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INTERNATIONAL TELECOMMUNICATION UNION

CCITT	I.113

THE INTERNATIONAL

TELEGRAPH AND TELEPHONE

CONSULTATIVE COMMITTEE

INTEGRATED SERVICES DIGITAL

NETWORK (ISDN)

GENERAL STRUCTURE AND SERVICE

CAPABILITIES

VOCABULARY OF TERMS FOR

BROADBAND ASPECTS OF ISDN

Recommendation I.113

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Geneva, 1991

Printed in Switzerland

FOREWORD

The CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (ITU). CCITT is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.

The Plenary Assembly of CCITT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendations by the members of CCITT between Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (Melbourne, 1988).

Recommendation I.113 was prepared by Study Group XVIII and was approved under the Resolution No. 2 procedure on the 5th of April 1991.

___________________

CCITT NOTES

concise

conciseness to indicate both a telecommunication Administration and a recognized private operating agency.

2)	A list of abbreviations used in this Recommendation can be found in Annex A.

c ITU 1991

All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.

Preamble to B-ISDN Recommendations

In 1990, CCITT SG XVIII approved a first set of Recommendations on B-ISDN. These are:

I.113 ù Vocabulary of terms for broadband aspects of ISDN

I.121 ù Broadband aspects of ISDN

I.150 ù B-ISDN asynchronous transfer mode functional characteristics

I.211 ù B-ISDN service aspects

I.311 ù B-ISDN general network aspects

I.321 ù B-ISDN Protocol Reference Model and its application

I.327 ù B-ISDN functional architecture

I.361 ù B-ISDN ATM Layer specification

I.362 ù B-ISDN ATM Adaptation Layer (AAL) functional description

I.363 ù B-ISDN ATM Adaptation Layer (AAL) specification

I.413 ù B-ISDN user-network interface

I.432 ù B-ISDN user-network interface ù Physical Layer specification

I.610 ù Operation and maintenance principles of B-ISDN access

These Recommendations address general B-ISDN aspects as well as specific service- and network-oriented issues, the fundamental characteristics of

the asynchronous transfer mode (ATM), a first set of relevant ATM oriented parameters and their application at the user-network interface as well as impact on operation and maintenance of the B-ISDN access. They are an integral part of the well established I-Series Recommendations. The set of Recommendations are intended to serve as a consolidated basis for ongoing work relative to B-ISDN both within CCITT and in other organizations. They may also be used as a first basis towards the development of network elements.

CCITT will continue to further develop and complete these Recommendations in areas where there are unresolved issues and develop additional Recommendations on B-ISDN in the I-Series and other series in the future.

PAGE BLANCHE

Recommendation I.113

Recommendation I.113

VOCABULARY OF TERMS FOR BROADBAND ASPECTS OF ISDN

1	Introduction

This Recommendation consists primarily of those terms and definitions that are considered essential to the understanding and application of the principles of broadband aspects of the integrated services digital network (BISDN). They are not exclusive to B-ISDN and are recommended also for application, in so far as they are relevant, to other types of telecommunication networks.

Included are terms that may already be defined in other CCITT/CCIR Recommendations. However, the definitions given here embrace only the

essential concepts and on that basis it is considered that they are not inconsistent with the more specialized definitions that appear in those Recommendations.

According to the conventions applied in this Recommendation, any term in common usage, but whose use is deprecated, is shown in brackets as in the following example: "broadband [wideband]".

Where a truncated term is widely used in an understood context the complete term is quoted following the colloquial form, for example, "contribution, contribution application".

Some definitions include terms in italics face to indicate that these terms are defined elsewhere in this Recommendation.

Annex A contains an alphabetical list of all the terms contained in this Recommendation.

Annex B contains a list of abbreviations which are used in B-ISDN Recommendations.

2	Vocabulary of terms

This section is divided into two sub-sections, 2.1 Services, and 2.2 Interfaces, channels and transfer modes. Within each sub-section the terms are listed and defined.

2.1	Services

101	broadband [wideband]

F: large bande

S: banda ancha

A service or system requiring transmission channels capable of supporting rates greater than the primary rate.

102	broadcast

F: diffusion

S: difusión

A value of the service attribute "communication configuration", which denotes unidirectional distribution to all users.

