This repository contains the assignments for the Academic Courses "Computer Networks I" in Aristotle University of Thessaloniki - Electrical and Computer Engineering. For the development of the projects was used Java and especially Eclipse IDE.
Running the project, a menu shows up, via with user can select an action.
Each action requires a keyword, available only for 2 hours that is obtained through the input of University info:
- Echo Request Code
- Image without Noise Request Code
- Image with Noise Request Code
- GPS Request Code
- ARQ Protocol, Ack/Nack Request Code
The application sends to server Ithaki a message in the form of EXXXX\r (where XXXX is the corresponding keyword described above) and receives packets in the form of:
PSTART DD-MM-YYYY HH-MM-SS PC PSTOP
DD-MM-YYYY is the date and HH-MM-SS is the time, while PC is a packet counter
The application sends to server Ithaki a message in the form of MXXXX\r (where XXXX is the corresponding keyword). The server Ithaki responds with an image with .jpeg encoding of a Camera placed on the Faculty of Electrical Engineering at Aristotle University of Thessaloniki that does not include noise.
Similarly as above, the application sends to server Ithaki a message in the form of GXXXX\r (where XXXX is the corresponding keyword). The server Ithaki responds with an image with .jpeg encoding of a Camera placed on the Faculty of Electrical Engineering at Aristotle University of Thessaloniki that includes noise.
The application sends to server Ithaki a message in the form of PXXXXR=ΧPPPPLL\r, where XXXX is the corresponding keyword, X (1 to 9) is the number of predefined routes saved in the server, PPPP is the starting point of the route and LL is the number of the points in route X.
The data received from the server stand for GPS positioning information coded with respect to NMEA protocol. A typical message received is in the form of:
$GPGGA,045208.000,4037.6331,N,02257.5633,E,1,07,1.5,57.8,M,36.1,M,,0000*6D
where GPGGA is the header, 04:52:08 is the time of the transmission, 40o 37.6331΄ is the latitude north, 22o 57.5633΄ is the longitude east, 07 the number of active satellites and 57.8 m the height of the position from the surface of the sea. To find a route we have to choose 9 of GPGGA messages with timestamps that abstain at least 4 seconds. To indicate the start of the transmission the server sends a message START ITHAKI GPS TRACKING\r\n, while to indicate the end of the transmission sends STOP ITHAKI GPS TRACKING\r\n. Finally, there is a parameter Τ=ΑΑΒΒΓΓΔΔΕΕΖΖ, that can be repeated 9 times after the keyword, which represents a trace with latitude AAoBB'ΓΓ'' and longitude ΔΔoΕΕ'ΖΖ'', depicted on image obtained by Google Maps.
The application sends to server Ithaki messages in the form of QXXXX\r and RXXXX\r for a Ack and Nack process. The purpose of this part is the testing of an ARQ (automatic repeat request) mechanism that detects and retransmits the errored packets. The sever responds with a message:
PSTART DD-MM-YYYY HH-MM-SS FCS PSTOP
where XXXXXXXXXXXXXXXX stands for an encrypted message. In order to detect potential wrong bits a FCS field exist that is the result of the logical XOR operator applied to the encrypted message for each character sequentially. In case of matching we have a correct transmission and the message QXXXX\r is written to the server. Otherwise we have a wrong transmission and the application asks the server for a retransmission via the message RXXXX\r. The number of Rebroadcasts is shown in the next graph:
