Subject: Re: [manet] Internet-MANET gateways?

From: Manish Karir <[email-masked]>
Date: Thu, 12 Jun 2003 10:47:26 -0400

this is entirely an engineering issue, therefore a generic solution is
not necessary.

a network designer who deploys the network can and probably will solve
the problem using method 1.

unless you can make a really convincing argument why you have addresss
in your MANET that can not be aggregated, I dont think there is a
problem here...I dont think we can come up with generic solutions that
handle every scenario.

-manish

Ralph Preston wrote:
 > Hello,
 >
 > An easy question, has it been defined how a MANET-Internet gateway will
 > work?  If it has, please point me to it and don't bother to read the
 > rest of this message.  :)
 >
 > I've been trying to figure out how a MANET gateway will interface with
 > the Internet and enable nodes outside the MANET to initiate
 > communication with nodes in the MANET.  The way I see it there are three
 > possibilities:
 >
 > 1) The gateway advertises routes to each node in the MANET to the entire
 > Internet.
 >
 > 2) The gateway runs NAT.
 >
 > 3) Any node who wants to be reachable from outside the MANET must be
 > running MobileIP and in IPv4 the gateway must be its Foreign Agent, or
 > Home Agent.
 >
 > Number 1 isn't a good solution since nodes in the MANET wont necessarily
 > be route aggregated.  Solution 2 doesn't allow nodes outside the MANET
 > to contact nodes within the MANET.  Which leaves solution 3, but
 > solution 3 wont work except for nodes that have a direct connection with
 > the gateway.  So, is there currently no way for outside nodes to contact
 > MANET nodes?
 >
 > Ralph A. Preston
 > The MITRE Corporation

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From: Erik Nordström <[email-masked]>
Date: 12 Jun 2003 17:31:26 +0200

> this is entirely an engineering issue, therefore a generic solution is

I am not sure I agree here. There are unresolved issues that are related
to have subnets are handled (if at all), gateway advertisement vs. node
solicitations, etc.

> the problem using method 1.

I believe gateway advertisements would make little sense in networks
running on-demand protocols. I.e. why put a proactive scheme ontop of an
on-demand routing algorithm? It would probably make more sense for
on-demand protocols to discover gateways on-demand.

> problem here...I dont think we can come up with generic solutions that

Address/route aggregation in multi-hop ad hoc networks is inherently
problematic.

Either you make assumptions about how nodes are assigned addresses, i.e.
it is mandated that nodes use a specific prefix in the network. This way
it is easy to distinguish (ad hoc network) local packets from outbound
packets (i.e. check the prefix). However, this will require specific
solutions for address assignment in these networks (probably a
centralized scheme).

The more likely case, is that the ad hoc network is flat, i.e. nodes use
any address. Internet connectivity is in this case provided through NAT.
Here we have a whole range of problems related to have we forward
outbound traffic. For example, for on-demand protocols it does not make
since to use default route entries since nodes do not maintain routes to
all nodes in the network. How will forwarding be solved in this case?
How do we discover gateways? How do we switch gateways when necessary?

My point is, that this is not necessarily only an engineering issue.

Erik

---

From: Jon Zeeff <[email-masked]>
Date: Thu, 12 Jun 2003 11:31:23 -0400

Your MANET node can tunnel to a fixed node on the Internet and thus be 
reached via that fixed node.  Ie, through tunneling and NAT
you can have just about any connectivity.

If you have a routable block of addresses, you could use these for your 
MANET nodes and have a gateway aggregate and announce
these addresses.

---

From: Erik Nordström <[email-masked]>
Date: 12 Jun 2003 18:38:19 +0200

On Thu, 2003-06-12 at 17:59, Manish Karir wrote:
> Erik,
> 
> I think we differ in our assumptions, I assume that we have a predefined 
> prefix that we use to allocate addresses to ad hoc nodes, you assume 
> that the ad hoc nodes can pick any address.

Can I assume that there is no problem? ;-)

I didn't assume one solution, but outlined what assumptions you can
make, and the inherent problems with those solutions. 

In the case with predefined prefix, we seem to agree that address
assignment/autoconfiguration is the problem. But I think this would be
limited to just a subset of the ad hoc scenarios. For this solution you
need an entity that decides on a prefix. This puts restrictions in the
"ad-hocness" of ad hoc networking.

