Robonet - MANET for Robot Communication Authors: Stiven Andre Supervisor: Aram Movsisian
Motivation Robotic developers need a way for robots to communicate. Swarm of robots want to communicate in a constantly changing environment Developers need an easy to use tool for sending data between this robots.
Requirements Communication should be done using a cheap and available mobile device (Android is chosen) Communication library should bypass the low signal capabilities of the average android device. Communication should not require any static station (AD-HOC) Communication library should transport the data sent between the robots using proxy robots in the middle seamlessly to the user. (MANET) Communication library should be light on traffic and system resources due to Android's limited resources (Distance Vector, not Link State).
Assumptions and limitations Each Android and or other host device is able to communicate with another device at least by layer 3. (Satisfied by previous project) Communication is limited to N hops, N predefined (We will in fact bypass it). Each station is given a unique integer ID on initialization (Lower ids preferred, the reason will be explained later) Data that user wants to send and receive is provided as a byte[] Any violation of this assumptions will lead to undefined behavior
Library functionality Send and receive data between robots. Without any limitation on data type and size. Verify that sent data arrived. List what robots are currently reachable Query the distance to another robot (distance is measured as a number of robots data will need to pass until it gets to the destination) All functionality is asynchronous so all functions return immediately All functionality is parallel allowing to send and receive multiple data at the same time.
MANET mobility (adopting to changes rapidly) A is sending the data to D. The intended route is A->B->C->D A B C D E A transferred the data to B C But B can no longer reach C as previously intended A B E D B will find out that it can reach destination D by sending the packet through E. Packet will arrive to D despite the change in topology in the middle of the transmission A B C E D
Robonet Discovery Advertiser: Constantly sends Advertisments using UDP broadcast. Ads include all known neighbors if the range to the neighbor is less than DEPTH parameter. Discoverer: Listens to ads. Updates database according to received ads. Old station are removed from the database if no advertisements received for longer than REMEMBER parameter. DEPTH: A performance related parameter defining maximal number of allowed hops. Database: Structure/Class holding all Dynamic run-time information.
User verify User send Receiver ACK queue Transporter Queue Transporter Database Discoverer Receive Queue Advertiser Class or object User receive Sender Single thread 1 or more threads
Library Interface Connector.java is the only class required to use the library (FConnector is an additional functionality explained later). Configuration.java is the class containing all the static defines. This is used to control various performance related constants. (Ex: How much time to remember a robot that stopped sending any signs of life) Connector.java is very well documented in JAVADOC style:
Library JavaDoc
Library Functions int init(int id): Initialize the library and set id as self identifier. Int[] getneighbors() Get all neighbors that are currently known and reachable. int getdistance(int neighbor) Get distance to the neighbor, in units of hops. -1 is returned if neighbor is unreachable. int send(int to, byte[] data): Send data byte array to station provided by to parameter. Return integer used for verification of the arrival (explained later) byte[] receive(): Receive data. Returns a received byte[] null is returned if nothing is received.
Library Functions - cont boolean verify(int verificationnum): Verify the arrival of message X. VreificationNum is the number that was returned by send() when X was sent. Returns true if message has arrived, false otherwise. int[] showverifications() Returns integer array of all verification numbers verify() would return true on. In other words, returns all verifications void clearverifications(): Clears all verifications. In a long run maybe used to free space. Int getmyid() Returns your own identigier. Prevents user from having to store it. void destroy() Stops all threads and destroys the library engine.
Connector and FConnector Introduction and differences What is FConnector? FConnector is an additional functionality for the connetor library. Fconnector adds 3 new functions to connector: - flood() - fsend() - map() All functions will be explained later. Who FConnector is implemented? FConnector class inherits from connector class all old functionality is still there. FConnector implements the new function ONLY by using Connector public functions that were explained before. Why FConnector is designed as library over library? You don't always want to use Fconnector maybe connector is enough for your tasks. FConnector is a very good example of connetor usage and abilities. Having smaller building blocks helps to design more agile project. What is most important about new Fconnector functions? The DEPTH parameter is irrelevant to them!
A bit of definitions before continuing Station A can hear station B: Station A can hear/see station B if and only if UPD broadcast from B arrives to station A. Connected stations as a graph: Let's define a directed graph G(V,E). V is the group of stations. If station V1 can see/hear station V2 there is an Edge V1 V2 in E. Graph of interconnected stations: Stations V1 and V2 are in the Graph of interconnected stations if there is a directed loop that includes both V1 and V2 in G(V,E). A connected to B by means of Fconnector if and only if: A and B are in the same Interconnected graph G Please Note: Two stations A and B may be connected to by means of FConnector but may not see/hear each other by the means of Connector
FConnector functions Flood Function declaration, parameters and return value: int flood(byte[] data): - data: data to send - returns: always 0. What it does? Sends data argument to all stations that are connected in regards to FConnector. How? Uses connector send function to send message to all directly connected neighbors. Each station that received such a message will pass it to all it's neighbors and to incoming queue. If the same message (sequencing is used to identify messages) is received again retransmission will not happen. Note: This function has no ability to verify the arrival of the message - by design.
FConnector functions FSend Function declaration, parameters and return value: int fsend(int to,byte[] data): - to: send to this station only - data: data to send - returns: always 0. What it does? Sends data to a station that is connected by the means of FConnector. How? The similar way flood() function works but only the station that with the id sepcified as the to parameter will receive the message. All others will only retransmit. Note: This function has no ability to verify the arrival of the message - by design.
FConnector functions map Function declaration, parameters and return value: int[][] map(): - returns: Integer matrix. What it does? Returns a matrix that represents to what station each of the stations is connected to. Assume the returned matrix is ret[][[]. ret[a][b] = 1 if and only if station a can hear/see station b. How? Map() sends a special message to all station using flood(). Once any of the station receives such a message it generates a message containing all the stations it can hear/see and sends it back using fsend(). Map() waits predefined time for the results and after the time passes build the matrix from the received messages before returning. Note: The map will hold all stations that are connected to the origin by means of FConnector
Links: Android tether application: http://code.google.com/p/android-wifi-tether/ Linux networking how-to http://tldp.org/howto/net3-4-howto.html