Subject: RE: [manet] Dumber Question?

From: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Wed, 15 May 2002 07:11:56 -0600

Hi Daniel,

I cannot answer your question in general, but in the military, the method of
IP address assignment is specified.  Field Manual 11-71 is an unrestricted
document that explains the general ideas used in Army tactical systems.
Since each military unit has a unique designator, it is unlikely that there
would be duplicate IP addresses when assigned by functional unit.

Appendix A of FM 11-71 explains how the Army system is connected to all
external systems.  The traffic on Army tactical systems is classified.
There is an interface to SIPRNET (which is rated for information up to
secret), but access to and from the Global Internet is blocked.

In general, packets formulated for wireless links are not efficient for
wired links and vice versa.  Data and bit error rates differ by one or more
orders of magnitude.  Interconnections to external systems are by means of
special gateway nodes that recode and reformat data to be compatible with
the target system. 

John Mullen

-----Original Message-----
From: Daniel Oldham [mailto:[email-masked]]
Sent: Wednesday, May 15, 2002 5:20 AM
To: Mullen, John P. (Contractor)
Cc: Nast, Douglas P; [email-masked]
Subject: RE: [manet] Dumber Question?

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 
Question?:

> 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

> _______________________________________________
> manet mailing list
> [email-masked]
> https://www1.ietf.org/mailman/listinfo/manet

> _______________________________________________
> manet mailing list
> [email-masked]
> https://www1.ietf.org/mailman/listinfo/manet

_______________________________________________
manet mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/manet

---

From: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Wed, 15 May 2002 07:11:56 -0600

Hi Daniel,

John Mullen

-----Original Message-----
From: Daniel Oldham [mailto:[email-masked]]
Sent: Wednesday, May 15, 2002 5:20 AM
To: Mullen, John P. (Contractor)
Cc: Nast, Douglas P; [email-masked]
Subject: RE: [manet] Dumber Question?

Hello Everyone:

in
wired
 I

three
who
operational

MANETs.
think
up

In
speculates
MANET

but

give

is

call

though.

say
via
possible.

between
This

process

been

---

From: Marwaha Shivanajay <[email-masked]>
Date: Wed, 15 May 2002 21:17:54 +0800

Hi,
Assignment of IP adresses is done using "autoconfiguration" in ad hoc
networks.
The draft that deals with this can be found here
http://www.cs.ucsb.edu/~eroyer/txt/autoconf.txt

To summarize it in short:
If a mobile node wants to have an IP address it broadcasting a RREQ kind of
message destined to that IP address. If there exists a mobile device with
the same address it gets a RREP back from it and reinitiates the process by
choosing a new IP address, otherwise (if it aint get any RREP) it assumes
that IP address.

The IP address seeking node keeps a temporary address for receiving RREP
back to it.

It does deal with avoiding duplicacy of IP addresses in one disconnected set
of mobiles. But there isn't any central mechanism to allot the same. Nor
does it guarentee uniqueness in disconnected networks. 

Regards,
Shivanajay Marwaha
-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~
Research Scholar
Electrical and Computer Engg. Dept.
National University of Singapore.
10 Kent Ridge Crescent,
Singapore 119260.
Ph. +65-68742136
-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~

-----Original Message-----
From: Daniel Oldham [mailto:[email-masked]] 
Sent: Wednesday, May 15, 2002 7:20 PM
To: Mullen, John P. (Contractor)
Cc: Nast, Douglas P; [email-masked]
Subject: RE: [manet] Dumber Question?

Hello Everyone:

in
wired
 I

three
who
operational

MANETs.
> 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
up

In
speculates
MANET

but

give

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

though.

say
via
possible.

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

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

process

been

---

From: Marwaha Shivanajay <[email-masked]>
Date: Wed, 15 May 2002 21:17:54 +0800

Hi,

Regards,
Shivanajay Marwaha

-----Original Message-----
From: Daniel Oldham [mailto:[email-masked]] 
Sent: Wednesday, May 15, 2002 7:20 PM
To: Mullen, John P. (Contractor)
Cc: Nast, Douglas P; [email-masked]
Subject: RE: [manet] Dumber Question?

Hello Everyone:

in
wired
 I

three
who
operational

MANETs.
think
up

In
speculates
MANET

but

give

is

call

though.

say
via
possible.

between
This

process

been

---

From: "Manfredi, Albert E" <[email-masked]>
Date: Wed, 15 May 2002 11:12:56 -0400

> From: Charlie Perkins [mailto:[email-masked]]

> 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.

