|
Home > Archive > alt.certification.cisco > September 2002 > Trying to get a handle on OSI
You are viewing an archived Text-only version of the thread.
To view this thread in it's original format and/or if you want to reply to
this thread please [click here]
| Author |
Trying to get a handle on OSI
|
|
| Seth C 2002-08-22, 9:28 am |
| This is my second crack at the OSI model, and it's giving me headaches for a
second time. The bottom 4 layers have always made sense to me, but I'm
trying to get a handle on the top 3. I think what I'm discovering is that
layers 5 and 6 are optional, or often all three are combined. For example,
SMTP. I've seen in various places that SMTP is application layer material.
However, to my knowledge when using SMTP, there is nothing below handling
either the presentation or session. If I were to, say, use PERL to write a
SMTP or HTTP app, I would use calls that resolved my host names, opened
ports, and sent data, and wrote data. What I can't figure out is where the
session layer fits into this. The Presentation layer is right out, because
nothing is formatting my data. In other words, if SMTP is application layer,
and SMTP builds directly on TCP/IP which is transport layer, who ate the
session layer? Is it generally not used? Or is it invisibly part of may
"application layer" entities?
Please forgive my rambling. Any help would be appreciated,
Seth C
| |
| Robert Yoder 2002-08-24, 5:41 pm |
| Seth C wrote:
> This is my second crack at the OSI model, and it's giving me headaches for a
> second time. The bottom 4 layers have always made sense to me, but I'm
> trying to get a handle on the top 3. I think what I'm discovering is that
> layers 5 and 6 are optional, or often all three are combined. For example,
> SMTP. I've seen in various places that SMTP is application layer material.
> However, to my knowledge when using SMTP, there is nothing below handling
> either the presentation or session. If I were to, say, use PERL to write a
> SMTP or HTTP app, I would use calls that resolved my host names, opened
> ports, and sent data, and wrote data. What I can't figure out is where the
> session layer fits into this. The Presentation layer is right out, because
> nothing is formatting my data. In other words, if SMTP is application layer,
> and SMTP builds directly on TCP/IP which is transport layer, who ate the
> session layer? Is it generally not used? Or is it invisibly part of may
> "application layer" entities?
>
> Please forgive my rambling. Any help would be appreciated,
The reason the bottom 4 layers make sense to you is because
they are real. Applications use layer 4 protocols, and every
application can do whatever it damn well pleases internally.
The "presentation" and "session" layers are just imaginary,
idealistic, overly-complicated, designed-by-committee bullshit,
characteristic of too much of what OSI produced.
Read Marshall Rose's books about email or SNMP for an
entertaining skewering of OSI.
ry
--
| |
| Robert Yoder 2002-08-24, 6:29 pm |
| Seth C wrote:
> This is my second crack at the OSI model, and it's giving me headaches for a
> second time. The bottom 4 layers have always made sense to me, but I'm
> trying to get a handle on the top 3. I think what I'm discovering is that
> layers 5 and 6 are optional, or often all three are combined. For example,
> SMTP. I've seen in various places that SMTP is application layer material.
> However, to my knowledge when using SMTP, there is nothing below handling
> either the presentation or session. If I were to, say, use PERL to write a
> SMTP or HTTP app, I would use calls that resolved my host names, opened
> ports, and sent data, and wrote data. What I can't figure out is where the
> session layer fits into this. The Presentation layer is right out, because
> nothing is formatting my data. In other words, if SMTP is application layer,
> and SMTP builds directly on TCP/IP which is transport layer, who ate the
> session layer? Is it generally not used? Or is it invisibly part of may
> "application layer" entities?
>
> Please forgive my rambling. Any help would be appreciated,
The reason the bottom 4 layers make sense to you is because
they are real. Applications use layer 4 protocols, and every
application can do whatever it damn well pleases internally.
The "presentation" and "session" layers are just imaginary,
idealistic, overly-complicated, designed-by-committee bullshit,
characteristic of too much of what OSI produced.
