Multicast Outline Multicast revisited Protocol Independent Multicast - SM Future Directions

Multicast Revisited Motivation: multiple hosts wish to receive the same data from one or more senders Multicast routing defines extensions to IP routers to support broadcasting data in IP networks Until now IP has only facilitated a point to point routing Multicast data is sent and received at a multicast address which defines a group Simple notion of a group is a TV channel Data is sent and received in multicast groups via routing trees from sender(s) to receivers. Protocols are principally concerned with setting up and maintaining trees Note: All multicast messaging is sent via unicast Fall, 2001 CS 640

Protocol types Dense mode protocols Sparse mode protocol assumes dense group membership Source distribution tree and NACK type DVMRP (Distance Vector Multicast Routing Protocol) PIM-DM (Protocol Independent Multicast, Dense Mode) Example: Company-wide announcement Sparse mode protocol assumes sparse group membership Shared distribution tree and ACK type PIM-SM (Protocol Independent Multicast, Sparse Mode) Examples: a Shuttle Launch Fall, 2001 CS 640

PIM-SM overview (1) Developed due to scaling issues Flooding is generally a real bad idea Based on creating routing tree for a group with Rendezvous Point (RP) as a root for the tree RP is a focus for both senders and receivers Explicit join model Receivers send Join towards the RP Sender send Register towards the RP Supports both shared (default) and source trees RPF check depends on tree type For shared tree (between RP and receivers), uses RP address For source tree (between RP and source), uses Source address Fall, 2001 CS 640

PIM-SM overview(2) Only one RP is chosen for a particular group RP statically configured or dynamically learned (Auto-RP, PIM v2 candidate RP advertisements) Data forwarded based on the source state (S, G) if it exists, otherwise use the shared state (*, G) (*,G) means all senders RFC2362 – “PIM Sparse Mode Protocol Spec” (experimental) Internet Draft: draft-ietf-pim-v2-sm-00.txt (October 1999) Fall, 2001 CS 640

PIM-SM Basics PIM Neighbor Discovery PIM SM Forwarding PIM SM Joining PIM SM Registering PIM SM SPT-Swichover PIM SM Pruning PIM SM Bootstrap PIM SM State Maintenance Fall, 2001 CS 640

PIM SM Tree Maintenance Periodic Join/Prunes are sent to all PIM neighbors Periodic Joins refresh interfaces in a PIM neighbor’s downstream list Periodic Prunes refresh pruned state of a PIM neighbor There is a designated router (DR) for each local network and all other routers get pruned Received multicast packets reset (S,G) entry expiration timers. (S,G) entries are deleted if timers expire Fall, 2001 CS 640

PIM-SM(1) S A B RP D C E R2 R1 Source Receiver 1 Receiver 2 Fall, 2001 CS 640

PIM-SM(2) S Receiver 1 Joins Group G C Creates (*, G) State, Sends (*, G) Join to the RP Source A B RP D Join C E R2 R1 Receiver 1 Receiver 2 Fall, 2001 CS 640

PIM-SM(3) S A B RP D C E R2 R1 RP Creates (*, G) State Source Receiver 1 Receiver 2 Fall, 2001 CS 640

PIM-SM(4) S Source Sends Data A Sends Registration to the RP Source IP tunnel between A and RP since multicast tree is not established Register Data A B RP D C E R2 R1 Receiver 1 Receiver 2 Fall, 2001 CS 640

PIM-SM(5) S RP decapsulates Registration Forwards Data Down the Shared Tree Sends Joins Towards the Source Source join join A B RP D C E R2 R1 Receiver 1 Receiver 2 Fall, 2001 CS 640

PIM-SM(6) S RP Sends Register-Stop Once Data Arrives Natively Source Register-Stop A B RP D C E R2 R1 Receiver 1 Receiver 2 Fall, 2001 CS 640

