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Introduction to Multicast

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					            Introduction to Multicast
                            Spencer Tsai
            Mobile Communication & Broadband Network Lab
                                CSIE
Multicast




                      Fu-Jen Catholic University



                                                           1
                             Outline
            •   Overview
            •   IGMP
            •   Multicast Routing on the Internet
            •   Multicast Routing between Domains
            •   Reference
Multicast




                                                    2
                           Overview
            •   Unicast
            •   Multicast
            •   Multicast Characteristic
            •   IP Multicast Address
            •   Examples of permanent groups
Multicast




            •   Architecture of Multicast

                                               3
                              Unicast
                                            Receiver




            Host

                              Router



            .Point to point
Multicast




            .N receivers, send n times
            .Not suitable for group communication
                                                       4
                               Multicast
                                                 Receiver




            Host

                                 Router



                   .1 sender and n receivers
Multicast




                   .N receivers, only send 1 times
                   .Suitable for group communication
                                                            5
                    Benefits of Multicast
            • Saves bandwidth by enhancing network
              efficiency in distribution of data
            • Group communication and services
            • Supports distributed applications
              – distance learning
              – videoconferencing
Multicast




            • Reduces the cost to deploy applications
                                                        6
                  Multicast Characteristic
            • RFC 1112
            • Each multicast group identified by class-
              D IP address
            • Receivers can present anywhere
            • Receivers can join and leave anytime
            • Sender don’t need to be a member
Multicast




            • No membership list exist, use routers to
              manage groups
                                                      7
                           IP Multicast Address
                                            8                 16                  24               32

            Class A    0       Net ID                    IP system

            Class B    1   0                Net ID                        IP system

            Class C    1   1     0                   Net ID                            IP system

            Class D    1   1     1      0                     Multicast address
                •Multicast address range
Multicast




                      Class D IP Address-higher order 4 bits are set
                      224.0.0.0 ---239.255.255.255
                                                                                              8
            Examples of permanent groups
            224.0.0.0   Reserved
            224.0.0.1   All systems in a subnet

            224.0.0.2   All routers in a subnet

            224.0.0.3   Not allocated
            224.0.0.4   All DVMRP routers in a subnet
Multicast




            224.0.0.9   Routers with RIP Version 2 in a
                        subnet
                                                          9
                       Architecture of Multicast
                            Sender




                                        Multicast Routing
                   Router
Multicast




                                        IGMP
                                        IGMP version 2
            Receiver
                                                            10
                             Outline
            •   Overview
            •   IGMP
            •   Multicast Routing on the Internet
            •   Multicast Routing between Domains
            •   Reference
Multicast




                                                    11
                                    IGMP
            •Internet Group Management Protocol (IGMP)
            •Group management within edge networks
            •RFC 1112 – IGMP version 1
            •RFC 2236 – IGMP version 2 (widely uesd)
            •Similar to the ICMP(Internet Control Message Protocol)
Multicast




            •Router sends query to their directly hosts to manage group
            membership
            •Different Hosts may join more than one multicast group
                                                                          12
                        IGMP – Join a Group
                                                     Multicast Router




            Report                                                      Report
                         Host 1          Host 2           Host 3
                     224.2.2.2                            224.2.2.3
Multicast




                     •Joining members sends report
                     •Different hosts can join different multicast group
                                                                            13
              IGMP – General Query

                                        Multicast Router
             General query to
             224.0.0.1




             Host 1          Host 2          Host 3
Multicast




            •Router periodically sends general query to
             224.0.0.1(all systems in a subnet)

                                                           14
               IGMP – Maintaining a Group
                                                     Multicast Router
                         General query to
                         224.0.0.1

            Report                                                  suppress
            224.2.2.2                                               224.2.2.2
                           Host 1           Host 2        Host 3
                        224.2.2.2                      224.2.2.2
                        •Two steps:
Multicast




                           First, router sends general query
                           Second, member send report
                        •Only one member needs to send report
                                                                        15
             IGMP – Leaving a Group
            General query to              Multicast Router
            224.0.0.1




                Host 1         Host 2          Host 3
             •Router continue to send general query periodically
             •Members silently leave group
Multicast




             • No report receive by router
             •Group times out

                                                                   16
                IGMP - Querier Selection
                               MRouter 1            MRouter 2
                               1.1.1.1              1.1.1.2




                 Host 1          Host 2          Host 3
            •    Initially, all routers are querier and send query
            •    Then, only one router with the lowest IP address is
Multicast




                 selected as the actual Querier
            •    The other routers are Non-Querier

                                                                       17
                             Outline
            •   Overview
            •   IGMP
            •   Multicast Routing on the Internet
            •   Multicast Routing between Domains
            •   Reference
Multicast




                                                    18
            Multicast Routing on the Internet
            •   DVMRP
            •   MOSPF
            •   PIM-DM
            •   PIM-SM
            •   CBT
Multicast




                                                19
                               DVMRP
            • Distance Vector Multicast Routing Protocol
              (DVMRP)
            • Distance vector algorithm that determines the
              shortest path (hop count)
            • Like RIP, maintains a routing table
            • Uses RPF(Reverse Path Forwarding)
Multicast




              – The first data is flooded to the entire network
              – No members or terminating membership, do pruning

