1、CCITT RECMN*I.223 (REV*L) 73 4862573 0580537 39T INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU INTEGRATED SERVICES DIGITAL NETWORK (ISDN) SE RVIC E CAPABI LI TI ES 1.221 (03/93) COMMON SPECIFIC CHARACTERISTICS OF SERVICES ITU-T Recommendation 1.221 (Prev
2、iously “CCIlT Recommendation”) CCITT RECflN*I.221 (REVtL) 93 .II 48b2591 0580538 226 FOREWORD The ITLJ Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions
3、 and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendat
4、ions on these topics. IT-T Recommendation 1.221 was revised by the ITU-T Study Group XVIII (1988-1993) and was approved by the WTSC (Helsinki, Marcb 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telmmmunication Union VU), the CCITT ceased to exist as of 28 Februa
5、ry 1993. In its place, the IT Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been ma
6、de in the text to references containing the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication administration and a re
7、cognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mecbanical, including photocopying and mi
8、crofilm, without permission in writing from the ITU. CCITT RECMN*I-221 (REVS11 93 111 48b259L 0580539 Lb2 111 CONTENTS Page 1 Scope and content of the Recommendation 1 2 Common specific characteristics 1 2.1 Defuiition of “busy” in an ISDN . 1 Annex A - Handling of active and held dis . 4 A.l Introd
9、uction 4 A.2 Functionality available to the served user controlling more than one call . 4 Recommendation 1.221 (03/93) 1 CCITT RECMNtI.22L (REV*L) 93 I 48b2591 0580540 984 INTRODUCTION The principles of telmmmunication services supported by an ISDN and the means to descxibe them are given in Recomm
10、endation 1.210. The attribute technique and values of attributes, which form part of the standardized description method, (see Recommendation I. 130) for services, are given in Recommendation I. 140. This Recommendation refers to and details the common specific charactefistics of services for both b
11、asic services and supplementary services. 11 Recommendation 1.221 (03/93) Recommendation 1.221 COMMON SPECIFIC CHARACTERISTICS OF SERVICES (Melbourne, 1988, amended at Helsinki, 1993) 1 Scope and content of the Recommendation This Recommendation identifies and describes those common specific charact
12、eristics of services which are a common feature of each of the individual services and which help to form a relationship between services. These characteristics are used in a consistent manner throughout the ISDN services and are intended to be service independent. They are used, for instance, to he
13、lp to idenafy the situations under which certain supplementary services are invoked during the operation of basic services. 2 Common specific characteristics 2.1 Definition of “busy” in an ISDN 2.1.1 Scope This clause describes the conditions under which a given ISDN destination is considered “busy”
14、. In general, this occurs whenever the resources associated with that destination (and needed to successfuy complete the call) exist but are not available for the call. In existing networks, such as the PSTN, this is indicated to the calling subscriber by “busy tone”. In addition, the operation of c
15、ertain ISDN supplementary services occurs when certain of these resources are busy. Therefore, these “resource busy” conditions are ais0 described herein. This clause does not cover the cases where network resources not associated with a given destination are unavailable, or when such resources are
16、out-of-service or otherwise non-functional. 2.1.2 Resources Two main categories of resources may become involved in the determination of “busy”: interface resources and customer resources. Interface resources include the signalling channel (D-channel), other physical channels (B- and H-channels), lo
17、gical channels (for packet-mode services) and maximum number of calls supported. It is noted that with the ongoing activities on “calls versus connections” other interface resources may become important in the future. For the purposes of this Recommendation, the signalling channel is considered to b
18、e always available and with sufficient capacity to handle signalling for new calls. Situations where this is not true are considered to be “failure conditions” and are not covered here. For the other interface resources, descriptions are given below of what is meant when they are considered busy, Su
19、bscriber resources include the terminal(s) themselves and the persons or processes using them. For the purposes of this Recommendation, it is not considered significant which of the subscriber resources are busy, or why. An indication from the subscriber that (some, necessary) subscriber resources a
