Network is a group of computers and other devices connected in a manner that promotes communication between them.
Networked comuters are most commonly connected by wire of some sort (often wire or twisted pair cable or similar phone lines) ; however machines on network can be linked by any virtual medium.
Protocol is the set of rules or regulation that must be followed in order to communicate. It is one of the most fundamental concept of the network communication.There are many levels of protocols : low level and high level protocol.
A low level protocol defines detail like the rate at which the bits are transmitted or voltage level required to interpret the signal as 0 or 1.
A high level protocol defines the format of data as wekk as sequence and syntax of messages.
Ex of protocol : TCP/IP, HTTP, etc.
HTTP (Hyper Text Transfer Protocol)
The HTTP protocol Defines the format of which the request that are recognized by the server and how the server should respond to the requests.
Ex : In some case browser requested a file called INDRX.HTML and the server returned the contents of file as well as some additional information to help the browser to construct the page..
TCP/IP( Transmission Control Protocol / Internet Protocol)
TCP/IP is a collection or suite of protocols used to communicate across network.
The TCP/IP is broken down into 4 layers as shown in diagram:
Network Interface Layer
The Network Interface Layer handles the lowest level details of communicating across the netwoks . The network interface layer insulates all layers above it for the complexities of interfacing with various network hardware and transmission medium .
The Internet Layer is responsible for transmitting packets arround the network. This layer uses IP(Internet pootocol).The job of this layer is to build a packet that conforms the standards of IP protocol .An IP packet is also called a datagram, contains a great deal of information.The information includes the length of the header, the total length of the packet, the type of service , source address , destination address and much more.
The transport layer manages the manner in which data flows between hosts.Though the Internet Layer does an excellent job routing network packets, it does not mechanism to ensure their arrival.If gureented arrival is desired, that functionality must be provided in the transport layer.
The application layer is responsible for providing services particular to an application.HTTP is an example of an application level protocol . HTTp defines how a browser (web client) communicates with aweb server .
Other example is FTP for file transfer
Each computer connected to the internet is identified by unique numeric addresses. The IP protocol requires that this address consist of 4 bytes. Each byte range from 0-255
To ensure the uniqueness all internet addresses are assigned by single orgnization, the Internet Network Information Center (the Internet NIC). IP address are difficuilt to remember so it has been aliased as host name.
Ex: By using IP address 188.8.131.52 means hostname.
Host machines are uniquely identified by IP addresses but the applications running on them are identified by port numbers.
A port is a logical channel to an application running on host.
Ex : web server typically listen for connections on port 80. This port has been reserved for HTTP.
A socket insulates the programmer from the complexities of the network programming by making network communication appear identical to reading or writing to file or any other standard stream. A socket connection is established between any available port in the client and specied port and IP address of the server
Domain Name Service
Domain Name Service is the distributed database containing all registered hostnames on the internet and their IP addresses.
Computer does not understand host name ,it only understand numeric IP address. Thus everytime Internet address is requested using hostname, the computer must look for the IP address that correspond it. Naming resolution is the process of mapping host mane to its corresponding IP address
A firewall is a piece of network hardware that serves as secure gateway between an internal network and the internet. It protects the internal network from unauthorised activity. The firewall examines each packet passes through it and verifies that the packet does not violate any eatablished secuity policies
Protocol tunneling is the process of encapsulating one protocol within another protocol that operates on same layer. Tunneling is commonly used to circumvent firewall restrictions .
Proxy Server is a host that makes Internet requests on behalf of other machines on the network. Proxy servers are often used to cache frequently requested file or to monitor Internet use within the corporation.