Remote Logging, E-mail and File Transfer
Remote logging is a client-server program that allows user to login to a remote computer. After logging on, a user can use the services available on the remote computer and transfer the results back to the local computer.
Terminal Network abbreviated as TELNET is a remote logging application. TELNET is a general-purpose client/server application program which enables the establishment of connection to remote system in such a way that the local terminal appears to be a terminal at the remote system. It is the standard TCP/IP protocol for virtual terminal service as proposed by the International Organization for Standards (ISO).
TELNET uses one TCP connection at port 23. Telnet operates in one of the three modes: default mode, character mode and line mode. It has command line interface.
Electronic Mail (e-mail)
E-mail is one of the most popular and widely used services on the internet. E-mail is the service that allows you to send and receive messages on the internet. It can send and receive file attachments, videos, images etc. There are many popular E-mail service available free of cost like gmail, yahoomail, Hotmail etc.
Architecture of E-mail system
Generally an email system consists of three mail components:
- User Agent: A user agent is a software program that composes, reads, replies to, and forwards messages. There are two types of user agents: command-driven and GUI-based. Command drive user agents are not in use now-a-days. Examples of command-drive agents are mail, pine, elm. Modern user agents are GUI based. Some of the example of GUI based user agents are: Microsoft Outlook, Firefox, Netscape etc. To deliver mail, a mail handling system must use an addressing system with unique addresses. In the Internet, the email address consists of two parts: a local part and a domain name, separated by an @ sign. For example, email@example.com is an email address.
- Message Transfer Agent (MTA): The actual mail transfer is done through message transfer agents. To send mail, a system must have the client MTA, and to receive mail, a system must have a server MTA. The formal protocol that defines the MTA client and server in the Internet is called the Simple Mail Transfer Protocol (SMTP). It pushed the message from client to server.
- Message Access Agent: The Message Access Agent pulls data from server to client. two message access protocols are available: Post Office Protocol, version 3 (POP3) and Internet Mail Access Protocol, version 4 (IMAP4).
Transferring files from one computer to another is one of the most common tasks required from a networking or internetworking environment. The largest volume of data exchange in the Internet today is due to file transfer. We will discuss a very popular involved in file transfer i.e. File Transfer Protocol (FTP).
File Transfer Protocol (FTP)
File Transfer Protocol (FTP) is the standard mechanism provided by TCP/IP for copying a file from one computer/host to another. It establishes two TCP connections between the hosts. One connection is used for data transfer, the other for control information (commands and responses). The well-known port 21 is used for the control connection and the well-known port 20 for the data connection. The control connection remains connected during the entire interactive FTP session. The data connection is opened and then closed for each file transferred. It opens each time commands that involve transferring files are used, and it closes when the file is transferred.