Table of Contents

V

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.

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

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

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.

ITU-T standard describing a synchronous, physical layer protocol used for communications between a network access device and a packet network. V.35 is most commonly used in the United States and in Europe, and is recommended for speeds up to 48 Kbps.

ITU-T standard protocol for error correction using LAPM. See also LAPM.

volts alternating current.

voice activity detection. When enabled on voice port or a dial peer, silence is not transmitted over the network, only audible speech. When VAD is enabled, the sound quality is slightly degraded, but the connection monopolizes much less bandwidth.

See VBR.

See VLSM.

variable bit rate. QoS class defined by the ATM Forum for ATM networks. VBR is subdivided into a real time (RT) class and non-real time (NRT) class. VBR (RT) is used for connections in which there is a fixed timing relationship between samples. VBR (NRT) is used for connections in which there is no fixed timing relationship between samples, but that still need a guaranteed QoS. Compare with ABR, CBR, and UBR.

See virtual circuit.

virtual channel connection. Logical circuit, made up of VCLs, that carries data between two end points in an ATM network. Sometimes called a virtual circuit connection. See also VCD, VCL, and VPI.

virtual channel identifier. 16-bit field in the header of an ATM cell. The VCI, together with the VPI, is used to identify the next destination of a cell as it passes through a series of ATM switches on its way to its destination. ATM switches use the VPI/VCI fields to identify the next network VCL that a cell needs to transit on its way to its final destination. The function of the VCI is similar to that of the DLCI in Frame Relay. Compare with DLCI. See also VCL and VPI.

virtual channel link. Connection between two ATM devices. A VCC is made up of one or more VCLs. See also VCC.

virtual circuit number. 12-bit field in an X.25 PLP header that identifies an X.25 virtual circuit. Allows DCE to determine how to route a packet through the X.25 network. See also LCI and LCN.

volts direct current.

very-high-data-rate digital subscriber line. One of four DSL technologies. VDSL delivers 13 to 52 Mbps downstream and 1.5 to 2.3 Mbps upstream over a single twisted copper pair. The operating range of VDSL is limited to 1,000 to 4,500 feet (304.8 to 1,372 meters). Compare with ADSL, HDSL, and SDSL.

Data segment of an SNA message. A vector consists of a length field, a key that describes the vector type, and vector-specific data.

very easy rodent oriented netwide index to computer archives. Gopher utility that effectively searches Gopher servers based on a user's list of keywords.

See VIP in the "Cisco Systems Terms and Acronyms" section.

variance factor. One of three link attributes exchanged using PTSPs to determine the available resources of an ATM network. VF is a relative measure of CRM normalized by the variance of the aggregate cell rate on the link.

See VIP (Versatile Interface Processor) in the "Cisco Systems Terms and Acronyms" section.

See network address.

See virtual circuit.

See VCC.

See VCD.

See VCL.

Logical circuit created to ensure reliable communication between two network devices. A virtual circuit is defined by a VPI/VCI pair, and can be either permanent (PVC) or switched (SVC). Virtual circuits are used in Frame Relay and X.25. In ATM, a virtual circuit is called a virtual channel. Sometimes abbreviated VC. See also PVC, SVC, VCD, virtual route, and VPI.

See VCC.

See VCN.

In ATM, a connection between end users that has a defined route and endpoints. See also PVC and SVC.

See VINES.

See VIP in the "Cisco Systems Terms and Acronyms" section.

Process of implementing a network based on virtual network segments. Devices are connected to virtual segments independent of their physical location and their physical connection to the network.

See VLAN.

See VLI.

See Virtual Networking Services in the "Cisco Systems Terms and Acronyms" section.

Logical grouping of virtual circuits that connect two sites. See also virtual circuit.

See VPC.

See VPI.

See VPI/VCI.

See VPL.

Entity in an SRB network that logically connects two or more physical rings together either locally or remotely. The concept of virtual rings can be expanded across router boundaries.

In SNA, a logical connection between subarea nodes that is physically realized as a particular explicit route. SNA terminology for virtual circuit. See also virtual circuit.

Logical grouping of devices that share a common Layer 3 subnet.

See VTAM.

See VTP.

virtual LAN internetwork. Internetwork composed of VLANs. See also VLAN.

See Virtual Networking Services in the "Cisco Systems Terms and Acronyms" section.

Voice Over ATM. Voice over ATM enables a router to carry voice traffic (for example, telephone calls and faxes) over an ATM network. When sending voice traffic over ATM, the voice traffic is encapsulated using a special AAL5 encapsulation for multiplexed voice.

Dial peer connected via an ATM network. VoATM peers point to specific VoATM devices.

Voice Over Frame Relay. Voice over Frame Relay enables a router to carry voice traffic (for example, telephone calls and faxes) over a Frame Relay network. When sending voice traffic over Frame Relay, the voice traffic is segmented and encapsulated for transit across the Frame Relay network using FRF.12 encapsulation.

Dial peer connected via a Frame Relay network. VoFR peers point to specific VoFR devices.

Voice Over HDLC. Voice over HDLC enables a router to carry live voice traffic (for example, telephone calls and faxes) back-to-back to a second router over a serial line.

Dial peer connected via an HDLC network. VoHDLC peers point to specific VoHDLC devices.

Voice over IP. The ability to carry normal telephony-style voice over an IP-based internet with POTS-like functionality, reliability, and voice quality

Voice over IP enables a router to carry voice traffic (for example, telephone calls and faxes) over an IP network. In Voice over IP, the DSP segments the voice signal into frames, which are then coupled in groups of two and stored in voice packets. These voice packets are transported using IP in compliance with ITU-T specification H.323.

virtual path. One of two types of ATM circuits identified by a VPI. A virtual path is a bundle of virtual channels, all of which are switched transparently across an ATM network based on a common VPI. See also VPI.

virtual path connection. Grouping of VCCs that share one or more contiguous VPL. See also VCC and VPL.

virtual private dial-up network. See also VPN.

virtual path identifier. 8-bit field in the header of an ATM cell. The VPI, together with the VCI, is used to identify the next destination of a cell as it passes through a series of ATM switches on its way to its destination. ATM switches use the VPI/VCI fields to identify the next VCL that a cell needs to transit on its way to its final destination. The function of the VPI is similar to that of the DLCI in Frame Relay. Compare with DLCI. See also VCD and VCL.

See VCD and VPI.

See VSC in the Cisco Systems Terms and Acronyms section.

Virtual Switch Interface

virtual source/virtual destination.

Virtual Tributary level n. SONET format for mapping a lower-rate signal into a SONET payload. For example, VT-1.5 is used to transport a DS-1 signal. See also DS-1 and SONET.

virtual telecommunications access method. Set of programs that control communication between LUs. VTAM controls data transmission between channel-attached devices and performs routing functions. See also LU.

Posted: Tue Sep 21 15:25:00 PDT 1999
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