| Author |
Message |
CJ
Guest
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 Posted:
Tue Apr 12, 2005 3:46 am Post subject:
OSI Model |
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I studied the OSI model, but nobody could ever tell me why I need to know
it.
The answer I always got was "you definitely need to know the OSI model" but
when I ask why I always get "you just do".
Can anyone tell me why I need to know it and how I would apply the
knowledge? Perhaps a lab exercise or something??
Thanks,
CJ |
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catwalker63
Guest
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| Posted:
Tue Apr 12, 2005 4:00 am Post subject:
Re: OSI Model |
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"CJ" <chrisj@illicom.net> prattled ceaslessly in
news:AwH6e.689$Cz3.64167@monger.newsread.com:
| Quote: | I studied the OSI model, but nobody could ever tell me why I need to
know it.
The answer I always got was "you definitely need to know the OSI
model" but when I ask why I always get "you just do".
Can anyone tell me why I need to know it and how I would apply the
knowledge? Perhaps a lab exercise or something??
Thanks,
CJ
|
The OSI model is a theoretical model that specifies, in a very general
way, how data gets from the application on one machine across the network
to the application on another machine. There are no labs unless you are
developing a protocol to operate at a layer in the model. Understanding
the model helps you undestand how the protocols fit together to get data
onto the network and back off of it.
--
Catwalker
aka Pu$$y Feet
BS, MCP, MCSA
MCNGP #43
www.mcngp.com
faq.mcngp.com
"If man could be crossed with the cat, it would improve man, but it would
deteriorate the cat." Mark Twain |
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Patrick Schaaf
Guest
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| Posted:
Tue Apr 12, 2005 6:39 am Post subject:
Re: OSI Model |
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"CJ" <chrisj@illicom.net> writes:
| Quote: | I studied the OSI model, but nobody could ever tell me why I need to know
it.
The answer I always got was "you definitely need to know the OSI model" but
when I ask why I always get "you just do".
|
You need to know it just like other kinds of terminology: to understand
people and publications which use it to illustrate something that they want
to teach you.
| Quote: | Can anyone tell me why I need to know it and how I would apply the
knowledge? Perhaps a lab exercise or something??
|
Definitely not. The OSI model has no relevance in _practise_.
best regards
Patrick |
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James Knott
Guest
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| Posted:
Tue Apr 12, 2005 10:44 am Post subject:
Re: OSI Model |
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CJ wrote:
| Quote: | I studied the OSI model, but nobody could ever tell me why I need to know
it.
The answer I always got was "you definitely need to know the OSI model"
but when I ask why I always get "you just do".
Can anyone tell me why I need to know it and how I would apply the
knowledge? Perhaps a lab exercise or something??
|
It's just a method of learning the general layers of the protocol stack.
It's also a stack that was intended to be used, but was soon surpassed by
TCP/IP. |
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James Knott
Guest
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Patrick Schaaf
Guest
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| Posted:
Tue Apr 12, 2005 10:51 am Post subject:
Re: OSI Model |
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James Knott <james.knott@rogers.com> writes:
| Quote: | Patrick Schaaf wrote:
Definitely not. The OSI model has no relevance in practice.
Actually, at one time, it was intended to be the "standard", but instead,
TCP/IP became the defacto standard.
|
No argument here. Some parts of those sets of standards even survive
today, for example the IS-IS routing protocol, which is used as an
interiour routing protocol in lots of contemporary IP networks.
best regards
Patrick |
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David Ross
Guest
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| Posted:
Tue Apr 12, 2005 11:16 am Post subject:
Re: OSI Model |
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| Quote: | I studied the OSI model, but nobody could ever tell me why I need to know
it.
The answer I always got was "you definitely need to know the OSI model" but
when I ask why I always get "you just do".
Can anyone tell me why I need to know it and how I would apply the
knowledge? Perhaps a lab exercise or something??
|
So you can read all those articles in Datamation and ComputerWorld in
the 80s that argued whether or not the OSI model should be a requirement
or not and whether or not IBM's SNA was OSI compliant and .....
It got rather tedious after a while. |
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catwalker63
Guest
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| Posted:
Tue Apr 12, 2005 11:21 am Post subject:
Re: OSI Model |
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James Knott <james.knott@rogers.com> prattled ceaslessly in
news:ouqdnYBYXaCkOsbfRVn-pg@rogers.com:
TCP/IP is a protocol suite. The OSI model is a general model for
networking. TCP/IP follows the OSI and DOD model and the various
protocols in the suite fit into the model at different layers.
