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Multimedia Networking

Multimedia Networking. #6 IP Multicast Semester Ganjil 2012 PTIIK Universitas Brawijaya. Schedule of Class Meeting. Introduction Applications of MN Requirements of MN Coding and Compression RTP IP Multicast IP Multicast (cont ’ d) . Overlay Multicast CDN: Solutions

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Multimedia Networking

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

  2. Schedule of Class Meeting • Introduction • Applications of MN • Requirements of MN • Coding and Compression • RTP • IP Multicast • IP Multicast (cont’d) • Overlay Multicast • CDN: Solutions • CDN: Case Studies • QoS on the Internet: Constraints • QoS on the Internet: Solutions • Discussion • Summary Multmedia Networking

  3. Today’s Outline • IP Multicast • Concept and components • Addressing architecture • IP Multicast Protocols Multmedia Networking

  4. IP Multicast

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

  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 Networking

  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 Networking

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

  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 Networking

  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 Data Data Sender Receiver Multmedia Networking

  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 Routing protocol Multicast Router Multicast Router Join/Leave request Query Announcement Sender Receiver Discovery Multmedia Networking

  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 Networking

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

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

  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 Networking

  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 Networking

  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 Networking

  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 Multicast Router Join/Leave request Query Sender host Receiver host Multmedia Networking

  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 Networking

  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 Networking

  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 Networking

  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 Networking

  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 Networking

  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 Networking

  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 Networking

  28. Router-to-Router Multicast Protocols

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

  30. legend group member not group member router with a group member router without group member source-based trees 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 • source-based:different tree from each sender to rcvrs shared tree Multmedia Networking

  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 Networking

  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 Networking

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

  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 Networking

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

  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 LEGEND s: source R1 router with attached group member R4 R2 router with no attached group member P P R5 prune message R3 P links with multicast forwarding R6 R7 Multmedia Networking

  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 Networking

  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 Networking

  39. Tunneling Q: how to connect “islands” of multicast routers in a “sea” of unicast routers? logical topology physical topology • 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 Multmedia Networking

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

  41. 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 Consequences of sparse-dense dichotomy: Multmedia Networking

  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 Networking

  43. R1 R4 explicit join and prune: center-based approach, SPT to the source router sends joinmsg 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 join R2 join R5 join R3 R6 R7 PIM - sparse mode all data multicast from rendezvous point rendezvous point Multmedia Networking

  44. R1 R4 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!” join R2 join R5 join R3 R6 R7 PIM - sparse mode all data multicast from rendezvous point rendezvous point Multmedia Networking

  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 Networking

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