Subject: RE: [manet] Ad-Hoc compared to TETRA

From: "Manfredi, Albert E" <[email-masked]>
Date: Thu, 20 Jun 2002 12:43:16 -0400

> -----Original Message-----
> From: Josephson, William [mailto:[email-masked]]
> 
> One shouldn't forget that UAVs and satellites can play a part 
> in a MANET.
> 
> So these can be the base stations.

Agreed.

I'd break that down into different categories, to decide whether the system qualifies as a MANET or not.

1. If these satellite base stations are stationary with respect to the earth's surface, for example satellites in geosynchronous orbit that also provide routing services, then this would not qualify as MANET. The satellites are merely an extension of the fixed Internet.

2. If the satellites are providing "bent pipes" only, and the routers are stationary on the earth's surface, again, I don't see where the resulting IP structure would be a MANET. It would be an extension of the fixed Internet.

3. If the satellites (or manned aircraft or UAVs) are not geosynchronous, and are providing routing services for devices not located on those moving platforms, or are providing a link to the fixed Internet by continuously handing over to new links to the fixed Internet as the vehicle moves, then we have the difficult problem MANET addresses.

The qualifications in #3 are important, IMO. You can postulate a case where aircraft are connected to the fixed Internet via a satellite link, routing services are only provided for hosts on that aircraft, and the satellite link always ties the aircraft to a single location on the earth's surface, where a router connects to the fixed Internet. In this scenario, there again is nothing MANET about the network, IMO. The routing problem sees all the hosts on the aircraft as being in a fixed location with respect to the earth's surface.

Bert

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---

From: Daniel Oldham <[email-masked]>
Date: Thu, 20 Jun 2002 18:45:01 GMT

Bert:

I would like to add my two cents to the satellite discussion about MANET. 

Satellites are normally classified based on their orbital regimes as low 
earth orbit (LEO), medium earth orbit (MEO), geosynchronous orbit (GEO)  
or deep space escape.  The altitude of LEO is generally above the 
atmosphere and below the first Van Allen radiation belt or below 1000 km. 
MEO lies between the first and second Van Allen radiation belts or above 
1,000 km and below 10,000 km. GEO is uniquely at 35,786 km, in order to 
synchronize the orbit of the satellite with the spin of the Earth. GEO 
satellites then appear stationary in the sky. Besides altitude, there are 
five orbital parameters, including inclination and eccentricity. 
Inclination is the tilt relative to the equatorial plane and eccentricity 
is the shape of the orbit. Deep space escape has an eccentricity of a 
parabola or hyperbola and the satellite, in effect leaves Earth orbit and 
goes around the Sun.

Most GEO satellites are as you say, bent-pipes in the sky that receive, 
translate and retransmit the information. Most of the non-GEO satellite 
systems have highly optimized communication systems that store and dump 
information to a ground station when it passes over head or transfers the 
information to a data relay satellite in GEO.  These space to ground 
systems are one to one and therefore not of interest for MANET. Of the 
LEO and MEO satellite systems to consider for MANET are the distributed 
satellite system that consist of multiple satellites that interact and 
cooperate to achieve mission goals. These systems can be broken into two 
types of crosslink communication systems, constellation and formation 
flying missions. Iridium is an example of a constellation system with 
crosslink communications. They use a fixed infrastructure to simplify the 
communication issues. In this case the satellites communication with the 
satellites in the same or adjacent orbital planes so that it appears the 
neighboring satellites are not moving. A constellation system is a good 
application for MANET if you can address all the communication issues. I 
well be happy to expand of these issues if you are interested. The 
formation flying systems can be broken down into crosslink communication 
systems with a centralized or distributed topology. The centralized 
systems have a "mothership" as the primary spacecraft and "daughter" 
spacecraft as secondary spacecraft. Again this system is not of interest 
for MANET because of the centralized topology. The distributed systems do 
not have a single point of control within the formation and therefore a 
good application for MANET. In formation flying the satellites do not 
move very much in relationship to each other but the topology requires 
this type of communication system.

I hope that helps...
--
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 6/20/02, 12:43:16 PM, "Manfredi, Albert E" 
<[email-masked]> wrote regarding RE: [manet] Ad-Hoc compared 

> 1. If these satellite base stations are stationary with respect to the 
earth's surface, for example satellites in geosynchronous orbit that also 
provide routing services, then this would not qualify as MANET. The 
satellites are merely an extension of the fixed Internet.

> 2. If the satellites are providing "bent pipes" only, and the routers are 
stationary on the earth's surface, again, I don't see where the resulting 
IP structure would be a MANET. It would be an extension of the fixed 
Internet.

> 3. If the satellites (or manned aircraft or UAVs) are not geosynchronous, 
and are providing routing services for devices not located on those moving 
platforms, or are providing a link to the fixed Internet by continuously 
handing over to new links to the fixed Internet as the vehicle moves, then 
we have the difficult problem MANET addresses.

> The qualifications in #3 are important, IMO. You can postulate a case 
where aircraft are connected to the fixed Internet via a satellite link, 
routing services are only provided for hosts on that aircraft, and the 
satellite link always ties the aircraft to a single location on the earth's 
surface, where a router connects to the fixed Internet. In this scenario, 
there again is nothing MANET about the network, IMO. The routing problem 
sees all the hosts on the aircraft as being in a fixed location with 
respect to the earth's surface.

---

From: Daniel Oldham <[email-masked]>
Date: Thu, 20 Jun 2002 18:45:01 GMT

Bert:

I hope that helps...