Protocol stack - disadvantages (revision)

I'm currently revising for my third year exams and came across the following
question (from a past paper):

The major advantages with the layered approach to network protocols (eg. the OSI
model) include modularity and manageability. List at least two major
disadvantages of such an approach. Explain your answer.

Any suggestions? All I can think of is performance loss... Which I don't think
is a major issue. I suppose it can be difficult to decide where to put things.
For example IPsec, network layer (therefore transparent) vs. higher layers
(better protection*).


Cheers,

Ben



* Assuming it is used correctly... (End-to-end cryptography in the hands of the
user is more secure than network layer protection [assuming user's can manage
it...])

On Tue, 26 Apr 2005 11:43:55 +0100, "bensmyth" <(E-Mail Removed)>
wrote:

Seems an odd question. I can't really see how you could build a
network without a layered approach.

Dan

>I'm currently revising for my third year exams and came across the following
>question (from a past paper):
>
>The major advantages with the layered approach to network protocols (eg. the OSI
>model) include modularity and manageability. List at least two major
>disadvantages of such an approach. Explain your answer.
>
>Any suggestions? All I can think of is performance loss... Which I don't think
>is a major issue. I suppose it can be difficult to decide where to put things.
>For example IPsec, network layer (therefore transparent) vs. higher layers
>(better protection*).
>
>
>Cheers,
>
>Ben
>
>
>
>* Assuming it is used correctly... (End-to-end cryptography in the hands of the
>user is more secure than network layer protection [assuming user's can manage
>it...])
>

Dan wrote:

> Seems an odd question.**I*can't*really*see*how*you*could*build*a
> network without a layered approach.
>

It's possible to do it all in one layer, but then it'd be difficult to
change anything. For example, you could conceiveably combine level 2 & 3
and reduce some headers, but then you'd be stuck with only one protocol
over only one type of network.

bensmyth wrote:
> I'm currently revising for my third year exams and came across the following
> question (from a past paper):
>
> The major advantages with the layered approach to network protocols (eg. the OSI
> model) include modularity and manageability. List at least two major
> disadvantages of such an approach. Explain your answer.
>
> Any suggestions? All I can think of is performance loss... Which I don't think
> is a major issue. I suppose it can be difficult to decide where to put things.
> For example IPsec, network layer (therefore transparent) vs. higher layers
> (better protection*).

Think about overhead. Each layer will add its own signaling, which takes
bandwidth. Those poor folks doing TCP-over-IP-over-AAL5-over-ATM know
what I mean ;-)

Also, having several layers can hide the work done below. A lot of
programmers today don't know that their XML/SOAP is going over HTTP,
then TCP, then IP. Sometimes you end-up re-inventing the wheel when you
are already driving a car. Or you end up making a CRC32 on your data ...
which is already done by the TCP layer.

I like your teacher ... makes people think in the other way round. Good
way to train students in creativity.

--
Jean-Francois "Jef" Stenuit

Jean-Francois "Jef" Stenuit wrote:

> I like your teacher ... makes people think in the other way round. Good
> way to train students in creativity.

Just the thing they need in book keeping classes. ;-)