[opendtv] Re: 5th gen receivers
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 23 Jan 2005 18:12:08 -0500
Tom Barry wrote:
> Why must someone have only one peer? What do you
> call getting a file from BitTorrent where it comes
> from multiple P2P sources?
You're right about bit torrent. A host has multiple
peers, and downloads segments of the whole file from
different sources. The server involved is only there
to do the choreography. This is unicast, though.
Each session is a unicast session. The advantage is
that downloads are distributed among many source
hosts, which prevents server congestion.
With multicast, instead, there is no concept of
sessions between sources and destinations. Each
destination host only ever signals back and forth to
the edge router of the network. Destinations express
their desires to edge routers, edge routers in turn
communicate with core routers in the network to build
and tear down multicast trees. And the sources are
oblivious to absolutely everything that's going on.
They just transmit their bit streams.
The advantage of IP multicast is that fat streams are
used by many destinations, instead of just one. The
disadvantage is that the network becomes a lot
smarter than it would have to be to support unicast
flows. There's no free lunch. That super dumb source
has to be balanced by smarts elsewhere.
Bert
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