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

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

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

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.

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

OSI/OSI layers are Application layer Presentation layer Session layer Transport layer Network layer Data Link layer Physical layer

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

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.