System Architecture

1
System Architecture

• you should list the layered Architecture
• Understand the ISO/OSI model used in data
  communications
• Understand the differences amongst various
  computer manufacturers

2
Line Protocol

• A protocol is a set of rules governing two
  communicating parties to exchange information
  correctly.
• In order to communicate, both parties must
  establish a communication session as follows
  (protocol between two computers)
• Initialization and finalization procedures
• Data transmission procedures
• Sender and receiver designation (which party is
  sender and which is receiver)
• Transmission error detection and subsequent
  handling

3
Layered Protocols

• Protocol within a computer for communication.
• To define the communication part of a computer
  with different layers.
• Modification to one of the layers will not impact
  the adjacent layers so long as the same
  interfaces are still maintained.
• It has been widely accepted as a good system
  structuring practice.
• Each layer is defined by
• An interface defining the services it provides to
  layer N 1 and above
• An interface defining the services it requires
  from layer N - 1 and below

4
Advantage of using this protocol

• Reduce design period as the whole network is
  broken into several manageable components.
• It is flexible for the equipment vendors to
  provide hardware/software services.
• The internal structures, mechanism, encoding, and
  algorithms used within a layer are not visible to
  other layers.
• This provides a way of hiding information.
• Alternative implementation for a layer can
  co-exist, providing opportunity for testing and
  reliability.
• The confidence in the correctness of a layered
  system is more easily established by testing and
  analyzing each layer in turn.

5
ISO/OSI Reference Model

• It is a seven-layered Open System.
• It clearly defines partitions to provide
  guidelines for the flow of data, control message
  etc.
• Provide interfaces at points where the service
  description and number of interactions can be
  made small
• Provide separation to handle functions that are
  clearly different in process and technology
• Provide boundaries where interfaces can be
  standardized
• Provide appropriate level of abstraction
• Allow layers to be bypassed where appropriate

6
OSI/OSI layers are

• Application layer
• Presentation layer
• Session layer
• Transport layer
• Network layer
• Data Link layer
• Physical layer

7
Brief explanation for each layer

• Physical layer, Provides for the transparent bit
  transmission over the communications medium such
  as communication for 56K modem, Network card
• Data Link layer, Provides an error-free
  environment between two computers.
• Network layer, Specifies path for message
  delivery.
• Transport layer, Provides an end-to-end host to
  host communication over a network.
• Session layer, Manages the flow of information
  between end-to-end host.
• Presentation layer, Responsible for the
  transformation of data such as data encryption
• Application layer, Concerned with the support of
  an end-user application process

8
Other Network Architectures

• Different computer vendors have been developing
  their own network architectures such as IBM and
  TCP/IP (the Internet) which are slightly
  different than ISO standard.
• The current trend is to migrate towards the OSI
  reference model to provide compatibility.