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DATA LINK LAYER
• Overview
• Properties
• Functions & Services
• Protocols
• MAC
• Demo-on simple LAN Network
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ARASU ENGINEERING COLLEGE / CSE

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Mr. V. KOVENDAN AP/ CSE, ARASU ENGINEERING COLLEGE07-07-2020 3
HOST
A
HOST
B
Intermediate Nodes

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7. Application Layer
6. Presentation Layer
5. Session Layer
4. Transport Layer
3. Network Layer
2. Data Link Layer
1. Physical Layer
The OSI reference Model, the 7 Layers are
User Supported
Layer
Network
Supported Layer
Transport
Supported Layer

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Mr. V. KOVENDAN AP/ CSE, ARASU ENGINEERING COLLEGE
Basic Terminologies
Frame PDU (Protocol Data Unit) A PDU at the DLL called Frame
Node A node is a device on a network
Media
The media are the physical means used
to carry data signals
Network
A Network is two are more devices
connected to a common medium
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DLL Overview
• Provides a well-defined service interface to the
network layer.
• Determines how the bits of the physical layer are
grouped into frames (Framing).
• Deals with transmission errors (CRC).
• Flow control: Regulates the flow of frames.
• Performs general link layer management.
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Data link layer has two sub-layers:
– Logical Link Control: It deals with protocols,
flow-control, and error control
– Media Access Control: It deals with actual
control of media
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Data Link Layer
MAC
LLC

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Properties of DLL
• Primarily Link Layer implemented in the software
• The link layer is implemented in a network adapter,
also sometimes known as a Network Interface Card
(NIC).
• A NIC controls the wired and wireless connections of a
computer to exchange information with other computers
and the Internet.
• This software Data Layer implementations may be
embedded in physical devices such as switches and
network adapters (firmware)
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Comparison of HUB Switch and Router
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HUB
Switch
Router

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Functionality of DLL
• Data link layer does many tasks on behalf of upper layer. They are:
1. Framing: Data-link layer takes packets from Network Layer and
encapsulates them into Frames.
– Then, it sends each frame bit-by-bit on the hardware.
– At receiver’ end, data link layer picks up signals from hardware and
assembles them into frames.
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Relationship between the frames and packets
Packet
Header Payload field Trailer
Packet
Header Payload field Trailer
Frame
Host
A
Host
B

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Functionality of DLL
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802.11 Wireless
Frame
PPP Frame
HDLC
HDLC
Frame Relay
Ethernet Frame
Ethernet Frame
High Level Data Link Control with
acknowledged data transfer
Frame relay is a packet-switching telecommunication service
designed for cost-efficient data transmission for intermittent traffic
between local area networks (LANs) and between endpoints in
wide area networks (WANs).
DLL protocol data unit and uses the
underlying Ethernet physical layer
transport mechanisms.(E-Payload)

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2. Addressing
Hardware address(Physical address)
3. Synchronization
Machines at both end
4. Error Control
Mechanisms: 1. ACK/NAK 2. Time-out 3. Sequence numbers
5. Flow control
Nodes in different speed controls flow in same speed
6. Multi Access
CSMA/CD (Host transfer – link get collision)
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• SDLC (Synchronous Data Link Protocol)
– IBM [used to connect remote device to mainframe] (P-to-P) (P-to-M)
• HDLC (High-level Data Link Control)
– Based on SDLC [ provides best effort reliable and unreliable services]
• SLIP (Serial Line Interface Protocol)
– Used to transmit IP packets with dialup service [lack of error detection and correction]
• PPP (Point-to-Point Protocol)
– Same as SLIP but more robust can transport not only IP and other packet types
• Asynchronous Transfer Mode is like Ethernet
– Aimed at WAN and LAN, ATM integrated both the data and voice.
• LAP (Link Access Procedure) Three varieties LAP, LAP Balanced- P-to-P on X.25 Pkt Switched N/W
– LAP D-channel provides service on ISDN, LAP-F frame mode (provides frame Relay n/w)
• LLC (Logical Link Control) IEEE defines in 802.x family of Standard
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Data Link Protocols

Data link
Protocol
Transmission
line to a router
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Placement of DLL Protocols
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2 3 2 2 3
Data Link
Layer Process
Routing Process
Frames Packets
2
Router

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PPP (Point-to-Point Protocol) Function

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Error Detection and Correction
Types of Errors
There may be three types of errors:
– Single bit error
• (Frame corrupted with single bit)
– Multiple bits error
• (Frame with more than one bit corrupted)
– Burst error
• (Frame corrupted with more than one consecutive bit)
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Error Detection and Correction
• Error control mechanism may involve two possible ways:
– Error Detection & Error correction
– Errors in the received frames are detected by means of
• Parity Check
• Cyclic Redundancy Check (CRC).
In both cases, few extra bits are sent along with actual data to confirm that bits
received at other end are same as they were sent. If the counter-check at
receiver’ end fails, the bits are considered corrupted.
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• Parity Check: One extra bit is sent along with the original bits to make number of
1s either even in case of even parity, or odd in case of odd parity.
• Cyclic Redundancy Check (CRC):
– Binary division
– Codeword (Actual data bits plus the remainder is called a codeword)
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Example for CRC
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Error Correction
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• Error correction can be done in two ways:
– Backward Error Correction
– Forward Error Correction
Eg: we take ASCII words (7 bits data),
For
m data bits, r redundant bits are used.
r bits can provide 2r of information.,
i.e. m+r+1.

