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IP Multicasting: Explaining Multicast

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  1. IP Multicasting: Explaining Multicast BSCI Module 7 Lesson 1

  2. Objectives • Describe the IP multicast group. • Compare and contrast Unicast packets and multicast packets. • List the advantages and disadvantages of multicast traffic. • Discuss two types of multicast applications. • Describe the types of IP multicast addresses. • Describe how receivers can learn about a scheduled multicast session.

  3. Multicast Overview

  4. IP Multicast Distribute information to large audiences over an IP network

  5. E Learning 150 Universities in US, Hawaii, Oregon, USC, UCLA, Berkley Corporate CommunicationHP, IBM, Intel, Ford, BMW, Dupont Research Community MBONE Financials NASDAQ, NYSE, LIFE, Morgan, GS, Prudential Early AdoptersNASA, DOD, Cisco, Microsoft, Sprint MXU & Content ProvidersFastweb, B2, Yahoo, BBC, CNN Multicast VPN C&W, MCI, AT&T, TI, FT, DT, NTT Surveillance Law Enforcement and Federal IPv6 MulticastNTT, Sony, Panasonic, z z z Multicast AdoptionPast, Present, and Future Multicast (1986-2005) Multicast Deployment 1986 1992 1996 1997 1998 2000 2001 2002 2003 2004 2005 Time

  6. Why Multicast? • Used when sending same data to multiple receivers • Better bandwidth utilization • Less host/router processing • Used when addresses of receivers unknown • Used when simultaneous delivery for a group of receivers is required (simulcast)

  7. Unicast vs. Multicast

  8. Multicast Advantages Enhancedefficiency: Controls network traffic and reduces server and CPU loads Optimizedperformance: Eliminates traffic redundancy Distributedapplications: Makes multipoint applications possible

  9. Other Multicast Advantages • For the equivalent amount of multicast traffic, the sender needs much less processing power and bandwidth. • Multicast packets do not impose as high a rate of bandwidth utilization as unicast packets, so there is a greater possibility that they will arrive almost simultaneously at the receivers.

  10. Multicast Disadvantages Multicast is UDP-based. • Best-effort delivery • Heavy drops in Voice traffic • Moderate to Heavy drops in Video • No congestion avoidance • Duplicate packets may be generated • Out-of-sequence delivery may occur • Efficiency issues in filtering and in security

  11. Types of Multicast Applications One-to-many • A single host sending to two or more (n) receivers Many-to-many • Any number of hosts sending to the same multicast group; hosts are also members of the group (sender = receiver) Many-to-one • Any number of receivers sending data back to a source (via unicast or multicast)

  12. IP Multicast Applications Corporate Broadcasts Live TV and Radio Broadcast to the Desktop Distance Learning Multicast File Transfer Data and File Replication Training Videoconferencing Video-on-Demand Whiteboard/Collaboration Real-Time Data Delivery—Financial

  13. Self Check • List some advantages of multicast transmission over unicast transmission. • How does the best effort delivery nature of UDP impact multicast transmissions? • What are the 3 basic types of multicast applications? • Give examples of one-to-many. • What model is used when a host can be a sender as well as a receiver simultaneously?

  14. Multicast Addressing

  15. IP Multicast Address Structure IP group addresses: • Class D address (high-order three bits are set) • Range from through

  16. Source - (Class A, B, C) Destination - (Class D)Multicast Group Address Range Multicast Addressing IPv4 Header Version IHL Type of Service Total Length Source Address can never be Class D Multicast Group Address Identification Flags Fragment Offset Time to Live Protocol Header Checksum Source Address Source Destination Address Destination Options Padding

  17. IP Multicast Address Groups • Local scope addresses • to • Global scope addresses • to • Administratively scoped addresses • to

  18. Local Scope Addresses Well-known addresses assigned by IANA • Reserved use: through • (all multicast systems on subnet) • (all routers on subnet) • (all DVMRP routers) • (all PIMv2 routers) •,,, and used by unicast routing protocols

  19. Global Scope Addresses • Transient addresses, assigned and reclaimed dynamically (within applications): • Global range: • 224.2.X.X usually used in MBONE applications • Part of a global scope recently used for new protocols and temporary usage

  20. Administratively Scoped Addresses Transient addresses, assigned and reclaimed dynamically (within applications): • Limited (local) scope: for private IP multicast addresses (RFC-2365) • Site-local scope: • Organization-local scope: to

  21. Layer 2 Multicast Addressing IEEE 802.3 MAC Address Format

  22. IANA Ethernet MAC Address Range Available range of MAC addresses for IP multicast 01-00-5e-00-00-00 through 01-00-5e-7f-ff-ff

  23. IANA Ethernet MAC Address Range Available range of MAC addresses for IP multicast • Within this range, these MAC addresses have the first 25 bits in common. • The remaining 23 bits are available for mapping to the lower 23 bits of the IP multicast group address. 00000001:00000000:01011110:00000000:00000000:00000000 through 00000001:00000000:01011110:01111111:11111111:11111111

  24. Ethernet MAC Address Mapping

  25. Multicast Addressing IP Multicast MAC Address Mapping (FDDI & Ethernet) Be Aware of the 32:1 Address Overlap 32 - IP Multicast Addresses . . . 1 - Multicast MAC Address (FDDI and Ethernet) 0x0100.5E01.0101

  26. Madcap in MS Server

  27. How are Multicast Addresses Assigned? Static Global Group Address Assignment • Temporary method to meet immediate needs • Group range: – • Your AS number is inserted in middle two octets • Remaining low-order octet used for group assignment • Defined in RFC 2770 • “GLOP Addressing in 233/8” Manual address allocation by the admin is still the most common practice.

  28. Learning About Multicast Sessions Potential receivers have to learn about multicast streams or sessions available before a multicast application is launched. Possibilities: • Another multicast application sending to a well-known group whose members are all potential receivers • Directory services • Web page, e-mail • Session Announcement Protocol (SAP)

  29. sdr—Session Directory

  30. A Cisco IP/TV Example Cisco IP/TV application • Clients (viewers) use program listing • Contact the server directly • Listen to SAP announcements

  31. Self Check • What is the address range for multicast addresses? • What are Local Scope Addresses? • What is Mbone? • What is the 32-to-1 overlap? • What is MADCAP?

  32. Summary • IP multicast is a much more efficient means of delivering content where a single sender needs to deliver the content to multiple receivers. This task may be achieved through the use of multicast groups. • IP multicasts are designated by the use of a specific Class D IP address range. This is achieved through global scope addresses, which are assigned dynamically, and administratively scoped, which are assigned locally and are reserved for use inside private domains.

  33. Q and A

  34. Resources • Wikipedia IP Multicast article • http://en.wikipedia.org/wiki/IP_Multicast • Webopedia Mbone article • http://www.webopedia.com/TERM/M/Mbone.html