The transmission medium can be defined as a pathway that can transmit information from a sender to a receiver. Transmission media are located below the physical layer and are controlled by the physical layer. Transmission media are also called communication channels.Transmission media are of two types −Guided Transmission MediumUnguided Transmission MediumThe following chart categorizes transmission media −Guided Transmission MediumGuided transmission media are also called bounded media or wired media. They comprise cables or wires through which data is transmitted. They are called guided since they provide a physical conduit from the sender device to the receiver device. The signal traveling ... Read More

Bandwidth The range of frequencies that are used for transmitting a signal without being substantially attenuated is called the bandwidth. It is calculated as the difference between the highest and the lowest frequencies. It is expressed in Hertz (Hz).For example, if the minimum frequency is 100 Hz and the maximum frequency is 1000 Hz, the bandwidth will be 900 Hz.The bandwidth of a transmission medium is the frequency width of the medium and is dependent upon its physical characteristics like thickness, material, length etc. For example, the bandwidth of a coaxial cable is 750 MHz ( MegaHertz).BasebandBaseband transmissions are those requiring ... Read More

Internet Standards refer to all the documented requirements both in technology as well as methodology pertaining to the Internet. The standardization process has three steps. The documentation laid down in a step is called the maturity level. There were previously three maturity levels but are merged to form only two maturity levels now which are:Proposed Standard: These are the standards that are ready for implementation. However, they can be revised according to circumstances of deployment. Draft Standard: When a Proposed Standard has been meticulously tested by at least two sites for at least 4 months, they are considered as Draft Standard. ... Read More

International Standards are needed so that products and systems developed in different parts of the world are interoperable and compatible with each other. The standards aim to ease out the technical differences and also to ensure product safety.The most prominent organization that lays down international standards is the ISO (International Standards Organization). Two other major organizations for technical standards are NIST (National Institute of Standards and Technology) and IEEE (Institute of Electrical and Electronics Engineers).International Standards Organization (ISO)ISO is an independent, voluntary, non-treaty, non-government standards organization. It issues standards of a vast number of subjects that may be proprietary, industrial ... Read More

The service domains, legal status, and scopes of telecommunication companies worldwide are varied. In order to provide compatibility among different agencies, International Telecommunication Union (ITU) was formed. ITU is a specialized agency of the United Nations Organizations that standardizes information and communication technologies worldwide. ITU membership lays down the who’s who of the telecommunications world.Some of the main functions of the ITU areAllocates global use of radio spectrumAssigns satellite orbits through international cooperationDevelops standards for networking technologiesStrives to improve communications in developing and underdeveloped countries.Protects and supports communications and information exchange.ITU has three main sectorsITU-T: It is the Telecommunications Standardization ... Read More

Network StandardsNetworking standards define the rules for data communications that are needed for interoperability of networking technologies and processes. Standards help in creating and maintaining open markets and allow different vendors to compete on the basis of the quality of their products while being compatible with existing market products.During data communication, a number of standards may be used simultaneously at the different layers. The commonly used standards at each layer are −Application layer − HTTP, HTML, POP, H.323, IMAPTransport layer − TCP, SPXNetwork layer −IP, IPXData link layer − Ethernet IEEE 802.3, X.25, Frame RelayPhysical layer −RS-232C (cable), V.92 (modem)Types ... Read More

Wireless LANs are those Local Area Networks that use high frequency radio waves instead of cables for connecting the devices in LAN. Users connected by WLANs can move around within the area of network coverage. Most WLANs are based upon the standard IEEE 802.11 or WiFi.IEEE 802.11 ArchitectureThe components of an IEEE 802.11 architecture are as follows1) Stations (STA) − Stations comprise all devices and equipments that are connected to the wireless LAN. A station can be of two types:Wireless Access Pointz (WAP) − WAPs or simply access points (AP) are generally wireless routers that form the base stations or ... Read More

Ethernet is a set of technologies and protocols that are used primarily in LANs. However, Ethernet can also be used in MANs and even WANs. It was first standardized in the 1980s as IEEE 802.3 standard. Since then, it has gone through four generations, as shown in the following chartStandard Ethernet is also referred to as Basic Ethernet. It uses 10Base5 coaxial cables for communications. Ethernet provides service up to the data link layer. At the data link layer, Ethernet divides the data stream received from the upper layers and encapsulates it into frames, before passing them on to the ... Read More

ATM and ATM NetworksATM stands for Asynchronous Transfer Mode. It is a switching technique that uses time division multiplexing (TDM) for data communications.ATM networks are connection oriented networks for cell relay that supports voice, video and data communications. It encodes data into small fixed - size cells so that they are suitable for TDM and transmits them over a physical medium.The size of an ATM cell is 53 bytes: 5 byte header and 48 byte payload. There are two different cell formats - user-network interface (UNI) and network-network interface (NNI). The below image represents the Functional Reference Model of the ... Read More

X.25X.25 is a protocol suite defined by ITU-T for packet switched communications over WAN (Wide Area Network). It was originally designed for use in the 1970s and became very popular in 1980s. Presently, it is used for networks for ATMs and credit card verification. It allows multiple logical channels to use the same physical line. It also permits data exchange between terminals with different communication speeds.X.25 has three protocol layers Physical Layer: It lays out the physical, electrical and functional characteristics that interface between the computer terminal and the link to the packet switched node. X.21 physical implementer is commonly used ... Read More