Read Marshall Rose's books about email or SNMP for an
entertaining skewering of OSI.
ry
--
| |
| Bernie M 2002-08-25, 2:28 am |
|
"Robert Yoder" <ryoder@dimensional.com> wrote in message
news:3D6815F1.8010407@dimensional.com...
> Seth C wrote:
> > This is my second crack at the OSI model, and it's giving me headaches
for a
> > second time. The bottom 4 layers have always made sense to me, but I'm
> > trying to get a handle on the top 3. I think what I'm discovering is
that
> > layers 5 and 6 are optional, or often all three are combined. For
example,
> > SMTP. I've seen in various places that SMTP is application layer
material.
> > However, to my knowledge when using SMTP, there is nothing below
handling
> > either the presentation or session. If I were to, say, use PERL to write
a
> > SMTP or HTTP app, I would use calls that resolved my host names, opened
> > ports, and sent data, and wrote data. What I can't figure out is where
the
> > session layer fits into this. The Presentation layer is right out,
because
> > nothing is formatting my data. In other words, if SMTP is application
layer,
> > and SMTP builds directly on TCP/IP which is transport layer, who ate the
> > session layer? Is it generally not used? Or is it invisibly part of may
> > "application layer" entities?
> >
> > Please forgive my rambling. Any help would be appreciated,
>
> The reason the bottom 4 layers make sense to you is because
> they are real. Applications use layer 4 protocols, and every
> application can do whatever it damn well pleases internally.
>
> The "presentation" and "session" layers are just imaginary,
> idealistic, overly-complicated, designed-by-committee bullshit,
> characteristic of too much of what OSI produced.
>
> Read Marshall Rose's books about email or SNMP for an
> entertaining skewering of OSI.
>
>
I think it's a bit harsh to state that the top three layers are "imaginary,
idealistic, .... bullshit" and in fact quite technically incorrect.
Take NetBIOS for example. It's naming structure operates at the Session
layer ... this is *real*.
The Presentation layers reflects how *bit and bytes* get transformed into
data the application understands eg. open an Excel file sitting on a server
.... bits become bytes which become the data making up the file. This is a
very simplistic overview but again very real.
As expected, the Application layer itself represents the actual application.
Take away those three layers and see what happens.
BernieM
| |
| Bernie M 2002-08-25, 3:28 am |
|
"Robert Yoder" <ryoder@dimensional.com> wrote in message
news:3D6815F1.8010407@dimensional.com...
> Seth C wrote:
> > This is my second crack at the OSI model, and it's giving me headaches
for a
> > second time. The bottom 4 layers have always made sense to me, but I'm
> > trying to get a handle on the top 3. I think what I'm discovering is
that
> > layers 5 and 6 are optional, or often all three are combined. For
example,
> > SMTP. I've seen in various places that SMTP is application layer
material.
> > However, to my knowledge when using SMTP, there is nothing below
handling
> > either the presentation or session. If I were to, say, use PERL to write
a
> > SMTP or HTTP app, I would use calls that resolved my host names, opened
> > ports, and sent data, and wrote data. What I can't figure out is where
the
> > session layer fits into this. The Presentation layer is right out,
because
> > nothing is formatting my data. In other words, if SMTP is application
layer,
> > and SMTP builds directly on TCP/IP which is transport layer, who ate the
> > session layer? Is it generally not used? Or is it invisibly part of may
> > "application layer" entities?
> >
> > Please forgive my rambling. Any help would be appreciated,
>
> The reason the bottom 4 layers make sense to you is because
> they are real. Applications use layer 4 protocols, and every
> application can do whatever it damn well pleases internally.
>
> The "presentation" and "session" layers are just imaginary,
> idealistic, overly-complicated, designed-by-committee bullshit,
> characteristic of too much of what OSI produced.
>
> Read Marshall Rose's books about email or SNMP for an
> entertaining skewering of OSI.
>
>
I think it's a bit harsh to state that the top three layers are "imaginary,
idealistic, .... bullshit" and in fact quite technically incorrect.
Take NetBIOS for example. It's naming structure operates at the Session
layer ... this is *real*.
The Presentation layers reflects how *bit and bytes* get transformed into
data the application understands eg. open an Excel file sitting on a server
.... bits become bytes which become the data making up the file. This is a
very simplistic overview but again very real.
