ITIS 1210 Introduction to Web-Based Information Systems Chapter 39 How Multicast IP and MBone Work

Introduction  Internet content  Originally it was just static content  Download it, view it  Branched out into other forms  Sound  Video  Animations  3D objects  Now interactive content is prevalent

Introduction  Problem:  Providing a richer experience  Implies correspondingly larger files  That take longer to download  Causing massive congestion within the Internet infrastructure  Some content cannot be sent over Internet at all because of capacity limitations

Introduction  Example: telecast of a concert  Assume a file size of 50MB  Assume an audience of 10,000 people  50MB must be sent individually to 10,000 subscribers  This might not be possible without seriously degrading the ability of local sections of the Internet to continue to service other customers

Introduction  One solution is the experimental MBone  Multicast Backbone  Virtual high-capacity backbone  Specifically designed to transmit broadcasts  Uses the IP multicast protocol  Begins as a single transmission  Instead of 10,000  Included are all addresses of every subscriber

Introduction  As the file is sent across the Internet it makes copies of itself  Those copies are routed to individual subscribers

Introduction  Example:  100 people want to see a broadcast of a 50MB file  Under normal circumstances, 5GB of data would be necessary  50 are connected to the Internet via ISP X  25 use ISP Y  25 are on corporate network Z  With multicast, the file is initially transmitted as a single file  Splits into three parts to X, Y, and Z

Introduction  Each network delivers their copy on to subscribers on that network alone  Instead of 5GB being necessary  Three 50MB files (150MB) are needed  Normally the Internet is a unicast environment  One transmission goes to one destination  Multicast enables simultaneous destinations

Introduction  MBone is a virtual network of host computers that use the IP Multicast for communications  Process starts by digitizing and compressing a video signal  The compressed signal is sent using the IP Multicast protocol  Multiple destinations simultaneously

Introduction  Major advantage is the single transmission  TCP would require a transmission to each recipient  Information about the multiple destinations goes into the packet  Two major problems:  Most networks and routers on the Internet do not understand the multicast protocol  Must still use standard Internet routes

Introduction  Solution is called tunneling  MBone data travels in tunnels built on top of existing Internet networks and routers  Ends of tunnel are workstations running a multicast routing demon  A demon (daemon) is a process that runs in the background and performs some useful service  The demon encloses the multicast packets inside regular TCP packets

Introduction  The now-standard TCP packets are sent over the regular Internet to the other end of the tunnel  There the multicast packets are extracted  Sent on via an MBone network that understands the multicast protocol

Introduction  Based on destination data in the multicast packets  The original data is sent to a number of different hosts  Individuals connected to these hosts can view the content  There are teleconferencing options that enable interaction  Audio and video

Introduction  Multicast will probably become obsolete  Hard to compute service charges for multicast traffic  Standard feature of IPV6