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Transcript
Communication Networks Recitation 10 Netcomm 2005 1 Multimedia, QoS & Multicast Routing Netcomm 2005 2 Quality of Service: What is it? Multimedia applications: network audio and video QoS network provides application with level of performance needed for application to function. Netcomm 2005 3 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 4 Why is QoS so hard? To provide performance (delay, loss) guarantees: need session’s input traffic • must know app’s traffic demand compute session’s output • scheduling discipline Netcomm 2005 5 Netcomm 2005 6 RTP - Real-time Transport Protocol • Ip-based protocol providing – time-reconstruction – loss detection – security – content identification • Designed primarily for multicast of realtime data Netcomm 2005 7 General View • and the result… Netcomm 2005 8 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 9 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 10 RTSP Cont. Ethernet IP header header UDP header Netcomm 2005 RTP header RTSP header Multimedia Data 11 Example: Media on Demand HTTP GET presentation description (sdp) client web server SETUP PLAY RTP audio/video media servers RTCP TEARDOWN Netcomm 2005 12 Intserv: QoS guarantees • Resource reservation – call setup, signaling (RSVP) – traffic, QoS declaration – admission control request/ reply – QoS-sensitive scheduling 2005 (e.g.,Netcomm WFQ) 13 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 14 Intserv QoS: Service Models Guaranteed service: Controlled load service: • worst case traffic arrival: leaky-bucket-policed source • simple bound on delay • "a quality of service closely approximating the QoS that same flow would receive from an unloaded network element." arriving traffic token rate, r bucket size, b WFQ per-flow rate, R D = b/R max Netcomm 2005 15 Differentiated Services 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 Netcomm 2005 “priority” over out-of-profile 16 Differentiated Services Cont. • 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 Netcomm 2005 17 QoS Routing C B A H E F D G K J I delay: 10 ms bandwidth :100 Mb/s cell loss ratio: 1.0e-6 • QoS Routing = Multiple parameter routing subject to constraints – Link metrics are vectors – NP-complete (good heuristics needed) Netcomm 2005 18 The Problem Traditional unicast model does not scale – Millions of clients – Server and network meltdown Netcomm 2005 19 Solution: IP Multicast • Source sends single stream • Routers split stream towards all clients • Guarantee only one copy in each link Netcomm 2005 20 Multicast Routing Tree Multicast Routing Protocol On tree relay router IGMP Router with directly attached group members Netcomm 2005 21 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 22 How IGMP Works routers: Q hosts: one router is elected the “querier” querier periodically sends a Membership Query message to 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 Netcomm 2005 23 How IGMP Works (cont.) Q G G G G 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 Netcomm 2005 24 Type of Service (TOS) Routing Does not support real QoS “high throughput” “low delay” Netcomm 2005 25 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 26 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 27 CBT Multicast Routing Core On tree relay router Sender On tree router Router with directly attached group member Netcomm 2005 28 Member Join in CBT Core join-ack join-request join-request join-ack Requesting router with a new member Netcomm 2005 29 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 30 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 31 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 32 Example Topology g g s g Netcomm 2005 33 Phase 1: Flooding g g s g Netcomm 2005 34 Phase 2: Pruning g g prune (s,g) s prune (s,g) g Netcomm 2005 35 Steady State g g g s g Netcomm 2005 36 Joining on New Receivers g g g report (g) graft (s,g) s graft (s,g) g Netcomm 2005 37 Steady State after Joining g g g s g Netcomm 2005 38 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 39 An example of a Steiner Tree 5 4 K F 1 3 Relay Nodes 5 2 3* 1 D A E C 4 I 1 2 5 J 2 B Mcast group members 4 6 H 1 G Netcomm 2005 40 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 41 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 42 KMB Example A A 4 1 10 H I 1/2 1/2 G 1 1 1 B 8 1 F 2 C 9 E 2 D B D 4 4 4 4 A 1 4 H C I 1/2 1/2 1 G A 4 1 D B 1 4 B 1 F 2 4 C E 2 D C Destination Nodes Intermediate NetcommNodes 2005 43 KMB Example Cont. A A 1 1 H 1/2 1/2 G B 1 1 F 2 C I I 1 1 E B 1 1 F 2 2 C D E 2 D Destination Nodes Intermediate Nodes Netcomm 2005 44