NETWORKING DAY 8 (Telnet, FTP, Multimedia Applications )

DAY - 8

Application and network management

Telnet - What is Telnet?

TELNET:  TELNET (TELecommunication NETwork) is a network protocol used on the Internet or local area network (LAN) connections. It was developed in 1969 beginning with RFC 15 and standardized as IETF STD 8, one of the first Internet standards.

It is a network protocol used on the Internet or local area networks to provide a bidirectional interactive communications facility. Typically, telnet provides access to a command-line interface on a remote host via a virtual terminal connection which consists of an 8-bit byte oriented data connection over the Transmission Control Protocol (TCP). User data is interspersed in-band with TELNET control information. The user's computer, which initiates the connection, is referred to as the local computer.

The computer being connected to, which accepts the connection, is rderred to as the remote computer. The remote compmer can be physically located in the next room, the next town or in another country.

The network terminal protocol (TELNET) allows a user to log in on any other computer on the network. We can start a remote session by specifying a computer to connect to. From that time until we finish the session, anything we type is sent to the other computer.

The Telnet program runs on the computer and connects your PC to a server on the network. We can then enter commands through the Telnet program and they will be executed as if we were entering them directly on the server console. This enables we to control the server and communicate with other servers on the network. To start a Telnet session, we must log in to a server by entering a valid username and password. Telnet is a common way to remotely control Web servers.

The term telnet also refers to software which implements the client part of the protocol. TELNET clients have been available on most Unix systems for many years and are available virtually for all platforms. Most network equipment and OSs with a TCP/IP stack support some kind of TELNET service server for their remote configuration including ones based on Windows NT. TELNET is a client server protocol, based on a reliable connection oriented transport. Typically this protocol used to establish a connection to TCP port 23, where a getty-equivalent program (telnetd) is listening, although TELNET predates.

Telnet was developed in 1969 to aid in remote connectivity between computers over a network. Telnet can connect to a remote machine that on a network and is port listening. Most common ports to which one can connect to through telnet are:

Port 21 ~ File Transfer Protocol

Port 22 - SSH Remote Login Protocol

Port 23 - Telnet Server

Port 25 - Simple Mail Transfer Protocol (SMTP)

Port 53 - Domain Name Server (DNS)

Port 69 - Trivial File Transfer Protocol (TFTP)

Port 70 - Gopher

Port 80 - Hyper Text Transfer Protocol (HTTP)

Port 110 - Post Office Protocol 3 (POP3)

Telnet can be used to connect to virtually any machine that listens on ports. In other words, you can connect to any machine that has certain ports open. Once connected to a machine, you need to issue UNIX based commands to interact with the remote service. For example, a user don't need to login, check and send mails only through his e-mail service provider's interface but this can be achieved using simple telnet commands.

It is because of this reason that many hackers can send spoofed emails or access information such as which services are running on the remote machine. This is also called banner grabbing or daemon tracking. Black hat hackers can also use telnet to sniff network packets which might contain sensitive information such as usernames and passwords. This is achieved by using telnet and network utilities such as TCP dump and wire shark.

Telnet client and server functionality comes built-in in most operating systems. However, there are several third-party applications like putty client that enable remote connectivity. A user can connect to a remote machine through several access modes such as raw access, SSH access, etc. SSH mode offers encryption and security and hence can prevent eavesdropping by hackers. This is by far the most secure way of connecting to a machine.

However, it is necessary that the remote machine supports SSH login to make use of the encryption and security features. On windows machines, telnet client can simply be started by issuing the telnet command in windows command shell. The following example would help you connect to a remote machine on the HTTP Port 80 and issue a GET command which would fetch a file as your web browser does it behind scenes:

Command Prompt> Telnet

Command Prompt> open (somedomain.com or ip address) 80

At this stage, you would be connected to somedomain.com or ip address on port 80 and the daemon that is running on port 80 (most probably HTTP Server) would be waiting for HTTP requests.

GET/HTTP/1.1host: Issuing the command above would make the HTTP Server return the file requested, in this case it would be the default file at the root location, most applications and embedded devices make use of the telnet technology to connect to remote server machines and provide end user functionality. The most common use of telnet stands to enable remote authentication and access,

Establishing Telnet Connection

To use Telnet, you need to know the address of the host whose resources you want to use.

