What is identifier? In application layer, what are the types of messages? What a

Question

What is identifier? In application layer, what are the types of messages? What are the needs for transport service? What are Internet transport protocols? Describe them? Give examples of applications that used them? What are application layer protocols? What are HTTP connections? Describe them? Describe in details (6 steps) what happens from client and the server sides when a user enters the following in his/her browser: www.apple.com Using non persistent HTTP protocol? Describe cookies? What is proxy server? What are its benefits? Describe FTP? Describe in details (6 steps) what happens when a user enters the following email from his/her mail client: To: Saqer@bbc.com Salam Omar Describe in details what happens when a client asks for IP of www.ku.edu? Kuwait university has a server with the hostname server1.kuniv.edu.kw with IP number 139.141.55.130. Assign an alias name www.kuniv.edu. Write The DNS database records (two records) for the above information.

Explanation / Answer

5)SOCKET:
Sockets in general allows the communication between two different processes on the same machine or

different machines.It is one endpoint in a communication flow between two programs or processes

running over a network.

Sockets are created and used with a set of programming requests also called as "function calls" in

which sometimes referred as the sockets application programming interface (API). The most common

sockets API is the Berkeley UNIX C interface for sockets.

6)IDENTIFIER:
Identifiers in general are the symbols used to uniquely identify a program element in the code.

They are also used to refer to types, constants, macros and parameters. An identifier name

particularlyn should indicate the synonym and usage of the element that is being referred.

In some other cases,identifiers are referred as the names given to the variables,constants and

functions.

7)An application layer protocol defines how an application processes that is running on different

end systems and pass messages to each other.The messages present in this layer are request messges

and response messages.
8)A transport layer protocol provides for logical communication between application processes

running on different hosts.The transport level provides end-to-end communication between processes

executing on different machines.

9)Transport protocols relies or depends on the service provided by the network layer. On the

Internet, the network layer provides a connectionless service. The network layer identifies each

host by using an IP address and enables hosts to transmit packets that contain up to 64 KBytes of

payload to any destination reachable through the network.

Transmission Control Protocol:
TCP is a connection oriented protocol and offers end-to-end packet delivery and acts as back bone

for connection.It is a reliable and connection oriented protocol.Some of its features are:

Stream Data Transfer

Reliability

Efficient Flow Control

Full-duplex operation

Multiplexing

10)Application layer protocols:
The following are the some of the application layer protocols.

1.SMTP-Simple Mail Transfer Protocol:

a.One of the most popular network service.

b.SMTP transfers messages from senders' mail servers to the recipients' mail servers using TCP

connections.

c.The TCP/IP protocol that supports electronic mail on the Internet is called Simple Mail Transfer

Protocol (SMTP).

2.FTP-File Transfer Protocol:

a.FTP is the standard mechanism provided which is provided by TCP/IP for copying a file from one

host to another.

b.FTP differs form other client-server applications because it establishes 2 connections between

hosts.One connection is used for data transferring and the other is used for the control of

information.

3.HTTP-Hyper Text Transfer Protocol:

a.This is a protocol used mainly to access data on the World Wide Web (www).

b.This protocol transfers data in the form of plain text, hyper text, audio, video and in many other

methods also.

c.HTTP utilizes TCP connections to send client requests and to receive server replies.

4.TELNET-Terminal Network:

TELNET is client-server application that allows a user to log onto remote machine and lets the user

to access any application program on a remote computer.Many of the application protocols are built

using this protocol i.e.,TELNET.

11)As mentioned HTTP is a stateless request-response based communication protocol. It is used to

send and receive data on the the Internet. This protocol uses reliable TCP connections either for

the transfer of data to and from clients which are Web Browsers.

The main connections that are present are:

a.HTTP request
b.HTTP response

a.HTTP request in turn contains:

->HTTP Request Method, URI, and Protocol Version
This should be the first line of an HTTP Request.

->HTTP Request Headers
Used to communicate information about the client environment.

->HTTP Request Body
Contains the actual request being that is being sent to the HTTP Server.

b.HTTP response:

->Protocol/Version, Status Code, and its Description
A status code of 200 means the processing of request was successful and the description in this

case will be 'OK'. Similarly, a status code of '404' means the file requested was not found at the

HTTP Server.

->HTTP response header
Contains useful infomation about the server environment.

->HTTP response body
Contains the actual information that is rendered at the client side.

13)Cookies:
   These are generally small files which are stored on the user's computer.In a different manner,it

records or saves your preferences when using a particular site.

14)Proxy server:
   A proxy server is a computer that offers a service to allow clients to make indirect network

connections to the other network services. A client connects to the proxy server, then requests a

connection, file, or other resource available on a different server.
   Then the proxy provides the required resource either by connecting to the specified server or by

obtaining through its cache.

15)FTP:

FTP means "File Transfer Protocol"

a.FTP is the standard mechanism provided which is provided by TCP/IP for copying a file from one

host to another.

b.FTP differs form other client-server applications because it establishes 2 connections between

hosts.One connection is used for data transferring and the other is used for the control of

information.

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