Subject: service model work...

From: Jon Crowcroft <[email-masked]>
Date: Wed, 29 Mar 95 14:53:19 +0100

i think a really useful excercise would be the following concrete
descriptions...

Given best effort, controlled delay, predictive or guaranteed applications
	given the following scenarios 1,2,3
		describe reservation traffic and user traffic control

scenarios - all traffic is over IP. some hops are legacy others are
multiservice link level provided by ATM.

1.  Host - ATM - Host

2. Host - LAN - Router - ATM - Router - LAN - Host

3. Host - LAN - Router - ATM - Host

for situations where the ATM service includes
UBR, ABR, VBR and CBR (i doubt the latter is very interesting, but...)
and the LAN is either light, or overloaded.

Assume that we have an RSVP<->Q2931 interworking box at the
Router<->ATM and Host<->ATM interfaces

I think it is quite straightforard except for the ABR interworking
with controlled delay or predictive in scenarios 2 and 3,
as i believe that this could have bad behviours for some values of
traffic control parameters for some values of RTTs in the
ATM loop and the end to end RTTs (basically, an adaptive application
like X over TCP, or IVS over RTP might have two control loops with
different time constants...)

anyhow soemthing for a first yr phd student to do...

jon

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From: [email-masked] (Hiroshi Esaki)
Date: Wed, 29 Mar 1995 17:46:10 -0500

Hi Jon, 

 >> Given best effort, controlled delay, predictive or guaranteed applications
By my stupid understanding, ABR and UBR is good for best effort service, 
and CBR and VBR is for both best effort service and the other three
services (i.e. controlled delay, predictive and guaranteed). 

ABR might be useful for controlled delay service, but it will not 
work for long-haul ABR connection. 

 >> and the LAN is either light, or overloaded.
ABR will be only good for short-haul connection, and could give 
some delay objective by the provision of miminum bandwidth for each VC. 
Therefore, ABR might be useful for short-haul link between the 
routers for controlled delay service. 

 >> with controlled delay or predictive in scenarios 2 and 3,
VBR and CBR are useful or three services (controlled delay, predictive 
and guaranteed), I think.
Moreover, ABR does not have delay quality performance objective. 

 >> different time constants...)
Yes. ABR's control loop should be very localized. 

By my view, ABR may be useful for hop-by-hop links for 
best-effort service, that is not resource reservation oriented. 
The best effort service, e.g.TCP, is very hard to estimate the 
required bandwidth requirement (i.e. Tspec). Therefore, ABR may be 
useful for short-haul link between the routers. 
For long-haul best effort connection, ABR will not work well. 
ABR could and will have VD/VS (Virtual Destination and Virtual Source)
along the long-haul path to have tandemly connected flow control loops. 
It is pretty much similar to have routers along the long-haul path
for me.  And, since ABR does not have delay objective, it would be 
much better to use packet forwarder (i.e. router), instead of 
VD/VS.    Now, why we need ABR ?   UBR may not able to provide 
high quality associated with cell loss (--> packet error/loss), but  
ABR will be able to provide high quality associated with cell loss 
quality or local connection (i.e. short-haul connection). 
I mean that ABR will be useful to provide high quality (associated 
with cell loss) for short-haul connection between routers and host, 
for best effort service. 
# Of course, the use of CBR and VBR is also fine for routers. 

Hiroshi Esaki 

P.S. I will talk briefly how to provide four services on ATM 
     at colip-atm BoF on April.4 
     I think, for a large cloud ATM network, long-haul ATM connection 
     is only available, when packet flow is resource reservation 
     oriented (can estimate the required bandwidth and Tspec) and 
     when the connection is really end-to-end.

---

From: Masataka Ohta <[email-masked]>
Date: Fri, 31 Mar 95 15:21:08 JST

> services (i.e. controlled delay, predictive and guaranteed). 

Too many people are hyped to believe ATM solves all the problems.

I was surprised to see end2end ML hyped to produce a draft saying that
ATM magically removes bandwidth limitation.

> routers for controlled delay service. 

Or, within a long-haul link between continent, if all swicthes are
equipped with gigabits of buffer memory. In this case, to avoid
all the end-end switches have a lot of buffer, the trans-continental
ABR control must be terminated at the proxy points within the
continent, which is effectively equivalent to have an IP router.
So, it is natural to make IP routers ABR proxy point.

						Masataka Ohta