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1 IP Multicasting Concepts Overview This lesson represents an entry point to IP multicast services, presents the functional model of IP multicasting, and gives an overview of technologies present in IP multicasting. The student will grasp the idea of IP multicasting, its benefits and associated caveats, and will determine various types of multicast applications. The student will gain an understanding of the IP multicast conceptual model and its implementation prerequisites. Objectives Upon completion of this chapter, the student will be able to: n Explain the benefits of multicasting and identify possible caveats n List various types of multicast applications and their requirements n Present the basic conceptual IP multicast model n Identify the addressing issues of IP multicasting n Explain the way multicast applications work and identify the prerequisites that have to be fulfilled for an implementation IP Multicast – Benefits and Caveats Objectives Upon completion of this section, the student will be able to: n Compare traditional unicast delivery to multicast data distribution n Explain the benefits of IP multicasting n Indicate possible problems associated with IP multicasting 1-2 IP Multicast Technology Copyright Ó 2000, Cisco Systems, Inc. Why Multicast? •Used when sending same data to multiple receivers •Better bandwidth utilization •Less host/router processing •Used when receivers’ addresses unknown •Used when simultaneous delivery for a group of receivers is required (“simulcast”) © 2000, Cisco Systems, Inc. www.cisco.com IP multicasting concepts Page 5 Multicast may be used to send the same data packets to multiple receivers. By sending to multiple receivers the packets are not duplicated for every receiver, but are sent in a single stream where downstream routers take care of packet multiplication over receiving links. Routers process fewer packets because they receive only a single copy of the packet. This packet is then multiplied and sent on outgoing interfaces where there are receivers. Because downstream routers take care of packet multiplication and delivery to receivers, the sender or source of multicast traffic does not have to know the receivers’ unicast addresses. Simulcast – simultaneous delivery for a group of receivers - can be used for several purposes including audio / video streaming, news and similar data delivery, deploying software upgrades, etc. Copyright Ó 2000, Cisco Systems, Inc. IP Multicasting Concepts 1-3 Sending to Multiple Destinations •Pure unicast: Send the same copy of data multiple times •Web technologies: webcasting - “push” the same data to multiple destinations • Traditionally, receivers subscribed to data and “pulled” it down periodically • The underlying transport for those technologies has been unicast © 2000, Cisco Systems, Inc. www.cisco.com IP multicasting concepts Page 6 In order to send data to multiple destinations using unicast we have to send for each receiver its own data flow. The sender has to make copies of the same packet and send them once for each receiver. Some web technologies (e.g. webcasting) use a push method to deliver the same data to multiple users. Instead of users clicking on a link to get the data, the data is delivered automatically. Users first had to subscribe to a channel in order to receive the data, and, after that, the data is periodically “pushed” to the user. The problem with the webcast is that the transport is still done using unicast. 1-4 IP Multicast Technology Copyright Ó 2000, Cisco Systems, Inc. Unicastt vs. Multicastt Unicast Host Router Multicast Host Router © 2000, Cisco Systems, Inc. www.cisco.com IP multicasting concepts Page 7 Unicast transmission sends multiple copies of data, one copy for each receiver: The top example shows a host transmitting three copies of data and a network forwards each packet to three separate receivers. The host can only send to one receiver at a time because it has to create a different packet destination address for each receiver. Multicast transmission sends a single copy of data to multiple receivers. The lower example shows a host transmitting one copy of data and a network replicates the packet at the last possible hop for each receiver. Each packet exists only in a single copy on any given network. The host can send to multiple receivers simultaneously because it’s sending only one packet. Copyright Ó 2000, Cisco Systems, Inc. IP Multicasting Concepts 1-5 ... - tailieumienphi.vn
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