Modulation
In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted. Modulation of a sine waveform is used to transform a baseband message signal into a passband signal, for example low-frequency audio signal into a radio-frequency signal (RF signal). In radio communications, cable TV systems or the public switched telephone network for instance, electrical signals can only be transferred over a limited passband frequency spectrum, with specific (non-zero) lower and upper cutoff frequencies. Modulating a sine-wave carrier makes it possible to keep the frequency content of the transferred signal as close as possible to the centre frequency (typically the carrier frequency) of the passband.
A device that performs modulation is known as a modulator and a device that performs the inverse operation of modulation is known as a demodulator (sometimes detector or demod). A device that can do both operations is a modem (modulator–demodulator).
Demodulation
Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave. A demodulator is an electronic circuit (or computer program in a software defined radio) that is used to recover the information content from the modulated carrier wave.
These terms are traditionally used in connection with radio receivers, but many other systems use many kinds of demodulators. Another common one is in a modem, which is a contraction of the terms modulator/demodulator.
Bandwidth
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a bit rate measure of available or consumed data communication resources expressed in bits/second or multiples of it (kilobits/s, megabits/s etc.).
Note that in textbooks on wireless communications, modem data transmission, digital communications, electronics, etc., bandwidth refers to analog signal bandwidth measured in hertz—the original meaning of the term. Some computer networking authors prefer less ambiguous terms such as bit rate, channel capacity and throughput rather than bandwidth in bit/s, to avoid this confusion.
TCP/IP
The Internet Protocol Suite is the set of communications protocols used for the Internet and other similar networks. It is commonly also known as TCP/IP named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were the first two networking protocols defined in this standard. Modern IP networking represents a synthesis of several developments that began to evolve in the 1960s and 1970s, namely the Internet and local area networks, which emerged during the 1980s, together with the advent of the World Wide Web in the early 1990s.
The Internet Protocol Suite consists of four abstraction layers. From the lowest to the highest layer, these are the Link Layer, the Internet Layer, the Transport Layer, and the Application Layer.[1][2] The layers define the operational scope or reach of the protocols in each layer, reflected loosely in the layer names. Each layer has functionality that solves a set of problems relevant in its scope.
The Link Layer contains communication technologies for the local network the host is connected to directly, the link. It provides the basic connectivity functions interacting with the networking hardware of the computer and the associated management of interface-to-interface messaging. The Internet Layer provides communication methods between multiple links of a computer and facilitates the interconnection of networks. As such, this layer establishes the Internet. It contains primarily the Internet Protocol, which defines the fundamental addressing namespaces, Internet Protocol Version 4 (IPv4) and Internet Protocol Version 6 (IPv6) used to identify and locate hosts on the network. Direct host-to-host communication tasks are handled in the Transport Layer, which provides a general framework to transmit data between hosts using protocols like the Transmission Control Protocol and the User Datagram Protocol (UDP). Finally, the highest-level Application Layer contains all protocols that are defined each specifically for the functioning of the vast array of data communications services. This layer handles application-based interaction on a process-to-process level between communicating Internet hosts.
Node
Client
A client is an application or system that accesses a remote service on another computer system, known as a server, by way of a network. The term was first applied to devices that were not capable of running their own stand-alone programs, but could interact with remote computers via a network. These dumb terminals were clients of the time-sharing mainframe computer.
The client–server model is still used today. Client and server can run on the same machine and connect via Unix domain sockets. Using Internet sockets a user may connect to a service operating on a possibly remote system through the Internet protocol suite. Servers set up listening sockets, and clients initiate connections that a server may accept. Web browsers are clients that connect to web servers and retrieve web pages for display. Most people use email clients to retrieve their email from their internet service provider's mail storage servers. Online chat uses a variety of clients, which vary depending on the chat protocol being used. Multiplayer online games may run as Game Clients on each local computer.
Increasingly, existing large client applications are being switched to websites, making the browser a sort of universal client. This avoids the hassle of downloading a large piece of software onto any computer you want to use the application on. An example of this is the rise of webmail.
In personal computers and computer workstations, the difference between client and server operating system is often just a matter of marketing - the server version may contain more operating system components, allow more simultaneous logins, and may be more expensive, while the client version may contain more end-user software.
Server
In computing, the term server is used to refer to one of the following:
- a computer program running to serve the needs or requests of other programs (referred to in this context as "clients") which may or may not be running on the same computer.
- a physical computer dedicated to running one or more such services, to serve the needs of programs running on other computers on the same network.
- a software/hardware system (i.e. a software service running on a dedicated computer) such as a database server, file server, mail server, or print server.
In computer networking, a server is a program that operates as a socket listener. The term server is also often generalized to describe a host that is deployed to execute one or more such programs.
A server computer is a computer, or series of computers, that link other computers or electronic devices together. They often provide essential services across a network, either to private users inside a large organization or to public users via the internet. For example, when you enter a query in a search engine, the query is sent from your computer over the internet to the servers that store all the relevant web pages. The results are sent back by the server to your computer.
Many servers have dedicated functionality such as web servers, print servers, and database servers. Enterprise servers are servers that are used in a business context.
Network Operating Systems
Network Administrator
A network administrator is a person responsible for the maintenance of computer hardware and software that comprises a computer network. This normally includes deploying, configuring, maintaining and monitoring active network equipment.
The network administrator (or "network admin") is usually the level of technical/network staff in an organization and will rarely be involved with direct user support.[citation needed] The network administrator will concentrate on the overall integrity of the network, server deployment, security, and ensuring that the network connectivity throughout a company's LAN/WAN infrastructure is on par with technical considerations at the network level of an organization's hierarchy. Network administrators are considered tier 3 support personnel that only work on break/fix issues that could not be resolved at the tier 1 (helpdesk) or tier 2 (desktop/network technician) levels. Depending on the company, the Network Administrator may also design and deploy networks.
The actual role of the Network Administrator will vary from company to company, but will commonly include activities and tasks such as network address assignment, assignment of routing protocols and routing table configuration as well as configuration of authentication and authorization – directory services. It often includes maintenance of network facilities in individual machines, such as drivers and settings of personal computers as well as printers and such. It sometimes also includes maintenance of certain network servers: file servers, VPNgateways, intrusion detection systems, etc.