20、re busy is sufficient. 2.1.3 Resource busy conditions Three resource busy conditions bave been found necessary to refer to, and are defined below: 1) Channels busy - This condition occurs when there is no appropriate information channel (physical or logicai) available for the network to use for the
21、call. It may be due to exceeding the information channel limit associated with the service or with the interface. Recommendation 1.221 (03/93) 1 CCITT RECHN*I.221 (REVtL) 93 E 46259L 050542 757 2) Maximwn number of total calls reached - This condition occus when the maximum number of total calls sup
22、ported, either at the given subscribers interface(s) or for a given service, has been reached. Subscriber busy - This condition is indicated by the subscribers terminal equipment, e.g. by having all compafible terminals which could respond to the call request indicate “user busy” either, when they a
23、re offered a call, or, in response to an enquiry from the network. 3) 2.1.4 Procedural aspects The resource busy conditions described above significantly influence the call offering procedures, both for the basic ISDN calls and for calls that may involve ISDN supplementary services. The procedural a
24、spects of call offering are outlined below and shown in Figure 1. Assume that a call of a telecornmuunications service subscribed to by the called subscriber is about to be offed. 1) 2) If all of the appropriate user-network interface information channels are busy .e. channels busy) and either the n
25、etwork does not support the offering of additional calls beyond the number of appropriate channels, or the maximum number of such additional calls has been reached, the network will clear the cai1 see also item 7), below and indicate “network determined user busy” back towards the calling subscriber
26、. 3) Similarly, if the maximum number of total calls supported at the given subscribers interface(s) has been reached, the network will clear the call see also item 7, below and indicate hetwork determined user busy” back towards the ding Subscriber. 4) Otherwise, the network offers the call to the
27、subscriber. 5) If any compatible terminal responds “positively” to the call offering, i.e. gives some indication that the call may progress towards successful completion, the normal call offering procedure should continue. If no compatible terminal responds “positively” but one or more compatible te
28、rminal responds “user busy”, then when the response-to-call-offering timeout occurs, the network will clear the call with the indication “user determined user busy”. 7) It is recognized that for the determination of a “network determined user busy” condition, the network does not have complete knowl
29、edge of whether or not a compatible terminal exists at the called interface. However, if NDUB is returned, the caller knows that the basic service is subscribed to at the destination, hence it is likely that compatible terminals exist. This may still mask the exact determination of a “no compatible
30、terminal available” condition, i.e. a NDUB condition may be returned when, in fact, no compatible terminal is connected if for some reason, the destination subscribes to the basic service but has no terminals compatible with the basic service connected or if there is some other incompatibility. The
31、use of an explicit compatibility check to prevent this (i.e. return of the NDUB condition when no compatible terminal is connected) from occurring is a service provider option and is for further study. 6) 2.1.5 Dennition of busy An ISDN destination is considered to be busy if either a “network deter
32、mined user busy” or a “user determined user busy” condition occurs, as described above. 2.1.6 Interface parameters The foilowing subscription options are applicable to the interface as a whole regardless of service: Subscription options Value Maximum number of information channels on the interface C
33、 Maximum number of calls present on the interface K These subscription parameters for the interface are expected to be negotiated and set at the time the user interface is provisioned. The parameters represent upper limits that cannot be exceeded when channeldcalls are being assigned for determining
34、 busy condition (see Figure 1). 2 Recommendation 1.221 (03/93) CCITT RECflN*I*221, (REV* iii) disconnect one of the held parties; iv) establish another call (having fust put the active call on hold). When the served user is in conml of only held calls the user can establish a further call; v) reques
35、t the service provider to connect two users (Explicit Call Transfer); vi) request the service provider to begin a three-way conversation. The served user can invoke this step only after the call to one party has reached the active state and at least one call is on hold; VU) request the service provider to begin the Conference Call, add on supplementary service, including the active call in the conference. 4 Recommendation 1.221 (03/93)
