Re: OSI does not mean X.25


Hassan Rajaei (mcvax!enea!ttds!rajaei@uunet.uu.net)
8 Apr 88 14:44:11 GMT


In article <76.008873@adam.DG.COM> <LYMAN_CHAPIN%ICE9.CEO.DG.COM@adam.DG.COM> writes:
>
>Evidently there are still people who see "OSI" and hear "X.25" and
>"connections". ** THIS IS NOT A VALID ASSUMPTION! **
>
>You can have OSI with a Transport protocol similar to TCP (ISO 8073)
>and a connectionless internetwork protocol (ISO 8473) even more similar
>to IP. You do not have to have X.25. You do not have to have PTTs.
>You do not have to have network connections. There is NO part of OSI

I am really glad you mentioned this. There has been a confusion between
OSI model and X.25 protocol for a long time just because X.25 was the only
available implementation of OSI.

The OSI model is so general that you may do any thing with it (except the
overhead!). If there is not an standard protocol available for your need
within the model, that doesn't mean the model itself is incapabel of doing
that. In spite of many standard protocols available for OSI at present
time, I believe we need many new ones in future even for the low layers
like physical, link and network.

The existing standars for low layers are incapable of handling the ultra
super speed networks of the future (FDDI can handle just 150 Mbps). The
same is true with X.25 and its IP X.75 which are not only limited by speed
but rather make the network very vulnerable because of their connection-
oriented behaviour throughout the network (internetworks). As Lyman Chapin
said the limitation is not in the model but in the protocols.

There is much to be done for OSI model to be accepted (or rejected!) world
wide, both with new standard protocols and implementations.

Hassan Rajaei
The Royal Inst. of Technology
Stockholm Sweden
rajaei@tds.kth.se



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