[e2e] a means to an end

Lloyd Wood L.Wood at surrey.ac.uk
Tue Dec 2 03:34:56 PST 2008

The DTNRG bundle architecture has some recursion in it - nesting of  
bundle security blocks to give security in the network, and the  
concept of security gateways which effectively do tunnelling by  
nesting these blocks. These have had to be reused for reliability and  
to enable better performance from the network (allowing nodes check  
outer reliability blocks for early resends of corrupted bundles). The  
behaviour sans any of these is no reliability or self-checking (of  
headers, even)/no security/slow network performance as the minimum.

But there's also layering - the assumption that bundling sits on top  
of a network-specific "convergence layer" to traverse each local  
subnet (but is somehow unaffected by the properties of said  
convergence layers. The desired properties of the convergence layers  
are unspecified.)

On induction: what the base case is, and where in layers, is  
interesting. Other than 'you can't start in the middle,' it's hard to  
say anything concrete about it, given that the computing principle of  
'anything can be achieved with a level of indirection' counters  
logical induction and following clear properties or behaviour up or  
down the stack. The end-to-end principle says the induction of layers  
of an unreliable network stack leading to unreliability can be  
countered at the topmost layer where reliability is assured e2e as a  
level of indirection. Performance is a system behaviour, though, and  
visible as an effect of the behaviour of all layers. Naming is  
usually  handled as indirection at every layer; looking at it through  
induction doesn't shed any light.

John Day's _Patterns in Network Architecture_ is big on recursion. I  
suppose one could argue that, with layering and indirection, you can  
fool most of the others most of the time; when relying on indirection  
in a recursive setup, you're only fooling yourself -- so the recursive  
architecture has to be better-thought-out.

On 2 Dec 2008, at 00:22, David P. Reed wrote:

> Two thoughts:
>   Any layering builds from something ... so it's interesting what  
> you posit as the base case from which the mathematical induction  
> follows.
>   There is an alternative to layering: constructing a system that  
> recurses or contains a looped-back-upon-itself dependency, in which  
> case, the resulting behavior can be characterized by the least-fixed- 
> point (LFP, result of the Y combinator, or some other formulation)  
> of the functional recursion.
> I realize these are abstract mathematical concepts, not always  
> taught to the kids these days.  HTML and Python are thought to be  
> verging on too difficult.
> Regarding the IRTF DTN stuff: is the system layered or based on a  
> least fixed point?
> L.Wood at surrey.ac.uk wrote:
>> David,
>> Interesting that he thrust of current IRTF delay-tolerant
>> networking work has effectively turned your statement below
>> on its head, in believing that there is no need for reliability
>> at the top of the network, and no need for location at the top
>> of the network, either.
>> How the network base assures sufficient reliability and assures
>> that endpoint identifiers map to something meaningful would seem
>> to be open problems...
>> L.
>> <http://www.ee.surrey.ac.uk/Personal/L.Wood/><L.Wood at surrey.ac.uk>
>> > Just as there is no need for "reliability" at the base of the  
>> network,
>> > there is no need for "location" at the base.

DTN work: http://info.ee.surrey.ac.uk/Personal/L.Wood/saratoga/

<http://info.surrey.ac.uk/Personal/L.Wood/><L.Wood at surrey.ac.uk>

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