[e2e] Port numbers in the network layer?
detlef.bosau at web.de
Fri Apr 26 03:01:14 PDT 2013
Am 26.04.2013 03:00, schrieb l.wood at surrey.ac.uk:
>> On the other hand: Do you know a current technology which is actually
>> being used that does not use Ethertypes?
> CANbus, SpaceWire, CCSDS, RapidIO, (A)X.25...
Oh, yes :-)
I'm sorry about that...
Additional question: Can you tell me which car uses TCP over CANbus,
e.g. to control his lamps? ;-)
But you made an important point: My view on this matter is too simplistic.
> But you can always layer (Cisco) HDLC or HDLC/ Frame Relay across any
> of these to get an Ethertype. Or lobby SpaceWire to put a value in
> their single-byte not-an-Ethertype field.
At least we have do agree on talking about "packet switching networks"
in a quite narrow sense here, when it comes to Ethertypes.
E.g. X.25 to my understanding is circuit switched. The packet switching
view is mounted upon the top ;-) The same holds true for Frame Relay in
a sense, however in FR the whole packets are switched IIRC and not
subdivided into smaller pieces.
However, this is in fact a discussion of implementation issues.
> (The CCSDS community finds the thought of layering HDLC over CCSDS
> especially abhorrent, because it cuts down their custom engineering,
> and any layering or modularity is considered to be inefficiency.)
At least, it is not a "holy cow". Layers should assist network design.
And not the other way round.
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