CS 455. Week Data Communications and Networking - Behrouz A Forouzan Edition: 4.

Transcription

1 CS 455 Week 15 Reading: 1. Data Communications and Networking - Behrouz A Forouzan Edition: 4. Objectives: 1. To implement and present the concepts described in the Project Description. Concepts: 1. Project Presentation Outline: 1. Project Presentation a. Application Layer b. Data Link Layer c. TX/RX Layer d. Circuit Layer References: 1. See the assigned text book. CS 455 Week 15 Page 1

2 CS 455 Week 15 Lecture Notes 1. Application Layer Application layer provides a user interface, which has 11 menu items (or functions): 1. Set Timer 2. Set frame size 3. Enter messages or Load text les 4. Idle RQ (Non-error) 4 ( ) 5. Idle RQ - Implicit I-frame error 6. Idle RQ - Implicit ACK-frame error 7. Idle RQ - Explicit I-frame error 8. Idle RQ - Explicit NAK-frame error 9. Continuous RQ - Non-error 10. Continuous RQ - Corrupted I-frame 11. Exit Menu 1 Set Timer Set how long a timer will expire Use actual time (e.g. msec) Menu 2 Set frame size Set how many bytes of data in one I frame Default: 1/3 of the length of the message Menu 3 Input Messages Enter messages to be sent Or load TXT file as message Menu 4 10 Simulations Simulate different errors for communication protocols Once any menu is selected, communication between both sides will start, following the rules of selected menu Message can only be sent in frame o Default frame size is 1/3 of the message or loaded file o Primary need to send multiple frames to Secondary Menu 4 Idle RQ (Non-error mode) Here, the program simulates non error mode of Idle RQ (no I-Frame, ACK or NACK frame is corrupted or missing) CS 455 Week 15 Page 2

3 Menu 5 and 6. Implicit error mode Simulate implicit Idle RQ protocol In these two simulations, S (secondary) send ACK back only if correctly received frames. S never sends NACK back to P. No ACK indicates corrupted frames P (Primary) re-sent if there is no ACK within a timer limit Menu 5. Implicit I-Frame error mode S does receive a frame, however some bits (flag) of the flame will indicate this frame is lost or wrong. So S does nothing. Menu 6. Implicit ACK error mode Notice: P does receive ACK(N), however there are some bits (flag) in the ACK(N) message will indicate this ACK is lost or malfunction (e.g., become a NACK). Menu 7 and 8. Explicit error mode These two menus simulate explicit Idle RQ protocol o In these two simulations, S (secondary) send ACK back only if correctly received frames. If not correctly received, S sends NACK back to P. o NACK indicates corrupted frames o P (Primary) resent the frames if it received a NACK Menu 7. Explicit I-frame error mode S does receive a frame, however some bits (flag) of the flame will indicate this frame is corrupted or not. If it is corrupted then S sends NACK. CS 455 Week 15 Page 3

4 Menu 8. Explicit NACK error mode While S sending NACK back to P, the NACK is corrupted. o Design and implement your mode o Provide your mechanism in document o Handle as many error cases as possible. For example: NACK lost; NACK malfunction. Menu 9 and 10. Continuour RQ For these two simulations, data link layer needs to maintain a retransmission list. o Menu 9 : See Lecture notes o Menu 10 : Use selective repeat Other Menus Menu 11 terminates the client-side program If necessary, you should add your own menus o For example, to set corrupted I-frame number or to select error type 2. Data Link Layer Thru application layer, user specify: protocol, error mode, message, etc. Data link layer fill these information into an package, before it is transmitted. So, in data link layer o Define format of IFrame, ACK frame, NACK frame o Write down your definition into document in details and indicate the function of each bit in your message CS 455 Week 15 Page 4

5 Both Primary and Secondary should log all the events (operations) into log file. For example, Primary side(file: client_log): Menu 3, timer duration of 2, corrupted frame number 2 4 (total # of frames receive) >> Send I-frame N(S) = 1 << Receive ACK-frame N(R) = 1 Wait idle time 1 Expire timer idle time 2 and timer is expired. << Receive ACK-frame N(R) = 2 >> Send I-frame N(S) = 3 << Receive ACK-frame N(R) = 3 Secondary side (file server_log) E.g.: Menu 3, timer duration is 2 seconds, corrupted frame number is 2 << Receive I-frame N(S) = 1 >> Send ACK-frame N(R) = 1 << Receive I-frame N(S) = 2 (Frame lost/wrong, do nothing) << Receive I-frame N(S) = 2 >> Send ACK-frame N(R) = 2 << Receive I-frame N(S) = 3 >> Send ACK-frame N(R) = 3 3. TX/RX and Circuit Layer TX/RX Layer o TX (transmitter) puts data into circuit layer o RX (receiver) retrieves data from circuit layer Circuit Layer o Circuit layer simulates a physical circuit, there is no physical circuit in this project. o You should use sockets to implement the communication between the primary and the secondary Test Case Example To test menu 5: Start Server (Secondary) First. Start Client (Primary), connect with S. CS 455 Week 15 Page 5

6 1. Set Timer 2 (here use second as an example) 2. Set frame size 20 (default byte) 3. Select Implicit Iframe error mode 4. Input Message: This project is to simulate the error control! 5. Press send button or press enter key on the keyboard 6. Check expected results on both sides Results at Server Side Contents of File data This project is to simulate the error control! Contents of File server_log Simulating: Idle RQ Implicit I-frame error << Receive I-frame N(S) = 1 >> Send ACK-frame N(R) = 1 << R i Receive I-frame N(S) = 2 (Frame lost/wrong) << Receive I-frame N(S) = 2 >> Send ACK-frame N(R) = 2 << Receive I-frame N(S) = 3 >> Send ACK-frame N(R) = 3 3 (total # of frames receive) Results at Client Side Contents of File client_log Simulating: Idle RQ Implicit I-frame error 3 (total # of frames will be sent) >> Send I-frame N(S) = 1 << Receive ACK-frame N(R) = 1 >> idle time 1 >> Expire timer idle time 2 and timer is expired. << Receive ACK-frame N(R) = 2 >> Send I-frame N(S) = 3 << Receive ACK-frame N(R) = 3 CS 455 Week 15 Page 6