Flow_Control-Error_Control

Flow_Control-Error_Control - Flow Control Refers to a set...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Flow Control Refers to a set of procedures used to restrict the amount of data the sender can send before waiting for acknowledgement. Flow control is, thwarting a fast sender so that the receiver is not overwhelmed with data. Any receiving device has a limited speed at which it can process incoming data, and limited amount of memory, in which to store the incoming data. The receiving device must inform the sending device before those limits are reached and to request that the transmitting device send fewer frames or stop temporarily. Incoming data must be checked and processed it can be used. The rate of such processing is slower than rate of transmission. For this reason , each receiving device has a block of memory, called a buffer, reserved for storing incoming data until the data is processed. If the buffer begins to fill-up, the receiver must be able tell the sender to halt transmission until it is once again able to receive. As frames come in, they are acknowledged, either frame by frame or several frames at a time. If a frame arrives damaged, the receiver sends an error message (a NAK frame). Two methods have been developed to control flow of data across communication links: a. Stop-and-wait flow control protocol – Send one frame at a time. b. Sliding Window flow control protocol. – Send several frames at a time. 1
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Stop-and-wait flow control protocol In this method the sender sends one frame and waits for an acknowledgement before sending the next frame. WT = Wait time. WT WT Time Time Figure shows Stop-and-wait flow control protocol. Advantage is, its simplicity : each frame is checked and acknowledged before the next frame is sent. The disadvantage is inefficiency : Stop-and-wait is slow. Each frame must travel all the way to the receiver and an acknowledgement must travel all the way back before the next frame can be sent. If the distance between the devices is long, the time spent waiting for acknowledgements (ACKs) between each frame can add significantly to the total transmission time. Although the transmission rate allows multiple frames to be in transit, only one frame is in transit at any time and hence, the transmission line capacity is under utilized. Sliding Window Several frames can be in transit at a time, i.e. allows sender to transmit several frames before waiting for an acknowledgement. The link can carry several frames at a time and its capacity can be used efficiently. The receiver acknowledges only some of the frames, using single ACK to confirm the receipt of multiple data frames. 2 Data 0 ACK 1 Data ACK EOT
Background image of page 2
The word window in the term “sliding window” refers to an extra buffer, created by both the Sender and Receiver. The window can hold frames at either end and provides the upper limit on the number of frames that can be transmitted before requiring an acknowledgement. Frames may be acknowledged at any point without waiting for the window to fill up and may be transmitted as long as the window is not yet full. To keep track of which frames have been transmitted and which have been
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/23/2012 for the course CS 101 taught by Professor Martand during the Spring '10 term at Punjab Engineering College.

Page1 / 13

Flow_Control-Error_Control - Flow Control Refers to a set...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online