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Packets, Packet Switching and The OSI Model. Packets. Transmissions are broken up into smaller units or data transmissions called packets. Example A file (might be an mp3 sound file) is divided into packets. It does not matter what the transmission is. It could be Word

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packets
Packets
  • Transmissions are broken up into smaller units or data transmissions called packets

Example

A file (might be an mp3 sound file) is divided into packets.

It does not matter what the transmission is. It could be Word

document, a PowerPoint or an MP3

PACKET

PACKET

PACKET

PACKET

packets and osi
Packets and OSI
  • After transmission is divided into packets extra information required to make sure it all goes back together correctly. The OSI model helps to look after this.
  • The OSI model also provides much more information which is included with each package.
osi 7 layer model
OSI 7 Layer Model

Originally Created by Bob Baker

Modified 2006

Graham Betts

More Information on OSI

  • OSI “Open System Interconnection”
  • OSI is not a protocol but a list of protocols divided between 7 layers with each layer having a different set of functions.
  • Each packet is layered/packaged with protocols from each of the layers as it is processed.
  • The process of layering the protocols around each package is called encapsulation. The final encapsulated data packet is called a frame.
open systems interconnection
Open Systems Interconnection

Originally Created by Bob Baker

Modified 2006

Graham Betts

  • OSI Reference model
    • Layer 7 application
    • Layer 6 presentation
    • Layer 5 session
    • Layer 4 transport
    • Layer 3 network
    • Layer 2 data link
    • Layer 1 physical

Sender

Receiver

File

Each file

is divided

into

packets

Each Packet

will

then be

Encapsulated

with

PROTOCOLS

The encapsulated

Packet is calleda frame

The protocols

Will be added

systematically

Layer

By layer

File

File

The received

frame is then

unpacked

in the

opposite order

Transmission Medium

services performed at each layer
Layer 7 application

Layer 6 presentation

Layer 5 session

Layer 4 transport

Layer 3 network

Layer 2 data link

Layer 1 physical

Identification, authentication

Format conversion

Set-up coordinate conversation

Ensures error-free transfer

Routing of data through network

Error control and synchronisation

Placing signals on the carrier

Services Performed at Each Layer

Originally Created by Bob Baker

Modified 2006

Graham Betts

examples of protocols
Layer 7 application

Layer 6 presentation

Layer 5 session

Layer 4 transport

Layer 3 network

Layer 2 data link

Layer 1 physical

E-mail, Web browser, Directory

POP, SMTP, FTP, HTTP, DNS

Sockets

TCP

IP

PPP, Ethernet, Token ring

100baseT

Examples of protocols

Originally Created by Bob Baker

Modified 2006

Graham Betts

More on Protocols

encapsulation

Application

Application

Presentation

Presentation

H6

data

T6

Session

Session

H5

data

T5

Transport

Transport

H4

data

T4

FRAME

FRAME

FRAME

Network

Network

(packet)

H3

data

T3

Data Link

Data Link

H2

data

T2

Physical

Physical

H1

data

T1

Preamble

Destination

Address

Source

Address

Data

Padding

CRC

A typical frame

Encapsulation

Originally Created by Bob Baker

Modified 2006

Graham Betts

Device 1

Device 2

data

packet

carrier

FRAME