As expected, the Application layer itself represents the actual application.
Take away those three layers and see what happens.
BernieM
| |
| CCIE 8122 2002-09-24, 8:29 pm |
| More accurately, layers 5-6 have no analog in the IP stack, which really
only maps to layers 1-4 and layer 7 (which really combines the functions
of the presentation, session and app layers in IP).
kr
Robert Yoder wrote:
> Seth C wrote:
>
>> This is my second crack at the OSI model, and it's giving me headaches
>> for a
>> second time. The bottom 4 layers have always made sense to me, but I'm
>> trying to get a handle on the top 3. I think what I'm discovering is that
>> layers 5 and 6 are optional, or often all three are combined. For
>> example,
>> SMTP. I've seen in various places that SMTP is application layer
>> material.
>> However, to my knowledge when using SMTP, there is nothing below handling
>> either the presentation or session. If I were to, say, use PERL to
>> write a
>> SMTP or HTTP app, I would use calls that resolved my host names, opened
>> ports, and sent data, and wrote data. What I can't figure out is where
>> the
>> session layer fits into this. The Presentation layer is right out,
>> because
>> nothing is formatting my data. In other words, if SMTP is application
>> layer,
>> and SMTP builds directly on TCP/IP which is transport layer, who ate the
>> session layer? Is it generally not used? Or is it invisibly part of may
>> "application layer" entities?
>>
>> Please forgive my rambling. Any help would be appreciated,
>
>
> The reason the bottom 4 layers make sense to you is because
> they are real. Applications use layer 4 protocols, and every
> application can do whatever it damn well pleases internally.
>
> The "presentation" and "session" layers are just imaginary,
> idealistic, overly-complicated, designed-by-committee bullshit,
> characteristic of too much of what OSI produced.
>
> Read Marshall Rose's books about email or SNMP for an
> entertaining skewering of OSI.
>
>
> ry
> --
>
| |
| CCIE 8122 2002-09-24, 9:29 pm |
| More accurately, layers 5-6 have no analog in the IP stack, which really
only maps to layers 1-4 and layer 7 (which really combines the functions
of the presentation, session and app layers in IP).
kr
Robert Yoder wrote:
> Seth C wrote:
>
>> This is my second crack at the OSI model, and it's giving me headaches
>> for a
>> second time. The bottom 4 layers have always made sense to me, but I'm
>> trying to get a handle on the top 3. I think what I'm discovering is that
>> layers 5 and 6 are optional, or often all three are combined. For
>> example,
>> SMTP. I've seen in various places that SMTP is application layer
>> material.
>> However, to my knowledge when using SMTP, there is nothing below handling
>> either the presentation or session. If I were to, say, use PERL to
>> write a
>> SMTP or HTTP app, I would use calls that resolved my host names, opened
>> ports, and sent data, and wrote data. What I can't figure out is where
>> the
>> session layer fits into this. The Presentation layer is right out,
>> because
>> nothing is formatting my data. In other words, if SMTP is application
>> layer,
>> and SMTP builds directly on TCP/IP which is transport layer, who ate the
>> session layer? Is it generally not used? Or is it invisibly part of may
>> "application layer" entities?
>>
>> Please forgive my rambling. Any help would be appreciated,
>
>
> The reason the bottom 4 layers make sense to you is because
> they are real. Applications use layer 4 protocols, and every
> application can do whatever it damn well pleases internally.
>
> The "presentation" and "session" layers are just imaginary,
> idealistic, overly-complicated, designed-by-committee bullshit,
> characteristic of too much of what OSI produced.
>
> Read Marshall Rose's books about email or SNMP for an
> entertaining skewering of OSI.
>
>
> ry
> --
>
| |
|
| I'm sure someone will tell me if I'm wrong, but I believe that it is the
operating system that manages the session layer's responsibilities -
remembering the UNIX TCP/IP sockets.
"CCIE 8122" <none@none.com> wrote in message
news:3D91199D.4050400@none.com...
