Re: Réf. : Re: Alcatel Space interest about IP/DVB

[Lloyd Wood <l.wood@eim.surrey.ac.uk>]

On Tue, 16 Apr 2002, Kearney wrote:

> > By "Ethernet-like" we only mean "connectionless layer 2 based on broadcast
> > medium".
> Question - why does it have to be connectionless?
> Most of the applications are anyhow sessio-oriented - TCP, HTTP, and in
> particulatr multicast applications are based on the concept of a session.

HTTP wasn't conceived as being session-like. Not all multicast
applications are based on a sessoin either.

> If you "tune" your receiver to a PID you are basically opening a
> session - so why wouild you like to have the next higher layer
> (link/encapsulation) connection-less?

that's exactly what the connectionless HTTP/1.0 does over the TCP
session; it ignores TCP session state (arguably lousy programming, and
slowly addressed in 1.1 implementations). But it made for ease of
specification and implementation.

If you look at protocol stacks you'll see connectionless/session
alternating as you go through the layers.

If you "tune" your receiver to a PID you might be joining a broadcast
session, and if several terminals share the same PID...

L.

<L.Wood@surrey.ac.uk>PGP<http://www.ee.surrey.ac.uk/Personal/L.Wood/>