Electronic mail protocols

Two types of protocols are used for the transmission of electronic mail. They are SMTP and MIME. SMTP supports only text messages while MIME supports both text message transmission and multimedia information transmission. SNMP is simple network management protocol which is designed to operate in both the TCP/IP and OSI environments. Simple mail transfer protocol (SMTP) which is defined in RFC 821 is the standard protocol for the transfer of mail between hosts in the TCP/IP environment. Here user creates mail which is comprised of a header that includes recipient’s e-mail address and other information and a body containing the message to be sent. These messages act as input to SMTP sender program. This program is usually an always-present server program on the host. Multipurpose internet mail extensions (MIME) which is an extension to the RFC 822 framework support multimedia information transfer. In MIME, five new message header fields are defined. It also defines a number of content formats and transfer encodings. The five header fields defined in MIME are MIME version, content type, content-transfer encoding, content-ID and content-description. Different MIME content type formats are test type, multipart type, message type, image type, video type, audio type and application type. MIME transfer encodings provides reliable delivery across the largest range of environments. The different MIME transfer encodings are 7-bit, 8-bit, binary, quoted-printable, base 64 (radix-64) and x-token.

Computer networks

Computer networks are now common in educational institutions, offices and even in homes. Companies which have large number of computers prefer a network between these computers to access data from one another. By the effective resource sharing, management can reduce the manpower as well as time. This also reduces the peripherals such as printer. Thus in an office a high volume networked printer can perform the work of many individual printers. This reduces cost as well as maintenance complexity. Servers are used in big offices which can store enormous amount of data. Thus client-server model is used for large network-huge data systems. World Wide Web uses this model. Electronic mail or e-mail is used for communication. Videoconferencing is a latest tool by which employees at different locations can interact with each other just like in a meeting. For doing business including buy and sell, electronic commerce is used. Internet is a network now used by individuals sitting at home. Mobile phones and laptops opened the door for accessing internet while travelling too.

History of LASER

LASER is the short form of light amplification by stimulated emission of radiation. LASER is a highly coherent, highly monochromatic, high intensity unidirectional source of light. Ruby laser was the first fabricated laser. Maiman operated it for the first time. Later Sorokin and Stevenson fabricated Uranium-calcium fluoride laser. In 1961, Neodymium: glass laser was fabricated by Snitzer and Neodymium: CaWO4 laser by Johnson. After 4 years, Johnson and team succeeded in the fabrication of Neodymium:YAG laser and Holmium: YAG laser. The working of Holmium laser is based on the cascade energy transfer phenomena. This enhances lasing efficiency. Later GaAs lasers were fabricated which are quite economical, efficient, compact and portable. Now many types of laser exist in the market that cover a wide range of wavelength from ultraviolet to infrared and with wide variety of output power. The main components of a laser system are active medium, pumping unit, cavity resonator and a cooling system.