Tim Bass wrote:
As pointed out by Zhang et. al. in the late 80's, real-time applications
over a store-and-forward datagram service is very problematic
because IP is a best-effort service and there are no bandwidth/delay
guarantees in the IP paradigm.
Real time applications are about as problematic with any transport
method in a public network, period.
Bandwidth reservation is nothing more than another name for
"higher priority". It works fine until your high priority
traffic does not overload the network -- with or without
resource reservation of any kind.
As soon as that point reached (i.e. network is overloaded)
resource-reservation starts to deny service; simple per-packet
prioritization starts to drop packets "fairly". That's the
On the other hand, ATM (based on the original ATM charter) was envisioned
to offer a guaranteed QoS. As pointed out by numerous people in
this thread and before, IP/ATM is not efficient; and it is for
this reason and others that many IP protagonists love to bash
ATM, and with good reason from an IP perspective.
Worse than that, ATM is unable to fulfill its promise of
"guaranteed QoS" in global networks. ATM folks didn't appear to
understand that all routing stability problems won't disappear
just because somebody shreds packets; in fact, it is easily
demonstrable that those problems will be worse than with IP.
There is no current architecture to *guarantee* a close to zero
packet loss in the IP world.
Moreover, nobody needs it. Packet loss is a necessary component
of distributed congestion control, and works better than previously
implemented ECN schemes. (That intuitively makes sense, as packet
loss removes packets from congested network, while ECN doesn't).
Do we need a real-time protocol that is highly reliable in the
world? The answer, is of course YES.
NO. Name the single application which couldn't be run over
Finally, as pointed out TCP/IP/ATM is not efficient. On the other
hand, transmitting packets, losing them in the network and
retransmitting them or just dropping packets from the stream
is not the most efficient method of delivery either.
Yawn. ATM also loses packets, in a screwy way. It was a way worse
since it used to lose _cells_.
I am not necessarily a protagonist for ATM, and my personal
opinion is that ATM is too complex and tries to be all things
to everyone, and that rarely if ever works.
No, it is simply a bell-head's idea of a data network. If they
no longer can shred things to bits they would shred them to cells.