Subject: < [manet] Re: How to do the simulation with ns2 for hybrid wireless network? > A different approach to support Internet connectivity for MANETs

From: "HyunWook Cha" <[email-masked]>
Date: Wed, 17 Dec 2003 21:28:15 +0900

Hello, Manish.

Thank you for your paper. I remember that you mentioned your idea during
discussion about the "Alien Node Problem" two or three months ago.
Please refer
http://www1.ietf.org/mail-archive/working-groups/manet/current/msg02701.
html for my reply at that time.

Uhm... Actually I did not understand what you meant. Now, I think that I
can get to the point. 

As Charlie Perkins mentioned, the virtual subnetting where all global
addresses of MANETs shares one global prefix is common in all(?)
existing approaches. The difference is that you want to define a new
prefix for all MANET nodes which want the Internet connection and
existing schemes have a node configure its global addresses from
available gateways in stateful or stateless manner. If an important
reason of your choice is to distinguish between nodes that are within a
MANET and those that are outside, I do not agree. In case of stateless
method, a manet node updates route information for its global address
through gateway discovery to refresh the GW_INFO or peridocal RREQ or
RREP to corresponding(affiliated) gateway. In case of stateful method,
all nodes in the MANET which configured a global address from a gateway
are cached in the gateway. Thus, as for autoconfigured global addresses,
the determination which you consider as complex does not require much
cost. When node A inside the MANET wants to communicate node B which has
a global address which is not globally routable(by manual
configuration), network partition can cause that A sends packets
destined to B using default route(toward the gateway chosen by A).
Yasser called this issue the Alien Node Problem. As I mentioned before,
node A finally receives ICMP Destination Unreachable and then tries to
discover host route for the destination. Caching of addresses that
caused ICMP unreachable message can help for preventing same wrong
decision in near future. This is also not expensive.   

Well. In your paper, gateways which detect the presence of MANETs via
Hellos or other methods(default router discovery) advertise the MANET
prefix throughout Internet. As you point out Fig 2(poor route
selection), Fig 3 (Unnecessary Failure due to Partition) in your paper,
there are serious issues to be addressed. Although you mentioned the use
of registration scheme as a possible solution for those, I do not agree.
A registration scheme assumes that a manet node should know all gateways
which advertise the MANET global prefix to Internet. However, frequent
network partitions and dynamic creations of MANETs which demand Internet
connectivity can break this assumption. How can you handle this issue?

Regards,

HyunWook Cha

> -----Original Message-----
> From: Manish Karir [mailto:[email-masked]] 
> Sent: Wednesday, December 17, 2003 12:16 AM
> To: HyunWook Cha
> Subject: RE: [manet] Re: How to do the simulation with ns2 
> for hybrid wireless network?
> 
> 
> 
> Did I forget to attach the paper last time or did you have 
> problem printing it?  In anycase I am attaching it here 
> again...pleaset let me know if you have any problems....
> 
> thanks
> manish
> 
> 
> On Tue, 16 Dec 2003, HyunWook Cha wrote:
> 
> > Could you check your paper, again?
> >
> > Thanks.
> >
> > HyunWook
> >
> 
> 

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