Note ù This term should not be confused with the term "broadcasting service" as defined in the ITU Radio Regulations.

103	connectionless service

F: service sans connexion

S: servicio sin conexión

A service which allows the transfer of information among service users without the need for end-to-end call establishment procedures.

Note ù Connectionless services may be used to support both interactive and distribution services.

104	constant bit rate service

F: service à débit constant

S: servicio de velocidad binaria constante

A type of telecommunication service characterized by a service bit rate specified by a constant value.

105	contribution, contribution application

F: contribution

S: contribución; aplicación de contribución

Use of a broadband service or channel for transferring audio or video information to a user for further post-production processing and subsequent distribution.

106	conversational service

F: service conversationnel

S: servicio conversacional

An interactive service which provides for bidirectional communication by means of real-time (no store-and-forward) end-to-end information transfer from user to user.

107	distribution, distribution application

F: distribution; application de distribution

S: distribución; aplicación de distribución

Use of a broadband service or channel for transferring audio, video or other information to a user or a number of users who will not be expected to apply post-production processing to the information.

108	distribution service

F: service de distribution

S: servicio de distribución

Service characterized by the unidirectional flow of information from a given point in the network to other (multiple) locations. Distribution services are subdivided into two classes: distribution services without user individual presentation control and distribution services with user individual presentation control.

109	distribution service with user individual presentation control

F: service distribué avec contrôle de présentation par l'usager

S: servicio de distribución con control de la presentación por el usuario

A distribution service in which the information is provided as a sequence of information entities e.g. frames with cyclical repetition, so that the user has the ability to select individual information entities and can control the start and order of the information.

110	distribution service without user individual presentation control

F: service distribué sans contrôle de présentation par l'usager

S: servicio de distribución sin control de la presentación por el usuario

A distribution service which users can access without having any control over the start and order of the presentation of the distributed information.

111	enhanced-quality television

F: télévision de qualité améliorée

S: televisión de calidad mejorada

Television of quality superior to existing-quality television, but less than the quality of high-definition television.

112	existing-quality television

F: télévision de qualité conventionnelle

S: televisión de calidad convencional

Television as defined in conventional 625-line and 525-line television standards, such as NTSC, PAL and SECAM.

113	interactive service

F: service interactif

S: servicio interactivo

A service which provides the means for bidirectional exchange of information between users or between users and hosts. Interactive services are subdivided into three classes of services: conversational services, messaging services and retrieval services.

114	messaging service

F: service de messagerie

S: servicio de mensajería

An interactive service which offers user-to-user communication between individual users via storage units with store-and-forward, mailbox and/or message handling, (e.g. information editing, processing and conversion) functions.

115	mixed document

F: document mixte

S: documento mixto

A document that may contain text, graphics, data, image and moving picture information as well as voice annotation

116	multimedia service

F: service multimédia

S: servicio multimedio

A service in which the interchanged information consists of more than one type, such as text, graphics, sound, image and video.

117	multipoint

F: multipoint

S: multipunto

A value of the attribute "communication configuration" which denotes that the communication involves more than two network terminations.

118	post-production processing

F: post-production (traitement après production)

S: tratamiento de posproducción

Further processing of contributed audio and video information, to change the form or presentation of the information prior to its final utilization.

119	retrieval service

F: service de consultation

S: servicio de consulta

An interactive service which provides the capability of accessing information stored in data base centres. This information will be sent to the user on demand only. The information can be retrieved on an individual basis, i.e. the time at which an information sequence is to start is under the control of the user.

120	service bit rate

F: débit de service

S: velocidad binaria de servicio

The bit rate which is available to a user for the transfer of user information.

121	sound retrieval service

F: service de consultation de programmes sonores

S: servicio de consulta de programas sonoros

On-demand (user initiated) retrieval of music and other audio information.

122	variable bit rate service

F: service à débit variable

S: servicio de velocidad binaria variable

A type of telecommunication service characterized by a service bit rate specified by statistically expressed parameters which allow the bit rate to vary within defined limits.

123	videomessaging

F: messagerie vidéo

S: videomensajería

A messaging service for the transfer for moving pictures with or without other information.

