Department of Computer and IT Engineering University of Kurdistan Computer Networks II Multicasting By: Dr. Alireza Abdollahpouri

2 یکی از مهمترین دلایل استفاده از چندپخشی، صرفه جویی در پهنای باند است Multicast vs. Unicast

3 IP multicast DVMRP,PIM, MOSPF IGMP Multicast routing protocols Group management protocol

4 دسترسی به پایگاه داده های توزیع شده انتشار اطلاعات و اخبار Teleconferencing آموزش از راه دور IPTV بازيهای چندنفره Some applications of multicasting

Multicast Applications ConferenceXP: An Example of Multicast application Video Conference Distance Learning 5

Multicast Issues  Naming and addressing (IP class D) ( نحوه آدرسدهی )  Membership Management (IGMP) ( نحوه مدیریت گروههای چندپخشی )  Routing (DVMRP, PIM, MOSPF, …) ( نحوه هدایت بسته های چندپخشی )

7 Network multicast Router actively participate in multicast, making copies of packets as needed and forwarding towards multicast receivers Multicast routers (red) duplicate and forward multicast datagrams Multicast: one sender to many receivers Multicast: act of sending datagram to multiple receivers with single “transmit” operation analogy: one teacher to many students Question: how to achieve multicast (چندپخشی در لایه شبکه)

8 In network-layer multicasting, the router may forward the received packet through several of its interfaces. Note:

9 Application-layer multicast end systems involved in multicast copy and forward unicast datagrams among themselves Multicast: one sender to many receivers (چندپخشی در لایه کاربرد)

10 Multicast groups  class D Internet addresses reserved for multicast:  host group semantics: oanyone can “join” (receive) multicast group oanyone can send to multicast group ono network-layer identification to hosts of members  needed: infrastructure to deliver mcast-addressed datagrams to all hosts that have joined that multicast group

11 تحویل‌بسته‌های‌چند‌پخشی‌در‌لایه‌پیوند‌داده

12 Change the multicast IP address to an Ethernet multicast physical address. Solution We can do this in two steps: 1- We write the rightmost 23 bits of the IP address in hexadecimal. This can be done by changing the rightmost 3 bytes to hexadecimal and then subtracting 8 from the leftmost digit if it is greater than or equal to 8. In our example, the result is 2B:0E: We add the result of part a to the starting Ethernet multicast address, which is 01:00:5E:00:00:00. The result is: Example

13 Group management protocol (IGMP) DVMRP,PIM, MOSPF IGMP Multicast routing protocols Group management protocol

14 IGMP is a group management protocol. It helps a multicast router create and update a list of loyal members related to each router interface. Note:

15 IGMP message types

16 Encapsulation of IGMP packet بسته بندی پیغامهایICMP در قالب بسته های IP و سپس فریمهای لایه پایینتر

17 IGMP message format 8 bytes حداکثر زمان پاسخ (بر حسب 1/0 ثانیه) در پیغامهای Query

18 IGMP type field TypeValue General or special query0x11 or Membership report0x16 or Leave report0x17 or

19 IGMP operation

20 Membership report

21 Leave report No Response

22 The general query message does not define a particular group. Note:

23 General query message No Response

24 Example Imagine there are three hosts in a network, as shown in Figure below. A query message was received at time 0; the random delay time (in tenths of seconds) for each group is shown next to the group address. Show the sequence of report messages.

25 Solution The events occur in this sequence: 1.Time 12. The timer for in host A expires and a membership report is sent, which is received by the router and every host including host B which cancels its timer for Time 30. The timer for in host A expires and a membership report is sent, which is received by the router and every host including host C which cancels its timer for Time 50. The timer for in host B expires and a membership report is sent, which is received by the router and every host. 4.Time 70. The timer for in host C expires and a membership report is sent, which is received by the router and every host including host A which cancels its timer for

26 Multicast routing protocols DVMRP,PIM, MOSPF IGMP Multicast routing protocols Group management protocol

27 In unicast routing, each router in the domain has a table that defines a shortest path tree to possible destinations. Note:

