The OSI-model Post: 17863

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Special Forums IP Networking The OSI-model Post 17863 by thomas.jones on Wednesday 20th of March 2002 07:38:06 PM

03-20-2002

Registered User

You are partially correct! The data does traverse down the OSI model on the source node.......across the network medium.......to the destination node....and back up the OSI model.

BUT, transmissions do not have to actually start at the application level. Have you ever heard of two or three tier routers? They only use part of the OSI model.....hence two or three layers are transmitted....not all 7.

It goes like this:

Data to be sent in this datagram = XXXXXXXXXX

Layer 7 puts on application specific headers:

AAXXXXXXXXXXA

Then Layer 6 for presentation:

PPAAXXXXXXXXXXAP

Then Layer 5 does the same on a session basis:

SSPPAAXXXXXXXXXXAPS

Layer 4 for transport portion:

TTSSPPAAXXXXXXXXXXAPST

Layer 3 goes next:

NNTTSSPPAAXXXXXXXXXXAPSTN

Layer 2 puts on the Data Link layer stuff:

DDNNTTSSPPAAXXXXXXXXXXAPSTND

The finally the Physical layer:

PPDDNNTTSSPPAAXXXXXXXXXXAPSTNDP

This is then transmitted. At the destination...each layer strips the corresponding layer and sends it up to the next layer....etc.

This is very basic...it's more complex than this tutorial...each layer does not have the same size of headers...and such...but this gets the idea across.

thomas.jones

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4s-import

4S-IMPORT(1J)							      4store							     4S-IMPORT(1J)

NAME

     4s-import -- Import RDF into a 4store KB

SYNOPSIS

     4s-import kbname [-v] [-a] [-M default-model] [-m model] [-f format] [rdf-file] ...

	       -v, --verbose
		       Increase verbosity (by default success is silent)

	       -a, --add
		       Ordinarily importing RDF to a model replaces any previous contents of that model, by using the --add flag this behaviour is
		       overridden and any triples which were previously in the model are retained.

	       -M, --model-default
		       Set a model (graph) URI which is used by default for all imported files

	       -m, --model
		       Set a model (graph) URI for the next named file only (overrides -M if it has been used)

	       -f, --format
		       Tell the RDF parser the format of the files (if not specified the parser will guess)

SEE ALSO

     4s-query(1), 4s-size(1), 4s-httpd(1), 4s-backend(1), 4s-delete-model(1)

EXAMPLES

     $ 4s-import demo one.ttl two.xrdf

     Imports two files into the demo KB, each as a separate model (graph) guessing the RDF format used for each file

     $ 4s-import demo -M http://example.com/menu starters.ttl mains.ttl sweets.ttl

     Imports three files into a single graph named <http://example.com/menu>

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