PIM-SM(7) SPT Switchover C Sends (S, G) Joins to Join the Shortest Path Tree (SPT) Source A B RP D join C E R2 R1 Receiver 1 Receiver 2 Fall, 2001 CS 640

PIM-SM(8) S A B RP D C E R2 R1 C starts receiving Data natively Source Receiver 1 Receiver 2 Fall, 2001 CS 640

PIM-SM(9) S C Sends Prunes Up the RP tree for the Source. RP Deletes (S, G) OIF and Sends Prune Towards the Source Source Prune Prune A B RP D Prune C E R2 R1 Receiver 1 Receiver 2 Fall, 2001 CS 640

PIM-SM(10) S A B RP D C E R2 R1 B, RP pruned Source Receiver 1 Fall, 2001 CS 640

PIM-SM(11) S A B RP D C E R2 R1 Source New receiver2 joins E Creates State and Sends (*, G) Join A B RP D C E join R2 R1 Receiver 1 Receiver 2 Fall, 2001 CS 640

PIM-SM(12) S A B RP D C E R2 R1 Source C Adds Link Towards E to the OIF List of Both (*, G) and (S, G) Data from Source Arrives at E A B RP D C E R2 R1 Receiver 1 Receiver 2 Fall, 2001 CS 640

Inter-Domain Multicast Routing BGP4+ (Multicast BGP) for short-term solution Tweeks to BGP4 to support multicast Multicast Address Set and Claim (MASC) Hierarchical multicast address allocation at domain level Dynamic allocation (not permanent) of addresses by “set and claim with collision” Border Gateway Multicast Protocol (BGMP) Use a PIM-like protocol between domains (“BGP for multicast”) Fall, 2001 CS 640

MASC Assume Addr(A) is allocated to domain A and domains B and C sit “below” A in a domain hierarchy B selects Addr(B) which is subset of Addr(A) and send claim (addr(B)) message to A and C A forwards claim to all children except B. If any of A’s children is already using Addr(B) they will report a collision to A. A will notify B of the collision and B will select other address space. Address space information is used to create distribution tree using BGMP. Stored in M-RIB (Multicast Routing Information Base) Fall, 2001 CS 640

BGMP BGMP builds shared tree of domains for a group Uses a rendezvous mechanism at the domain level Shared tree is bidirectional Root of shared tree of domains is at root domain Runs in routers that border a multicast routing domain Runs over TCP Joins and prunes travel across domains Can build unidirectional source trees M-IGP (multicast Intra-Gateway Protocol) tells the borders about group membership Fall, 2001 CS 640

Multicast Routers mrouted (Xerox PARC) : DVMRP GateD (Merit) : DVMRP, PIM-DM, PIM-SM Cisco IOS : DVMRP, PIM-DM, PIM-SM Fall, 2001 CS 640

M-Bone Wide area IP multicast test bed using IP-in-IP tunneling Routing protocol DVMRP is used Transition to PIM (DM, SM) is ongoing Started in March 1992 for audio broadcasting of IETF meeting (San Diego) Latest tolopology ftp://ftp.parcftp.xerox.com/pub/net-research/mbone/maps/mbone-map-big.ps About 6000 (S,G) entries Discussion list: mbone@isi.edu Fall, 2001 CS 640

Session Directory Fall, 2001 CS 640

Example Session Fall, 2001 CS 640

M-BONE in 1994 Fall, 2001 CS 640

M-BONE in 1996 Fall, 2001 CS 640

M-BONE in 1998 Fall, 2001 CS 640

Future Mulicast Service Current multicast service - latency and packet drop Research for “Reliable multicast” is actively going on for; large scale interactive gaming on the Internet Distributed databases large scale news distribution etc. Fall, 2001 CS 640

Reliable multicast technology SRM ( Scalable Reliable Multicast) multicast with re-transmit (with random back-off) All nodes can re-transmit datagram (Multicast/Unicast) MTP (Multicast Transport Protocol: RFC1301) FEC (Forward Error Correction) error packet recovery by redundant packets Fall, 2001 CS 640