Enrico Marocco wrote:
>> I understand. Routing policy can result in TIVs, if the policy
>> considers factors other than latency.
>> I think the technical limitation could be the reason of TIVs too.
>> Resolving TIVs caused by technical reasons in IP layer may be hard,
>> but resolving with relay is easier.
> 
> Could you provide examples of such routing layer limitations that would
> be best addressed at the application layer?
> 
>> Take AS routing as an example. Suppose both AS B and AS C can route
>> traffic from AS A to AS D. AS B charges a higher price for routing
>> traffic, but routing through AS B is fast. Suppose AS A's operator's
>> will is: a flow to AS D should route through AS C (slow but cheap) if
>> QOS meets the application's requirement, otherwise route through AS B
>> (fast but expensive). If using routing policy only, out-bound router
>> must sense the exact QOS requirement of every traffic flow and the
>> latency of AS path. So only configuring routing policy at IP layer may
>> not fulfill the will of operator entirely. Both routing policy and
>> relay should be used to fulfill operator's will.
> 
> I would say that's what RSVP was invented for. In which way do you think
> a solution based on application-level relays would work better?

Woops, of course I meant DiffServ, sorry. It may have been a Freudian
slip though ;)

-- 
Ciao,
Enrico

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