2.2	Interfaces, channels and transfer modes

201	asynchronous time-division multiplexing

F: multiplexage temporel asynchrone

S: multiplexación asíncrona por división en el tiempo; multiplexación temporal asíncrona

A multiplexing technique in which a transmission capability is organized in undedicated slots filled with cells with respect to each application's instantaneous real need. In this case, the terminal equipment (i.e. the customer application) defines the actual transmitted bit rate, whatever this rate is, possibly variable during the communication. This technique carries a labelled interface structure over a frame or a self-delineating labelled interface.

202	asynchronous transfer mode (ATM)

F: mode de transfert asynchrone (ATM)

S: modo de transferencia asíncrono (MTA)

A transfer mode in which the information is organized into cells; it is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic.

203	block

F: bloc

S: bloque

A unit of information consisting of a header and an information field.

204	block payload

F: capacité utile de bloc

S: cabida til del bloque; contenido til del bloque

The bits in the information field within a block.

205	broadband access

F: accès large bande

S: acceso de banda ancha

An ISDN access able to contain at least one channel capable of supporting a rate greater than the primary rate, or supporting an equivalent information transfer rate.

206	broadband communication channel

F: canal de communication large bande

S: canal de comunicación de banda ancha

A specific portion of the information payload capacity, available to the user for ISDN services. A broadband communication channel exists only during a call, as set-up by a signalling or administrative procedure.

207	cell

F: cellule

S: célula

A block of fixed length. It is identified by a label at the asynchronous transfer mode layer of the B-ISDN protocol reference model.

208	cell delineation

F: cadrage cellule

S: delimitación de la célula

The identification of cell boundaries in a cell stream.

209	circuit transfer mode

F: mode de transfert par circuit

S: modo de transferencia circuito; modo de transferencia por circuitos

A transfer mode in which transmission and switching functions are achieved by permanent allocation of channels/bandwidth between the connections.

210	connection admission control

F: contrôle d'admission des connexions

S: control de admisión de una conexión

The procedure within the control part of network nodes used to decide whether or not a request for a (virtual) connection can be accepted based on the requested usage parameters and already established connections.

211	deterministic; ATM deterministic

F: déterministe; ATM déterministe

S: determinístico; MTA determinístico

A mode of the asynchronous transfer mode in which a constant information transfer capacity expressed in terms of a predetermined limiting value for a given service is provided to the user throughout a call.

212	frame

F: trame

S: trama

A block of variable length identified by a label at layer 2 of the OSI reference model, e.g. an HDLC block.

213	framed interface

F: interface tramée

S: interfaz entramado

An interface where the serial bit stream is segmented into periodic physical frames. Each frame is divided by a fixed partition into an overhead and an information payload portion.

214	general broadcast signalling virtual channel

F: canal virtuel de diffusion générale de la signalisation

S: canal virtual de señalización de difusión general

A virtual channel independent of service profiles and used for broadcast signalling.

215	header, cell header

F: en-tête; en-tête de cellule

S: encabezamiento; encabezamiento de célula

The bits within a cell allocated for functions required to transfer the cell payload within the network.

216	hybrid interface structure

F: structure d'interface hybride

S: estructura híbrida de interfaz

An interface structure which has a mixture of labelled channels and positioned channels.

217	information payload capacity

F: capacité utile d'information

S: cabida til de información

The difference between the interface rate and the interface overhead rate, that is the bit rate of the interface payload.

218	interface overhead

F: résidu de l'interface

S: tara del interfaz

The remaining portion of the bit stream after deducting the information payload. The interface overhead may be essential (e.g. framing for an interface shared by users) or ancillary (e.g. performance monitoring).

219	interface payload

F: capacité utile de l'interface

S: cabida til del interfaz

The portion of the bit stream of a framed interface which can be used for telecommunication services. Any signalling is included in the interface payload.

220	interface rate; interface bit rate

F: débit à l'interface; débit binaire à l'interface

S: velocidad del interfaz; velocidad binaria del interfaz

The gross bit rate at an interface, that is, the sum of the bit rates of the interface payload and the interface overhead. Example: the bit rate at the boundary between the physical layer and the physical medium.

221	invalid cell

F: cellule invalide

S: célula no válida

A cell where the header is declared by the header error control process to contain errors.

