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Using the network package for multicasting

 
 
Sona
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      09-26-2003
Hi,

Can someone point me out to a good article on how to create/use IP
multicasting in Java applications? I'm interested in developing a
program that will use it. Thanks

Sona

 
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Roedy Green
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      09-26-2003
On Sat, 27 Sep 2003 03:09:47 +1000, Sona <(E-Mail Removed)>
wrote or quoted :

>
>Can someone point me out to a good article on how to create/use IP
>multicasting in Java applications?


I can show you some code to do UDP. If the multicast IP is set up
already, all you would have to do is send to that magic IP.

How you go about setting up a list of recipients for a multicast, I
don't know.

I have not yet found a description of just how multicast works and
what its limitations are. There are "send to everyone on the LAN"
addresses in Ethernet that might be useful in implementing it.

I proposed a multicast protocol that does not need multicast IPs.
See http://mindprod.com/projinternetradio.html

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Coaching, problem solving, economical contract programming.
See http://mindprod.com/jgloss/jgloss.html for The Java Glossary.
 
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Rene
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      09-26-2003
Roedy Green <(E-Mail Removed)> wrote:
> On Sat, 27 Sep 2003 03:09:47 +1000, Sona <(E-Mail Removed)>
> wrote or quoted :
>
> >
> >Can someone point me out to a good article on how to create/use IP
> >multicasting in Java applications?

>
> I can show you some code to do UDP. If the multicast IP is set up
> already, all you would have to do is send to that magic IP.


Yep. But there is no need to specially mention UDP. There is no multicast
TCP and there can't be. (TCP requires acknowledgmentes, a back channel. But
there is only one sender that sends his one single stream of packages and
does not ever get anything return - there is no retransmission or
acknowledge in multicast)

> How you go about setting up a list of recipients for a multicast, I
> don't know.


You don't - the system does it for you. Just look at it this way, imagine
the multicast IP the sender sends to is not an address but a channel. The
recievers then tune in to the channel and get the messages. Like with a
standard radio broadcast, the sender does not know how many people are
tuned in.

On a technical level, the recievers send a sort of "I want to join that
channel/IP" which then causes their routers to try to get the multicast
stream so that they can serve their client. The routers split (multiply)
the multicast traffic down all their physical nodes that want to recieve
that stream, they are forming a sort of one way flow tree.

There are different ways how those trees are built up. (A trivial but
wasteful one is: Send to every other router and then cut back/prune those
out who don't want it) You can do that on a local scope but not on the
internet.

Btw. multicast doesn't work on the whole internet. There are only a
fraction of nodes who can do multicast. It usually only works in LANs where
support for multicast is explicitly enabled and configured.

> I have not yet found a description of just how multicast works and
> what its limitations are. There are "send to everyone on the LAN"
> addresses in Ethernet that might be useful in implementing it.


That's what you can do on one single ethernet segment, just a physical
ethernet broadcast. However when your stream spans different segments or
subnets, you need routers that know how to handle and forward multicast.

As for documentation, this one from Cisco is the best I have:
http://www.cisco.com/en/US/tech/tk82...mily_home.html

If you don't want the nutty details, click left on "Overview" and then on
"Technology Briefs" followed by "Internet Protocol IP Multicast Technology"

> I proposed a multicast protocol that does not need multicast IPs.
> See http://mindprod.com/projinternetradio.html


I skimmed through that page of yours. It does already exist. Search google
for "P2P radio" and you should find plenty of links.

CU

Rene

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