Subject: Re: Simulation parameters for comparative results?

From: [email-masked] (Joseph P. Macker)
Date: Thu, 24 Jul 1997 19:10:15 -0400

Great topic for more open discussion!  Several of us have been putting together some thoughts in this area.  Scott and I will partly discuss this issue in a draft informational document we are working on.  Hope you and others can help refine the thoughts here through some healthy dialogue within the working group.

>Has there been discussion or conclusions regarding parameters for
>simulation scenarios?  Some possibilities I can think of:
>
>-network size
>-network topology, such as average degree/connectivity of nodes, also
>  any specific topologies
>-physical considerations, such as area covered, transmission range,
>  received power, bandwidth constraints.
>-mobility model, such as the rate of change, the type of changes
>  modelled--i.e., independent link changes vs. movement of nodes (so that
>  link changes are NOT independent), the choice of static topology with 
>  random failures vs. mobile topology with random movement

As you point out there are many dimensions over which to define performance (you nicely listed many to consider).  Another to add to the list could be traffic loading assumptions,etc.  Are traffic sources/receivers uniform in distribution and in offered load? Do we consider cases with nonuniform distributions (probably more realistic, but harder to quantify unless we can agree on some models).

I expect, as in other routing work (e.g., IDMR), different protocols may alternately outshine each other when looked at under different light.  This is not a problem unique to wireless mobile routing, but here we have a set of added dimensions to consider.

-joe

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From: Kenneth CARLBERG <[email-masked]>
Date: Fri, 25 Jul 1997 12:47:44 +0100

Joe,

> As you point out there are many dimensions over which to define 
> performance (you nicely listed many to consider).  Another to add 
> to the list could be traffic loading assumptions,etc.

Adding to this line of thought, I would also add the notion of the
time in which the network/node is unreachable -- ie, when it is outside
the coverage area of any layer 2 subnet media.

Something else to consider is to add several axis in relation to the
above characteristics of ad-hoc networking.  At the risk of going
on a slight limb, one could characterize the focus of ad-hoc
networking in terms of supporting best-effort unicast routing between 
any two points.  Further, for the sake of arguement, one could
label aspects like QoS routing, resource reservation (aka RSVP), 
and IP multicasting as value added services to what ad-hoc networking 
is trying to accomplish.  By value added, I mean that it primarily 
refines or enhances the atomic capability of best-effort unicast routing.
Beyond this, there is also reliable vs. unreliable multicasting.

Having said that, it would probably be of interest to compare the
items you and Bevan mentioned against situations of what happens 
when you add, for example, QoS, RSVP, or PIM to an ad-hoc routing 
protocol -- admittidly, the QoS is more of a direct add-on capability 
than the other two layered protocols.  But in doing this exercise, 
there are two basic questions that come to mind. The first is can you 
do it (eg, plug RSVP with PIM-dm on top of ad-hoc routers) ?  The second
question is what is the system impact?  In this second question,
I get curious to find out how much overhead traffic (non-data packets)
are generated by adding these value added capabilities.  Actually, for 
that matter, you can ask the same question about different ad-hoc
proposals.  The reason this question becomes so important is because
wireless technology (based on $ per bit) typically offers a much
smaller pipe to work with than does terestrial pipes.  Hence, the 
overhead traffic plays more of a role in congestion and subsequent 
packet loss or denial of service.

-ken

can find your self asking 2 questions