Implement the simplex protocol for a noisy channel (Fig. 3-12 from Tannenbaum).General rules: source code must be commented and a description how to run the programs must be attached. The goal is to implement a data transmission programs that involve two layers: Physical layer and Data link layer. We will simulate the physical layer by the transport layer using the programs described in the lecture 'Unix Network Programming'. For the programs on the data link layer follow the Fig. You will need to modify the meaning of functions in Fig. 3-12 so that they relate to the regular Unix Network Programming functions.
Sender sends data every Pt = 500ms and always has data to send. Sender timeout is Rt = 1 sec. Send packets over UDP. Sender follows the usual logic. We need to simulate losses since our network will almost never lose packet.
At the receiver, write additional code in two places 1. As soon as the receives gets a packet (before any update to variables): Ignore the packet with probability P = 0.2. This simulates a lost data packet. Just before the receiver sends an ack (after updating variables): Don't send the ack with probability P = 0.2. This simulates a lost ack.How to drop/ignore packet with probability P?.
Generate a random float point number p, between 0 and 1. If p: For example, the sender log might look like the following: 19:43: Sentpacket seqnum=0 19:12: Receivedack seqnum=0 19:43: Sentpacket seqnum=1 19:43 Receivedack seqnum=1 19:43: Sentpacket seqnum=0 19:35: Timeout seqnum=0 19:55: Sentpacket seqnum=0 Retransmit 19:55: Receivedack seqnum=0 This shows what the sends log would like with a data packet is lost and timer expires. Play around with with varying Pt, Rt and P values and see if the results are as expected. It is best to accept these values as command line parameters so that it is easy to experiment. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) READ THE INSTRUCTIONS TO SEE WHAT NEEDS TO BE DONE, HOW THE OUTPUT IS TO BE SHOWED I HAVE TWO SAMPLE CODES WITH ME FOR THE SAME ASSIGNMENT.
IF U R READY TO DO THIS ASSIGNMENT, I CAN PROVIDE U WITH THAT TO HELP U MORE UNDERSTAND WHAT IS NEEDED. ## Platform UNIX C OR C IS OK. Skills:, See more:,.
I am implementing a client/server echo program using the Stop-and-Wait protocol. Part of the implementation is to randomly introduce drops from the server. I am actually randomly dropping ACKs as well as FRAMEs. A side effect of this is the introduction of a corner case: If the last ACK from the server is dropped, both client and server end up in a 'send' mode. This happens because the server doesn't know the last ACK was dropped, and from its perspective, everything worked and it now should echo back everything the client sent to it. The client, on the other hand, doesn't know if the last FRAME was dropped or if just the ACK was dropped, so it tries to resend the last FRAME. I could see this being solved by the use of a FIN or something - basically an extra ACK going the opposite direction when both sides think transmission is complete.
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However, I want to conform to the expected approach for Stop-and-Wait. How should Stop-and-Wait handle this case? Good point about the ACK. However, I'm implementing in UDP, so would it actually get the timeout?
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Also, the drops are fake, because I'm randomly introducing them and simulating the drop by just not sending the packet (either a frame or an ACK). The send mode is there because the assignment is to build an echo server. This means I need to create a client and server, built on top of Stop-and-Wait, which operate in two modes: send and receive. The server is in receive mode until it gets an entire file, at which point it switches to send mode to echo the entire file back. – Dec 8 '13 at 21:46. One way to handle this situation is to have a one-bit sequence number included in every frame.
Every time you send a frame and receive an ACK, you flip the bit for the next frame. If you send a frame, don't receive an ACK, and have to retransmit the frame, you resend it with the same sequence bit. At the receiver, if you receive two (or more) frames in a row with the same sequence bit, you know it's a retransmission, so you can resend the ACK but ignore the frame, since you've already acted on it. Don't bother trying to acknowledge acknowledgements.
You just run into the same problem where the network might drop the ACK for the ACK. I've actually been using 32-bit SEQ #'s for my sanity. My problem fundamentally lies in the fact that I have app-level logic because it's an echo program. What this means is that once the server has received the entire file (via S-a-W protocol), it switches modes to send and begins transmitting that same file back.
Conversely, the client is in the send mode to begin with and will try to switch to the receive mode after the server has acknowledged all the frames, in anticipation of receiving the echo'd file back. When the last ACK is lost, both server and client end up in send mode. – Dec 8 '13 at 21:18.
Home Page 'Stop-and-Wait' protocol 1. Background 'stop-n-wait' (sometimes known as 'positive acknowledgement with retransmission') is the fundamental technique to provide reliable transfer under unreliable packet delivery system. How this protocol works.
1) Normal operation After transmitting one packet, the sender waits for an acknowledgment (ACK)from the receiver before transmitting the next one. In this way, the sender can recognize that the previous packet is transmitted successfuly and we could say 'stop-n-wait' guarantees reliable transfer between nodes. To support this feature, the sender keeps a record of each packet it sends. Also, to avoid confusion caused by delayed or duplicated ACKs, 'stop-n-wait' sends each packets with unique sequence numbers and receives that numbers in each ACKs. 2) Timeout If the sender doesn't receive ACK for previous sent packet after a certain period of time, the sender times out and retransmits that packet again. There are two cases when the sender doesn't receive ACK; One is when the ACK is lost and the other is when the frame itself is not transmitted.
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Go Back N Protocol
To support this feature, the sender keeps timer per each packet. How it is shown in nam (network animator). 'stop-n-wait' protocol can be shown as below in nam. Packet0 is sent and ACK0 is received 2.
C Program For Stop And Wait Protocol
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Program For Stop And Wait Arq Protocol In C
Packet1 is sent and ACK1 is received 3. Packet2 will be sent and be received and so on. Here is for this simulation. You can download and and run it by yourself. Shortcoming The main shortcoming of the stop-and-wait algorithm is that it allows the sender to have only one outstanding frame on the link at a time. The sender should wait till it gets an ACK of previous frame before it sends next frame.
As a result, it wastes a substantial amount of network bandwidth. To improve efficiency while providing reliability, 'sliding window' protocol is appeared. The detail comparison will be discussed with an example.