Packets, Packet Switching and The OSI Model

1
Packets, Packet Switching and The OSI Model
2
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
3
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.

4
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.

5
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
Each file is divided into packets
Each Packet will then be Encapsulated with PROT
OCOLS
The protocols Will be added systematically Layer
By layer
File
The encapsulated Packet is calleda frame
File
File
The received frame is then unpacked in
the opposite order
Transmission Medium
6
Services Performed at Each Layer
Originally Created by Bob Baker Modified
2006 Graham Betts

• 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

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

7
Examples of protocols
Originally Created by Bob Baker Modified
2006 Graham Betts
More on 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

8
Encapsulation
Originally Created by Bob Baker Modified
2006 Graham Betts
Device 1
Device 2
data
packet
carrier
FRAME