> Sure, you can assume that, but why does your assumption make any more 
> sense than mine, why would you consider it "more likely"?
> Besides your assumption creates more problems than it solves.:)
> 

To my knowledge, it is commonly assumed (or allowed) that ad hoc
networks are flat. If you for example study some drafts (e.g. AODV
draft) and follow some of the discussions, you will find that this is
the case.

> I think the hard problem that has remained unsolved in MANETs is address
> allocation/assignment.  Clearly, a centralized approach is not 
> desirable, and clearly a distributed approach of picking random 
> addresses, is not scalable(birthday paradox).
> 

So what do you propose?

> I think the "more likely" case is the centralized address distribution 
> during deployment.  The most scalable structure built to date the 
> Internet has followed this policy and I think that turned out "okay". :)
> 

I thought that the whole idea of ad hoc was to not have structure? 

Erik

> Erik Nordström wrote:

---

From: Jon Zeeff <[email-masked]>
Date: Thu, 12 Jun 2003 13:44:20 -0400

One way is a central registry.  There aren't many MANET users yet so there 
is an address for
everyone.

Just picking an address randomly would work if the routing protocols had 
mechanisms for
detecting collisions.  Perhaps a large number of additional bits serving as 
a signature would allow
a node to detect that different systems are using the same ip address (and 
notify them to
change).

Or use IPV6 and don't worry about it.

---

From: Manish Karir <[email-masked]>
Date: Thu, 12 Jun 2003 14:01:46 -0400

the random address picking will not work, to get an idea of the problem 
try the following in C or matlab:
pick a 3x3 array.  Try to fill this array with random numbers between 
1-16(4-bit address space). Check for any duplicates, if you have 
duplicates, try again.
Count how many rounds it takes to end up with all unique numbers.

and this is only for a 9 node network!.

Actually, some simple analysis would show the same result.

-manish karir

Jon Zeeff wrote:
> 
> One way is a central registry.  There aren't many MANET users yet so 
> there is an address for
> everyone.
> 
> detecting collisions.  Perhaps a large number of additional bits serving 
> as a signature would allow
> a node to detect that different systems are using the same ip address 
> (and notify them to
> change).
>

---

From: Jon Zeeff <[email-masked]>
Date: Thu, 12 Jun 2003 14:12:29 -0400

Let's try it with a 24 bit address space, a 10x10 array, and when a 
collision is detected, you
don't throw the whole thing out and start over, you simply pick another 
address for that
single node in the array.

Answer: one round

---

From: Erik Nordström <[email-masked]>
Date: 12 Jun 2003 20:01:54 +0200

On Thu, 2003-06-12 at 19:51, Manish Karir wrote:

> And, no I do not have a solution to the address allocation problem
> distributed or centralized.  I wish I did though...:)
> 

IPv6?

Erik

---

From: Manish Karir <[email-masked]>
Date: Thu, 12 Jun 2003 13:51:49 -0400

well it might be an implicit assumption, but lets try to approach it 
from the other side. Lets try to list the different capabilities that 
are added to the MANET if we allow the addresses to be randomly picked.

- flat network: okay sure, but what does that allow us to do that we
   cannot do if the address space allowed aggregation.

- easier to add/remove nodes: partially true, easy to remove nodes, but
   adding nodes is a horribly complex problem, try to resolve possible
   conflicts acrosss say a hundred nodes!!
   (e.g. I think appletalk used to work this way...but ofcourse they
    limited themselves to a single network segment with small numbers
    of nodes)

- consistent with "ad hoc" concept: true, but does the purist view
   of ad hoc networks add any key functionality to the MANET

-manish

---

From: Manish Karir <[email-masked]>
Date: Thu, 12 Jun 2003 11:59:56 -0400

Erik,

-manish

---

From: "John Mullen" <[email-masked]>
Date: Thu, 12 Jun 2003 17:49:42 -0600

Hi,

There are a number of possible situations, but a common set of problems.
The main problem is how an Internet user finds out that another user is
available on a MANET.  There is no single solution that works for all.

For example, tunneling to a fixed Internet node works well as long as
the mobile users are not too distant.  Imagine two  participants at
conferences in London, located one km apart.  One is from San Francisco
and the other from Sydney.  If they burrow to a home Internet node, they
will communicate via thousands of kilometers and many, many intermediate
nodes, while a much shorter path would suffice.  

Internet directories seem like a logical solution, but there has to be a
common protocol.  Also, to avoid having replicates (with possible
latency) of gigantic databases all over the world, the directory would
probably be distributed.  Thus, even if you know a person's IP address,
some system will have to try to figure out which region that user is in.

