NI-1 (National ISDN1) ◆ A specification for a standard ISDN phone line. National ISDN 1 is intended to be a set of standards to which every manufacturer's equipment should conform for maximum interoperability. NI-2 and NI-3 are future standards currently under development.

NRZI (Non Return to Zero Inverted) ◆ Encodingtechniqueinwhicha change in state represents 0. Also known as invert-on-zerocoding.

NSAP (Network Services Access Point) ◆ IntheOSIenvironment,it is the SAP between the network and the transport layers. It identifies a Data Terminal Equipment by a unique address.

NT1 (Network Termination 1) ◆ The device that connects to your ISDN hardware and also works as a converter between an ISDN U- interface and an ISDN S/T-Interface. An NT1 converts a line from a 2- wire to a 4-wire connection. Some ISDN adapters have a NT1 already built into them.

NT2 (Network Termination 2) ◆ AnNT2handlesterminationformul- tiple B channels on a PRI line. NT2s are typically found embedded into PBXs or switches on network servers which support Primary Rate Interface (PRI).

OSI (Open Systems Interconnection) Model ◆ The 7-layer protocol model defined by the ISO for data communications.

PABX ◆ Private Automatic Branch Exchange.

PBX (Private Branch Exchange) ◆ PBX is a private telephone switch. It is connected to groups of lines from one or more central offices and to all of the telephones at the location served by the PBX.

PCI (Peripheral Component Interconnect) (bus) ◆ A high-performance multiplexed address and data bus. Supporting 32-bit with optional 64-bit data transfers, the PCI bus is intended to be an interconnect between peripheral controllers, peripheral add-in boards, and pro- cessor/memory systems. The PCI bus operates at up to 66 MHz, providing burst transfer rates up to 264 MBps 32 bits wide, or up to 528 MBps 64 bits wide.

PDU (Protocol Data Unit) ◆ Datainahighly-structuredformatforthe purpose of transmission. Frame, packet, and PDU are equivalent in most contexts.

PHY (Physical Layer) ◆ Layer 1 of the OSI model. Defines and handles the electrical and physical connections between systems. The Physical layer can also encode data in a form that is compatible with the medium (coaxial, twisted pair, fiber, and so on).

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