[Internet Esoterica] Whatever happened to Multicast Protocol?

[Doug Elrod]

   When I hear about football games being streamed (such as on Christmas, tomorrow),
and the fact that apparently a Thursday night game took 30% of the Internet bandwidth
(however that is measured :-)), I wonder if somehow the Multicast Protocol (which I
read about decades ago) is not being used.  From what I remember, it's like shouting
to everyone (say UDP), rather than requiring handshaking with everyone individually
(like TCP).

I guess if you want to personalize ads you need the extra bandwidth, but it seems
incredibly wasteful, IMHO.

-Doug Elrod (dr...@cornell.edu)
   waiting for someone to reinvent "Television" ;-)

[Steve VanDevender]

'Doug Elrod' via World News Now Discussion List writes:
> When I hear about football games being streamed (such as on
> Christmas, tomorrow), and the fact that apparently a Thursday night
> game took 30% of the Internet bandwidth (however that is measured
> :-)), I wonder if somehow the Multicast Protocol (which I read
> about decades ago) is not being used. From what I remember, it's
> like shouting to everyone (say UDP), rather than requiring
> handshaking with everyone individually (like TCP).

In the earlier days of the Internet when bandwidth was limited, IP
multicast was pretty intensively researched as a way to stream live
content with less bandwidth usage. The main savings was that a single
copy of the multicast data could be sent on a common link shared by a
number of receivers; at a point where there were multiple networks
containing recievers of multicast data, the single copy on a shared
upstream link would be copied into each of the downstream links. This
meant routers had to dynamically track when members of a multicast
session existed in networks connected to them and share that
information with other routers involved in that session. Consequently
routing multicast packets is much more complicated than normal IP
routing, which in principle needs only to track which destination
addresses are reachable via connected networks.

Multicast is actually handled as as particular address range whose
addresses are used for multicast groups (224.0.0.0 through
239.255.255.255 are reserved for multicast in IPv4) and with some
additional protocols like IGMP (Internet Group Management Protocol)
for passing around information about multicast group membership.
Multicast also used only UDP for data transmission since the
individual session handling of TCP doesn't fit well with multicast
routing.

The only major advantage of using multicast for streaming was reduced
bandwidth usage on Internet backbone links, which was a concern in the
early 1990s when bandwidth was in shorter supply and there were
concerns that routers weren't going to be able to keep up with
explosive growth in the number of networks connected to the Internet.
It was also like broadcast radio or television in that audio or video
streamed by multicast could only be live. While it was entirely
possible to stream movies or television shows on multicast, it would
have to be on a schedule so you couldn't start watching a movie or
show from the beginning whenever you wanted.

Since the original concerns about bandwidth and router limitations
were solved, streaming over regular UDP or TCP became standard. Even
though it does use more bandwidth, it's much more flexible than
multicast streaming and actually takes less complicated routing
infrastructure.

There are still some applications besides audio or video streaming
where multicast is still used.

> I guess if you want to personalize ads you need the extra
> bandwidth, but it seems incredibly wasteful, IMHO.

If multicast had taken off I'm sure they would have found a way to do
this in multicast, much as how ad time is divided between the national
network and slots where local affiliates can insert their own ads into
broadcasts.

> -Doug Elrod (dr...@cornell.edu)

[Paul Pietromonaco]

So - when I first got fiber optic from CenturyLink, they had a IPTV (Internet protocol TV) service called Prism. It was great!

Basically - they used multicast for all of their TV channels. This effectively meant that you could watch TV over your fiber optic system without losing any of the bandwidth you were paying for. I know - I used to fire up the three Prism boxes I had, and then run network speed tests.

Add to this the original IPoE (Internet Protocol over Ethernet) configuration of the fiber optic boxes - necessary for multicast support - and it was a potent system. Almost no latency or lag.

Sadly - they abandoned the whole Prism infrastructure and converted us to PPPoE to gain the TV bandwidth back.

Cheers,
Paul

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[Steve VanDevender]

Paul Pietromonaco writes:
> Basically - they used multicast for all of their TV channels. This
> effectively meant that you could watch TV over your fiber optic
> system without losing any of the bandwidth you were paying for. I
> know - I used to fire up the three Prism boxes I had, and then run
> network speed tests.

Multicast doesn't save bandwidth for *you*, it only saves bandwidth
for the network service providers that can consolidate traffic for
multicast customers. You still have to receive the same amount of
data for multicast as you would for unicast of the same quality.

[Michael King]

I'm guessing that US viewers will be out in the cold for at least a portion of the games, while Canadian viewers (watching on CTV/TSN - as will I, thanks to certain options I have) will be able to watch without a problem. 

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