--
Catwalker
aka Pu$$y Feet
BS, MCP, MCSA
MCNGP #43
www.mcngp.com
faq.mcngp.com
"If man could be crossed with the cat, it would improve man, but it
would deteriorate the cat." Mark Twain |
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catwalker63
Guest
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| Posted:
Tue Apr 12, 2005 11:23 am Post subject:
Re: OSI Model |
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James Knott <james.knott@rogers.com> prattled ceaslessly in
news:ouqdnYFYXaDuO8bfRVn-pg@rogers.com:
| Quote: | CJ wrote:
I studied the OSI model, but nobody could ever tell me why I need to
know it.
The answer I always got was "you definitely need to know the OSI
model" but when I ask why I always get "you just do".
Can anyone tell me why I need to know it and how I would apply the
knowledge? Perhaps a lab exercise or something??
It's just a method of learning the general layers of the protocol
stack. It's also a stack that was intended to be used, but was soon
surpassed by TCP/IP.
|
Once again, OSI is not a protocol stack. It is a general model that was
actually followed when developing TCP/IP as well as other protocol
stacks.
--
Catwalker
aka Pu$$y Feet
BS, MCP, MCSA
MCNGP #43
www.mcngp.com
faq.mcngp.com
"If man could be crossed with the cat, it would improve man, but it would
deteriorate the cat." Mark Twain |
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Al Dykes
Guest
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| Posted:
Tue Apr 12, 2005 11:39 am Post subject:
Re: OSI Model |
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In article <425ba814$0$17607$9b622d9e@news.freenet.de>,
Patrick Schaaf <mailer-daemon@bof.de> wrote:
| Quote: | James Knott <james.knott@rogers.com> writes:
Patrick Schaaf wrote:
Definitely not. The OSI model has no relevance in practice.
Actually, at one time, it was intended to be the "standard", but instead,
TCP/IP became the defacto standard.
No argument here. Some parts of those sets of standards even survive
today, for example the IS-IS routing protocol, which is used as an
interiour routing protocol in lots of contemporary IP networks.
best regards
Patrick
|
ISTR that LDAP is a version of X.400, another standard from
the same period.
Remember to keep OSI (Open System Interconnect) and ISO
(International Standards Org). The fact that the ISO standards were
created by ISO can be confusing.)
The 7 layer model OSI is important and very useful when you are trying
to understand different protocols, ie IP and SS7, even in one or both
are not OSI-based, and figure out how to make them work together.
It's a common framework when you are trying to explain how some
component fits with other components. Try explaining how IP runs over
a broadcast medium (ethernet) and also a serial connection without
refering to layers.
For a few years the US gov't had a policy that said as of some date
all equipment purchased had to conform to relevant OSI standards and
there was lots of lip service but departments started to buy TCP-based
systems anyway. At some point they came out with GOSSIP (Government
Open Systems .something... Plan) to tray to make something of
themess. Google for it.
Padlipsky's _The Elements of Networking Style_ is a great book about
how IP and ISO competed in the 80's. Every communications book by
Tannenbaum I've seen has covered the 7 layer model well.
--
a d y k e s @ p a n i x . c o m
Don't blame me. I voted for Gore. |
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J. Clarke
Guest
|
| Posted:
Tue Apr 12, 2005 12:15 pm Post subject:
Re: OSI Model |
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catwalker63 wrote:
| Quote: | James Knott <james.knott@rogers.com> prattled ceaslessly in
news:ouqdnYFYXaDuO8bfRVn-pg@rogers.com:
CJ wrote:
I studied the OSI model, but nobody could ever tell me why I need to
know it.
The answer I always got was "you definitely need to know the OSI
model" but when I ask why I always get "you just do".
Can anyone tell me why I need to know it and how I would apply the
knowledge? Perhaps a lab exercise or something??
It's just a method of learning the general layers of the protocol
stack. It's also a stack that was intended to be used, but was soon
surpassed by TCP/IP.
Once again, OSI is not a protocol stack. It is a general model that was
actually followed when developing TCP/IP as well as other protocol
stacks.
|
??? The OSI model was first proposed in 1977 published in preliminary form
in March 1978, with a second preliminary release in June, 1979, and
adoption as a standard coming later. TCP/IP was first defined in 1973 as
TCP, and split out into TCP and IP as separate components in TCP/IP
Revision 4, released in January, 1978.
So it's difficult to attribute any part of the development of TCP/IP to the
influence of the OSI model. It could be that the 1979 or 1980 or later
specification revisions may reference the OSI model in some manner but that
is not the same as using the model when developing the protocol.
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net) |
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Guest
|
| Posted:
Tue Apr 12, 2005 1:45 pm Post subject:
Re: OSI Model |
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| Quote: | The answer I always got was "you definitely
need to know the OSI model" but
when I ask why I always get "you just do".
|
The issue is that the people who create all of
this networking stuff use this model to simplify
what would otherwise be a more difficult problem.
