Multi-Tech Systems MT4X56USB - Manual (Page 88)

MultiModemUSB User Guide
MT4X56USB 88
Packet Mode: Refers to the switching of chunks of information for different users using statistical multiplexing to send them
over the same transmission facility.
Parity bit: An extra bit attached to each byte of synchronous data used to detect errors in transmission.
Permanent Virtual Circuit (PVC): A connection between two endpoints dedicated to a single user. In ISDN, PVCs are
establised by network administration and are held for as long as the user subscribes to the service.
Physical Unit (PU): The component that manages and monitors the resources (such as attached links and adjacent link
stations) associated with a node, as requested by an SSCP via an SSCP-PU session. An SSCP activates a session with the
physical unit in order to indirectly manage, through the PU, resources of the node such as attached links. This term applies
to type 2.0, type 4, and type 5 nodes only.
Pipe: A logical abstraction representing the association between an endpoint on a device and software on the host. A pipe
has several attributes; for example, a pipe may transfer data as streams (Stream Pipe) or messages (Message Pipe).
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.
Point of Presence (POP): The central office’s end points of the long distance carriers.
Point-to-Point Protocol (PPP): A protocol that lets a PC user access TCP/IP (Internet memeber) using an ISDN terminal
adapter or a high-speed modem over a standard phone line.
Polling: Asking multiple devices, one at a time, if they have any data to transmit.
Port: Point of access to or from a system or circuit. For Universal Serial Bus, the point where a Universal Serial Bus device
is attached.
Primary Rate Interface (PRI): Used on ISDN. In North America, and Japan, PRI is one 64Kbps D channel and 23 B
channels. Elsewhere, it is one D channel and 30 B channels.
Primitive: An abstract representation of interaction across 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.
Private Branch Exchange (PBX): A phone exchange located on the customer’s premises. The PBX provides a circuit
switching facility for phone extension lines within the building, and access to the public phone network. See also
“Exchange”.
PROM (Programmable Read Only Memory - pronounced “prom”): A permanent memory chip that can be programmed
or filled by the customer after by the manufacturer has set initial values. Contrast with ROM.
Protocol: 1. A set of semantic and syntactic rules that determines the behavior of functional units in achieving
communication. 2. In Open Systems Interconnection architecture, a set of semantic and syntactic rules that determine the
behavior of entities in the same layer in performing communication functions. 3. In SNA, the meanings of and the
sequencing rules for requests and responses used for managing the network, transferring data, and synchronizing the
states of network components. 4. Synonymous with line control discipline.
PSTN (Public Switched Telephone Network): A worldwide public voice telephone network that is used as a
telecommunications medium for the transmission of voice, data and other information.
Public Data Network (PDN): A packet-switched network that is available to the public for individual (“subscriber”) use.
Typically, controlled by a government or a national monopoly.
Public Switched Telephone Network (PSTN): The group of circuit-switching voice carriers, which are commonly used as
analog data communications services.
Pulse Code Modulation (PCM): 1. In data communication, variation of a digital signal to represent information; for
example, by means of pulse amplitude modulation (PAM), pulse duration modulation (PDM), or pulse position modulation
(PPM). 2. Transmissions of analog information in digital form through sampling and encoding the samples with a fixed
number of bits.
Pulse dialing: One of two methods of dialing a telephone, usually associated with rotary-dial phones. Compare with “tone
dialing”.
Q
Quantizing: The process of analog-to-digital conversion by assigning a range, from the contiguous analog values, to a
discrete number.
R
Random Access Memory (RAM): A computer’s primary workspace. All data must be stored in RAM (even for a short
while), before software can use the processor to manipulate the data. Before a PC can do anything useful it must move
programs from disk to RAM. When you turn it off, all information in RAM is lost.