Your Telnet client contacts the host using its internet address. When you contact the host, the distant computer and your computer negotiate how they will communicate with each other. They decide which terminal emulation will be used. Telnet emulation determines how your keyboard will transmit information to the distant computer and how information will be displayed on your screen.

Type text in a Telnet session accumulates in a buffer on your computer. When a complete line of data is ready for transmission, or when you give a command to transmit data (such as pressing the Enter key), the data is sent across the Internet from your Network Virtual Terminal (NVT) keyboard. Along with the data is the host's IP address, which makes sure that the packet is sent to the proper location.

Your IP address is also sent so that information can be routed back to you. Additionally, specific Telnet commands that the other NVT will use, are sent to decide what to do with the data, or how to respond to the data. E.g. when data is sent from one NVT to another and certain information must be sent back to the originating NVT for a process to proceed, the Telnet Go Ahead (GA) command is sent.

After Telnet host receives data you have sent it, processes the data and returns to your screen and give the results of using the data or running the command on a distant computer.

Connecting to a Remote Host

Follow these steps to connect to a remote host using Telnet

1.         Open Telnet by clicking on Start menu and choose run. Now type Telnet, and press Enter key from the keyboard or by clicking on the OK button.

2.         From the Menu, choose Connect. Remote

3.         Enter the name or IP address of the system that you want to connect to in the Host Name Field.

4.         If required, a port in the Port field.

5.         In the term Type, select the type of terminal that you want Telnet to emulate.

6.         After you are finished with the remote host, you can disconnect from a remote host by choosing Connect, Disconnect.

Telnet Protocol Characteristics

There are the various characteristics of Telnet which are described below:

Telnet is a terminal emulation protocol. When you start installing and configuring native TCP/IP devices, you are going to need some way to connect to the device to issue its commands.

Telnet is versatile. You can establish Telnet sessions over the phone. If there is no phone connection and your device is accessible to the Internet, you can establish a Telnet session over the Internet. In any of these conditions you can establish a Telnet session with a remote host.

FTP – File Transfer Protocol

FTP allows you to transfer files between two computers on the Internet. FTP is a simple network protocol based on Internet Protocol and also a term used when referring to the process of copying files when using FTP technology.

To transfer files with FTP, you use a program often called the client. An FTP client program initiates a connection to a remote computer running FTP server software. After the connection is established, the client can choose to send and/or receive copies of files, singly or in groups. To connect to an FTP server, a client requires a username and password as set by the administrator of the server. Many public FTP archives follow a special convention for that accepts a username of "anonymous."

Simple FTP clients are included with most network operating systems, but most of these clients (such as FTP.EXE on Windows) support a relatively unfriendly command-line interface. Many alternative third-party FTP clients have been developed that support graphic user interfaces (GUIs) and additional convenience features. In any FTP interface, clients identify the FTP server either by its IP address (such as 192.168.0.1) or by its host name (such as ftp.about.com).

FTP supports two modes of data transfer: plain text (ASCII), and binary. You set the mode in the FTP client. A common error when using FTP is attempting to transfer a binary file (such as a program or music file) while in text mode, causing the transferred file to be unusable.

 

DNS - Domain Name System

The DNS translates Internet domain and host names to IP addresses. DNS automatically converts the names we type in our Web browser address bar to the IP addresses of Web servers hosting those sites.

DNS implements a distributed database to store this name and address information for all public hosts on the Internet. DNS assumes IP addresses do not change (are statically assigned rather than dynamically assigned).

The DNS database resides on a hierarchy of special database servers. When clients like Web browsers issue requests involving Internet host names, a piece of software called the DNS resolver (usually built into the network operating system) first contacts a DNS server to determine the server's IP address. If the DNS server does not contain the needed mapping, it will in turn forward the request to a different DNS server at the next higher level in the hierarchy. After potentially several forwarding and delegation messages are sent within the DNS hierarchy, the IP address for the given host eventually arrives at the resolver, that in turn completes the request over Internet Protocol.

DNS additionally includes support for caching requests and for redundancy. Most network operating systems support configuration of primary, secondary, and tertiary DNS servers, each of which can service initial requests from clients. Internet Service Providers (ISPs) maintain their own DNS servers and use DHCP to automatically configure clients, relieving most home users of the burden of DNS configuration.

Multimedia Applications

In everyday life, multimedia is everything you hear or see, e.g. text in

books, sound in music, and graphics in pictures.

