Networking CSI 3125 Preliminaries page 1 Networking A

Networking CSI 3125, Preliminaries, page 1

Networking • A network represents interconnection of computers that is capable of sharing files and information between multiple systems. • The computer which receives service is called client and • The computer which provides service is called server. • The term network programming refers to writing programs that execute across multiple devices (computers), in which the devices are all connected to each other using a network. • There is a unique identification number called IP address (Internet Protocol) allotted to every computer on a network or Internet. • An IP address consists of four dotted decimal numbers between 0 and 255, such as 130. 254. 204. 36. CSI 3125, Preliminaries, page 2

Networking • The computers in a network make use of this IP address in order to communicate with each other. • Since it is not easy to remember an IP address, they are often mapped to meaningful names called domain names or hostnames. • Special servers called Domain Name Servers (DNS) are available on the Internet that translate host names into IP addresses. CSI 3125, Preliminaries, page 3

Networking • When a computer specifies a site address, it first asks the DNS to translate this domain name into a numeric IP address and then sends the request using the IP address. • Need to specify certain set of rules to communicates with another system. • A protocol is a set of rules defining how computers communicate: such as the format of addresses, how data is split into packets, etc. CSI 3125, Preliminaries, page 4

Networking • There are many different protocols defining different aspects of network communication. • For example HTTP is used to transfer HTML documents on the Web and • FTP allows you to transfer binary files over the Internet. • Both protocols have their own set of rules and standards on how data is transferred. CSI 3125, Preliminaries, page 5

Networking • Each computer with an IP address has several thousand logical ports • Each computer on the internet can provide a variety of services and the type of service • Each port is identified by a number from 1 to 65, 535. • and each port can be allocated to a particular service. • For example, the HTTP service, generally runs on port 80: • we say that a web server listens on port 80 for incoming connections. • SMTP or email servers run on port 25. CSI 3125, Preliminaries, page 6

Networking • When data is sent to a web server on a particular machine at a particular IP address, it is also sent to a particular port on that machine. • The receiver checks each packet it sees for the port and sends the data to any programs that are listening to the specified port. • Port numbers from 1 to 1023 are reserved for well-known services such as FTP, HTTP, and email. CSI 3125, Preliminaries, page 7

Socket Communication • The socket is the software abstraction used to represent the "terminals" of a connection between two machines. • Network programming usually involves a server and one or more clients. • The client sends requests for information/services own by the Server. • Once the connection is established between Client and Server, they can start sending / receiving information. • Socket acts as an interface between sever and client • It create a communication channel • A programmer can use that channel to send data between the two machines. CSI 3125, Preliminaries, page 8

Socket Communication • Java treats socket communications as I/O operations; thus programs can read from or write to sockets. • The socket associates the server program with a specific port on the machine where it runs so any client program anywhere in the network with a socket associated with that same port can communicate with the server program. • The server waits and listens to the socket for a client to make a connection request CSI 3125, Preliminaries, page 9

Socket Communication CSI 3125, Preliminaries, page 10

Client Server Comminication • The server accepts the connection request from client which contains the name of the server and port number. • Upon acceptance, the server creates a new socket bound to a different port and this new socket is dedicated for serving the client that had sent request. • The original socket can continue to listen for further connection requests CSI 3125, Preliminaries, page 11

Client Server Comminication CSI 3125, Preliminaries, page 12

The Java Networking Package • The java. net package contains a collection of classes and interfaces that provide functionalities for writing programs • Some of the important classes available in java. net Package are: • Inet. Address • Server. Socket • Datagram. Packet • Datagram. Socket • URL CSI 3125, Preliminaries, page 13