Subject: RE: [manet] Dumb Question?

From: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Tue, 14 May 2002 12:16:26 -0600

Hi Doug,

My concern was that the forwarding process might be called something else in
a MANET, since it functions differently from the analogous process in wired
networks.  However, the consensus seems to be that the same term is used.  I
think I've gotten my answer on that.

The process would be the consequence of the chosen protocol.  As I
understand it, the process by which a node obtains link information is
called "routing" and the process by which a node decides which of the three
things to do is called either "forwarding" or "switching," depending on who
you talk to.  The details of the processes would be limited by operational
and hardware constraints and defined in the protocols.

The scheme used to assign node addresses is a key issue in military MANETs.
At the upper levels, one wants a scheme that reflects the hierarchical
military organization.  This facilitates the proper routing of orders,
partial orders, etc.  However, at the lower levels, one would want an
addressing scheme that reflects the actual network topology.  This would
allow clustering, which would make route determination and forwarding
simpler.  One solution is to do both, coordinating the system via the
interface.  However, the nodes are in constant motion, so the interface
would need to update its information on the fly.  Offsetting the higher
efficiency of the clusterable scheme at the lower levels is a more
complicated interface and more difficulty enforcing security.  I don't think
this issue has been resolved yet, so, of course, the protocols are also up
in the air.

I just started reading _Ad Hoc Networking_, edited by Charles Perkins.  In
"A DoD Perspective on Mobile Ad Hoc Networks," James Freebersyser speculates
on p. 33 that it is unlikely a single protocol will be able to operate
efficiently over the full range of conditions under which a military MANET
must operate.  If he is correct, the issue may never be fully resolved.

But, there is always hope,

And, graduate students.

:-)

John Mullen

-----Original Message-----
From: Nast, Douglas P [mailto:[email-masked]]
Sent: Tuesday, May 14, 2002 11:10 AM
To: 'Mullen, John P. (Contractor)'
Cc: [email-masked]
Subject: RE: [manet] Dumb Question?

John,

You sent a reply saying you understood that layer 3 routing was going on but
wondered what this other process was.  Thanks for the clarification.

Note that in your question you say that "such a thing is not possible.
Instead, each node that receives a packet decides to..."  and then you give
3 possible behaviors, consume, re-broadcast, or discard.

By what process do the nodes come to understand which of these behaviors is
appropriate for them? Who/What is doing the teaching and to what purpose?
Are the decisions you describe being made on the basis of MAC layer
addresses or IP? 

The first thing that occurs to me is that this behavior was learned via a
route discovery process, sort of like source route bridging in 802 LANs.
This approach to routing in Manets was proposed a while back by David B.
Johnson, and is, I think, the basis of the reactive approach to manet
routing.  If that's the case, then you can call it routing or you can call
it switching, but it is not worthy of a new name.

Based on Perkins and Ram responses, I guess I am missing something, though.
Do you think your question has been resolved? If so how? 

Doug Nast, Boeing

-----Original Message-----
From: Mullen, John P. (Contractor)
[mailto:[email-masked]]
Sent: Monday, May 06, 2002 2:08 PM
To: [email-masked]
Subject: [manet] Dumb Question?

Hello,

I am looking for a term, but have had no luck.

In wired nets, a packet is routed through the network from node to node, say
by routing tables.  However, in MANETs, in which packets are broadcast via
omnidirectional antennae on a shared channel, such a thing is not possible.
Instead, each node that receives a packet  decides to:
     1.  Discard the packet,
     2.  "Read" the packet, since it is addressed to the node, and/or
     3.  Rebroadcast the packet.

If the node is not to be an intermediary node in the end-to-end path between
the source and the destination, or if the node is receiving a copy of a
packet it had previously broadcast, it will not broadcast the packet.  This
is necessary to avoid overutilizing the channel.

If the node is an intermediary node on the path, then it must rebroadcast
the packet.  

I've got this much figured out, but what I do not know is what this process
is called.  It is the MANET equivalent to "routing," but is not really
routing, since the sending node has no way of directing the packet.  

I've tried a number of searches and read a few glossaries, but have not been
able to find this term.

I'd appreciate any help.

Thanks,

John P. Mullen

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---

From: [email-masked]
Date: Tue, 14 May 2002 14:55:37 -0400 (EDT)

Hi John,

> must operate.  If he is correct, the issue may never be fully resolved.

Yes, I read this book too (:-) ...

I hate to bring this point over again ... and self-promote our work ... 
but the issue of "efficient operation over a wide range of conditions" can
and should be addressed by a *hybrid* routing scheme, where the "proactive" 
and "reactive" behavior are "mixed" in the amounts that match these
operational conditions. In other words, *adaptivity* is the key issue
here.

