nasa ad hoc networking demonstration dave johnson computer science department rice university 30...

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


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

nasa ad hoc networking demonstration dave johnson computer science department rice university 30...

Documents

university wireless

infrastructure slide

r oute r equest slide

r oute r eply

broadcast r oute r equest

routes slide

abc slide

cache slide