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Network Models (Tutorial-5)

Peer to Peer and Client Server Models

Introduction

  • Selecting a Network Architecture 
  • Peer-to-Peer Networks 
  • Client-Server Networks 
  • Hybrid Networks

Selecting a Network Architecture

  • Network Architecture – The way in which computers participate in a network. 
  • The type of architecture chosen by an organisation may include geographical location, number of users, the requirements of specific application packages, level of technical support available, existing systems, and of course cost etc.

Peer-to-Peer Networks

Peer-to-Peer Networks

Stations, No Server, Equal Priority

  • Resources shared in a de-centralised manner 
  • Shared resources include files and printers 
  • Should be used where nodes less than ten 
  • Files are not stored centrally, e.g. Morpheus 
  • Allows easy node-to-node communication
  • Support is usually part of OS 
  • Sharing of files is responsibility of each participant 
  • Participants form a ‘Workgroup’ 
  • Workgroup is assigned a name – important where there are multiple workgroups (eg dept.s)

Selecting a Peer-to-Peer Network

  • Research the current situation 
  • Employees have little or no network experience 
  • Use with less than ten nodes 
  • Does not require a server 
  • No Network Manager available 
  • Little concern about security

Advantages

  • Easy to configure 
  • No requirement for server hardware/software 
  • Users can mange their own resources 
  • No need for a network administrator 
  • Reduce total cost

Disadvantages

  • Provide a limited number of connections 
  • May slow performance of nodes 
  • Do not allow central management 
  • Do not have a central store of files 
  • Users responsible for managing own resources 
  • Offers very poor security

Security on Peer-to-Peer Networks

  • Uses share-level security 
  • Allows password protection of resources 
  • Options are: 
  • Give access to all 
  • Assign a single password and give to all users who require access to the resource 
  • With share-level security a password can not be assigned to a single individual – it assigned to the resource (soon everyone knows what the password is).

Implementation

  • NICs for each computer 
  • Cable media to connect PCs (options) 
  • A Hub has ports for connecting the cables from each computer 
  • Software with the OS should allow sharing of files, directories, disks, printers, scanners, fax modems etc 
  • Note – Windows ’98 and Apple Macs can use their serial port instead of a NIC (much slower)

Implementing under Windows

  • Windows ’95 & ’98 near identical 
  • Windows ME/2000 use a wizard 
  • Install: 
  1. NIC 
  2. Protocol (try NetBUI) 
  3. File and Printer Sharing 
  • Right mouse click to allow sharing of resources.

Client-Server

Client- Server Networks.


  • Most common architecture 
  • Sometimes ‘next step’ after an organisation has outgrown peer-to-peer 
  • Centralised model for data storage, security, running applications and network administration
  • Based on a scalable model 
  • Users network servers 
  • Provide services such as printing, email etc 
  • Allow a high level of security to be implemented 
  • Can be centrally managed

Client-Server Terminology

  • Applications Programming Interface (API) 
  • Client 
  • Middleware 
  • Relational Database 
  • Server 
  • Structured Query Language (SQL)

Why is Client-Server Different?

  • Emphasis on user-friendly client applications 
  • Focus on access to centralized databases 
  • Commitment to open and modular applications 
  • Networking is fundamental to the organization

Client-Server Pros & Cons

Advantages

  • Networked web of computers 
  • Inexpensive but powerful array of processors 
  • Open systems 
  • Grows easily 
  • Individual client operating systems

Disadvantages

  • Maintenance nightmares 
  • Support tools lacking 
  • Retraining required

Generic Client/Server Architecture


Database Client/Server Architecture


3-Tier Client/Server Architecture


Middleware

  • Standardized interfaces and protocols between clients and back-end databases 
  • Hides complexity of data sources from the end-user 
  • Compatible with a range of client and server options 
  • All applications operate over a uniform applications programming interface (API).
Middleware Architecture


Middleware Mechanisms

  • Message-Oriented Middleware 
  • Remote Procedure Calls 
  • Object Request Brokers

Remote Procedure Call Mechanism

Object-Oriented Mechanisms

  • Clients and servers ship messages between objects. 
  • May rely on an underlying message or RPC structure or be developed directly on top of object-oriented capabilities in the operating system 
  • Success depends on standardization of the object mechanism, but competing models exist 
  • COM, OLE, CORBA

Multiserver Networks

  • Each server provides a different service (or duplicates to provide redundancy) 
  • Typically 50 – 500 users 
  • Improves performance 
  • Servers optimised for their service 
  • Much more complex than single-server

Enterprise Networks

  • Supports thousands of users across company’s geographical locations 
  • May involve hundreds of servers 
  • Each location looks like a simple client-server system, but is linked to the corporate network 
  • A WAN extends the client-server model across many LANs (involving several servers to satisfy a request).

Hybrid Networks

  • Incorporates the best features of workgroups in Peer-to-Peer with the performance, reliability and security of server-based systems. 
  • Allows access to central resources, but also allows users to function at the Peer-to-Peer level 
  • Users do not have to log in to a central server

Hybrid Networks – Advantages

  • Client-server apps are still centrally managed 
  • Users can assign loacl access to their resources 
  • Workgroups can manage resources without need for assistance from network administrator

Hybrid Networks – Disadvantages

  • Network access can become burdensome 
  • Users required to remember multiple passwords 
  • Files can be duplicated !! 
  • Files stored on the workstation are not backed up
  • Network access can become burdensome 
  • Users required to remember multiple passwords 
  • Files can be duplicated !! 
  • Files stored on the workstation are not backed up

Conclusion

  • Peer-to-Peer-a type of network in which each workstation has equivalent capabilities and responsibilities. 
  • Client Server- contains a service provider means server and a service requester means client . 
  • Hybrid- contains mixed topology like Allows access to central resources, but also allows users to function at the Peer-to-Peer level 
  • Enterprise Networks-Each location looks like a simple client-server system, but is linked to the corporate network 













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