Hmmm. This is something that has puzzled me too. The only way the wired Internet can route packets reasonably, i.e. without building exhaustive tables with individual host addresses, is to use the IP address prefix. If a MANET node is not provided with a dynamic address somehow, an address with the proper prefix for its current location, _and_ if that address is not changed as the MANET node moves geographically, then I don't see how the wired Internet can continue to find the MANET node. Not unless there is a single, fixed connection point between the wired Internet and the MANET. (If there is that fixed border router, then the answer is pretty straightforward.)

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

Mobile IP either has the home server forward everything to the current location of the mobile host, or it can set up a shortcut to that remote location after the current address of the mobile host is provided. But for this to work, the location of the mobile must remain constant for the duration of the session. I'm not sure how use of the Mobile IP care-of address can be a solution to the MANET scenario.

I can understand the chaotic "routing" environment related to MANET, and the tradeoffs between proactive and reactive so-called "routing" protocols. But so far, I only understand these discussions if they are limited to the ad-hoc environment.

Bert

---

From: "Manfredi, Albert E" <[email-masked]>
Date: Wed, 15 May 2002 11:12:56 -0400

Bert

---

From: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Wed, 15 May 2002 14:42:58 -0600

Hi Richard,

I'm not so sure this is a clear advantage, at least not in highly dynamic
MANETs.

If link status changes rapidly, say every minute or so, a proactive protocol
would have to have nodes advertise about twice a minute in order to have
routing tables that are reasonably accurate.  Because of the possibility of
data collisions, this will tie up the MANET, at least locally, for a sizable
chunk of the available time, leading to significantly less bandwidth
available for the transmission of data.  

Also, if the MANET is sizable, not only will there be more bandwidth lost to
advertisements, but the propagation the advertisements to all nodes in the
net will take a considerable amount of additional time.  This may be long
enough that at no time do all nodes have an accurate picture of the network.

Another complication arises in the case of asymmetric links.  In this case,
the fact that Node A can hear B does not mean Node B can hear Node A.  So,
if Node A receives an advertisement from Node B, it is not assurance that
Node B is reachable directly from Node A.  Node A must respond to Node B's
advertisement, in which case both A and B will know they can reach each
other.  This means we need about twice as many packets to establish the
proactive routing.

Of course, both problems become worse rapidly with the size of the net, so
one might be able to have a proactive protocol locally (involving just a few
nodes), but a reactive protocol globally.

John Mullen
-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Wednesday, May 15, 2002 12:16 PM
To: [email-masked]
Cc: [email-masked]
Subject: Re: [manet] Dumber Question? 

> <snip> 

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: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Wed, 15 May 2002 16:08:19 -0600

Hello Lin,

Perhaps, we are not discussing the same sorts of MANETs.

In general, Node A does not know it is reachable from Node B until it
receives a packet from Node B.  Node B does not know that it can reach Node
A until it receives an ACK from Node A, indicating that it received the
packet from Node B.  Whether the protocol is proactive or not, data
collisions, etc. can cause the impression that a node is not reachable.  

If Node A's status changes from reachable to unreachable from Node B, it
will not know, unless it is expecting a packet from Node B, that such a
thing has happened.  Node B, however, will know, since its packet was not
ACKed, that either Node A did not get the packet or Node B could not hear
Node A's reply. 

If Node A later becomes reachable, it will still not know until Node B sends
it a packet.  These control packets are as likely to suffer a data collision
or be damaged by temporary interference as those of a reactive protocol, so
I see no inherent advantage.

The only difference I see in the protocols is their impact on overhead.
This would include the re-transmission of packets directed onto obsolete
paths, those lost in data collisions, and those lost in buffer overflows, as
well as the packets needed to inform each node about the others.  Since
these would depend on the traffic load, network density, propagation
conditions, and operational factors, it would seem that an adaptive hybrid
protocol would be best.

However, I would have to say that giving the protocol more degrees of
freedom also introduces the problem of how to control those settings and
admits the possibility of instability.

John Mullen

-----Original Message-----
From: Tao Lin [mailto:[email-masked]]
Sent: Wednesday, May 15, 2002 3:45 PM
To: Mullen, John P. (Contractor)
Cc: [email-masked]
Subject: Re: [manet] Dumber Question?

I agree that proactive protocols may have higher overhead if a topology
change does not affect a in-use route. We have to admit that this is a
disadvantage for proactive protocols in MANET. However, proactive protocols
have many advantages, e.g. they can respond to route changes faster, they
provide immediate notification of reachable or unreachable destinations
(reactive protocols can not decide whether the destination is unreachable or
not because there could be packet collisions when broadcasting route
requests or destination unreachable.), in general they build shorter paths,
and an overhead with proactive protocols is independent of traffic profiles.
If we use a mixed protocol, we may suffer both disadvanatges. So my point is
that proactive protocols are good approaches for MANET routing, especially
with a low mobility MANET. When the network mobility increases, (AND with
certain traffic profiles), we should introduce some reactive features. We
are looking into the performance (in term of overhead) of MANET routing
protocols given several network and traffic profiles. Hopefully these
results will be available soon.

