This document discusses flow control in data link layer communication networks. It describes the need for flow control to regulate data packet flow and avoid congestion. The main types of flow control mechanisms are simple protocol, stop and wait protocol, go back N protocol, and selective repeat protocol. Stop and wait protocol is explained, where the sender sends one frame at a time and waits for an acknowledgment before sending the next frame to ensure reliable transmission. The session summary reiterates flow control functions similarly to traffic signals and outlines simple protocol and stop and wait protocol.

1. Communication
Networks
Flow Control
in Datalink Layer
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2. Overview of Module - 2
• Framing
• What is Framing
• Types of Framing
• Methods for identifying the
boundaries
• Flow Control
• What is flow control
• Types of flow control
• Access Control
• What is access control
• Types of access control
• Ethernet – IEEE 802.3
• Evolution of Ethernet
• Frame Format of Ethernet
• Access Control for Ethernet
• Performance Evaluation of Ethernet
• WLAN – IEEE 802.11
• Architecture
• Bluetooth
• WIFI
• Zigbee
• 6LowPan
• Network Layer Services
• IPv4
• Packet switching
• Network Layer Protocols
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3. Flow Control - Understanding
HOME
OFFICE
SOURCE
DESTINATION

4. Need for Flow Control
What if the Left Image is Transmitter and the Right Image is Receiver?
Or
Vice Versa
This scenario necessitates the need for Flow Control Mechanism to
regulate the flow of data packets in the network. If not , it leads to
congestion

5. Types of Flow Control Mechanism
• Traditionally four protocols have been defined for the data-
link layer to deal with flow and error control
•Simple Protocol
•Stop and wait Protocol
•Go Back N Protocol
•Selective Repeat Protocol
@ Sliding Window
Protocols
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6. 1. Simple Protocol
• Our first protocol is a simple protocol with neither flow nor error
Control. We assume that the receiver can immediately handle any
frame it receives. In other words, the receiver can never be over
whelmed with incoming frames.
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7. 2. Stop and Wait Protocol
• In this protocol, the sender
sends one frame at a time and
waits for an acknowledgment
before sending the next one.
• If the frame is received
successfully by the receiver, an
ACK is sent to the Transmitter.
• If frame is lost, then there will
not be any ACK from the
receiver, so that the frame will
be retransmitted.
• If the frame is received and
ACK sent by the receiver is lost.
Even then, the frame is
retransmitted assuming that the
frame is lost.
Successful transmission of Frame
What if, Frame is Lost or Damaged ?
What if, ACK is Lost or Damaged ?

8. Session Summary
•Flow Control [Similar to traffic control signal]
•Simple Protocol
•Stop and wait protocol
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9. References:
• Behrouz A. Forouzan, ―Data communication and Networking, Fifth
Edition, Tata McGraw – Hill, 2013
• Larry L. Peterson, Bruce S. Davie, ―Computer Networks: A Systems
Approach, Fifth Edition, Morgan Kaufmann Publishers, 2011.
• Few online References (Will be Mentioned in the description Section)
Thank You…