222	labelled channel

F: canal étiqueté

S: canal etiquetado

A temporally-ordered collection of all block payloads having a common label value.

223	labelled deterministic channel

F: canal étiqueté déterministe

S: canal etiquetado determinístico

A labelled channel with the property that the aggregated payload capacity of all blocks in each successive interval of specified constant duration is a constant.

224	labelled interface structure

F: structure d'interface étiquetée

S: estructura de interfaz etiquetado

An interface structure in which all services and signalling are provided by labelled channels. A labelled interface structure can be accommodated within a framed interface or a self-delineating labelled interface.

225	labelled multiplexing

F: multiplexage par étiquetage

S: multiplexación por etiquetado

The multiplexing of labelled channels by concatenating the blocks of the different channels.

226	labelled statistical channel

F: canal étiqueté statistique

S: canal etiquetado estadístico

A labelled channel in which the payload of the successive blocks of the channel is random and/or the block durations are random.

227	logical signalling channel

F: canal logique de signalisation

S: canal lógico de señalización

A logical channel for signalling information which is contained within an information channel or a physical signalling channel.

228	meta-signalling

F: méta-signalisation

S: metaseñalización

The procedure for establishing, checking and releasing signalling virtual channels.

229	network node interface (NNI)

F: interface de noeud de réseau (NNI)

S: interfaz de nodo de red (INR)

The interface at a network node which is used to interconnect with another network node.

230	packet

F: paquet

S: paquete

An information block identified by a label at layer 3 of the OSI reference model.

231	packet transfer mode

F: mode de transfert par paquets

S: modo de transferencia paquete; modo de transferencia por paquetes

A transfer mode in which the transmission and switching functions are achieved by packet oriented techniques, so as to dynamically share network transmission and switching resources between a multiplicity of connections.

232	payload module

F: module de capacité utile

S: módulo de cabida til

That portion of the information payload, of an interface, within which one or more channels entirely exist.

233	periodic frame

F: trame périodique

S: trama periódica

A transmission segment which is repeated at intervals of equal duration (e.g. 125 sec), and may be delineated by incorporating fixed periodic patterns into the bit stream.

234	physical frame

F: trame physique

S: trama física

A segment of a serial logical bit stream at an interface, partitioned into successive segments.

235	physical signalling channel

F: canal physique de signalisation

S: canal físico de señalización

A dedicated physical channel (e.g. D-channel) used for signalling information. It may be used to carry other information.

236	positioned channel

F: canal positionné

S: canal ubicado; canal identificado por su posición

A channel that occupies bit positions which form a fixed periodic pattern (e.g. B-, H- and D-channels in ISDN user network interfaces).

237	positioned interface structure

F: structure d'interface positionnée

S: estructura de interfaz de canales ubicados

A structure in which all services and signalling are provided by positioned channels. Such a structure can exist only within a framed interface.

238	selective broadcast signalling virtual channel

F: canal virtuel de diffusion sélective de la signalisation

S: canal virtual de señalización de difusión selectiva

A virtual channel allocated to a service profile and used for broadcast signalling.

239	self-delineating block

F: bloc à auto-cadrage

S: bloque autodelimitado

A block with the property that its endpoints can be identified by examining the block itself. A defined pattern or flag at the beginning of each block might serve to demarcate the block.

240	self-delineating labelled interface

F: interface étiquetée à auto-cadrage

S: interfaz etiquetado autodelimitado

An interface whose entire serial bit stream consists of a self-delineating labelled multiplexing.

241	signalling virtual channel

F: canal virtuel de signalisation

S: canal virtual de señalización

A virtual channel for transporting signalling information.

242	statistical; ATM statistical

F: statistique; ATM statistique

S: estadístico; MTA estadístico

A mode of the asynchronous transfer mode in which the information transfer capacity specified for a given service provided to the user throughout a call is expressed in terms of values of parameters such as mean, peak and standard deviation.

243	synchronous time division multiplexing

F: multiplexage temporel synchrone

S: multiplexación síncrona por división en el tiempo; multiplicación temporal síncrona

A multiplexing technique supporting the synchronous transfer mode (STM).