---

From: Fred Baker <[email-masked]>
Date: Wed, 15 May 2002 10:31:07 -0700

>Assignment of IP adresses is done using "autoconfiguration" in ad hoc

ahem; one mechanism for address assignment is autoconfiguration. Never tell 
your customer that he's not allowed to type it in :^)

---

From: Fred Baker <[email-masked]>
Date: Wed, 15 May 2002 10:31:07 -0700

---

From: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Thu, 16 May 2002 08:23:40 -0600

Hi Mike,

By "packet," I meant any packet, data or control.

All I know about OLSR is what I've read at: 

http://menetou.inria.fr/olsr/draft-ietf-manet-olsr-04.txt

>From that, I gather that the primary advantage of OLSR is that it reduces
the number of nodes retransmitting packets to a subset, called Multipoint
Relays.  In a sense, the protocol defines a subset of nodes to be routers
according to the conditions in effect.  This is, of course, most useful when
the net is both large and dense.  At times, this is true of the nets I work
with, so this could be a useful strategy.

The problem is that since the links are not symmetric, it is often true that
Node A receiving a HELLO from Node B does not mean Node B can receive a
packet from Node A.  If the HELLO message does not contain A's address, Node
A knows that it can receive packets from B, but it is probable that it
cannot send packets directly to B.  It can send B's address in its own
HELLO, but, as I read the protocol, unless B is a two-hop neighbor, Node B
will never know that Node A can receive its packets.

Of course, this would also be a problem for a reactive protocol.  The point
is that one may more HELLO packets per unit time to maintain the routing
tables in the presence of asymmetric links than with symmetric ones.  If the
bandwidth is limited, this can lead to very high overhead.

In general, the nets I work with are uneven in density.  For example, if a
company is attempting to cross a minefield using a cleared path, its units
will be near each other and the net will be locally dense.  However, if the
same company is involved in scouting, the net is liable to be sparse.  The
OLSR might be advantageous in the first case, but in the second, the added
overhead, together with the reduced link capacity (capacity is a decreasing
function of the distance between nodes), might make it a liability.  An
adaptive protocol could switch to OLSR when and where the net is dense and
switch to a different protocol when and where it is not.

John Mullen

-----Original Message-----
From: Mike Christman [mailto:[email-masked]]
Sent: Wednesday, May 15, 2002 5:47 PM
To: Mullen, John P. (Contractor)
Cc: Tao Lin; [email-masked]
Subject: RE: [manet] Dumber Question?

Mr. Mullen,

Perhaps I am not understanding your point of view here or I have not read 
the earlier threads closely enough.  It would seem like a proactive
algorithm, 
like OLSR, would not have the problem that you described.  When you 
say that "Node A does not know it is reachable from Node B until it
 receives a packet from Node B." I assume that you mean a data packet.  
However, it would seem as if using periodic "hello" messages, as OLSR 
does, would avoid this problem.  If a collisions can prevent "hello" 
messages from being received, but I believe that OLSR allows for 3 missed 
messages before timing out.  In this case Nodes A and B are ALWAYS 
expecting a packet from other nodes.  But, as we all know by know, this 
consumes more bandwidth.  I hope that this comment is relevant! :)

---

From: "Fleischman, Eric" <[email-masked]>
Date: Thu, 16 May 2002 17:07:26 -0700

Mike Christman wrote (in part):
<snip>
> If a collisions can prevent "hello" messages 
> from being received, but I believe that OLSR allows 
> for 3 missed messages before timing out.  
<snip>

Since the topic of this thread is "dumber question", 
I feel brave enough to publicly question whether timing 
out after three missed messages is a good idea or not. 

That is, I have just begun experimenting with TORA and 
I've been very impressed at how even a few feet of antenna
placement directly impacts network availability for 
our omni-directional antennas. I've noted that as my 
devices approach their furthest (distance) range at a 
given transmission rate, using the filtering option (at 
which the link was dropped for two successive missed 
messages) significantly decreased that range. Thus, 
for my tests, I quickly decided that we could not 
afford to have our broadcast range needlessly 
truncated by that restriction.

For example, I found that the filtering option would shut 
down a link that was experiencing 80% availability. 
Envisioning military operations (especially in view of the
2001 Marine Corps Littoral study) I would say that 80% 
availability is significantly better than "the norm". Hence 
my skepticism as to whether the "3 missed messages" 
restriction is desirable.

I would be very appreciative to receive "push back" or 
agreement from this list since I value your greater maturity 
in this field and would like to learn from your experience.

--Eric

---

From: "Fleischman, Eric" <[email-masked]>
Date: Thu, 16 May 2002 17:07:26 -0700

<snip>

--Eric