In this chapter we have discussed the following:
IP Multicast enables many new types of applications and has the potential to significantly reduce network congestion and server load for certain classes of legacy applications. For applications that distribute identical information to multiple users, multicasts represent the best solution available to date; neither unicast nor broadcast mechanisms scale. Furthermore, multicasts are handled more efficiently by the receiver's NIC, and multicasts can be filtered or have security policy applied if required.
The emergence of networked multimedia applications is driving the development of protocols to support and control multicast packet flows from one or more sources to multiple recipients. IP Multicast traffic for a particular source-destination group pair (s, g) is delivered via a Spanning Tree, which connects all the hosts in the group. Different IP Multicast routing protocols use different techniques to construct these delivery trees.
IGMP operates effectively as an ES-IS type protocol for multicasts; it allows multicast group members to join or leave a group dynamically and maintains state information on router interfaces that can subsequently be used by multicast routing protocols to determine the delivery tree.
There are several multicast routing protocols available today, including PIM-SM, PIM-DM, MOSPF, DVMRP, and CBT. There are two basic distribution models: dense mode and sparse mode. Dense mode is generally only applicable to high-density enterprises; for internetworking applications sparse mode is preferred. CBT is optimized for gaming environments by producing a single delivery tree. DVMRP is a dense-mode, distance-vector protocol, now showing its age. MOSPF works well in environments that have relatively few source-group pairs active at any given time. PIM-DM is applicable for small, densely populated, pilot networks. PIM-SM is, for practical purposes, the only scalable solution for multicast routing in interior networks.
The MBone is an experimental overlay network that supports IP multicasting on the Internet. The MBone uses DVMRP tunneling techniques to interconnect islands of multicast use over unicast back-bone. In the future it is envisaged that many more Internet routers will become multicast enabled, and this will eventually negate the use of tunneling (in which case the MBone is likely to become obsolete). This could take some time.
A new breed of protocols has emerged in recent years to support real-time, reliable multicast distribution. These protocols include RTP, RTCP, RTSP, and RMP. The subject of reliable multicasting is an active area of research and experimentation, and the user is encouraged to keep up-to-date through the list of references and Web sites provided at the end of this chapter.
 www.ipmulticast.com, Home site for the IP Multicast Initiative (IPMI). Provides in-depth information including white papers and relevant RFCs on IP multicast. The site also offers a product and services directory and lists members of the IP Multicast Initiative who can be contacted for information and assistance.
 www.isi.edu/in-notes/iana/assignments/multicast-addresses, Current IANA multicast assignments.
 T. Kenyon, High-Performance Network Design: Design Techniques and Tools (Woburn, MA: Digital Press, 2001).
 Host Extensions for IP Multicasting, RFC 1112, August 1989.
 R. W. Stevens, UNIX Network Programming, vol. I (Englewood Cliffs, NJ: Prentice Hall, 1990).
 S. Deering, "IP Multicast Extensions for 4.3BSD and Related Systems," Stanford University, 1989. See http://portal.research.belllabs.com/ipmulticast.README.new.
 R. Davis, Win32 Network Programming (Reading, M: Addison-Wesley, 1996).
 www.sockets.com, Winsock development home page.
 www.intel.com, Search on Windows Sockets 2 Application Programming Interface, revision 2.2.0.
 www.intel.com, Search on Windows Sockets 2 Protocol-Specific Annex, revision 2.0.3, contains Sockets-compatible multicast APIs in the TCP/IP section and RSVP APIs.
 http://developer.apple.com/macos/opentransport, Apple MAC Open Transport Developer home page.
 Internet Group Management Protocol, Version 2, RFC 2236, November 1997.
 IP Router Alert Option, RFC 2113, February 1997.
 Distance Vector Multicast Routing Protocol, RFC 1075, November 1988.
