© 2005 Cisco Systems, Inc. All rights reserved. Course acronym vx.x#-1 Implementing Multicast Explaining Multicast. - презентация

1 © 2005 Cisco Systems, Inc. All rights reserved. Course acronym vx.x#-1 Implementing Multicast Explaining Multicast

2 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v 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)

3 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v Unicast vs. Multicast

4 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v Multicast Advantages Enhanced efficiency: Controls network traffic and reduces server and CPU loads Optimized performance: Eliminates traffic redundancy Distributed applications: Makes multipoint applications possible

5 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v Multicast Disadvantages Multicast is UDP-based. Best-effort delivery: Drops are to be expected. Multicast applications must not expect reliable delivery of data and should be designed accordingly. Reliable multicast applications will address this issue. No congestion avoidance: The lack of TCP windowing and slow- start mechanisms can result in network congestion. If possible, multicast applications should attempt to detect and avoid congestion conditions. Duplicates: Some multicast protocol mechanisms result in the occasional generation of duplicate packets. Multicast applications should be designed to expect occasional duplicate packets. Out-of-sequence delivery: Network topology changes affect the order of deliverythe application must properly address the issue.

6 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v 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)

7 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v Corporate Broadcasts Distance Learning Training Videoconferencing Whiteboard/Collaboration Multicast File Transfer Data and File Replication Real-Time Data DeliveryFinancial Video-on-Demand Live TV and Radio Broadcast to the Desktop IP Multicast Applications

8 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v IP Multicast Basic Addressing IP group addresses: Class D address (high-order three bits are set) Range from through 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

9 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v IP Multicast Basic Addressing (Cont.) Transient addresses, assigned and reclaimed dynamically (within applications): Global range: –224.2.X.X usually used in MBONE applications Limited (local) scope: /8 for private IP multicast addresses (RFC-2365) –Site-local scope: /16 –Organization-local scope: to Part of a global scope recently used for new protocols and temporary usage

10 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v Layer 2 Multicast Addressing IP Multicast MAC Address Mapping Ethernet

11 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v Learning About Multicast Sessions Potential receivers have to learn about multicast streams or sessions available before multicast application is launched. Possibilities: Another multicast application sending to a well-known group whose members are all potential receivers Directory services Web page, Session Announcement Protocol

12 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v A Cisco IP/TV Example Cisco IP/TV application Clients (viewers) use program listing –Contact the server directly –Listen to SAP announcements

13 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v 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.

14 © 2006 Cisco Systems, Inc. All rights reserved. BSCI v