Re: OSI does not mean X.25


Erik Forsberg (linus!philabs!ttidca!retix!erik@husc6.harvard.edu)
12 Apr 88 07:25:12 GMT


In article <In article <1157@ttds.UUCP> In article <1157@ttds.UUCP> rajaei@ttds.UUCP (Hassan Rajaei) writes:
>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.
>
Please make a distinction between the OSI MODEL and the protocols
specified by ISO that implements services defined by the ISO model.

I don't think you can do anything with the OSI model. Just because
you invent your own protocol, which happens to provide some service
defined by the OSI model, doesn't really make this new protocol an
OSI protocol. There will be just confusion and interoperability problems
if every new protocol claims to be an "OSI protocol". Before it could
be considered as a protocol to be used to implement a service as defined
by OSI, it should become an ISO standard. Otherwise, it's not too useful
for the majority of the worlds data communications users.

Anyway, there certainly is a place for new protocols for new, higher
performing LAN technologies. But, even the existing ISO 8073/8473
protocol combinations are quite performing. (This is the ISO Class 4
Transport protocol operating over a connection-less network service,
almost identical with DoD IP). For example, by eliminating overhead
imposed by non-perfect hardware, this protocol combination has proven
able to have a substained transport layer user data throughput of more
than 2000 packets per second (each packet 1024 bytes) which is approximately
16 Megabits/second (this is measured on a VAX 8650). Now, if you add
some well-known, supposedly reasonable Ethernet controllers on an
otherwise idle Ethernet network, performance drops to a measly 60-180
packets per second, it is my opinion that controller hardware technology,
computer buses and software used to interface with the host operating
system needs some large improvements.

I do not understand why so many believes that X.25 is the only way to
implement OSI. It is certainly true that the european continent started
work in ISO, specifying the Connection-oriented network service as
examplified by X.25, but I think the US has been as successfull in
providing equally good protocols when Local Area Networks are
the primary technology of interest. Now, there are very reasonable
standards in how to inter-connect multiple Local Area Networks using
these venerable and perfectly working X.25's as provided by any Public
Data Network service provider (in most any country of the world).

One of the major problems is that there is no natural way to interoperate
between networks using ISO 8473 (IP) or ISO 8208 (X.25) as the network layer.
There will always be limitations when such attempts are made (there are
several proposals discussed as of this time).

--
----------------------------------------------------------------------------
Erik Forsberg, Retix, 2644 30th	Street,	Santa Monica CA	90405 (213) 399-2200
UUCP: {cepu,ttidca,rutgers,oliveb}!retix!erik, erik@retix.com



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