28 Shortest path tree in unicast routing

29 In multicast routing, each involved router needs to construct a tree for each group. Note:

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  source-based: different tree from each sender to rcvrs  shared-tree: same tree used by all group members Shared treeSource-based trees

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

Shortest Path Tree  mcast forwarding tree: tree of shortest path routes from source to all receivers  Dijkstra’s algorithm R1 R2 R3 R4 R5 R6 R i router with attached group member router with no attached group member link used for forwarding, i indicates order link added by algorithm LEGEND S: source

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:

Reverse Path Forwarding: example result is a source-specific reverse SPT –may be a bad choice with asymmetric links R1 R2 R3 R4 R5 R6 R7 router with attached group member router with no attached group member datagram will be forwarded S: source datagram will not be forwarded

Multicast Forwarding RPF Check Fails! Unicast Route Table Unicast Route Table Network Interface /16S /24S /24E0 RPF Check Fails A closer look: RPF Check Fails Packet Arrived on Wrong Interface! E0 S1 S0 S2 S1 Multicast Packet from Source X Discard Packet!

Multicast Forwarding RPF Check Succeeds A closer look: RPF Check Succeeds RPF Check Succeeds! Unicast Route Table Unicast Route Table Network Interface /16S /24S /24E0 E0 S1 S0 S2 Multicast Packet from Source Packet Arrived on Correct Interface!S1 Forward out all outgoing interfaces. (i. e. down the distribution tree)

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

38 Problem with RPF

39 RPF versus RPB برای اینکه هر شبکه یک کپی از بسته چندپخشی را دریافت کند برای آن یک روتر به عنوان والد تعریف می کنیم.

Center-based trees  single delivery tree shared by all  one router identified as “center” of tree  to join:  edge router sends unicast join-msg addressed to center router  join-msg “processed” by intermediate routers and forwarded towards center  join-msg either hits existing tree branch for this center, or arrives at center  path taken by join-msg becomes new branch of tree for this router

Center-based trees: an example Suppose R6 chosen as center: R1 R2 R3 R4 R5 R6 R7 router with attached group member router with no attached group member path order in which join messages generated

42 Group-shared tree with rendezvous router

43 Sending a multicast packet to the rendezvous router

44 In CBT, the source sends the multicast packet (encapsulated in a unicast packet) to the core router. The core router decapsulates the packet and forwards it to all interested interfaces. Note:

45 Taxonomy of common multicast protocols

DVMRP  Distance Vector Multicast Routing Protocol  DV + RPF + Pruning  DV vector carries distance to multicast sources  Pruning carries a timeout (prune lifetime)  Afterwards, traffic delivery is resumed  Explicit graft message to reverse pruning  Done upon join Prune جهت هرس کردن درخت و Graft برای ایجاد شاخه جدید در درخت

MOSPF  Multicast Extensions to OSPF  Link-state advertisements include multicast group membership  Only report directly connected hosts  Compute shortest-path spanning tree rooted at source  On demand, when receiving packet from source for the first time  Forward multicast traffic along tree

48 PIM Protocol Independent Multicast (PIM) is the name given to two independent multicast routing protocols: Protocol Independent Multicast, Dense Mode (PIM-DM) and Protocol Independent Multicast, Sparse Mode (PIM-SM).

49 PIM-DM is used in a dense multicast environment, such as a LAN. Note:

50 PIM-DM uses RPF and pruning/grafting strategies to handle multicasting. However, it is independent from the underlying unicast protocol. Note:

51 PIM-SM is used in a sparse multicast environment such as a WAN. Note: PIM-SM is similar to CBT but uses a simpler procedure.

52 MBONE A multicast router may not find another multicast router in the neighborhood to forward the multicast packet. A solution for this problem is tunneling. We make a multicast backbone (MBONE) out of these isolated routers using the concept of tunneling.

53 Logical tunneling

54 MBONE

55 QuestionsQuestions