IP Multicast for Access Grid
Or: Just what IS that weird network stuff
you’re always talking about?
Bill Nickless
nickless@mcs.anl.gov
http://www.mcs.anl.gov/home/nickless
Presented by: Bill Nickless
Unicast vs. Multicast
Network communication is done by sending
packets from Sources to Receivers. The Access
Grid is no exception. Normally networks transport
packets from one Source to one Receiver, like this:
Presented by: Bill Nickless
Unicast vs. Multicast
If the Source (S) wants to send a packet to a
different Receiver (R2), the network looks at the
address in the packet and routes it appropriately.
This is called Unicast.
Presented by: Bill Nickless
Unicast Addressing
• In the Unicast case, the end station puts together a
packet with a Source address (S) and a receiver
address (R) and gives it to the network.
• The network looks at the (S,R) fields in the packet
and figures out how to move the packet towards (R)
where it is eventually delivered.
Presented by: Bill Nickless
Unicast vs. Multicast
If Source (S) wants to get some data to three
Receivers (R1-R3), it has to send three copies of
the data into the network:
Presented by: Bill Nickless
Unicast vs. Multicast
Wouldn’t it be better to have the network deliver the exact
same data to all the Receivers? That’s called Multicast!
Presented by: Bill Nickless
Multicast Addressing
• In the Multicast case, the end station puts together a
packet with a Source address (S) and a Group
address (G) and gives it to the network.
• The network “knows” what Receivers are part of
Group (G), and the routers conspire to get the
packet to all of them (copies where necessary).
Presented by: Bill Nickless
Internet Group
Management Protocol (IGMP)
The Receivers all tell the network which Groups (G) they’re
interested in hearing, by talking IGMP to their local router.
Give Me
(G) please
Give Me
(G) please
Give Me
(G) please
Presented by: Bill Nickless
Virtual Venues
Virtual Venues are, fundamentally, Multicast Groups. The
VV software is what tells each application what Group (G)
to ask for, and the network does the rest.
Give Me
(G) please
Give Me
(G) please
Give Me
(G) please
Presented by: Bill Nickless
So: What does the network need, to support
my Access Grid Node?
• Your network must support:
– IGMP: so the node computers can tell the network what
Groups (G) to join.
– PIM-Sparse Mode: the routing protocol that the routers
conspire with to deliver packets to all the Group (G)
members.
– MSDP and M-BGP: the protocols used between
institutions and wide area networks to support PIMSparse Mode.
Presented by: Bill Nickless
Getting Started
• You can’t debug IP multicast without Sources (S),
Receivers (R), and Groups (G) active.
• Finding out whether your network is already IP
Multicast capable can be tough.
Presented by: Bill Nickless
The Beacon
• Best thing to do: run a Beacon!
• http://dast.nlanr.net/projects/beacon
• In Java,so
runs
anywhere
Presented by: Bill Nickless
Questions?
Presented by: Bill Nickless