One such an example of a hybrid scheme is (of course, you have guessed)
the ZRP protocol, in which the amount of proactive vs reactive behavior is
*dynamically* adjusted through a single parameter - the zone radius.

Now imagine this - one could use the AODV (or DSR, or your favorite
reactive protocol) as the reactive protocol in ZRP and OLSR (or TBRPF, or
your favorite proactive protocol) as the proactive protocol in ZRP (I
tried to offend the smallest number of people here (;-)). This is why ZRP
is a framework for ... for exactly this - for "efficient operation over a 
wide range of conditions". So, maybe, there is a hope to resolve this
issue after all.

Zygmunt.
==-=-=====
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-
Prof. Zygmunt J. Haas                    http://people.ece.cornell.edu/haas 
Wireless Networks Laboratory		 http://wnl.ece.cornell.edu
School of Electrical Engineering         
Cornell University			 tel: +1-607-255-3454
323 Frank Rhodes Hall			 fax: +1-607-255-9072
Ithaca, NY 14853			 e-mail: [email-masked]
U.S.A                             
	WNL web page: http://wnl.ece.cornell.edu
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-

---

From: [email-masked]
Date: Tue, 14 May 2002 14:55:37 -0400 (EDT)

Hi John,

Zygmunt.
==-=-=====

---

From: Daniel Oldham <[email-masked]>
Date: Wed, 15 May 2002 11:19:38 GMT

Hello Everyone:

Good point, on the Internet IP addresses are regulated and assigned to 
provide a hierarchical structure to allow for proper routing. 

For an ad-hoc network what controls the assignment of IP addresses? 

What happens if there are duplicate IP addresses in an ad-hoc network? 

How is an ad-hoc network connected to the Internet?

How do packets from the Internet get an IP address in an ad-hoc network? 
--
Daniel R. Oldham Ph.D.
Computer Engineer
Satellite Networks and Architectures Branch
NASA Glenn Research Center
21000 Brookpark Road (MS 54-5)
Cleveland OH 44135
216.433.6307 - voice
216.433.8705 - fax
[email-masked]

>>>>>>>>>>>>>>>>>> Original Message <<<<<<<<<<<<<<<<<<

On 5/14/02, 2:16:26 PM, "Mullen, John P. (Contractor)" 
<[email-masked]> wrote regarding RE: [manet] Dumb

---

From: Daniel Oldham <[email-masked]>
Date: Wed, 15 May 2002 11:19:38 GMT

Hello Everyone:

---

From: Charlie Perkins <[email-masked]>
Date: Wed, 15 May 2002 07:32:38 -0700

Hello Daniel,

These are not dumb questions, or dumber questions...

> For an ad-hoc network what controls the assignment of IP addresses?

I guess it depends on which ad-hoc network you're working on.
There is no single answer that applies to every ad-hoc network.

> What happens if there are duplicate IP addresses in an ad-hoc network?

Lose, lose.

> How is an ad-hoc network connected to the Internet?

I would like it if our techniques were found useful.  We have
drafts for both IPv4 and IPv6 connectivity, along with implementations
and instructions for address autoconfiguratoin and operation with
Mobile IP.

> How do packets from the Internet get an IP address in an ad-hoc network?

What does it mean for a packet to get an address?

If the question is, how a packet gets from the Internet to an address
in an ad-hoc network, then it would be because the ad hoc node
has a connection (perhaps through one of our Internet gateways)
to the Internet, and the gateway advertises reachability to the address
of the ad hoc node.  The gateway should advertise its routing
prefix (RFC 1256 or RFC 2461) for use by the ad hoc nodes.

If the ad hoc node is running Mobile IP, then the advertised
address can be used for formulating a care-of address.

Regards,
Charlie P.

---

From: Charlie Perkins <[email-masked]>
Date: Wed, 15 May 2002 07:32:38 -0700

Hello Daniel,

Lose, lose.

Regards,
Charlie P.

---

From: "Philippe Jacquet" <[email-masked]>
Date: Wed, 15 May 2002 18:09:38 +0200

----- Original Message -----
From: Charlie Perkins <[email-masked]>
To: Daniel Oldham <[email-masked]>
Cc: Mullen, John P. (Contractor) <[email-masked]>;
Nast, Douglas P <[email-masked]>; <[email-masked]>
Sent: Wednesday, May 15, 2002 4:32 PM
Subject: Re: [manet] Dumber Question?

> > What happens if there are duplicate IP addresses in an ad-hoc network?
Not a very funny situation. I think proactive protocols have more means to
detect such events (e.g. when non-common neighbors are advertized) and to
trigger appropriate action (e.g. address reconfiguration).

