ADSL is short for Asymmetric Digital Subscriber Line. It is a networking technology that, like the older dial up modem technology that proceeded it, works over standard telephone lines. Unlike modems, it is completely digital and offers broadband class performance. It also doesn't require you to dial a number to connect to a remote computer and is an "always on" system. Additionally, it still allows the telephone line to be used for voice calls even when the ADSL connection is in use.
The service is asymmetric, meaning that the rate you can send information is different from the rate at which you can receive it. In almost all cases you can receive at a faster rate than you can send because domestic internet use tends to involve far more downloading than uploading.
A measure of performance for a network connection. It can also be referred to as bit rate, data rate, or baud rate, and is measured in bits per second, kilobits (thousands of bits) per second or megabits (millions of bits) per second.
Ethernet is the standard computer networking technology, used today in nearly all forms of computer networking. It comes in two main forms, wired Ethernet using cables similar to telephone cable to connect computers and and network devices, and wireless Ethernet which uses radio signals to transmit data over short ranges. Ethernet has been around for a long time and has evolved over the years, but most versions of wired ethernet use the same style of connector and are broadly compatible (though all devices on a particular section of a network can only communicate at the speed of the slowest node on the network). Very old versions of Ethernet use a different cable and connector and are not compatible with current versions without adaptors.
A firewall is a hardware device or a piece of software that monitors and limits access between a computer and the network it is attached to. Software firewalls are normally used to protect a personal PC from malicious access attempts, while a hardware firewall can also be used to limit the attached computer's ability to access internet services. This should not be confused with web filtering software, which is intended to limit a computer's ability to access individual or classes of sites.
Firewalls are considered a vital line of defence for computers connected to the internet, and no computer should be put online without a firewall to protect it. Many routers also incorporate a firewall.
Hz, (Khz, MHz, GHz)
Hz is short for Hertz, a measure of cycles per second. Khz, MHz, and GHz are short for KiloHertz, MegaHertz and GigaHertz respectively. These terms are used to express the frequency of an electronic or radio signal, for example wireless networking systems work in a 2.4 GHz radio frequency range.
How a computer interconnects with the network it is attached to. The interfaces typically in use today are wired over ethernet cabling, or wireless using one of the 802.11 wireless networking standards.
IrDA (Infrared Data Association) is a wireless networking standard based on infra red light, similar to television remote controls. It is a short range system that requires a direct line of sight between the communicating devices. It is popular on mobile phones, PDAs and other portable equipment.
ISDN is short for Intergrated Services Digital Network. It was a precursor to ADSL. Like ADSL it provided a way of using standard telephone lines to transmit digital data, provided an always-on capability and allowed voice and data communication at the same time. It was, however, considerably slower and more expensive to install and run than ADSL. ISDN is considered a legacy standard today and has mostly been supersceded by ADSL and Cable internet access.
LAN stands for Local Area Network. While the term "Local Area" is not well defined, it tends to describe a network that covers a single room or a single building. LANs are built using Ethernet (either using wired or wireless interfaces) and allow several computers to exchange email with other machines on the LAN and share files and resources such as laser printers or internet access. There is some overlap between the concepts of LANs and Intranet, though an Intranet can cover a much wider area and tends to be confined to an organization rather than a physical location.
The connecting of two or more computers together in order to exchange data and share resources. A network can range from two computers connected by a cable all the way up to the global internet.
A data transmission method where several bits are transmitted simultaneously along several conductors running in parallel to each other. The video (VGA or DVI) connector on your computer is a good example of a parallel transmission system.
Point to Point Tunnelling Protocol (PPTP) is a protocol that allows corporations to extend their own corporate networks through private secure "tunnels" over the public internet. It is therefore a protocol for enabling the establishment of Virtual Private Networks.
A routing protocol is a protocol that specifies how routers communicate with each other to disseminate information that allows them to select routes between any two nodes on a computer network (while the choice of the route is done by routing algorithms). Typically, each router has a priori knowledge only of its directly attached networks. A routing protocol shares this information successively, first among immediate neighbours and then throughout the entire network. This way routers can gain knowledge of the network topology at large. This process happens entirely automatically, and allows internet traffic to route itself around damaged or degraded parts of the internet.
A data transmission method where data is transmitted as a stream of bits, one bit at a time along a single conductor or other transmission media. This has advantages over parallel transmission as the single data channel is cheaper than the multiple data channels of parallel systems, and several synchronization problems that can occur in parallel transmission systems are avoided in serial. USB and wired ethernet are examples of serial transmission systems.
Tunnelling is the process that allows for the sending of network traffic that needs to be secure over an untrusted network, such as the public internet. The tunnel provides a secure encrypted connection between two computers in order to allow unencrypted traffic of a different type to be transmitted safely across the connection. For example, the Windows File and Printer Sharing protocol does not support encryption and is therefore insecure, but if you use a tunnel then you can safely use this service without fear of your network traffic being intercepted. Tunnelling allows for Virtual Private Networks to be deployed over public networks.
Virtual Private Network
A Virtual Private Network (VPN) is a private network between computers where some or all of the nodes in the network are connected using an open public network, such as the public internet. However, all communication between these computers remains private because it runs over a secure encrypted tunnel, meaning that traffic on the network cannot be intercepted by other machines on the network that are not part of the VPN. While the physical network that connects the machines is public, the virtual network that exists between them is private because the traffic is unreadable to any computer that is not part of the VPN.