PROGRAMMING PROJECT ASSIGNMENT

1. Development Setup

For this programming assignment you will work in the CS Linux Lab (linuxlab.cs.pdx.edu) located in FAB 88-09 and 88-10. If you don't already have an account.

For this Project you must use C/C++, UDP Sockets, POSIX Threads, Timers and Make. Refrain from any other languages or 3 rd party libraries. We will use the GNU C/C++ Compiler (gcc/g++) and Make already installed in the development machines in the lab.

2. Problem Description

For the second part of the class project we will design and implement an upgraded version of the simple File Transfer Protocol from Part 1. Our focus will be on improving the performance of the reliable channel and implementing flow control and congestion control mechanisms.

You will implement both the Client and the Server applications for our Simplified Remote Copy Protocol. As with Part 1, your pro client and server must use command line parameters to allow the user to specify the IP address, port, and file to transfer. It must also allow the user to specify the following control parameters: retransmission timeout and maximum window size.

3. Implementation Overview

For the second part of the project we will implement the Selective Repeat flow control protocol. We will modify our stop and go implementation from Part 1 to allow to send multiple packets and pipeline the acknowledgments to improve throughput. Selective Repeat is a sliding-window based protocol, that is, the protocol operates over a limited but configurable number of packets.

Selective Repeat can be used with a static window size or a dynamic window size. We will use a dynamic window size and scale the window size based on the AIMD (Additive Increase-Multiplicative Decrease) algorithm. The window will be controlled by the sender, the initial size of the sliding window will be 1 packet and we will increase the size of the window by 1 until a packet is lost. When a packet is lost we will cut the size of the sending window by half. The algorithm will never exceed the size of the window specified by the user through the command line.

You are allowed to use only one socket to receive packets and one socket to send packets. This is important as our protocol is a pipelined protocol and not a parallel version of Stop and Go. Therefore for this part of the project you might have to change the architecture of your implementation a bit from what you implemented in Part 1. More specifically you will probably need to use system timers and threads as opposed to just use the internal socket timeout.Finally as part of the project your program should print statistics about the performance of Selective

Repeat: the number of packets lost, total packets sent and the time elapsed to send the entire file.

These are a few key concepts you must address as part of your implementation:

1) You must implement a protocol that establishes handshake between the client and the server.

That is the client must send a packet to request a connection with the server, the server must reply with an ACK packet.

2) After the connection is established the user can request a file to be sent to the client. To do this your protocol must implement a file request packet. A file request packet must specify the exact path of the file that the client wants to retrieve. It is recommended that the server acknowledges the request and notifies of the file size to the client. Also if the file does not exist in the server the client must be notified and the connection terminated.

3) After the request is acknowledged, the server can start sending the data to the client, by sending up to w packets at a time, where w is the size of the window. More specifically your program must use Selective Repeat with Additive Increase Multiplicative Decrease window size

4) Your server must wait for a timer to expire in case the packet is lost. If no ACK has been received before the timer expires it means the packet was lost in transit and must be resent.

5) After the file transfer completes your server must notify the client using a Close packet before closing the connection. After a Close packet is received the client can also terminate the connection and exit.