                                                                   20
                         DVMRP (cont.)
            • Graft is used to reconnect an old area or
              connect a new area
              – Member to source
            • Graft ack. Indicates that a graft has been
              received correctly
              – Source to member
Multicast




            • Designated forwarder
              – First, lowest metric to a source
              – Second, lowest IP address
                                                       21
                                 MOSPF
            • Multicast Extensions to Open Shortest Path
              First
            • OSPF
              – Hello
              – Synchronize database description
              – Link state advertisement
            • MOSPF
Multicast




              – Local group membership must be known in the routers
              – A separate multicast tree has to be calculated for each
                pair consisting of sender and group G(S,G)
                                                                          22
                     MOSPF (cont.)
                     Autonomous System
                                              Boundary AS
                                                 router
                        BR
             Domain
                                                            AS
                                    R

                                              R
                      BR        Backbone
            Domain
Multicast




                                         BR
                               Domain


                                                             23
                             PIM-DM
            • Protocol Independent Multicasting-
              Dense Mode (PIM-DM)
            • Members are not widely distributed,
              density of group member is very high
            • Uses flooding, pruning and graft
            • Similar to DVMRP
Multicast




              – Without the routing information exchange part
              – Differs in some details
                                                                24
                     PIM-DM (cont.)
                             Source       Initial



                                 A


                         B            D
Multicast




                    C                        E



            Receiver 1
                                                    25
                     PIM-DM (cont.)
                             Source
                                          Flooding

                                 A


                         B            D
Multicast




                    C                     E



            Receiver 1
                                                     26
                     PIM-DM (cont.)
                             Source
                                                   Pruning

                                 A
                                      Pruning
                         B               D

                                                Pruning
Multicast




                    C                             E

                                                  Pruning

            Receiver 1
                                                             27
                     PIM-DM (cont.)
                             Source
                                          Steady state

                                 A


                         B            D
Multicast




                    C                     E



            Receiver 1
                                                         28
                     PIM-DM (cont.)
                             Source
                                                        A receiver is joining
                                                        Graft
                                 A


                         B                         D
                                                       Graft
Multicast




                    C                                     E



            Receiver 1                Receiver 2
                                                                           29
                     PIM-DM (cont.)
                             Source
                                                       Steady state

                                 A


                         B                         D
Multicast




                    C                                  E



            Receiver 1                Receiver 2
                                                                      30
                          PIM-SM
            • Protocol Independent Multicasting-
              Sparse Mode (PIM-SM)
            • Based on that systems are located far
              away from each other, density of group
              member is low=>B.W. tends to be small
            • Membership is based on explicit join
Multicast




              operations
            • Data is sent to the rendezvous point
                                                       31
                             PIM-SM (cont.)
            • Bootstrap routers distribute information
              about rendezvous points
                                                Multicast
                                                 border
                            PIM router           router
                                                               Non-PIM
                                                            enabled domain
Multicast




               PIM router          PIM router


                        Bootstrap router
                            PIM domain                                       32
                       PIM-SM (cont.)
                                Sender

                                              Data
                           PIM Router 3              PIM resister
                                                     data unit
                                            PIM join
                 PIM Router 2                                       Rendezvous
                                             PIM join
                                 PIM join
Multicast




            PIM Router 1

                              IGMP join

               Receiver
                                                                            33
                       PIM-SM (cont.)
                                Sender



                           PIM Router 3
                                          delete

                 PIM Router 2                             Rendezvous
Multicast




            PIM Router 1                           PIM join
                                                   Pruning data unit
                                                   Data
               Receiver
                                                                       34
                                    CBT
            • Core-Based Trees(CBT)
            • Based on concept of rendezvous point, in this
              case called cores
            • Uses a bidirectional multicast tree
              – PIM is unidirectional
            • Use of Hello mechanism
Multicast




            • Restriction to one rendezvous point
            • Bootstrap mechanism
                                                              35
                            Outline
            •   Overview
            •   IGMP
            •   Multicast Routing on the Internet
            •   Multicast Routing between Domains
            •   Reference
Multicast




                                                    36
            Multicast Routing Between
                     Domains
                                                               Multicast
                                                               Domain
                                                      BGMP
                                                      Router
                        BGMP
            Multicast   Router
                                       BGMP routing
            Domain
Multicast




                              BGMP              BGMP
                  Multicast   Router            Router
                                                          Multicast
                  Domain                                  Domain

                                                                           37
                 Multicast Routing Between
                      Domains (cont.)
            • BGMP(Border Gateway Multicast Protocol)
               – Based on CBT and PIM-SM(avoid flooding)
               – BGMP join and prune data unit are transmitted
                 over TCP
               – Multicast routing can throughout the internet by
                 using BGMP
Multicast




               – Connection between multicast domain
                 autonomous system
                                                                38
                          Reference
            • Multicast Communication, writed by
              Ralph Wittmann and Martina Zitterbart,
              Morgan Kaufmann publish
            • http://www.ietf.org/html.charters/pim-
              charter.html
            • http://www.cs.ucsb.edu/~almeroth
Multicast




            • http://www.cisco.com
            • http://www.cs.wisc.edu/~lhl/
                                                       39

				
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