Objective:

i. To learn about Network Architecture

ii. To introduce the concepts of OSI and the service primitives

iii. To introduce a simple client and server interaction on a connection oriented network

Network: A network is an interconnection of a set of devices capable of communicating using well defined set of rules called protocol. Network allows us to share message,  in the form of text, numbers, pictures/images, audio and video, among networked devices

Network Architecture: A set of layers and protocols is called a network architecture.The specification of an architecture must contain enough information to allow an implementer to write a program or build for each layer so that it will correctly obey the appropriate protocol.

Reference Model ISO-OSI: Open System Interconnect

Historically, communication between devices of single manufacturers was only permitted which mean that two devices of different manufacturers would not be allowed to communicate. This was because many systems used either IBM’s system network architecture (SNA) or the DEC’s digital network architecture(DNA).

ISO formulated  its OSI reference model in 1970s to address the problem of inter connectivity between different user systems.

• OSI gives users of data network the freedom and flexibility to choose equipment, software and systems of any vendor.
• It aims to sweep away proprietary system
• It is concept of common standards to which all components must confirm

N-Layer Service : To reduce the design complexity, most networks are designed as a stack of layers or levels. The purpose of each layer is to offer some services to the higher layers while shielding those layers from the details of how the offered services are actually implemented.

When a layer N wish to communicate with layer N on another machine, the rule and conventions are collectively known as layer n protocol.

Peer to-peer protocol :- horizontally between peer layers. The entities comprising the corresponding layers on different machines are called peers. The peer may be a software process, hardware devices or human being

Between each adjacent layers is its interface. The interface defines which primitive operations and services the lower layers make available to the higher layers. Network designers when deciding the number of layers and what each should do, one of the most important consideration is to define a clean interface between each layers.

Encapsulation – through the use of PDU (protocol data unit) which encapsulates data by adding a header at each layer.

Primitive– The way in which a layer provide service is by mean of primitive. A service is formally specified by a set of primitives (operations) available to user processes to access the services. These primitives tell the services to perform some action or report on an action taken by a peer entity.

Some of the primitives are:

 

Primitive	Meaning
LISTEN	Block waiting for an incoming connection
CONNECT	Establish a connection with a waiting peer
ACCEPT	Accept an incoming connection from a peer
RECEIVE	Block waiting for an incoming message
SEND	Send a message to the peer
DISCONNECT	Terminate a connection

A simple conversation between client-server is shown in the following figure

 

In Client Server communication as shown, a client request the server for a service, The server acknowledges. Then the client request for data after which the server replies with the data. Following this the service is completed, so the client disconnects and sends it to server and in turn server also disconnects.

 

 

 

 

 

 

 

 

 

Questions

Why are the protocol needed

What are two types of line Configuration

Briefly describe OSI Model

What is peer-to-peer protocols

What is service primitives