> More accurately, layers 5-6 have no analog in the IP stack, which really
> only maps to layers 1-4 and layer 7 (which really combines the functions
> of the presentation, session and app layers in IP).
>
> kr
>
> Robert Yoder wrote:
> > Seth C wrote:
> >
> >> This is my second crack at the OSI model, and it's giving me headaches
> >> for a
> >> second time. The bottom 4 layers have always made sense to me, but I'm
> >> trying to get a handle on the top 3. I think what I'm discovering is
that[
color=darkred]
> >> layers 5 and 6 are optional, or often all three are combined. For
> >> example,
> >> SMTP. I've seen in various places that SMTP is application layer
> >> material.
> >> However, to my knowledge when using SMTP, there is nothing below[/color]
handling
> >> either the presentation or session. If I were to, say, use PERL to
> >> write a
> >> SMTP or HTTP app, I would use calls that resolved my host names, opened
> >> ports, and sent data, and wrote data. What I can't figure out is where
> >> the
> >> session layer fits into this. The Presentation layer is right out,
> >> because
> >> nothing is formatting my data. In other words, if SMTP is application
> >> layer,
> >> and SMTP builds directly on TCP/IP which is transport layer, who ate
the[c
olor=darkred]
> >> session layer? Is it generally not used? Or is it invisibly part of may
> >> "application layer" entities?
> >>
> >> Please forgive my rambling. Any help would be appreciated,
> >
> >
> > The reason the bottom 4 layers make sense to you is because
> > they are real. Applications use layer 4 protocols, and every
> > application can do whatever it damn well pleases internally.
> >
> > The "presentation" and "session" layers are just imaginary,
> > idealistic, overly-complicated, designed-by-committee bullshit,
> > characteristic of too much of what OSI produced.
> >
> > Read Marshall Rose's books about email or SNMP for an
> > entertaining skewering of OSI.
> >
> >
> > ry
> > --
> >
>[/color]
| |
|
| I'm sure someone will tell me if I'm wrong, but I believe that it is the
operating system that manages the session layer's responsibilities -
remembering the UNIX TCP/IP sockets.
"CCIE 8122" <none@none.com> wrote in message
news:3D91199D.4050400@none.com...
> More accurately, layers 5-6 have no analog in the IP stack, which really
> only maps to layers 1-4 and layer 7 (which really combines the functions
> of the presentation, session and app layers in IP).
>
> kr
>
> Robert Yoder wrote:
> > Seth C wrote:
> >
> >> This is my second crack at the OSI model, and it's giving me headaches
> >> for a
> >> second time. The bottom 4 layers have always made sense to me, but I'm
> >> trying to get a handle on the top 3. I think what I'm discovering is
that[
color=darkred]
> >> layers 5 and 6 are optional, or often all three are combined. For
> >> example,
> >> SMTP. I've seen in various places that SMTP is application layer
> >> material.
> >> However, to my knowledge when using SMTP, there is nothing below[/color]
handling
> >> either the presentation or session. If I were to, say, use PERL to
> >> write a
> >> SMTP or HTTP app, I would use calls that resolved my host names, opened
> >> ports, and sent data, and wrote data. What I can't figure out is where
> >> the
> >> session layer fits into this. The Presentation layer is right out,
> >> because
> >> nothing is formatting my data. In other words, if SMTP is application
> >> layer,
> >> and SMTP builds directly on TCP/IP which is transport layer, who ate
the[c
olor=darkred]
> >> session layer? Is it generally not used? Or is it invisibly part of may
> >> "application layer" entities?
> >>
> >> Please forgive my rambling. Any help would be appreciated,
> >
> >
> > The reason the bottom 4 layers make sense to you is because
> > they are real. Applications use layer 4 protocols, and every
> > application can do whatever it damn well pleases internally.
> >
> > The "presentation" and "session" layers are just imaginary,
> > idealistic, overly-complicated, designed-by-committee bullshit,
> > characteristic of too much of what OSI produced.
> >
> > Read Marshall Rose's books about email or SNMP for an
> > entertaining skewering of OSI.
> >
> >
> > ry
> > --
> >
>[/color]
|
|
|
|
|