CPSC 441 Assignment-3 Discussion. Department of Computer Science University of Calgary

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1 CPSC 441 Assignment-3 Discussion Department of Computer Science University of Calgary

Overview of FastFTP protocol TCP for Initial Handshake Port: 2245 Port: 4576 You may choose

2245 Port: 4576 Port: 2245 CLIENT Run Time Arguments: 1. Client Window Size 2. Time Out 3.

File Name TCP for Final handshake Port: 4576 SERVER Go-Back-N protocol used for reliability

2 Overview of FastFTP protocol TCP for Initial Handshake Port: 2245 Port: 4576 You may choose any free port >1024 at client side You have to implement UDP for File Content Transfer Port: 2245 Port: 4576 Port: 2245 CLIENT Run Time Arguments: 1. Client Window Size 2. Time Out 3. Server Name 4. Server Port 5. File Name TCP for Final handshake Port: 4576 SERVER Go-Back-N protocol used for reliability Given NOTE: SAME PORT NUMBER USED BY TCP AND UDP There is only one TCP connection. Connection opened at the beginning is kept open during the entire process 2

3 How to get TCP Local Port Number for Creating UDP Socket Create TCP Socket Socket socket = new Socket("localhost", 8888); Create UDP Socket with same local port number as used by TCP DatagramSocket clientsocket = new DatagramSocket(socket.getLocalPort()); 3

4 Before you start.. Run client and server in different directories. This is required since server creates a file with name same as what is passed to it by the client If you don t do this, server will delete the file that client wants to transfer 4

5 Algorithm at Client (A high level description of what you need to implement) Step-1: Open a TCP connection Step-2: Send file name to the server over TCP Step-3: Wait for server response over TCP Step-4: Open a UDP socket Step-5: Send file content to server as UDP segments Step-6: Send an end of Transmission message to server over TCP Step-7 Clean up and close TCP/UDP sockets Note: All communication (TCP and UDP) in binary format 5

6 Writing/Reading from TCP Socket Use Java stream classes DataInputStream DataOutputStream 6

7 Writing to TCP Socket: File Name DataOuputStream outputstream = new DataOuputStream (socket.getoutputstream()); String Filename = testfile"; try outputstream.writeutf(filename); outputstream.flush(); catch (IOException e) Note the stream type used Note that file name is a run time argument First 2 bytes is the string length. The string itself follows later in UTF-8 encoding format (Step 2) Make sure that filename is indeed send // code for Exception Handling

8 Writing to TCP Socket: End of Transmission try outputstream.writebyte(0); outputstream.flush(); End of transmission message (Step-6) catch (IOException e) // code for Exception Handling

9 Reading from TCP Socket: Server Response DataInputStream inputstream = new DataInputStream(socket.getInputStream()); try byte respcode = inputstrean.readbyte(); catch (IOException e) Server response during initial handshake (Step-3) //Exception handling

10 Client Program Structure Following slides will give you (hopefully!) an idea on how to implement step-5 of the algorithm Disclaimer: Following implementation may not be the simplest or best 10

11 Complete initial TCP handshake Start ACK RCV Thread Spawn ACK RCV thread Sender Thread Yes Is EOF No Create segment Wait No Is Trans. Queue Empty Wait Yes Is Transmission queue full Yes Send end of transmission message Cancel Timer, cancel ACK RCV Thread, Close Sockets No Send segment End 11

12 Send Thread (Main thread): sending file content Send segment Add segment to transmission queue If this segment is the only segment in queue, start the timer (see slide on timer ) try Sending data segment Segment segment_send = new Segment(seqnum, payload) DatagramPacket sendpacket = new DatagramPacket(segment_send.getBytes(), segment_send.getbytes().length, ServerIP, ServerPort); clientsocket.send(sendpacket); catch(exception e) // handle exception Byte array containing part of file content Type InetAddress: Refer UDP client code Number of bytes to write Convert segment to byte array 12

13 ACK Receive Thread Cancel Timer if ACK is valid Get ACK number from UDP packet While( txqueue.element().getseqnum() < ackseg.getseqnum() ) txqueue.remove() If queue not empty, start timer Receiving ACK Note: Same UDP socket should be used for sending messages to the server and receiving ACKs from the server Byte array to receive a Datagram packet. DatagramPacket receivepacket = new DatagramPacket(receiveData, receivedata.length); clientsocket.receive(receivepacket); Segment ackseg = new Segment(receiveData); acknum = ackseg.seqnum(); Get ack number from the segment Convert the datagram packet received into segment format 13

Timer Thread Use Timer class Need not create thread explicitly Java does this in the background Use Timer class Similar to thread creation! Timer timer = new Timer(true) Create timer thread timer.

14 Timer Thread Use Timer class Need not create thread explicitly Java does this in the background Use Timer class Similar to thread creation! Timer timer = new Timer(true) Create timer thread timer.schedule(new TimeoutHandler(), 1000) Schedule timer to go off in 1000 ms. Execute the run method in TimeoutHandler class TimeoutHandler extends TimerTask // define constructor public void run() // call method to process time out 14

15 Steps to Process Time-outs 1. Get list of all pending segments from transmission queue Segment[ ] pending_seg; pending_seg = txqueue.toarray() 2. Send all these segments for (int i = 0; i < pending_seg.length; i++) // send segments similar way as described in slide If queue is not empty, start the timer if(!txqueue.isempty()) // start timer 15

CPSC 441 Assignment-3 Discussion. Department of Computer Science University of Calgary

CPSC 441 Assignment-3 Discussion Department of Computer Science University of Calgary Overview of FastFTP protocol TCP for Initial Handshake Port: 1111 Port: 4444 UDP for File Content Transfer Port: 3333