1. Multimedia Networking #6 IP Multicast Semester Ganjil 2012 PTIIK Universitas Brawijaya

2. Schedule of Class Meeting 1.Introduction 2.Applications of MN 3.Requirements of MN 4.Coding and Compression 5.RTP 6.IP Multicast 7.IP Multicast (cont’d) 8.Overlay Multicast 9.CDN: Solutions 10.CDN: Case Studies 11.QoS on the Internet: Constraints 12.QoS on the Internet: Solutions 13.Discussion 14.Summary Multmedia Networking2

3. Today’s Outline IP Multicast – Concept and components – Addressing architecture – IP Multicast Protocols Multmedia Networking3

4. IP Multicast

5. Multicast Many receivers – Receiving the same content Applications – Video conferencing – Online gaming – IP television (IPTV) – Financial data feeds Multmedia Networking5

6. Iterated Unicast Unicast message to each recipient Advantages – Simple to implement – No modifications to network Disadvantages – High overhead on sender – Redundant packets on links – Sender must maintain list of receivers Multmedia Networking6

7. IP Multicast Embed receiver-driven tree in network layer – Sender sends a single packet to the group – Receivers “join” and “leave” the tree Advantages – Low overhead on the sender – Effective use of network resources Avoids redundant network traffic Disadvantages – Control-plane protocols for multicast groups – Overhead of duplicating packets in the routers Multmedia Networking7

8. Multicast Communication 1 flows of a packet 10 flows of the same packet Unicast Multicast sender Multmedia Networking8

9. IP Multicast Communication Concept – Multicast data sender sends the data only once, and only the intended recipients (who want to receive the data) receive the data IP multicast provides one-to-many or many-to-many communication effectively – Each data (i.e. multicast stream) is classified by multicast address (and source address if SSM is used) – Non-reliable communication (i.e. on top of UDP) IP multicast is basically applied to real-time applications Multmedia Networking9

10. Data Flow Data sender – Sender sends data once Data receiver – Receiver that has requested getting the data receives the data Multicast routers – Router copies and forwards the data only toward the data receivers Multicast Router SenderReceiver Data Multmedia Networking10

11. Communication Flow Control messages – Sender announces the session information or receivers discover the session information – Each receiver requests to start and stop receiving data by “join and leave” operations – Multicast routers maintains membership state by having reports Multicast Router SenderReceiver Join/Leave request Announcement Discovery Query Multicast Router Routing protocol Multmedia Networking11

12. Multicast Addresses Multicast “group” defined by IP address – Multicast addresses look like unicast addresses – 224.0.0.0 to 239.255.255.255 Using multicast IP addresses – Sender sends to the IP address – Receivers join the group based on IP address – Network sends packets along the tree Multmedia Networking12

13. Example Multicast Protocol Receiver sends a “join” messages to the sender – And grafts to the tree at the nearest point A B G D E c F Multmedia Networking13

14. IP Multicast is Best Effort Sender sends packet to IP multicast address – Loss may affect multiple receivers A B G D E c F Multmedia Networking14

15. Terminologies Group address (or multicast address) – Used for destination address Join and leave – Data reception state requested by receiver hosts Join and prune – Data reception state requested by routers (*,G) and (S,G) – Notation of source address and group address in join-and-leave (or join-and-prune) state Multmedia Networking15

16. Terminologies Scope – Expected data distribution area – Classified by multicast address or TTL TTL (Time To Live) or Hop limit – Expected maximum hop count of each packet IIF and OIF – IIF: Incoming interface from which data is received – OIF: Outgoing interface to which data is sent Multmedia Networking16

17. Terminologies Multicast session – Multicast data stream classified by the “multicast address” is called “multicast session” Multicast channel – Multicast data stream explicitly classified by the pair of “multicast address” and “source address” is called “multicast channel” Used for SSM Multmedia Networking17

18. Multicast Protocols Host-to-Router Protocols – IGMPv1, IGMPv2, IGMPv3, MLDv1, MLDv2 Router-to-Router Protocols – DVMRP, MOSPF, CBT, PIM-DM, PIM-SM, PIM-SSM Multicast Router Sender host Receiver host Join/Leave request Query Multicast Router Multmedia Networking18