244	synchronous transfer mode (STM)

F: mode de transfert synchrone (STM)

S: modo de transferencia síncrono (MTS)

A transfer mode which offers periodically to each connection a fixed-length word.

245	throughput

F: charge utile

S: caudal de tráfico; caudal

The number of data bits contained in a block (e.g. between the address field and the CRC field of the LAPD-based frames) successfully transferred in one direction across a section per unit time.

246	transfer mode

F: mode de transfert

S: modo de transferencia

Aspects covering transmission, multiplexing and switching in a telecommunications network.

247	transit delay

F: délai de transit

S: retardo de tránsito

The time difference between the instant at which the first bit of the address field of a frame crosses one designated boundary, and the instant

at which the last bit of the closing flag of the frame crosses a second designated boundary.

248	usage parameter control

F: contrôle des paramètres d'utilisation

S: control de los parámetros de utilización

The taking of appropriate action if usage monitoring establishes that the negotiated values of the information transfer parameters of a virtual channel or a virtual path are exceeded.

249	valid cell

F: cellule valide

S: célula válida

A cell where the header is declared by the header error control process to be free of errors.

250	virtual channel (VC)

F: canal virtuel (VC)

S: canal virtual (CV)

A concept used to describe unidirectional transport of ATM cells associated by a common unique identifier value.

251	virtual channel connection

F: connexion de canal virtuel

S: conexión de canal virtual

A concatenation of virtual channel links that extends between two points where the adaptation layer is accessed.

252	virtual channel link

F: liaison de canal virtuel

S: enlace de canal virtual

A mean of unidirectional transport of ATM cells between a point where a virtual channel identifier value is assigned and the point where that value is translated or removed.

253	virtual path (VP)

F: trajet virtuel (VP)

S: trayecto virtual (TYV)

A concept used to describe unidirectional transport of ATM cells belonging to virtual channels that are associated by a common identifier value.

254	virtual path connection

F: connexion de trajet virtuel

S: conexión de trayecto virtual

A concatenation of virtual path links that extends between the point where the virtual channel identifier values are assigned and the point where those values are translated or removed.

255	virtual path link

F: liaison de trajet virtuel

S: enlace de trayecto virtual

The group of virtual channel links, identified by a common value of the virtual path identifier, between the point where the VPI value is assigned and the point where the VPI value is translated or removed.

ANNEX A

(to Recommendation I.113)

Alphabetical list of terms contained in this Recommendation1)

201	asynchronous time-division multiplexing

202	asynchronous transfer mode

203	block

204	block payload

101	broadband [wideband]

205	broadband access

206	broadband communication channel

102	broadcast

207	cell

208	cell delineation

209	circuit transfer mode

210	connection admission control

103	connectionless service

104	constant bit rate service

105	contribution; contribution application

106	conversational service

211	deterministic; ATM deterministic

108	distribution service

109	distribution service with user individual presentation control

110	distribution service without user individual presentation control

107	distribution; distribution application

111	enhanced-quality television

112	existing-quality television

212	frame

213	frame interface

214	general broadcast signalling virtual channel

215	header; cell header

216	hybrid interface structure

217	information payload capacity

113	interactive service

218	interface overhead

219	interface payload

220	interface rate; interface bit rate

221	invalid cell

222	labelled channel

223	labelled deterministic channel

224	labelled interface structure

225	labelled multiplexing

226	labelled statistical channel

227	logical signalling channel

114	messaging service

228	meta-signalling

115	mixed document

116	multimedia service

117	multipoint

229	network node interface

230	packet

231	packet transfer mode

232	payload module

233	periodic frame

234	physical frame

235	physical signalling channel

236	positioned channel

237	positioned interface structure

118	post-production processing

119	retrieval service

238	selective broadcast signalling virtual channel

239	self-delineating block

240	self-delineating labelled interface

120	service bit rate

241	signalling virtual channel

121	sound retrieval service

242	statistical; ATM statistical

243	synchronous time division multiplexing

244	synchronous transfer mode

245	throughput

246	transfer mode

247	transit delay

248	usage parameter control

249	valid cell

122	variable bit rate service

123	videomessaging

250	virtual channel

251	virtual channel connection

252	virtual channel link

253	virtual path

254	virtual path connection

255	virtual path link

ANNEX B

(to Recommendation I.113)

