netcomm 2005

  26. Multicast Tree with QoS • QoS constraints • Link: minimum bandwidth; available buffer space. • Tree constraints: end-to-end delay; jitter. • Optimization objectives • Link: maximize bandwidth. • Tree optimization: minimize the cost. Netcomm 2005

  27. Core-Based Trees (CBT) • Core-based multicast routing: • One router is selected as the core for each multicast group. • A tree rooted at the core spans all group members. • Data packets are forwarded on all on-tree interfaces except the one on which packets arrive. Netcomm 2005

  28. CBT Multicast Routing Core Sender On tree relay router On tree router Router with directly attached group member Netcomm 2005

  29. Member Join in CBT Core join-ack join-request join-request join-ack Requesting router with a new member Netcomm 2005

  30. QoS-Aware Member Join Core Eligibility Test u On tree relay router join-request On tree group router join-request v Only after the join-request passes the eligibility tests will a join-acknowledgement be returned. Netcomm 2005

  31. Shortest Path Tree (SPT) • Source Based Tree:Rooted at the source, composed of the shortest paths between the source and each of the receivers in the multicast group. • If the routing metric used is the latency between neighbors, the resulted tree will minimize delay over the multicast group. • Example: DVMRP. Netcomm 2005

  32. Distance-Vector Multicast Routing Protocol (DMVRP) DVMRP consists of two major components: (1) a conventional distance-vector routing protocol (like RIP) (2) a protocol for determining how to forward multicast packets, based on the routing table and routing messages of (1) Netcomm 2005

  33. Example Topology g g s g Netcomm 2005

  34. Phase 1: Flooding g g s g Netcomm 2005

  35. Phase 2: Pruning g g prune (s,g) prune (s,g) s g Netcomm 2005

  36. Steady State g g g s g Netcomm 2005

  37. Joining on New Receivers g g g report (g) graft (s,g) graft (s,g) s g Netcomm 2005

  38. Steady State after Joining g g g s g Netcomm 2005

  39. Steiner Minimal Tree (SMT) • Shared Tree: All sources use the same shared tree. • SMT is defined to be the minimal cost subgraph (tree) spanning a given subset of nodes in a graph • Approximate SMT: KMB Netcomm 2005

  40. 5 Mcast group members 4 4 K J B A Relay Nodes F 2 1 2 5 3 5 E 2 1 C H 3 * 1 1 4 6 I D G An example of a Steiner Tree Netcomm 2005

  41. KMB Algorithm • Step 1: Construct a complete directed distance graph G1=(V1,E1,c1). • Step 2: Find the min spanning tree T1 of G1. • Step3: Construct a subgraph GS of G by replacing each edge in T1 by its corresponding shortest path in G. • Step 4: Find the min spanning tree TS of GS. • Step 5: Construct a Steiner tree TH from TS by deleting edges in TS if necessary, so that all the leaves in TH are Steiner points. Netcomm 2005

  42. KMB Algorithm Cont. Due to [Kou, Markowsky and Berman 81’] Worst case time complexity O(|S||V|2). Cost no more than 2(1 - 1/l) *optimal cost where l = number of leaves in the steiner tree. Netcomm 2005

  43. KMB Example A D 4 A A 4 1 1 4 4 4 10 4 H H 1/2 I B C 1/2 I 1/2 1/2 1 G G 1 1 A D 1 4 1 1 E F 1 1 B B F E 4 2 2 8 2 2 C D C 9 D 4 B C Destination Nodes Intermediate Nodes Netcomm 2005

  44. KMB Example Cont. A A 1 1 H I 1/2 I 1/2 1 1 G 1 1 E 1 1 E F F B B 2 2 2 2 C D C D Destination Nodes Intermediate Nodes Netcomm 2005

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