19. Multicast Address Assignment

20. IP Multicast Simple to use in applications – Multicast “group” defined by IP multicast address IP multicast addresses look similar to IP unicast addrs 224.0.0.0 to 239.255.255.255 (RPC 3171) – 265 M multicast groups at most – Best effort delivery only Sender issues single datagram to IP multicast address Routers delivery packets to all subnetworks that have a receiver “belonging” to the group Receiver-driven membership – Receivers join groups by informing upstream routers – Internet Group Management Protocol (v3: RFC 3376) Multmedia Networking20

21. IP Multicast Address IP multicast address – IPv4: 224.0.0.0 – 239.255.255.255 – IPv6: FFx0::1 – MUST be specified as a destination address – MUST NOT be specified as a source address Dynamic address assignment – Regular applications select their multicast addresses dynamically Some multicast addresses are assigned by IANA for special uses Multmedia Networking21

22. IPv4 Multicast Addresses IPv4 multicast address – 224.0.0.0 (0xe0000000) - 239.255.255.255 (0xefffffff) +----+----+---------+------------+ | 4 | 28 bits | +----+----+---------+------------+ |1110| group address | +----+----+---------+------------+ – Administrative scope [RFC2365] – Local address (224/24) – Administrative scope (239/8) – Organization-Local (239.192/14) – GLOP address (233/8) [RFC3180] – EGLOP (233.252.0.0 - 233.255.255.255) [RFC3138] – SSM address (232/8) [RFC] Multmedia Networking22

23. IPv6 Multicast Addresses IPv6 multicast address: FFxx:: +--------+----+----+---------------------------------------------+ | 8 | 4 | 4 | 112 bits | +--------+----+----+---------------------------------------------+ |11111111|flgs|scop| group ID | +--------+----+----+---------------------------------------------+ – Flags 000T (T=1: transient, T=0: well-known) – Scope 0x1: Interface Local 0x2: Link-Local 0x3: Subnet-Local 0x4: Admin-Local 0x5: Site-Local 0x8: Organization-Local 0xE: Global – SSM address (FF3x::/32 (or 96)) [RFC3306] Multmedia Networking23

24. Host-to-Router Multicast Protocols

25. IGMP v1 Two types of IGMP msgs (both have IP TTL of 1) – Host membership query: Routers query local networks to discover which groups have members – Host membership report: Hosts report each group (e.g., multicast addr) to which belong, by broadcast on net interface from which query was received Routers maintain group membership – Host senders an IGMP “report” to join a group – Multicast routers periodically issue host membership query to determine liveness of group members – Note: No explicit “leave” message from clients Multmedia Networking25

26. IGMP: Improvements IGMP v2 added: – If multiple routers, one with lowest IP elected querier – Explicit leave messages for faster pruning – Group-specific query messages IGMP v3 added: – Source filtering: Join specifies multicast “only from” or “all but from” specific source addresses Multmedia Networking26

27. IGMP: Parameters and Design Parameters – Maximum report delay: 10 sec – Membership query internal default: 125 sec – Time-out interval: 270 sec = 2 * (query interval + max delay) Is a router tracking each attached peer? – No, only each network, which are broadcast media Should clients respond immediately to queries? – Random delay (from 0..D) to minimize responses to queries – Only one response from single broadcast domain needed What if local networks are layer-2 switched? – L2 switches typically broadcast multicast traffic out all ports – Or, IGMP snooping (sneak peek into layer-3 contents), Cisco’s proprietary protocols, or static forwarding tables Multmedia Networking27

28. Router-to-Router Multicast Protocols

29. Multicast Tree A B G D E c F Multmedia Networking29

30. Multicast routing: problem statement goal: find a tree (or trees) connecting routers having local mcast group members tree: not all paths between routers used shared-tree: same tree used by all group members shared tree source-based trees group member not group member router with a group member router without group member legend  source-based: different tree from each sender to rcvrs Multmedia Networking30

31. Approaches for building mcast trees approaches: source-based tree: one tree per source – shortest path trees – reverse path forwarding group-shared tree: group uses one tree – minimal spanning (Steiner) – center-based trees …we first look at basic approaches, then specific protocols adopting these approaches Multmedia Networking31

32. Single vs. Multiple Senders Source-based tree – Separate tree for each sender – Tree is optimized for that sender – But, requires multiple trees for multiple senders Shared tree – One common tree – Spanning tree that reaches all participants – Single tree may be inefficient – But, avoids having many different trees Multmedia Networking32

