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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
30 September 2003Dave Johnson [email protected] University
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
30 September 2003Dave Johnson [email protected] University
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
30 September 2003Dave Johnson [email protected] University
Example NASA Uses
30 September 2003Dave Johnson [email protected] University
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
30 September 2003Dave Johnson [email protected] University
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
30 September 2003Dave Johnson [email protected] University
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
30 September 2003Dave Johnson [email protected] University
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
30 September 2003Dave Johnson [email protected] University
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
30 September 2003Dave Johnson [email protected] University
Demo Area Map
Duncan Hall third floor: Control Room
30 September 2003Dave Johnson [email protected] University
Demo Area Map
Duncan Hall third floor: Control Room
30 September 2003Dave Johnson [email protected] University
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
30 September 2003Dave Johnson [email protected] University
Control Room Configuration
30 September 2003Dave Johnson [email protected] University
Stationary Node Configuration
30 September 2003Dave Johnson [email protected] University
Robot Configuration
30 September 2003Dave Johnson [email protected] University
Robots in the Hall
30 September 2003Dave Johnson [email protected] University
Active Route Display
30 September 2003Dave Johnson [email protected] University
Remote Robot Driving Interface
• Can control by the mouse (FORWARD, BACKWARD, LEFT, RIGHT, STOP)
• Can control by cursor keys (space bar for stop)
30 September 2003Dave Johnson [email protected] University
The Whole Screen
30 September 2003Dave Johnson [email protected] University
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
30 September 2003Dave Johnson [email protected] University
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
30 September 2003Dave Johnson [email protected] University
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