List of abbreviations used in B-ISDN Recommendations

AAL	ATM Adaptation Layer

AAL-PCI	AAL protocol control information

AAL-SDU	AAL service data unit

ACE	Access connection element

AIS	Alarm indication signal

AL	Access Link

ATM	Asynchronous transfer mode

ATM-SDU	ATM service data unit

AU	Administrative unit

B-ISDN	Broadband aspects of integrated services digital network

B-ISDN PRM	Protocol reference model of the broadband aspects of ISDN

B-ISPBX	Private branch exchange for B-ISDN

B-NT	Network termination for B-ISDN

B-NT1	Network termination 1 for B-ISDN

B-NT2	Network termination 2 for B-ISDN

B-TA	Terminal adaptor for B-ISDN

B-TE	Terminal equipment for B-ISDN

BER	Bit error ratio

BIP	Bit interleaved parity

BOM	Beginning of message

C-n	Container-n

CAD-CAM	Computer aided design/computer aided manufacturing

CAMC	Customer access maintenance centre

CBR	Constant bit rate

CE	Connection element

CEQ	Customer equipment

CIME	Customer installation manintenance entities

CL	Connectionless

CLP	Cell loss priority

CLSF	Connectionless service function

CMI	Coded mark inversion

CN	Customer network

COH	Connection overhead

COM	Continuation of message

CON	Concentrator

CRC	Cyclic redundancy check

CRF	Connection related function

CRF(VC)	Virtual channel connection related function

CRF(VP)	Virtual path connection related function

CS	Convergence sublayer

CS-PDU	Convergence sublayer protocol data unit

DPL	Primary link for distribution services

DS	Digital section

EOM	End of message

ET	Exchange termination

FDDI	Fibre distributed data interface

FEBE	Far end blok error

FERF	Far end receive failure

GFC	Generic flow control

HDLC	High-level data link control

HDTV	High definition television

HEC	Header error control

HLF	Higher layer function

IPL	Primary link for interactive services

IRP	Internal reference point

IT	Information type

LAN	Local area network

LE	Local exchange

LFC	Local function capabilities

LI	Length indicator

LT	Line termination

MA	Medium adaptor

MAN	Metropolitan area network

MCD	Maintenance cell description

MID	Multiplexing identification

MSB	Most significant bit

MSP	Maintenance service provider

MUX	Multiplexor

NNI	Network-node interface

NP	Network performance

NT	Network termination

OAM	Operation and maintenance

OAMC	Operation, administration and maintenance centre

OSI	Open systems interconnection

PCI	Protocol control information

PDH	Plesiochronous digital hierarchy

PDU	Protocol data unit

PL	Physical layer

PL-OAM	Physical layer-operation and maintenance (cell)

PLK	Primary link

PM	Physical medium (sublayer)

POH	Path overhead

PON	Passive optical network

PRM	Protocol reference model

PT	Payload type

PTR	Pointer

QOS	Quality of service

RAI	Remote alarm indication

RES	Reserved

RG	Regenerator

RPOA	Recognized private operating agency

RS	Regenerator section

RU	Remote unit

SAP	Service access point

SAR	Segmentation and reassembly sublayer

SDH	Synchronous digital hierarchy

SDU	Service data unit

SFET	Synchronous frequency encoding technique

SN	Sequence number

SN	Sequence number protection

SOH	Section overhead

SP	Service provider

SPL	Service provider link

SPN	Subscriber premises network

SSM	Single segment message

ST	Segment type

STM	Synchronous transfer mode

STM-n	Synchronous transport module-n

SVC	Signalling virtual channel

TA	Terminal adaptor

TC	Transmission convergence sublayer

TCE	Transit connection element

TCRF	Transit connection related function

TE	Terminal equipment

TMN	Telecommunication management network

TPE	Transmission path endpoint

UNI	User-network interface

VBR	Variable bit rate

VC	Virtual channel

VC	Virtual container-n

VCC	Virtual channel connection

VCCE	Virtual channel connection endpoint

VCI	Virtual channel identifier

VP	Virtual path

VPC	Virtual path connection

VPCE	Virtual path connection endpoint

VPI	Virtual path identifier