Format

1
Format

• Layered models of processes
• The seven layers OSI Model
• Network Requirements
• Network Topology

2
ISO OSI Reference Model

• International Standards Organisation
• the standards body
• Open Systems Interconnection seven layer
  reference model
• tasks of a communications system broken down into
  manageable parts
• organised into a hierarchical architecture.

3
OSI model Why bother?

• Real-world network protocols dont implement the
  OSI seven layer protocol stack model
• But nearly all network protocols are based on a
  simplified layered model
• The layered model helps us think about the many
  processes involved in communicating over networks
• A good model provides support for thinking

4
Communication Between Two Systems
5
ISO OSI Reference Model
6
ISO OSI Reference Model

• Each layer takes data (a Protocol Data Unit(PDU))
  from the layer above
• Each layer processes and encapsulates the data
  into a new PDU
• Each layer passes the new PDU to the lower layer

7
Data Transformation
8
Encapsulation
----DATA----
TCP PDU
Transport Layer (TCP)
----DATA----
TCP - HEAD
Data field
IP Packet
Network Layer (IP)
----DATA----
TCP - HEAD
IP - HEAD
Data field
MAC frame
MAC Layer
----DATA----
TCP - HEAD
IP - HEAD
MAC - HEAD
CRC
Data field
Physical Layer
9
The Seven Layer Model
Application

• Please do not throw sausage pizza away!
• All People Seem To Need Data Processing
• At the top, the Application layer provides OS
  services for application software
• At the bottom, the Physical layer deals with
  wiring issues

Presentation
Session
Transport
Network
Data link
Physical
10
TCP / IP Reference model

• Existed before OSI model
• Uses
• TCP - Transmission Control Protocol
• IP Internet Protocol

11
Transmission Control Protocol/Internet Protocol
(TCP/IP)
OSI Model
TCP/IP
12
(No Transcript)
13
Network Requirements

• High data rate ?
• Bank transaction
• Web browsing
• Low delay ?
• live video/ audio links
• routine backup

14
Network Requirements

• Low (zero) error rate ?
• video signal
• bank account details
• Guaranteed Connection
• safety critical control
• internet phone

15
Mesh Topology

• Fully connected

3 lines 2 ports per machine
16
Mesh Topology

• Fully connected

6 lines 3 ports per machine
17
Mesh Topology

• Fully connected

10 lines 4 ports per machine
18
Mesh Topology

• Fully connected systems use too much wiring.
• Each computer may need an interface for each
  connection.
• Not a practical system.

19
Star Topology

• STAR

20
Ring Topology

• RING

21
Bus Topology

• BUS

• BUS

22
Conclusion

• We have discussed-
• Standard root concepts of networking
• Layered models of processes and layers in our
  conceptual model of networking
• Why protocols are required for interoperability
• Brief of the seven layers of the OSI model and
  encapsulation
• Basics of Network Requirements
• Types of network topologies