This document provides an introduction to the data link layer. It discusses that communication at this layer is node-to-node as data needs to pass through multiple networks to reach its destination. The data link layer is responsible for encapsulating datagrams into frames and delivering them to the next node. It also implements services like flow control, error control, and congestion control. There are two main categories of links - point-to-point and broadcast links. The data link layer consists of two sublayers - the link layer addressing sublayer and the logical link control sublayer. Link layer addressing assigns MAC addresses for communication between nodes on the same network.

1. ROHINI COLLEGE OF ENGINEERING & TECHNOLOGY
Near Anjugrammam Junction, Palkulam - 629401
(Approved by AICTE, New Delhi and Affiliated to Anna University, Chennai)
(An ISO Certified Institution)
Course Name : NETWORKS AND SECURITY
Title : Introduction to data link layer
Mr.NAGARAJAN R V
Assistant Professor
Department of Electronics and Communication Engineering

2. On completion, students will be
able to
NAGARAJAN R V AP/ ECE,RCET

3. NAGARAJAN R V AP/ ECE,RCET
Communication at the data-link layer is node-to-node. A data unit from one point in the
Internet needs to pass through many networks (LANs and WANs) to reach another point.
two end hosts and the routers as nodes and the networks in between as links.
Nodes and Links
Services
When a packet is travelling in the Internet, the data-link layer of a node (host or router) is
responsible for delivering a datagram to the next node in the path.
Framing
The data-link layer at each node needs to encapsulate the datagram (packet received from
the network layer) in a frame before sending it to the next node.

4. NAGARAJAN R V AP/ ECE,RCET
Flow Control
Error Control
Congestion Control
If the rate at which the data are absorbed by the receiver is less than the rate at which data are
produced in the sender, the data link layer imposes a flow control mechanism to avoid
overwhelming the receiver.
The data link layer adds reliability to the physical layer by adding mechanisms to detect and
retransmit damaged or lost frames. It also uses a mechanism to recognize duplicate frames.
Error control is normally achieved through a trailer added to the end of the frame.
Two Categories of Links
point-to-point link
In a point-to-point link, the link is dedicated to the two devices
broadcast link
the link is shared between several pairs of devices.

5. NAGARAJAN R V AP/ ECE,RCET
Two Sublayers
LINK-LAYER ADDRESSING
A link-layer address is sometimes called a link address, sometimes a physical address, and
some-times a MAC address
Three Types of addresses
Unicast Address Multicast Address Broadcast Address
one-to-one communication one-to-many communication one-to-all communication

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LINK-LAYER ADDRESSING

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Address Resolution Protocol (ARP)

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Caching
Packet Format
link-layer protocol
network-layer protocol

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An Example of Communication
Activities at Alice’s Site

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Activities at Router R1

11. Activities at Router R2

12. Activities at Bob’s Site

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14. THANK YOU
NAGARAJAN R V AP/ ECE,RCET