Subject: [manet] Re: Qos on Adhoc nets: SWAN, vs Diffserv

From: "Gahng-Seop Ahn" <[email-masked]>
Date: Tue, 11 Feb 2003 14:23:05 -0500

Hello:

Thanks for your questions on SWAN.

>Is the results shown in "Supporting Service
>Differentiation for Real-Time and Best Effort Traffic in
>Stateless Wireless Ad Hoc Networks (SWAN)", IEEE Transactions
>on Mobile Computing, September 2002---dependent on a specific
>MAC layer behaviour? (The studies cite DCF 802.11 best effort
>networks.) What if there is an adhoc internetwork with
>multiple link layers in place including TDMA? Or is  the best
>effort MAC  the worst case?

SWAN is designed to support soft real-time QOS - even though
it is agnostic to the MAC it is designed to operate over 
(in the worst case) best effort MACs. The SWAN rate controller 
is introduced to resolve the limitation of best effort MACs. 
However, if nodes are equipped with QOS capable MACs (e.g., 
TDMA, EDCF, etc.) then SWAN would perform even better. In this case, 
the SWAN rate controller could be disabled, still allowing the 
SWAN admission controller to perform sender-based 
admission control and dynamic session regulation.

>SWAN is stateless, but so is diffserv. If diffserv were used
>with bandwidth brokers, with appropriate heuristics by which
>to do the bandwidth brokering, mightnt it be an acceptable
>alternative? (the overprovisioning could be bounded by the
>admission control)
>Edge routers need to be identified; but layer 2 self
>organization algorithms exist which do the equivalent. It
>should be  possible to augment IP layer autoconfiguration to
>do the same-
>The advantage diffserv might have would be as a
>heterogeneous qos framework, which is applicable to any
>underlying adhoc technology.Also more classification
>categories than SWAN--

I think the DiffServ model is too (wireline) Internet centric and 
probably not immediately mappable to MANETs. As we all know MANETs 
are quite different from Internet. For example, there is no notion of 
edge and core routers in ad hoc networks allowing us to easily 
map equivalent wireline DiffServ functions too. I also think 
that it may not be practical to have bandwidth brokers (servers) 
in ad hoc networks. Therefore, the original wireline DiffServ model may 
not be deployable in ad hoc networks without major
changes to its design. However, this is an open question.

SWAN follows the philosophy of DiffServ but is designed to fit into 
the structure and behavior of MANETs - and is targeted
to operate over (in the worst case and most likely case) 
best-effort MACs.

Best Regards,
Gahng-Seop Ahn