1 Netcomm 2005 Communication Networks Recitation 10

2 Netcomm 2005 Multimedia, QoS & Multicast Routing

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

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

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

6 Netcomm 2005

7 RTP - Real-time Transport Protocol Ip-based protocol providingIp-based protocol providing –time-reconstruction –loss detection –security –content identification Designed primarily for multicast of real- time dataDesigned primarily for multicast of real- time data

8 Netcomm 2005 General View and the result…and the result…

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

24 Netcomm 2005 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 GGGG

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

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

27 Netcomm 2005 Core-Based Trees (CBT) Core-based multicast routing: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.

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

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

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

31 Netcomm 2005 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.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.If the routing metric used is the latency between neighbors, the resulted tree will minimize delay over the multicast group. Example: DVMRP.Example: DVMRP.

32 Netcomm 2005 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)

33 Netcomm 2005 Example Topology gg s g

34 Netcomm 2005 Phase 1: Flooding gg s g

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

36 Netcomm 2005 Steady State gg s g g

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

38 Netcomm 2005 Steady State after Joining gg s g g

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

40 Netcomm 2005 An example of a Steiner Tree A B DG H I C F KJ E Mcast group members Relay Nodes *

41 Netcomm 2005 Step 1: Construct a complete directed distance graph G 1 =(V 1,E 1,c 1 ).Step 1: Construct a complete directed distance graph G 1 =(V 1,E 1,c 1 ). Step 2: Find the min spanning tree T 1 of G 1.Step 2: Find the min spanning tree T 1 of G 1. Step3: Construct a subgraph G S of G by replacing each edge in T 1 by its corresponding shortest path in G.Step3: Construct a subgraph G S of G by replacing each edge in T 1 by its corresponding shortest path in G. Step 4: Find the min spanning tree T S of G S.Step 4: Find the min spanning tree T S of G S. Step 5: Construct a Steiner tree T H from T S by deleting edges in T S if necessary, so that all the leaves in T H are Steiner points.Step 5: Construct a Steiner tree T H from T S by deleting edges in T S if necessary, so that all the leaves in T H are Steiner points. KMB Algorithm

42 Netcomm 2005 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. KMB Algorithm Cont.

43 Netcomm 2005 KMB Example A C D B A C D B A B CD EF G H I /2 2 1 B CD E F G H I A Destination Nodes Intermediate Nodes

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