ucti_spacc_06_client server model socket interface

8/13/2019 UCTI_SPACC_06_Client Server Model Socket Interface

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Client-Server Model: Socket Interface

Prepared by: KL First Prepared on: 9-09-07 Last Modified on:Quality checked by: xxx

Copyright 2007 Asia Pacific Institute of Information Technology

Level-2

System Programming and Computer ControlCT047-3-2-SPCC


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CT014-1 Hardware, Systems Software and Networks

Topic & Structure of the lesson

Client-Server Model

Socket Interface


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Key Terms you must be able touse

Active close Active open Application program Application programming

interface (API) Client Client-server model Concurrent client

Concurrent server Connectionless iterative server Connection-oriented concurrent

server

Datagram socket Iterative client Iterative server Process Raw socket Server Socket Socket interface Stream socket

If you have mastered this topic, you should be able to use the following termscorrectly in your assignments and exams :-


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Client-Server

M odel :

Socket I nter f ace


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Client and Server Programs

Client-server program are written in languages suchas C, C++, Java, Lab View and Perl.

This type of programming is very involved andrequires and advanced knowledge of programmingas well as knowledge of the particular language.


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Client-Server Model

Rela t ionship

Concur rency

Processes


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8/35CT014-1 Hardware, Systems Software and Networks

Client-server model



RelationshipQ. Should an application program provide services only to one

specific application program installed somewhere in an internet, orshould it provide services for any application program that requestthis service?

A. A server providing service for any client, not a particular client.

Q. When should an application program be running all the time or just when there is a need for the service?

A. A client program, which request a service, should run only when it

is needed. The server program, which provides a service, shouldrun all the time because it does not know when its services will beneeded.



RelationshipQ. Should there be only one universal application program that can

provide any type of service a user wants? Or should there be oneapplication program for each type of service?

A. In the internet, services needed frequently and by many users havespecific client-server application programs such Internet Explore,Firefox, Mozilla and so on.We do have separate client-server application programs that allowusers to access files or send email such windows mail, FTP, officeoutlook and so on.

Services that are more customized, we should have one genericapplication program that allows users to access the servicesavailable on a remote computer.



Client-server relationship



Client

A client is a program running on the local machine requesting servicefrom a server.

A client program is started by the user and terminates when theservice is complete.

A client opens the communication channel using the IP address of theremote host and the well-known port address of the specific server

program running on that machine. This is called an active open.

The client sends its request and receives a response. The whole process is finite and eventually comes to an end.

The client closes the communication channel with an active close.



Server

A server is a program running on the remote machine and providingservice to the clients.

When it starts, it opens the door for incoming requests from clients, but it never initiates a service until it is requested to do so. This iscalled a passive open.

A server program is an infinite program.

It waits for incoming requests from clients. When a request arrives, itresponds to the request.



Concurrency

Concurrency in Clients

Clients can be run on a machine either iteratively or

concurrently. Running clients iteratively means running them one by one; one client must start, run and terminate.

Concurrent clients ; that is, two or more clients can run

at the same time.


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Connectionless iterative server

UDP are normally iterative. Server processes one requestat a time.



Connection-oriented concurrent server

TCP are normally concurrent. Server can serve manyclients at the same time.


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Socket Interface

Sockets

Con n ect io n less Iterat ive Server

Con n ect io n -Oriented Server


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Socket Interface The Socket Interface was originally based on UNIX

and defines a set of system calls (Procedures). Communication structure need in socket programming

and it is define in the operating system as a structurewith five fields.

1. Family The protocol group: IPv4, IPv6, UNIXdomain protocolsl

2. Type Stream socket, Packet Socket, or raw socket.

3. Protocol

Set to zero for TCP and UDP4. Local socket address A combination of the local IPaddress and the port address.

5. Remote socket address A combination of remote IP

address and the port address.


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Socket structure


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Socket types


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Socket types The Socket Interface defines three types of sockets: the

stream socket , the packet socket , and the raw socket. A stream socket is designed to be used with a connection-

oriented protocol such as TCP. It is connect one

application program to another across the Internet. A Datagram Socket is designed to be used with a

connectionless protocol such as UDP. It send a messagefrom one application to another across the Internet.

Raw Socket Some protocols such as ICMP or OSPF thatdirectly use the services of IP use neither stream socket nordatagram socket.


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Connectionless Iterative Server

Iterative client-server communication using UDPand datagram sockets.

The server pay no attention to the other packets.

The packets from one client or from many client,are store in a queue, waiting for service. They are processed one by one by in order of arrival.

The server uses one single well-known port; Allthe packets arriving at this port wait in line to beserved.


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S k i f f i i d


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Socket interface for connection-oriented concurrentserver


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Connection-Oriented Concurrent Server Concurrent client-server communication using Iterative TCP and

stream socket. This server serves many client at the same time . It is a stream of bytes that could arrive in several segments , and the

response could occupy several segments. The connection remains open until the entire stream is processed, and

then the connection is terminated . The server must have one buffers for each connection. It use parent and child servers. A parent server use well known port and running infinitely and

accepting connection from clients is called a parent server. The parent server creates a child server and an ephemeral port and letsthe child server handle the client.

It free itself so that it can wait for another connection and server canserve several clients concurrently.

C ti O i t d C t S


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Connection Oriented Concurrent ServerFunction

Clients1. Create a socket Asks

the OS to create a socket.2. Connect asks the OS to

make a connection.3. Repeat

a) Write Client sends

a stream of bytes tobe sent to theserver.

b) Read The clientreceives a stream ofbytes from theserver.

4. Destroy After theclient has finished, itasks the operatingsystem to destroythe socket . Theconnection is also

closed .

Server1. Create a socket Asks the OS to create a socket

2. Bind

Asks the OS to enter information in the socketrelated to the server. This is called binding the serversocket .

3. Listen Asks OS to listen to the client. TCP is aconnection orientated protocol.

4. Repeat

a) Create a child - OS create temporary child processand assigns the duty of serving the client to the child.The parent process it free to listen for new clients.

b) Create a new socket - .A new socket is created to beused by the child process.

c) Repeating Child repeats the following steps.

Read

child reads a stream of bytesProcess Processes the stream of bytesWrite Child writes the results as a stream of bytesto the connection.

d) Destroy socket After the client has been served, thechild process asks the OS to destroy the temporary

socket


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Quick Review Questions

Refer to tutorial question.


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Summary Client-Server Model: Socket Interface

In the client-server model, the client runs a program

to request a service and the server runs a program to provide the service. These two programscommunicate with each other.

One server program can provide services for manyclient programs.

Clients can be run either iteratively (one at a time)or concurrently (many at a time).

Servers can handle clients either iteratively (one at atime) or concurrently (many at a time).


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Summary Client-Server Model: Socket Interface

A connectionless iterative server uses UDP as its transport

layer protocol and can serve one client at a time.

A connection-oriented concurrent server uses TCP as itstransport layer protocol and can serve many clients at the

same time. When the operating system executes a program, an instance

of the program, called a process, is created.

If two application programs, one running on a local systemand the other running on the remote system, need tocommunicate with each other, a network program isrequired.


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Summary Client-Server Model: Socket Interface The socket interface is a set of declarations, definitions, and

procedures for writing client-server programs.

The communication structure needed for socket programming is called a socket.

A stream socket is used with a connection-oriented protocolsuch as TCP.

A datagram socket is used with a connectionless protocolsuch as UDP.

A raw socket is sued by protocols such as ICMP or OSPFthat directly use the services of IP.


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Q & A

Question and Answer Session


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