1 Client Server Architecture over the Internet Week - 2

2 Reference Chapter 4: Internet Architecture from Electronic Commerce-From Vision to Reality by Elias M. Awad.

3 A computer network is collection of computers interconnected for the purpose of communication and sharing resources.

4 Peer to Peer Networks A network of computers where each computer is consider equivalent to others. No centralised repository of information and services. Information and applications need to be replicated in each computer on the network. Administration of application becomes difficult when the size of the network increase. Integrity of replicated information is questionable.

5 Relative Advantages and Disadvantages Key AdvantagesKey Disadvantages User control over resourcesIndividual security policies Easy installation and configuration Difficult administration Cost effective for small businesses Backup of replicated information results in higher cost Fault tolerant as no single point of failure on the network Integrity of replicated resources is questionable

6 Client Server Architecture Server –A special purpose computer or specialised hardware and software designed for specific functions. Client –A computer connected to one or more servers on a network or the Internet. Client Server Networks –A cluster of client computers connected to one or more servers on a network. –Servers provide centralised repository of information and services.

7 Typical Services over a Network Application services –Server based programs Instant messaging services –Winpop, IRC chat, Netmeeting, MSN & Yahoo Meeangers services Database services Information services –File services Communication services –Fax, data relay, Internet access

8 Typical Client Server Interaction Servers wait for clients to send a request for accessing a resource. Clients requiring access to a resource connect to the server and submit a request for the resource. Servers accept clients’ requests and respond with the access to the requested resource. Clients disconnect from the servers. This protocol is known as the request-reply protocol and forms the basis of client server architecture.

9 Typical Client Server Interaction (Contd.) Connect Request Reply Accept Disconnect Time

10 Relative Advantages and Disadvantages Key AdvantagesKey Disadvantages Centralised administrationSpecialised installation and configuration ScalableRequires installation of specialised servers Integrity of shared resources guaranteed Single points of failures Can be extended over the Internet Require high speed access to accommodate large number of requests.

11 Providing Global Services Clients and servers installed over local area networks (LANs) –A LAN is a cluster of computers within a confined space, e.g., an office building, a department etc. LANs within a particular geographical area can be interconnected via metropolitan area networks (MANs). –E.g., city-wide networks A backbone network owned by a tele- communications company can be used to inter- connect LANs and MANs –Referred to as wide area networks (WANs).

12 Providing Global Services (Contd.)

13 Addressing Machines Each computer connected to the network has to be identified uniquely on that network. –Computers connected to networks that form part of the Internet must have globally unique identification. Computers are identified in two ways, –Using machine understandable numeric addresses. –Using human understandable names. Humans address computers using their names. Before communications takes place, computer names are to be translated into their numeric addresses.

14 IP Addresses – Numeric Address for the Internet Two types of IP addresses –IPv4 addresses: 32 bit numeric integers –IPv6 addresses: 128 bit numeric integers IPv4 addresses represented as 4 dotted decimal integer ranging from 0 to 255. –E.g., Each IP address is divided into network address and the host address. –E.g., is the network address and 234 is a host residing on that network. Network addresses are used to locate the networks where the destination hosts reside.

15 Internet Zones and Domains Internet host names are decoded from right to left. E.g., –edu is the zone name and is used to categorise the host. –stanford is the name of the host. –Traditionally 3 letter zone names have been specified for US, e.g., edu, com, mil, net, org. –For other countries two letter zones have been specified to identify geographical locations E.g., ae, uk, pk, fr, etc.,

16 Information Transfer ClientServer Communications Subsystem Communications Subsystem Transmission Control Protocol Transmission Control Protocol Reliable Delivery Internet Protocol Internet Protocol Addressing and Relay Network Interface Network Interface Physical Communication

17 Information Transfer (Contd.) Application components (i.e., clients and servers) communicate virtually. Physically –Clients pass requests to their communication subsystems. –Communications subsystems communicate client requests to the communications subsystems of the server. –Communications subsystem of the server passes the request to the server subsystem. –Replies from the server follow the reverse path.

18 Information Transfer (Contd.) Communication subsystem of the Internet Protocol suite –Transmission Control Protocol (TCP) Provides reliable message delivery. –Internet Protocol (IP) Provides addressing of hosts and best effort relay of packets to the destination. –Network Interface Provides physical communication over the Internet. Messages of arbitrary lengths are segmented into packets, size and structure of which are pre-specified for efficient communication.

19 Designing a Network Essential Considerations –Location, physical layout and installation –Capacity requirements –Scalability requirements –Cost –Security Architectural Design –Hardware requirements –Software requirements –Disaster recovery and fault tolerance –Corporate culture and organisational factors

20 Designing a Network Essential Considerations –Location, physical layout and installation –Capacity requirements –Scalability requirements –Cost –Security Architectural Design –Hardware requirements –Software requirements –Disaster recovery and fault tolerance –Corporate culture and organisational factors DOCUMENT IT ALL