CS 145A Lab 2 (due: Nov 7th)

Reliable Transmission over Unreliable Channel (I): Packet

Tasks for Lab 2

Assume there is no “packet corruption” ("packet corruption": Bit error inside a packet. Bit error can be detected or even corrected by checksum. Details about error correcting codes can be found in EE127.)

• Design a packet format that can be used to transmit data reliably, over unreliable channels
• Implement conversion from a file to packets, at sender side.
• Implement error detection and file reassembly, at receiver side.

Sender

The parameter format of the sender is: "sender <filename> <PacketSize>", where <filename> is the name of the file for "transmission", <PacketSize> is the maximum size of a packet (including header). The size of the file is smaller than 64M bytes. The file contains English characters and numbers only.

The sender should implement the following functions:

• Read the file specified by <filename> (The file contains English characters and numbers only)
• Convert this file into packets, each packet has at most <PacketSize> bytes, including header.
• Save each packet to one file, with a file name as “P0000001.txt”, “P0000002.txt”...

Receiver

The parameter format of the receiver is: "receiver <number of “packets”> <PacketSize> <filename>", where <number of "packets"> is number of files for packets "received" by the receiver side. The files are in order of: "P0000001.txt", "P0000002.txt"... However, the packet in each file may not be the same packet "sent" by the sender, due to "packet loss", "packet reordering" and/or "packet duplication". <filename> is the file that the receiver should write to.

The receiver should implement the following functions:

• Read the files for packets (“P0000001.txt”, “P0000002.txt”...)
• Reassemble the packets into a file (specified by <filename>).
• Use one character “#” to indicate each lost packet.

Example

Assume we have a file with 7 characters: “abcdefg”. The Packet Size is 10 bytes.
If the packet header in your design has a size of 7 bytes, the payload of each packet is 3 bytes.
So, the sender should output 3 files:
P0000001.txt: <header>+ “abc”
P0000002.txt: <header>+ “def”
P0000003.txt: <header>+ “g”

If these three files are provided to the receiver without change, the receiver should output a file with 7 characters "abcdefg".

If packet 1 is lost, the receiver will see:

P0000001.txt: <header>+ “def”
P0000002.txt: <header>+ “g”

(Note that the file names are still sequent numbers.)

The receiver should output a file with 5 characters: "#defg". "#" indicates a packet loss.

Submission

Please submit your codes in "sender.c","receiver.c" or "sender.cpp","receiver.cpp", and your documents in "readme.txt"

Tips

• Read the lecture slides to see the details.
• Useful functions for file operations: fopen, fclose, fprintf, fscanf
• See the "man" page for these functions, and then maybe you can see other useful ones.
• Be careful of the data structures (especially at the receiver side)
• Design some small examples to test your program
  

Suggestions

• Write the codes in a graceful style. (You may need to re-use your code in the coming labs)
• Think thoroughly (or discuss with TA about your design) before you type in the codes.

Grading

• Correctness (70%)
• Documentation and comments (20%)
• Program style (10%)