[e2e] Layering vs. modularization
David P. Reed
dpreed at reed.com
Thu May 15 18:27:28 PDT 2008
Encasulation means that the "totally ordered stack of layers" suddenly
can grow to infinite depth, as the sequence of layers is laid on top of
a subsequence selected from the same layers.
Layering has nothing to do with "looking inside the packets". That
concept is not layering, it is something quite different - having to do
with lack of "interpretation" of bit strings.
George Michaelson wrote:
> On 16/05/2008, at 8:20 AM, David P. Reed wrote:
>> b) Explain protocol encapsulation (sending IPv6 datagrams within UDP
>> VPN packets over a TCP based overlay network implemented in userspace
>> stacks on machines that offload part of the VPN implementation to a
>> peer within a bluetooth subnet) as a form of layering? It seems to
>> me that encapsulation is akin to allowing recursion in one's
>> language. Languages that allow recursion are unlike FORTRAN 77,
>> which is "layered".
> recursion requires that first-class data constructs in the language be
> respected, so stack frame boundaries, globals etc are meaningful.
> encapsulation doesn't require this. the encapsulated protocol has its
> own e2e significance and its own routing. for the purposes of
> encapsulation, its just data.
> therefore the comparison (as in most analogies?) for me, is not a good
> fit. actually, I think most things described as recursive usually
> stateful packet inspectors *might* need a re-write, but that aside, I
> don't see how anything other than a bug would make the outer V6
> active units need to read the inner V4 payload, or vice versa
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