Re: [tlug] Cable modem, which mode ?

[Jim Breen <jwb@example.com>]

[Mario Luoni (Re: [tlug] Cable modem, which mode ?) writes:]
JB>> > Issues of connectionless and connection-oriented really have nothing to
JB>> > do with whether a channel, real or virtual, is full or half-duplex.
>> 
>> i probably didn't ask the question accurately enough. i would think that in
>> a /shared physical medium/ context there cannot be full-duplex 

Correct.

>> unless it's connection oriented, 

No, it still can't be full-duplex. If you can't have more than one
signal/frame/whatever  in/on the medium at a time, and that's what
"shared physical medium" means, then you can't have full-duplex.

The so-called "full-duplex Ethernet" setups  don't use shared-medium, in
fact I'd say they use two distinct physical channels.

>> and in this case also it would just only be "quasi"
>> full duplex (fdd or tdd). but a shared medium connectionless environment
>> (like the ethernet) can never be anything but half duplex. or am i wrong?

You are mostly right. Quasi-full-duplex is sometimes used to describe
things like TCP running across an Ethernet. The higher-layer acts as
though it is full-duplex, but down at the frame layer it's packet
interleaving. Quasi-full-duplex is also sometimes used for ping-pong
systems, such as are sometimes used for ISDN 2B+D connections where the
144kbps full-duplex is achieved by running a 288kbps half-duplex system
with alternating fixed size frames. It waddles like full-duplex, quacks 
like full-duplex, but deep inside it is only half-duplex.

Jim

-- 
Jim Breen  [j.breen@example.com  http://www.csse.monash.edu.au/~jwb/]
Computer Science & Software Engineering,                Tel: +61 3 9905 3298
P.O Box 26, Monash University,                          Fax: +61 3 9905 5146
Clayton VIC 3800, Australia      ジム・ブリーン@モナシュ大学