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A look at IP-multicasting

A look at IP-multicasting. We propose a programming project to acquaint ourselves with TCP/IP ‘multicast’ capabilities. Multicast IP addresses. 32-bits. Address Range. Class A address. 0. 0.0.0.0 - 127.255.255.255. Class B address. 1. 0. 128.0.0.0 - 191.255.255.255. Class C address.

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A look at IP-multicasting

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  1. A look at IP-multicasting We propose a programming project to acquaint ourselves with TCP/IP ‘multicast’ capabilities

  2. Multicast IP addresses 32-bits Address Range Class A address 0 0.0.0.0 - 127.255.255.255 Class B address 1 0 128.0.0.0 - 191.255.255.255 Class C address 1 1 0 192.0.0.0 - 223.255.255.255 1 MULTICAST address 1 1 0 224.0.0.0 - 239.255.255.255 1 Reserved 1 1 1 0 240.0.0.0 - 247.255.255.255 The range of IPv4 Network-Layer Addresses is subdivided into “classes” based on the high-order bits in these 32-bit addresses, with those which begin with “1110” (the Class D addresses) being allocated to multicasting

  3. Multicast Groups • The remaining 28-bits of an IP multicast address are used to identify the “group” that a datagram should be delivered to • There are some special multicast groups whose addresses you should avoid using • 224.0.0.1 (the all-hosts group) • 224.0.0.2 (the all-routers group) • 224.0.0.3 (address-purpose is unassigned) • 224.0.0.x (for local administration purpose)

  4. Our multicast group • Multicast applications should not use any multicast-addresses in the ‘special’ range (i.e., 224.0.0.0 – 224.0.0.255) designated for use by utilities devoted to maintenance and administration of the local network • So our example-programs define a ‘group’ whose IP-address lies outside this range, namely: 224.3.3.6 (easily remembered?)

  5. The ‘multicast’ concept Host A Host B Host C Host D Host E Local Area Network With IP-broadcasting, a datagram whose destination-address is equal to 255.255.255.255 will be received by every host on the local network Host A Host B Host C Host D Host E Local Area Network With IP-multicasting, a datagram whose destination-address is equal to 224.3.3.6 would be received only by those hosts on the local network that have chosen to become ‘members’ of this specific multicast-group

  6. Routers Host A Host I Modern routers do not ‘forward’ broadcast datagrams, but they can be configured to ‘forward’ any multicast datagrams Host B Host J Host C Host K Host D Host L Router X Router Y Host E Host M Host F Host N Host G Host O Host H Host P (Older routers can use ‘tunneling’)

  7. The socket API • Programming languages that support the ‘sockets’ interface can allow you to write client-and-server ‘multicast’ applications server client client client client But obviously the TCP ‘connection-based’ protocol is NOT used in multicasting!

  8. A Python example • We put up a very simple client-and-server multicast application on our class website, written in Python (for brevity) • ‘multisend.py’ (the ‘server’ program) • ‘multirecv.py’ (the ‘client’ program) • The server just sends a ‘Hello’ message to current group-members once each second • The client can be run on multiple hosts

  9. Project #2 • Write a multicast server-program (named ‘deadline.cpp’) that periodically sends out reminder-messages about upcoming due-dates for course-assignments or exams • Write the multicast client-program (named ‘timeleft.cpp’) that a student who desires to receive reminders can use to ‘join’ the server’s multicast-group

  10. The C++ versions • Your programs are required to be written in the C++ language, so we have put the rewritten versions of our ‘multisend’ and ‘multirecv’ application-programs on the class website as demonstration examples

  11. Organization ‘multirecv.cpp’ socket() setsockopt( REUSEADDR ) ‘multisend.cpp’ socket() bind() setsockopt( ADDMEMBERSHIP ) sleep( 1 ) sendto() recv() puts()

  12. ‘Unique’ group-address • For developing your own application, you will be sharing our local USF networks as the hardware ‘testbed’ for your C++ code • You’ll be annoyed if everyone’s messages arrive and get displayed on your screen! • So we need a different IP-multicast group address for each classmember 224.3.36.xxx ‘xxx’ equals 100 plus your number on the Instructor’s class-list (you can find it handwritten on your Midterm Exam)

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