Lets not forget that wireless connections are spotty and that a node may
temporarily be disconnected from an Internet gateway.  How will
advertisements be handled in the event that a connection is not
reliable?

If a MANET is smallish, being flat is not a problem within the MANET.
The real problem is how a mobile node that is one day in a MANET in Iowa
and the next in France will be advertised in such a way that it is clear
to anyone trying to reach him that he is the same person.  This implies
some sort of permanent IP address that the Internet can use to find the
user and some other mechanism so it can find the right MANET.  If
burrowing isn't used, there will probably have to be some sort of
directory system.

A military MANET could consist of thousands of nodes, but members belong
to a single organization.  It might be desirable to allow members of
different MANETs to communicate with each other via the Internet without
revealing to outsiders who is talking and from where.  Yet, members of
the organization should be able to find each other quickly.  

Some communities have set up public wireless nets.  I'm not sure if any
of them are MANETs.  They may be all stub nets.  However, they have a
similar problem in how to resolve the address problem.

Whatever the solution is, it needs to be compatible with Internet
protocol.  I suspect, however, because of differing needs of different
users, several solutions may be implemented within the MANETs
themselves.  That is, a person who doesn't travel much might prefer a
home node while a globe trotter might prefer a directory.  I suspect,
there will be a virtual ISP somewhere and the tradeoffs of the differing
services will be reflected in different options and fees.

Truth is, there are several different cellular and other phone schemes
in the world, yet it is generally possible to talk to each other, as
long as we know which numbers to key in.  I suspect, the same situation
will evolve under pressures of technology and the market.  

Whether or not this is a MANET issue, though, I am not sure.  As long as
a gateway knows who is in the MANET, I suspect any Internet referencing
scheme can be made to work with the MANET.  The main issues are really
Internet ones.

John Mullen

---

From: Fred Templin <[email-masked]>
Date: Fri, 13 Jun 2003 10:31:34 -0700

John Mullen wrote:

>available on a MANET.
When you say: "finds out", do you mean discovery by  by IP address
or by domain name?

Fred
[email-masked]

---

From: Joe Macker <[email-masked]>
Date: Fri, 13 Jun 2003 15:27:10 -0400

>When you say: "finds out", do you mean discovery by  by IP address

How do you find me on the Internet?
Good luck?! I might not be where you think I am and why do you care?

---

From: "John Mullen" <[email-masked]>
Date: Fri, 13 Jun 2003 13:01:27 -0600

Hi Fred,

Yes!

:-)

I've been lurking on this topic and don't feel that this issue has been
resolved.  Clearly, if a user is to be found via a global search of the
Internet, then some sort of permanent label is needed.  I favor the idea
of domain name because Internet IPs are hierarchal analogs of the
Internet structure.  This allows one to let the MANET assign IPs in
whatever way makes sense.  However, not all users have the same
interests.

I have accounts with two IPs.  One I use for University business, the
other for personal business.  This allows me to get through the work day
without being interrupted by personal messages and through my evening
conversations without intrusions from work.  Via the Internet, however,
I can access my email from either IP.  This allows me to control my
environment.

A person at a conference might have three domains of interest: 1)
everyday work, 2) personal, and 3) conference.  He or she might choose
to use a MANET for domain 3, while using a stub or wire interconnection
for the first two.  That is, he or she might be comfortable with an IP
address valid within the MANET, but unknown to the Internet.  On the
other hand, that person might want to reachable by his or her coworkers
and would want an IP on the MANET that is reachable by them.  In the
first case, the user might simply log on using a generic domain, but in
the second use an Internet domain name or report to the gateway his or
her permanent IP.

At any rate, it is not just that MANETs differ, but also that users
differ.  What works for one might be viewed as unnecessary or even
intrusive to another.  I think the market will sort this one out, though
is certainly a good idea to keep thinking about possible solutions.

John Mullen

-----Original Message-----
From: Fred Templin [mailto:[email-masked]] 
Sent: Friday, June 13, 2003 10:32 AM
To: John Mullen
Cc: [email-masked]
Subject: Re: [manet] Internet-MANET gateways?

John Mullen wrote:

>Hi,
>
>There are a number of possible situations, but a common set of 
>problems. The main problem is how an Internet user finds out that 
>another user is available on a MANET.
>
When you say: "finds out", do you mean discovery by  by IP address or by
domain name?

Fred
[email-masked]