33. Shortest path tree mcast forwarding tree: tree of shortest path routes from source to all receivers – Dijkstra’s algorithm i router with attached group member router with no attached group member link used for forwarding, i indicates order link added by algorithm LEGEND R1 R2 R3 R4 R5 R6 R7 2 1 6 3 4 5 s: source Multmedia Networking33

34. Reverse path forwarding if (mcast datagram received on incoming link on shortest path back to center) then flood datagram onto all outgoing links else ignore datagram  rely on router’s knowledge of unicast shortest path from it to sender  each router has simple forwarding behavior: Multmedia Networking34

35. Reverse path forwarding: example  result is a source-specific reverse SPT  may be a bad choice with asymmetric links router with attached group member router with no attached group member datagram will be forwarded LEGEND R1 R2 R3 R4 R5 R6 R7 s: source datagram will not be forwarded Multmedia Networking35

36. Reverse path forwarding: pruning forwarding tree contains subtrees with no mcast group members – no need to forward datagrams down subtree – “prune” msgs sent upstream by router with no downstream group members router with attached group member router with no attached group member prune message LEGEND links with multicast forwarding P R1 R2 R3 R4 R5 R6 R7 s: source P P Multmedia Networking36

37. Internet Multicasting Routing: DVMRP DVMRP: distance vector multicast routing protocol, RFC1075 flood and prune: reverse path forwarding, source- based tree – RPF tree based on DVMRP’s own routing tables constructed by communicating DVMRP routers – no assumptions about underlying unicast – initial datagram to mcast group flooded everywhere via RPF – routers not wanting group: send upstream prune msgs Multmedia Networking37

38. DVMRP: continued… soft state: DVMRP router periodically (1 min.) “forgets” branches are pruned: – mcast data again flows down unpruned branch – downstream router: reprune or else continue to receive data routers can quickly regraft to tree – following IGMP join at leaf odds and ends – commonly implemented in commercial router Multmedia Networking38

39. Tunneling Q: how to connect “islands” of multicast routers in a “sea” of unicast routers?  mcast datagram encapsulated inside “normal” (non- multicast-addressed) datagram  normal IP datagram sent thru “tunnel” via regular IP unicast to receiving mcast router (recall IPv6 inside IPv4 tunneling)  receiving mcast router unencapsulates to get mcast datagram physical topology logical topology Multmedia Networking39

40. PIM: Protocol Independent Multicast not dependent on any specific underlying unicast routing algorithm (works with all) two different multicast distribution scenarios : dense:  group members densely packed, in “close” proximity.  bandwidth more plentiful sparse:  # networks with group members small wrt # interconnected networks  group members “widely dispersed”  bandwidth not plentiful Multmedia Networking40

41. Consequences of sparse-dense dichotomy: dense group membership by routers assumed until routers explicitly prune data-driven construction on mcast tree (e.g., RPF) bandwidth and non-group- router processing profligate sparse : no membership until routers explicitly join receiver- driven construction of mcast tree (e.g., center- based) bandwidth and non-group- router processing conservative Multmedia Networking41

42. PIM- dense mode flood-and-prune RPF: similar to DVMRP but…  underlying unicast protocol provides RPF info for incoming datagram  less complicated (less efficient) downstream flood than DVMRP reduces reliance on underlying routing algorithm  has protocol mechanism for router to detect it is a leaf-node router Multmedia Networking42

43. PIM - sparse mode explicit join and prune: center-based approach, SPT to the source router sends join msg to rendezvous point (RP) – intermediate routers update state and forward join after joining via RP, router can switch to source-specific tree – increased performance: less concentration, shorter paths all data multicast from rendezvous point rendezvous point join R1 R2 R3 R4 R5 R6 R7 Multmedia Networking43

44. sender(s): unicast data to RP, which distributes down RP-rooted tree RP can extend mcast tree upstream to source RP can send stop msg if no attached receivers – “no one is listening!” all data multicast from rendezvous point rendezvous point join R1 R2 R3 R4 R5 R6 R7 PIM - sparse mode Multmedia Networking44

45. Conclusion of Today’s Lecture IP Multicast runs on top of UDP under best-effort IP network – suitable for real-time applications IP Multicast is efficient-use of network resources – suitable for one-many or many-many communication IP Multicast requires – specific address assignment – host-to-router protocols – router-to-router protocols Multmedia Networking45