Glossary
OHCI (OpenHCI): Open Host Controller Interface Specification for USB. All transfers on the USB are initiated by the host system’s host controller. The host controller is responsible for controlling traffic on the USB and can be appropriately programmed to transfer data to and from USB devices. This is typically a PCI device that can be programmed to run a given schedule of transfers on the USB and bus master the results into memory for processing by the host software. There are currently two standards for host controllers: OpenHCI (OHCI or Open Host Controller Interface) and UHCI (Universal Host Controller Interface). Both these standards define register level interfaces of the host controller to PCI bus. Bandwidth allocation over the USB is software managed and is done by the programming of the host controller.
off-hook—The condition of a device that has accessed a phone line (with or without using the line). In modem use, this is equivalent to a telephone handset being picked up. Dialing and transmission are allowed, but incoming calls are not answered.
on-demanddialing—A cost-saving feature of ISDN that sets up, transfers, and then closes a call only when the ISDN device detects a data packet addressed to the remote network, but will not perform setup/transfers of just administrative (non-user data) packets.
out-of-bandsignaling—A system that uses a separate communications channel or frequency outside the voice band for signaling. Modern systems use a separate channel, either TDM or virtual. SS7 uses messages for signaling that are carried on signaling links distinct from voice channels. ISDN uses messages for signaling that are carried on the
D-channel distinct from the voice carried on the B-channels. Frame Relay and ATM use messages that are carried on a separate virtual connection reserved for signaling.
on-hook—The condition of a device which has not accessed a phone line. In modem use, this is equivalent to a telephone handset that has not been picked up. In other words, it can receive an incoming call.
P
packet data—Packet-mode calls.
packet mode—The switching of chunks of information for different users using statistical multiplexing to send them over the same transmission facility. ISDN packet mode capabilities are based on the ITU-TSS Recommendation X.25 procedures.
parity bit—An extra bit attached to each byte of synchronous data used to detect errors in transmission.
PBX (private branch exchange)—A telephone exchange located on the customer’s premises. The PBX provides a circuit switching facilit y for tlephone extension lines within the building, and access to the public telephone network. See also exchange.
P-channel(PCHAN)—The ISDN physical channel identification; contrast logical channel or virtual channel.
PDN (public data network)—A packet-switched network that is available to the public for individual (subscriber) use. Typically, con trolled by a government or a national monopoly.
Plug and Play (PnP): A technology for configuring I/O devices to use non-conflicting resources in a host. Resources managed by Plug and Play include I/O address ranges, memory address ranges, IRQs, and DMA channels.
port—A location for input or output data exchange. Computers, muxes, etc. have ports for various purposes.
PPP(Point to Point Protocol)—A protocol that lets a computer user access a TCP/IP address using an ISDN terminal adapter or a hig h- speed modem over a standard telephone line.
PRI (Primary Rate Interface)—One
of two forms of ISDN service. PRI provides 23 64 Kbps B-channels for video, voice or data, and one 64 Kbps D-channel for control information. Usually used to connect high-cpacity CPE, such as PBXs, to the network. Also called 23B+D in the U.S. and 30B+D in Europe.) See also ISDN and BRI.
primitive—An abstract representation of interaction accross the access points indicating that information is being passed between the service user and the service provider. The OSI Reference Model defines four types of primitives: Request, Indication, Response and Confirm.
PSTN (public switched telephone network)—The group of circuit-switching voice carriers, which are commonly used as analog data communications services. A worldwide public voice telephone network that is used as a telecommunications medium for the transmission of voice, data and other information.
pulse dialing—One of two methods of dialing a telephone, usually associated with rotary-dial phones. Compare with tone dialing.
PVC (permanent virtual circuit)—A connection between two endpoints dedicated to a single user. In ISDN, PVCs are established by network administration and are held for as long as the user subscribes to the service.
Q
Q.921—The ITU-T recommendation for user-network interface layer 2 specifications for D-channel signaling. Similar to LAPD. See also ISDN.
Q.931—The ITU-T recommendation for user-network interface layer 3 specifications for D-channel signalling. See also ISDN.
