>There are many advantages/disadvantages of using the concept of layering
>in protocol stack. Advantages are obvious to me...can someone list the
>disadvantages ? More precisely there are instances where the strict
>layering in protocol stack has been compromised to achieve performance
>improvement. can someone give a list of such instances ?
A list might be tricky to find, but there's one obvious example: tcp/ip.
That's an excellent example of a protocol stack that was conceived of
in terms of a layered design, but where the layering has been heavily
compromised in practice.
For further study, just pick up an book on tcp/ip. Most of the books
focus on a Unix perspective, but that's not a serious disadvantage
since the OS/2 implementation is very similar to the Unix implementation.