In computing multimedia is the presentation of information by a

computer system using text, sound and graphics.

Who uses multimedia?

Multimedia can be used in a variety of ways, and a multimedia presentation can be put together in a variety of different formats.

Education

In education, multimedia can be used as a source of information. Students can search encyclopaedias such as Encarta, which provide facts on a variety of different topics using multimedia presentations. Teachers can use multimedia presentations to make lessons more interesting by using animations to highlight or demonstrate key points. A multimedia presentation can also make it easier for pupils to read text rather than trying to read a teacher’s writing on the board. Programs which show pictures and text whilst children are reading a story can help them learn to read; these too are a form of multimedia

presentation.

Business

Multimedia is used for advertising and selling products on the Internet. Some businesses use multimedia for training where CD-ROMs or on-line tutorials allow staff to learn at their own speed, and at a suitable time to the staff and the company. Another benefit is that this form of training saves the company money, as they do not have to pay the additional expenses of an employee attending a course away

from the workplace.

Leisure

People use the Internet for a wide range of reasons, including shopping and finding out about their hobbies. The Internet has many multimedia elements embedded in web pages and web browsers support a variety of multimedia formats. Many computer games use sound tracks, 3D graphics and video clips.

A multimedia presentation

A basic multimedia system includes input devices, output devices, memory, backing storage, and a variety of software.

Input devices and software

1.     Keyboard and mouse

For text entry, a standard QWERTY keyboard and mouse are needed.

2.     Scanner

A scanner allows the input of drawings, photographs or text directly into the computer’s memory. A Scanner is similar to a photocopier as it shines a light onto the item to be scanned and then reads the light

That is reflected.

3.     Optical Character Recognition Software (OCR)

Optical Character Recognition Software is usually known as OCR software. When you use OCR software with a scanner you can scan text directly into the computer’s memory as a word-processed document. Once scanned into the computer’s word processor text can be edited and saved just like any text you may have typed into the word processor. OCR software has a limited number of characters it recognises, and

Therefore mistakes in scanned text are common.

4.     Microphone

A microphone can be used to allow sound to be entered into a computer’s memory. Most computers have in-built microphones, or have an interface which allows a microphone to be plugged into the computer. The quality of sound generated by a microphone is generally poor so it would not be used for recording music.

5.     Voice Recognition Software

Voice Recognition Software allows the user to enter text by speaking rather than typing. The user speaks into the microphone and the words spoken are converted into text in a word-processing package.

Voice recognition has drawbacks:

•The user must speak slowly and clearly to allow the software to recognise all the words.

•The software has difficulty with strong accents and the user may have to repeat words and phrases before they are recognised.

6.     Graphics tablet

A graphics tablet has a pen or pointer connected to a flat board, which is sensitive to pressure. When pressure is applied to the board using the pen or pointer, the position of the pen or pointer is sent to the computer. A graphics tablet allows the user to draw or trace shapes which will go directly into the computer. A graphics tablet can allow the user to write text directly into the computer with the correct software.

7.     Handwriting Recognition Software

Handwriting Recognition Software allows the user to write in his or her normal handwriting. The software reads the shape of the writing and converts it into text that goes into the computer’s word-processing program. One drawback of handwriting software is that if you are a poor writer the software many not read the handwriting correctly and errors will occur.

                         

8.     Digital camera

Photographs taken using a digital camera can be easily saved to a computer’s memory. The camera is connected to the computer using a cable, which then allows pictures stored in the camera to be uploaded into the computer’s memory. The amount of memory that a digital camera has will restrict the number of images that can be stored. A camera with 4mb of memory will be able to store between 30 to 100 JPEG images depending on the level of resolution used for the images.  Resolution is the amount of detail in an image. If high-quality images are required they will need to be saved as a high-resolution image. The higher the resolution the more memory is required. Therefore, if you take pictures with a high resolution you will not be able to store as many pictures in your camera

9.     Digital Camera Software

Most digital cameras come with photo-enhancing software, which will allow you to alter the content as well as the brightness, contrast and colours of the photographs.

10.     Video camera

A digital video camera is used for taking movies and works in a similar way to a still video camera but the pictures are stored on a tape. A digital video camera can be connected to a computer system using a cable normally supplied with the camera. If the computer has the correct software, videos can be transferred onto the computer. Once the video is in the computer’s memory the videos can be edited.

Movies require a great deal of memory, so to store videos would require a large backing storage.