This has a couple of consequences:-
If you are designing or troubleshooting a network
then it helps to be able to think about the kit in the same
way as the designers and implementors do.
In a purer application of the model, the most critical
phase of troubleshooting for me is to determine
what layer the problem resides in.
e.g. 1. If the link light is not on it is an L1 problem and
we do not (yet) need to worry about possible IP
addressing issues (L3).
e.g. 2. If we are getting ARP entries in our arp cache for
the target then L2 must be working since we are exchanging frames.
There is no point in worrying about STP any further.
In many cases this is just _obvious_ however in more
subtle cases or when learning about networking
it can help a great deal to have a formal structure
to hang on to.
The KEY idea is that the respective layers at each end of
a communications link talk DIRECTLY to each other.
If L3 at end A can talk to L3 at end B then L1 and L2 and L3
must be working correctly at both ends and at all points
between.
Finally, it is a MODEL and for example, TCP/IP is quite a close fit
to the OSI model but it seems to be generally accepted that it
is a 4 layer system with layes 5, 6, 7 of the OSI model not being
applicable.
PS
The critical thing is not knowing the names of the 7 layers (which
I don't, unless you need to pass tests) but having the concept in
your head that TCP/IP has been constructed using a layered model. |
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catwalker63
Guest
|
| Posted:
Tue Apr 12, 2005 2:06 pm Post subject:
Re: OSI Model |
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James Knott <james.knott@rogers.com> prattled ceaslessly in
news:ouqdnYBYXaCkOsbfRVn-pg@rogers.com:
The OSI model is not a protocol suite. TCP/IP is a protocol stack based
on the OSI or DOD model. TCP/IP did not replace the OSI model, it
followed it. The OSI model is a very general specification for how to
build a protocol stack.
--
Catwalker
aka Pu$$y Feet
BS, MCP, MCSA
MCNGP #43
www.mcngp.com
faq.mcngp.com
"If man could be crossed with the cat, it would improve man, but it
would deteriorate the cat." Mark Twain |
|
| Back to top |
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J. Clarke
Guest
|
| Posted:
Tue Apr 12, 2005 5:02 pm Post subject:
Re: OSI Model |
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catwalker63 wrote:
| Quote: | James Knott <james.knott@rogers.com> prattled ceaslessly in
news:ouqdnYBYXaCkOsbfRVn-pg@rogers.com:
Patrick Schaaf wrote:
Definitely not. The OSI model has no relevance in practice.
Actually, at one time, it was intended to be the "standard", but
instead, TCP/IP became the defacto standard.
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/osi_prot.htm
The OSI model is not a protocol suite. TCP/IP is a protocol stack based
on the OSI or DOD model. TCP/IP did not replace the OSI model, it
followed it. The OSI model is a very general specification for how to
build a protocol stack.
|
Since TCP/IP preceded the OSI model it's difficult to see how it could be
based on that model.
As for the DOD model, since TCP/IP was developed as part of a DOD advanced
research project, one would expect the DOD model to be based on TCP/IP.
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net) |
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J. Clarke
Guest
|
| Posted:
Tue Apr 12, 2005 8:05 pm Post subject:
Re: OSI Model |
|
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CJ wrote:
| Quote: | I understand how OSI works in general. But I can know alot of information
about alot of things....doesn't mean its of any use to me.
From what I am reading knowing the OSI is a "nice to know" thing, but
knowing it, unless I am a protocol developer or something, is useless to
me.
Sound about right?
|
Until some guy in a job interview asks you to explain your understanding of
the OSI model.
| Quote: | "catwalker63" <_catwalker63_@hotmamamail.com> wrote in message
news:Xns9635D5BA2DD3Bcatwalker63athotmail@216.196.97.136...
"CJ" <chrisj@illicom.net> prattled ceaslessly in
news:AwH6e.689$Cz3.64167@monger.newsread.com:
I studied the OSI model, but nobody could ever tell me why I need to
know it.
The answer I always got was "you definitely need to know the OSI
model" but when I ask why I always get "you just do".
Can anyone tell me why I need to know it and how I would apply the
knowledge? Perhaps a lab exercise or something??
Thanks,
CJ
The OSI model is a theoretical model that specifies, in a very general
way, how data gets from the application on one machine across the network
to the application on another machine. There are no labs unless you are
developing a protocol to operate at a layer in the model. Understanding
the model helps you undestand how the protocols fit together to get data
onto the network and back off of it.
--
Catwalker
aka Pu$$y Feet
BS, MCP, MCSA
MCNGP #43
www.mcngp.com
faq.mcngp.com
"If man could be crossed with the cat, it would improve man, but it would
deteriorate the cat." Mark Twain
|
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net) |
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