 T. Pusateri, Distance Vector Multicast Routing Protocol. Internet Draft, draft-ietf-idmr-dvmrp-v3-09.txt, March 2000.
 S. Deering, "Multicast Routing in a Datagram Internetwork," Ph.D. dissertation, Stanford University, Electrical Engineering Dept., 1991.
 IP Encapsulation within IP, RFC 2003, October 1996.
 Multicast Extensions to OSPF, RFC 1584, March 1994.
 Protocol-Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification, RFC 2362, June 1998.
 Estrin,Farinacci,Helmy,Jacobson, and Wei, Protocol Independent Multicast (PIM), Dense Mode Protocol Specification. Internet Draft, draft-ietf-idmr-pim-dm-spec-05.ps, May 1997.
 Multicast Source Discovery Protocol (MSDP). Internet Draft, draft-ietf-msdp-spec-05.txt, February 2000.
 Core-Based Trees (CBT version 2) Multicast Routing: Protocol Specification, RFC 2189, September 1997.
 Core-Based Trees (CBT) Multicast Routing Architecture, RFC 2201, September 1997.
 D. Thaler,D. Estrin, and D. Meyer, Border Gateway Multicast Protocol (BGMP): Protocol Specification. Internet Draft draft-ietf-idmr-gum-01.txt, October 1997.
 A. J. Ballardie, Core-Based Tree (CBT) Multicast Border Router Specification. Internet Draft, draft-ietf-idmr-cbt-br-spec-01.txt, November 1997.
 V. Kumar, MBone: Interactive Media on the Internet (New Riders, 1996).
 Several MBONE topology maps are available at ftp://ftp.isi.edu/mbone/:
 www-sop.inria.fr/eng/welcome.html, Home page with links for INRIA videoconferencing system.
 Multiprotocol Extensions for BGP-4, RFC 2283, February 1998.
 D. Minoli and E. Minoli., Delivering Voice over IP Networks (New York: John Wiley & Sons, 1998).
 RTP: A Transport Protocol for Real-Time Applications, RFC 1889.
 RTP Profile for Audio- and VideoConferences with Minimal Control, RFC 1890.
 www.cs.columbia.edu/~hgs/rtp, a good source of information about RTP.
 www.realaudio.com/prognet/rt/, Research and General Information on RTSP.
 Criteria for Evaluating Reliable Multicast Transport and Application Protocols, RFC 2357, June 1998.
 gaia.cs.umass.edu/sigcomm_mcast/talkl.html, an overview of Reliable Multicast Protocols from the 8/96 ACM SIGCOMM Multicast Workshop.
 www.tascnets.com/mist/doc/mcpCompare.html, MIST Reliable Multicast Protocols Survey.
 RMF: A Transport Protocol Framework for Reliable Multicast Applications. Internet Draft <draft-decleene-rmf-01.txt>, February 1998.
 www.gcast.com, GlobalCast Communications home site. Commercial implementation of Reliable Multicast Protocol (RMP).
 research.ivv.nasa.gov/RMP/Docs/index.html, research information and specifications for Reliable Multicast Protocol (RMP).
 www.tascnets.com/panama/AER/index.html, The Active Error Recovery/Nominee-based Congestion Algorithm (AER/NCA) protocol. Version 1.1 of the software is available from this site.
 M. Handley,S. Floyd, and B. Whetten. Strawman Specification for TCP Friendly (Reliable) Multicast Congestion Control (TFMCC), IRTF Reliable Multicast Research Group (RMRG), work in progress.
 Internet Draft <draft-ietf-rmt-buildingblocks-02.txt>, Reliable Multicast Transport Building Blocks for One-to-Many Bulk-Data Transfer. March 2000.
 www.stardust.com, publishes several excellent white papers on IP multicasting.
 SDP: Session Description Protocol, RFC 2327, April 1998.
 SIP: Session Initiation Protocol, RFC 2543.
 SAP: Session Announcement Protocol, Version 2. Internet draft draft-ietf-mmusic-sap-v2-01.txt, June 1999.