Philippe

---

From: "Philippe Jacquet" <[email-masked]>
Date: Wed, 15 May 2002 18:09:38 +0200

----- Original Message -----
From: Charlie Perkins <[email-masked]>
To: Daniel Oldham <[email-masked]>
Cc: Mullen, John P. (Contractor) <[email-masked]>;

Philippe

---

From: "Nitin Vaidya" <[email-masked]>
Date: Wed, 15 May 2002 11:09:28 -0500

>>From: [email-masked] [mailto:[email-masked]]On Behalf Of
  >>Charlie Perkins

  >>> What happens if there are duplicate IP addresses in an ad-hoc network?

Are you sure?
What if the packets reach their intended destinations despite address
duplication? In that case, duplicate addresses may not be so bad.
See www.crhc.uiuc.edu/~nhv/publications.html for a MobiHoc 2002
paper based on this theme.

The above paper essentially uses IP address as "labels" which are used for
routing, and some other unique string as "key" which is used to set
up routes. The "key" can be made unique with adequately low
probability simply by choosing a sufficiently long string of bits
randomly. IP address duplicate is detected when two different "keys"
are assigned the same label (i.e., same IP address). (By the way, the
paper does not describe the scheme this way, since I did not see the
analogy with labels until recently.)

Trivial idea, but can use some improvements (as elaborated in the paper).

- nitin

---

From: "Nitin Vaidya" <[email-masked]>
Date: Wed, 15 May 2002 11:09:28 -0500

Are you sure?

- nitin

---

From: Charlie Perkins <[email-masked]>
Date: Wed, 15 May 2002 09:26:34 -0700

Hello Philippe,

> trigger appropriate action (e.g. address reconfiguration).

I reckon you are right, that being in this losing situation
isn't funny.  But I wouldn't jump right away to a 100%
proactive solution...

Regards,
Charlie P.

---

From: Charlie Perkins <[email-masked]>
Date: Wed, 15 May 2002 09:26:34 -0700

Hello Philippe,

Regards,
Charlie P.

---

From: [email-masked]
Date: Wed, 15 May 2002 11:15:44 -0700

> trigger appropriate action (e.g. address reconfiguration).

Yes, proactive protocols have a lot of advantages over on-demand
protocols that have not been discussed much.
For example, if one node wants to send a message to another
node that is currently unreachable, an on-demand protocol will
try to discover a route a few times and then give up (and then perhaps 
try periodically).  If proactive routing is used, the sending node 
will be informed as soon as the unreachable node becomes reachable.

Another advantage of proactive protocols is that more efficient flooding 
is possible at no extra cost, using the topology information provided 
by the proactive protocol (e.g., parents in TBRPF or MPRs in OLSR.)

Of course there are other advantages (e.g., proactive protocols are 
more efficient when the number of sources is large, proactive protocols 
can ensure that an alternate route is always maintained, etc.).

Richard

---

From: [email-masked]
Date: Wed, 15 May 2002 11:15:44 -0700

Richard

---

From: Saad Biaz <[email-masked]>
Date: Wed, 15 May 2002 14:43:57 -0500 (CDT)

> will be informed as soon as the unreachable node becomes reachable.

Maybe I am missing something of your reasoning.
But, this is not not an argument in favor of proactive routing algorithms. 
What is the interest of being informed that the unreachable node is now
reachable? There is no interest if upper layers (transport and up) gave
up. We do not keep (for a long time) packets to route until a route is
found.
In other words, what is the point of being informed that a node is
reachable if I do not have packets to send to it?

For the case where the upper layers did not give up, the reactive
algorithm will keep trying too.....

---

From: Saad Biaz <[email-masked]>
Date: Wed, 15 May 2002 14:43:57 -0500 (CDT)

---

From: [email-masked]
Date: Wed, 15 May 2002 13:52:33 -0700

> up. We do not keep (for a long time) packets to route until a route is

Suppose there was an urgent need for you to send a message to someone.
Would you give up after a few tries?
Instead of trying periodically (thus consuming bandwidth with RREQs),
wouldn't it be nice if the network would inform you when the person
becomes reachable?

Richard

---

From: [email-masked]
Date: Wed, 15 May 2002 13:52:33 -0700

Richard

---

From: "Nitin Vaidya" <[email-masked]>
Date: Wed, 15 May 2002 11:01:13 -0500

Are you sure?

- nitin

---

From: "Nitin Vaidya" <[email-masked]>
Date: Wed, 15 May 2002 11:01:13 -0500

Are you sure?

- nitin