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Flow Control
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• Stop and Wait
• Sliding Window
• Stop and Wait
– Forces sender after sends a frame to stop
and wait until ACK is received
Most commonly used protocols to
control the flow of data

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Stop and Wait
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a. Frame lost
b. ACK lost

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• Duplex mode
• Error prone channel
• Allows multiple frames
• Receiver has the buffer W called (window size)
• ACK includes no. of frame expected
Sliding Window Protocol
6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5
Window

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• Sender Sliding Window
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6
Direction Direction
This wall moves to the right,
frame by frame, when a
frame is sent.
This wall moves to the right, the size
of several frames at a time, when an
ACK is received.
Sender Window

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• Receiver Sliding Window
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6
Direction Direction
This wall moves to the right,
frame by frame, when a
frame is received.
This wall moves to the right, the size
of several frames at a time, when an
ACK is sent.
Receiver Window

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Sliding Window example
Sender Receiver

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Error Control
• Requirements for error control mechanism:
– Error detection
– Positive ACK
– Negative ACK
– Retransmission (sender maintain clock and Set timeout)
• There are three types to control the errors by
Automatic Repeat Requests (ARQ):
– Stop-and-wait ARQ
– Go-Back-N ARQ
– Selective Repeat ARQ

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Error Control
• Stop-and-wait ARQ
– Cases of operations:
1. Normal operation
2. Frame lost
3. ACK lost
4. ACK delay

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Error Control
• Stop-and-wait ARQ (Normal operation)
ACK 0
ACK 1
Frame 0
Frame 1
Sender Receiver
S=0
S=1
S=0
R=0
R=1
Time Time

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• Stop-and-wait ARQ (Frame lost)
Lost
ACK 1
Frame 0
Frame 1
Sender Receiver
S=0
S=1
S=0
R=0
R=1
Time Time
R=1
R=0
S=1
Time out

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• Stop-and-wait ARQ (ACK lost)
ACK Lost
ACK 1
Frame 0
Frame 1
Sender Receiver
S=0
S=1
S=0
R=0
R=1
Time Time
R=1
R=0
S=1
Time out

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• Stop-and-wait ARQ (ACK Delay)
Delay in receiving
ACK

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Go-Back-N ARQ
• Protocol based on sliding window
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Selective Repeat ARQ
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• Go-Back-N is inefficient of a noisy link. (Higher probability of damage) makes
resending is complex in bandwidth which slow down the transmission rate.
• Solution: Selective Repeat ARQ: It resends only the damaged frames. Before timer
expires
• Processing at receiver end is complex.
Sender Receiver

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LINK-LAYER ADDRESSING
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• Link-layer protocols define three types of addresses:
– Unicast
– Multicast
– Broadcast
• Unicast Address
– One to one communication
– Eg.: phone call
• Multicast Address
– one-to-many communication.
– Eg.: e-mail message to a mailing list.
• Teleconferencing and videoconferencing
• Broadcast Address
– one-to-all communication.
– Eg.: digital TV subscribers

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Address Resolution Protocols:
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• The actual communication happens over the physical address. (MAC Address)
• Mission is to get the destination MAC address.
• ARP functionality is to translate IP address to physical address.
• Position of ARP in TCP/IP suite

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ARP Frame Format
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Media Access Control
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• To transfer the data we need some address
• Network provides various addressing types.
• Media Access Control Address ( physical address)
• MAC Addresses are unique 48-bits
• IEEE 802 standard, Data Link Layer is divided into two sublayers
– 1. Logical Link Control(LLC) Sublayer
– 2. Media Access Control(MAC) Sublayer
• MAC address is used by Media Access Control (MAC) sublayer of Data-Link Layer.
• Word wide unique address.
• 12-digit hexadecimal number (6-Byte binary number)
• First 6-digits (say 00:40:96) represents OUI
• OUI of well known manufacturers:
– CC:46:D6 - Cisco
– 3C:5A:B4 - Google
– Inc. 3C:D9:2B - Hewlett Packard

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MAC Structure
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Example MAC Address: E4-E7-49-61-DF-74

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• MAC address can be represented using any of the following
formats
• Hyphen-Hexadecimal notation
• E4-E7-49-61-DF-74
• Colon-Hexadecimal notation
• E4:E7:49:61:DF:74
• Period-Separated-Hexadecimal notation
• E4.E7.49.61.DF.74

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• How to find MAC address
– Command for UNIX/Linux: ifconfig -a
ip link list
ip address show
– Command for Windows OS:
ipconfig /all
- Command for MacOS:
TCP/IP Control Panel

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Unicast
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Multicast
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Broadcast
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Demonstration of simple network module on
how to connect Devices
(Hub, Switch, Router) with a simple LAN….
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Data link layer

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