CN_lec 3_Protocol_Layering

SNS COLLEGE OF ENGINEERING
Kurumbapalayam(Po), Coimbatore – 641 107
Accredited by NAAC-UGC with ‘A’ Grade
Approved by AICTE, Recognized by UGC & Affiliated to Anna University, Chennai
Department of Information Technology
Course Name : CS8591 Computer Networks
III Year / V Sem
5/23/2020 SNSCE / IT/ Sem V / S Rijutha / AP / IT
Unit 1: Introduction and Physical Layer
Topic 3: Protocol Layering

➢ A set of rules, govern how systems
communicate.
➢For networking they govern
how data is transferred from one
system to another.
What is a Protocol ?
A Human Protocol vs Computer
Protocol
2/20

A protocol suite is a collection of
protocols that are designed to
work together.
What is a Protocol Suite ?
3/20

Protocol Data Unit
• Specific block of information transferred over a network.
• It is often used in reference to the OSI model
• It describes the different types of data that are transferred from each layer.
4/20

Protocol Data Unit
The PDU for each layer of the OSI model is listed below.
LAYERS PDU
Physical layer raw bits (1s or 0s) transmitted physically via the hardware
Data Link layer a frame (or series of bits)
Network layer a packet that contains the source and destination address
Transport layer a segment that includes a TCP header and data
Session layer the data passed to the network connection
Presentation layer the data formatted for presentation
Application layer the data received or transmitted by a software application
5/20

Protocol Stacks
➢ A protocol stack is a prescribed hierarchy of software layers, starting from the application
layer at the top (the source of the data being sent) to the data link layer at the bottom
(transmitting the bits on the wire).
➢ The TCP/IP protocol stack is a good example.
○ Layer 1: Network Interface - Physical and Data layers
○ Layer 2: Internet - Network layer
○ Layer 3: Transport - Transport Control Protocol
○ Layer 4: Application - Session, Presentation and Application layers
6/20

Protocol Stacks
Layered Protocol Stacks:
➢ Each level of the stack performs a particular function and communicates with the levels above and
below it.
➢ The OSI Reference Model that defines seven protocol layers is often called a stack, as is the set of
TCP/IP protocols that define communication over the internet
7/20

Protocol Stacks
Example: Parcel service between two offices.
• The task is simple – send parcels between people in each office.
• We will divide the task into two distinct processes as follows:
⮚Take a package, wrap it and address it.
⮚Send it to the destination
• at the receiving end
⮚Receive the package
⮚Deliver it to the recipient
8/20

Protocol Stacks
Typically you would have an internal mail man that:
⮚ Collects the parcels from the senders and takes then to a mail dispatch room.
⮚ The parcels are placed in a van by the dispatcher and then driven to the remote
office.
•At the remote office
⮚ The parcels are received by the dispatcher and placed into a tray for the mail man
⮚ The mail man collects the parcels and delivers them to the recipients
9/20

Protocol Stacks
Components Functionality
Hostel
Letters
Students
Support
students
Generate
Letters
Components
Computer
Messages
Process
10/20

Protocol Stacks
Components Functionality
Hostel Boy
Infrastructure
Postman
Multiplexing /
Demultiplexing
Path of letters
Bundle of
letters
Transporting
Components
Routers
Software - hop
to hop
transfer
Hardware
Physical Cables
11/20

Here is a simple diagram to illustrate the process:
Protocol Stacks
12/20

Challenges
⮚ Large reach (International, National, Village)
⮚Need to be scalable (Many users)
⮚ Many user requirements (reliable, express, cheap)
⮚Heterogeneous Technology (Airplane, Trucks, Trains, etc.,)
13/20

Challenges
⮚ Complex System
⮚ Many users (Billions)
⮚ World wide reach
⮚ Many user requirements (reliable, express, cheap, interactive, multicast)
⮚ Heterogeneous Technology (Ethernet, Wireless, Bluetooth, Wifi, Cellular)
14/20

Challenges
⮚ Application - Support application processes which generates messages
(Email, Web, File transfer)
⮚ Transport - Supervise process to process communication - Multiplexing /
Demultiplexing messages (TCP, UDP)
⮚ Network - Enable end to end routing of messages (IP)
⮚ Data Link- Enable hop to hop messages transfer (Ethernet)
⮚ Physical - Enable bit transmission on media (Wire / air)
15/20

⮚ The question really is what is the advantage of splitting the task into
different layers/tasks?
Protocol Stacks
Any of the layers/tasks can be changed without affecting the other layers.
16/20

⮚ If we decide to use a train instead of a van to transport the messages between
the offices we could do so without affecting the mail man.
Protocol Stacks
The mail man doesn’t know, and doesn’t care, how the parcels are transported
between the offices, as all he does is collect them, and pass them to the delivery man.
17/20

Quiz
Multiple Choice Questions
1. ____________ are rules that govern communication exchange
a. Media b. Interface c. Protocols d. All the above
2. A ___________ is a collection of protocols that are designed to work together
a. TCP/IP b. Protocols c. OSI d. Protocol Suite
3. How many layers are present in the Internet protocol stack (TCP/IP model)
a. Four Layer b. Five Layer c. Six Layer d. Seven Layer
4. The Transmission Control Protocol divides the stream of data into smaller units
that are called ____________________
a. Frames b. Segments c. Packets d. Bits
18/20

THANK YOU !
SNSCE / IT/ Sem V / S Rijutha / AP / IT 19/20

CN_lec 3_Protocol_Layering

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