A firewall method in which each packet that attempts to pass through the firewall is examined to determine its contents. The packet is then allowed to pass or it is blocked, as appropriate.
A device or an application that allows data to be copied from the network and analyzed. In legitimate applications, it is a useful network troubleshooting tool.
A hub that has no power and therefore does not regenerate the signals it receives. Compare with active hub.
A SCSI bus terminator that uses a terminating resistor pack that is placed at the end of the bus. This resistor relies on the interface card to provide it with a consistent level of power.
A set of characters that is used with a username to authenticate a user on a network and to provide the user with rights and permissions to files and resources.
A fix for a bug in a software application. Patches can be downloaded from the Internet to correct errors or security problems in software applications.
A cable, normally twisted-pair, that is used to connect two devices together. Strictly speaking, a patch cable is the cable that connects a port on a hub or switch to the patch panel, but today people commonly use the term to refer to any cable connection.
A device in which the cables used in coaxial or twisted-pair networks converge and are connected. The patch panel is usually in a central location.
A software program that allows users to gain control of a computer remotely.
A relatively new high-speed bus designed for Pentium systems.
An industry group that was organized in 1989 to promote standards for credit card–sized devices such as memory cards, modems, and network cards. Almost all laptop computers today have multiple PCMCIA slots. PCMCIA cards are now generally referred to simply as PC cards.
In a Windows NT network, the server that acts as the main repository for the user, group, and security information of the domain.
A network environment that does not have dedicated servers, where communication occurs between similarly capable network nodes that act as both clients and servers.
Authorization provided to users that allows them to access objects on a network. The network administrators generally assign permissions. Permissions is slightly different from but often used with rights.
The MAC address on every NIC. The physical address cannot be changed.
Layer 1 of the OSI model, where all physical connectivity is defined.
The actual physical layout of the network. Common physical topologies include star, bus, and ring. Compare with logical topology.
A TCP/IP protocol stack utility that works with ICMP and uses echo requests and replies to test connectivity to other systems.
The space between the structural ceiling and a drop-down ceiling that is commonly used for heating, ventilation, and air-conditioning systems as well as for running network cables. Network cables placed in this space must have a fire-retardant coating, which gives rise to the term “plenum rated.”
An architecture designed to allow hardware devices to be detected by the operating system and for the driver to be automatically loaded.
The media-access method for transmitting data in which a controlling device is used to contact each node to determine whether it has data to send.
The physical location where a long-distance carrier or a cellular provider interfaces with the network of the local exchange carrier or local telephone company.
A protocol that is part of the TCP/IP protocol suite and is used for retrieving mail stored on a remote server. The most commonly used version of POP is POP3.
In physical networking terms, a socket on a networking device that allows other devices to be connected. In software terms, a port is the entry point into an application, a system, or a protocol stack.
A process by which two ports on a device, such as a switch, are configured to receive the same information. Port mirroring is useful in troubleshooting scenarios.
The current analog public telephone system.
A common dial-up networking protocol that includes provisions for security and protocol negotiation and provides host-to-network and switch-to-switch connections for one or more user sessions. It is the common modem connection used for Internet dial-up.
A protocol that encapsulates private network data in IP packets. These packets are transmitted over synchronous and asynchronous circuits to hide the underlying routing and switching infrastructure of the Internet from both senders and receivers.
Layer 6 of the OSI model, which prepares information to be used by the application layer.
A high-level network interface standard for use with ISDN. PRI is defined as having a rate of 1.544Mbps, and it consists of a single 64Kbps D channel plus 23 T1 B channels for voice or data.
The DNS server that offers zone data from files that are stored locally on the machine.
A network to which access is limited, restricted, or controlled. Most corporate networks are private networks. Compare with public network.
A standard or specification that is created by a single manufacturer, vendor, or other private enterprise.
A set of rules or standards that control data transmission and other interactions between networks, computers, peripheral devices, and operating systems.
In a frame, a 5-byte field that is used to identify to the destination node the protocol that is being used in the data transmission.
Two or more protocols that work together, such as TCP and IP or IPX and SPX. Also known as a protocol stack.
A device, an application, or a service that acts as an intermediary between two hosts on a network, eliminating the ability for direct communication.
A server that acts as a go-between for a workstation and the Internet. A proxy server typically provides an increased level of security, caching, and administrative control.
A term that refers to all the telephone networks and services in the world. The same as POTS, PSTN refers to the world's collection of interconnected public telephone networks that are both commercial and government owned. All of the PSTN is digital, except the connection between local exchanges and customers (which is called the local loop or last mile), which remains analog.
A network, such as the Internet, to which anyone can connect with the most minimal of restrictions. Compare with private network.
A set of ports that are connected to the network ports throughout a building. Connections to networking equipment such as hubs or switches are established at the punchdown block.
A hand tool that enables the connection of twisted-pair wires to wiring equipment such as a patch panel.
A logical path that is established between two locations in a packet-switching network. A PVC is similar to a dedicated line, and is known as a permanent virtual connection in ATM terminology. (Note that private virtual circuits are also called PVCs.)
A circuit that provides a logical connection between locations through a Frame Relay/ATM cloud (for example, a company with three branch offices, where each location physically connects to the Frame Relay provider's network through a series of switches). To end users, the three branch offices appear to be directly connected to each other, and the PVC appears to be an unbroken circuit. (Note that permanent virtual circuits are also called PVCs.)