X terminal
Terminal that allows a user simultaneous access to several different applications and resources in a multivendor environment through implementation of X Windows. See also X Window System

X Window System
Distributed, network-transparent, device-independent, multitasking windowing and graphics system originally developed by MIT for communication between X terminals and UNIX workstations. See also X terminal.

X.121
ITU-T standard describing an addressing scheme used in X.25 networks. X.121 addresses are sometimes called IDNs.

X.21
ITU-T standard for serial communications over synchronous digital lines. The X.21 protocol is used primarily in Europe and Japan. [Read more…]

WAN
wide-area network. Data communications network that serves users across a broad geographic area and often uses transmission devices provided by common carriers. Frame Relay, SMDS, and X.25 are examples ofWANs. Compare with LAN and MAN.

WDM
wavelength division multiplexing. Multiple optical wavelengths can share the same transmission fiber. The spectrum occupied by each channel must be adequately separated from the others.

Web
World Wide Web (also called WWW). A client/server system based on HTML and HTTP. [Read more…]

V.24
ITU-T standard for a physical layer interface between DTE and DCE. V.24 is essentially the same as the EIA/TIA-232 standard. See also EIA/TIA-232.

V.25bis
ITU-T specification describing procedures for call setup and tear down over the DTE-DCE interface in a PSDN.

V.32
ITU-T standard serial line protocol for bidirectional data transmissions at speeds of 4.8 or 9.6 kbps. See also V.32bis.

V.32bis
ITU-T standard that extends V.32 to speeds up to 14.4 kbps. See also V.32.

V.34
ITU-T standard that specifies a serial line protocol. V.34 offers improvements to the V.32 standard, including higher transmission rates (28.8 kbps) and enhanced data compression. Compare with V.32. [Read more…]

U interface
The interface between the telco and the user, also known as the local digital subscriber line (DSL) loop.

UDP
User Datagram Protocol. Connectionless transport layer protocol in the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams without acknowledgments or guaranteed delivery, requiring that error processing and retransmission be handled by other protocols. UDP is defined in RFC 768.

U-law
Companding technique commonly used in North America. U-law is standardized as a 64-kbps CODEC in ITU-T G.711.

UMTS
Universal Mobile Telephone Service. A 3G mobile wireless telecommunications system whose standards are being developed by the Third Generation Partnership Project (3GPP). [Read more…]

T.120
ITU standard that describes data conferencing. H.323 provides for the capability to establish T.120 data sessions inside an existing H.323 session.

T.30
Describes the overall procedure for establishing and managing communication between two fax machines.

T.38
Defines procedures for real-time Group 3 facsimile communication over IP networks.

T1
Digital WAN carrier facility. T1 transmits DS-1–formatted data at 1.544 Mbps through the telephone-switching network, using AMI or B8ZS coding. Compare with E1. See also AMI, B8ZS, and DS-1. [Read more…]

SAN
storage area networking. An emerging data communications platform that interconnects servers and storage at Gigabaud speeds. By combining LAN networking models with the core building blocks of server performance and mass storage capacity, SAN eliminates the bandwidth bottlenecks and scalability limitations imposed by previous SCSI bus-based architectures.

SAP
1. service access point. Field defined by the IEEE 802.2 specification that is part of an address specification. Thus, the destination plus the DSAP define the recipient of a packet. The same applies to the SSAP. See also DSAP and SSAP.
2. Service Advertising Protocol. IPX protocol that provides a means of informing network clients, via routers and servers, of available network resources and services. See also IPX.

scan
Scan is a nonintrusive analysis technique that identifies the open ports found on each live network device and collects the associated port banners found as each port is scanned. Each port banner is compared against a table of rules to identify the network device, its operating system, and all potential vulnerabilities. [Read more…]

RA
registration authority. Optional PKI entity (separate from the CAs) that does not sign either digital certificates or CRLs but has responsibility for recording or verifying some or all of the information (particularly the identities of subjects) needed by a CA to issue certificates and CRLs and to perform other certificate management functions.

RADIUS
Remote Authentication Dial-In User Service. Database for authenticating modem and ISDN connections and for tracking connection time.

random early detection
Congestion avoidance algorithm in which a small percentage of packets are dropped when congestion is detected and before the queue in question overflows completely. [Read more…]

Q.2931
ITU-T specification, based on Q.931, for establishing, maintaining, and clearing network connections at the B-ISDN user-network interface. The UNI 3.1 specification is based on Q.2931. See also Q.931 and UNI.

Q.920/Q.921
ITU-T specifications for the ISDN UNI data link layer. See also UNI

Q.922A
ITU-T specification for Frame Relay encapsulation. [Read more…]

p2mp
point-to-multipoint. Communication between a series of receivers and transmitters to a central location. Cisco p2mp typically is set up in three segments to enable frequency re-use. Cisco offers MMDS, U-NII, and LMDS systems in p2mp.

p2p
point-to-point. Communication between one receiver and one location. P2p has a higher bandwidth than p2mp for reasons including that it has less overhead to manage the data paths and there is only one receiver per transmitter. Cisco offers MMDS,
U-NII, and LMDS systems in p2p.

PABX
private automatic branch exchange. Telephone switch for use inside a corporation. PABX is the preferred term in Europe, whereas PBX is used in the United States. [Read more…]

OAKLEY
Key establishment protocol (proposed for IPsec but superseded by IKE) based on the Diffie-Hellman algorithm and designed to be a compatible component of ISAKMP.

OC
optical carrier. Series of physical protocols (OC-1, OC-2, OC-3, and so on), defined for SONET optical signal transmissions. OC signal levels put STS frames onto multimode fiber-optic line at a variety of speeds. The base rate is 51.84 Mbps (OC-1); each signal level thereafter operates at a speed divisible by that number (thus, OC-3 runs at 155.52 Mbps). See also SONET, STS-1, and STS-3c.

ODBC
Open DataBase Connectivity. Standard application programming interface for accessing data in both relational and nonrelational database management systems. Using this application programming interface, database applications can access data stored in database management systems on a variety of computers even if each database management system uses a different data storage format and programming interface. ODBC is based on the call level interface specification of the X/Open SQL Access Group and was developed by Digitial Equipment Corporation, Lotus, Microsoft, and Sybase. [Read more…]