NASA Ad Hoc Networking Demonstration

NASA Ad Hoc Networking Demonstration

Dave JohnsonComputer Science Department

Rice University

30 September 2003

30 September 2003Dave Johnson [email protected] University

Traditional Wireless Networks

Many forms, but all have similar architecture:

• Wireless cellular networks, wireless LANs, …

Relies on a fixed infrastructure:

• Centralized base station or access point

• All users within wireless range of it

• Needs planning, installation, management, …

Wireless LANWireless Cellular


Wireless Ad Hoc Networking

May be no network infrastructure available:

• Remote areas

• Unplanned meetings

• Emergency relief personnel quickly deployed

• Military troops

May not want to use the available infrastructure:

• Time or cost to access and register on the service

• Performance or capacity of existing service and infrastructure

Dynamically extend coverage of infrastructure:

• Allow users to be further away from infrastructure


Ad Hoc Network Routing

• May be out of wireless transmitter range of others• Need to use other nodes as routers for forwarding• Find new routes after movement or change

A B C


Example NASA Uses


DSR Overview

Dynamic Source Routing:

• Divides routing problem into two parts:

– Route Discovery: only try to find route when you don’thave one and need one

– Route Maintenance: only while you’re actually using a route, try to keep working or fix it

• All parts of protocol operate entirely on-demand

• Ignores all topology changes not affecting you

• Overhead scales automatically with movement

• No overhead when stationary and found routes


Basic DSR Route Discovery

To discover a route to some address:

• Broadcast ROUTE REQUEST with unique request id

• When receiving a ROUTE REQUEST:

– If target is yourself, return the recorded routeto the initiator in a ROUTE REPLY

– Else, if recently seen this id, drop the REQUEST

– Otherwise, append your own address and rebroadcast the ROUTE REQUEST


Basic DSR Route Maintenance

After transmitting a packet to the next hop:

• Listen for link-level per-hop acknowledgement, or

• Listen for that node sending packet to next hop, or

• Set a bit in the packet to request explicit next-hop acknowledgement

When a problem with forwarding is detected:

• Send a ROUTE ERROR to original sender

• Sender removes the broken link from its cache


Ad Hoc Network Simulation

Example: Compared DSR with 3 other routing protocols: • 50 nodes moving maximum 20 m/s• Route lengths: average 3 hops, max 8

Fraction of data packetssuccessfully delivered

Number of routing overheadpackets sent


NASA Demo Overview

A six-node ad hoc network:

• Two mobile Koala robots:

– FreeBSD 5.1 DSR implementation

– Microsoft Windows NetMeetingvideo with Logitech QuickCamUSB cameras

• Four stationary nodes:

– FreeBSD 5.1 DSR implementation

– Automatically used as part of routes as needed formobile communication

• Each robot sends continuous video back to stationary endpoint node to display on screen in control room

• Robots are remotely driven by user controls on this stationary endpoint node


Demo Area Map

Duncan Hall third floor: Control Room


Demo Area Map

Duncan Hall third floor: Control Room


DSR Implementation Overview

A new DSR implementation:

• Runs almost entirely in a single user-level process

• Only very small tap inserted in kernel IP input and output

• DSR code is shared with ns simulator DSR source code:

– DSR is the identical code used in ns simulator

– Just a few #ifdef’s due to different interface to link level

• Advantages of the new implementation:

– Runs on up-to-date versions of FreeBSD

– Designed to be very portable to other Unix-like systems(NetBSD, OpenBSD, Linux, Mac OS X), and even Windows

– Only need to implement protocol once, share with simulation

– Can test real system in simulation

– Can validate simulation in real experiments


Control Room Configuration


Stationary Node Configuration


Robot Configuration


Robots in the Hall


Active Route Display


Remote Robot Driving Interface

• Can control by the mouse (FORWARD, BACKWARD, LEFT, RIGHT, STOP)

• Can control by cursor keys (space bar for stop)


The Whole Screen


Challenges: FreeBSD Video

FreeBSD doesn’t support video as well as we expected:• FreeBSD supports more desktop video hardware than laptop• FreeBSD’s USB support also could be better• The routing protocol and the network can carry the video,

but we had to find a way to interface the camera• Solution: Two laptops on each robot:

– One running FreeBSD for the routing software– One running Windows for the video– Plugged together with a cross-over Ethernet cable

• Also demonstrates DSR protocol features:– Compatible with standard IP applications (running unmodified

Windows and unmodified NetMeeting)– Can route to/from nodes behind DSR “gateway” into the

ad hoc network


Challenges: Weight and Robots

• The Koala robots can only carry limited weight:

• K-Team specification says 3 kg (6.6 lbs)

• Our weight problem was made worse by the video solution:

– The two laptops alone weigh about 6.5 lbs

• K-Team said extra weight can’t break the robots:

– It monitors current draw from motor, shuts down before overload

– We have had problems with this, but the robots generally tolerate the load

– Could be solved better by running everything on a single laptop, or by using ultra-lightweight laptops

• We also had one robot die during development:

– The wheel motor doesn’t turn on its right side


Thanks!

My students:

• Santashil PalChaudhuri

• Amit Saha

• Shu Du

• Khoa To

• Jorjeta Jetcheva

• Yih-Chun Hu (now graduated)

Rice CS administrative support:

• Darnell Price

• Rhonda Guajardo

Funding:

• NASA, NSF, Schlumberger

Documents

NASA Ad Hoc Networking Demonstration