============================================================ Question 1/XVIII - General aspects of ISDN Considering (a) the existing Recommendations on digital networks and ISDN; (b) that the work on systems and services carried out by other Study Groups has an impact on ISDN studies; (c) that Study Group XVIII has overall responsibility for the continuing studies of ISDN; the following should be studied: 1. What amendments are required to the structure of the Recommendations on digital networks and ISDNs? 2. What new or revised Recommendations are needed to address issues not included in other Questions? 3. What guidance should be given to ensure coordination of ISDN studies, including network operation and maintenance aspects? ============================================================ Question 2/XVIII - Asynchronous Transfer Mode (ATM) Considering (a) that Recommendation I.121 recognizes that ATM is the target transfer mode solution for implementing broadband capabilities within an ISDN; (b) that in future ATM could be also applicable to 64 kbit/s based ISDN; (c) that there is a need to give guidance to other Study Groups of the impact of the ATM technique on network components; the following should be studied: 1. What are the fields of application for ATM techniques? 2. What basic characteristics and parameters should be defined for the ATM? 3. What is the impact of introducing ATM techniques into the network e.g., on signalling, switching, transmission, multiplexing and cross- connect functions and capabilities, and on UNI and NNI? 4. What network concepts and standardization aspects are needed in ISDN during the evolutionary period from 64 kbit/s based networks to networks with broadband capabilities? 5. What is the relationship between Asynchronous Transfer Mode based network capabilities supporting existing and new services and network management functionality and architectural modelling during the evolution of ISDN? Note - The study should be conducted in close relation with Question 13/XVIII. ============================================================ Question 3/XVIII - Network aspects of digital hierarchies Considering (a) that Recommendations G.702, G.707, G.708, G.709 and G.802 give information concerning digital hierarchies; (b) that transport of high capacity digital signals and that network arrangements can be done in the future on the basis of synchronous digital multiplexing techniques; (c) that the concept of synchronous multiplexing and of a Synchronous Digital Hierarchy should be transmission media independent; (d) that broadband services may require transmission capacities in excess of the capacity provided by the basic building block of the Synchronous Digital Hierarchy (150 Mbit/s); (e) that the concept of Synchronous Digital Hierarchy allows for easy growth to higher bit rates in step with the evolution of transmission technology; (f) that Path Overhead (POH) and Section Overhead (SOH) associated with Virtual Containers (VC) and with the Synchronous Transport Module (STM) respectively provide the opportunity for enhanced OAM capabilities; (g) that ATM techniques are being studied for broadband access to the ISDN; (h) that many new terms, not yet included in Recommendations G.701, I.112 or I.113, are being used in Recommendations G.707, 708 and 709; the following should be studied: 1. What higher levels (above STM-4) of the Synchronous Digital Hierarchy should be recommended? 2. What multiplexing structures should be recommended for Broadband Signals requiring STM-1 concatenation? 3. What are the amendments that may be required to Recommendations G.708 and G.709 to facilitate media independence, in particular with regard to interfaces? 4. What are the implications on Recommendations G.708 and G.709 of different applications of the Synchronous Digital Hierarchy concept (for example, within station, short-haul, long-haul)? 5. What overhead specifications should be included in Recommendations G.708 and G.709 to take advantage of enhanced OAM capabilities? 6. What mappings of source signals over and above those already contained in Recommendation G.709 are required and how should they be specified? 7. What provisions have to be made to allow for the transport of ATM based signals? 8. What terms used in Recommendations G.707, 708, and 709 should be included in the Recommendations G.701, I.112 or I.113 on terminology and how should they be defined? 9. What revisions need to be made to Recommendations G.702, G.703, G.704 and G.706? Note - To be studied in close liaison with Study Group XV. ============================================================ Question 4/XVIII - Network application of Synchronous Digital Hierarchy with reference to the Network Node Interface (NNI) Considering (a) that Recommendations G.707, G.708 and G.709 specify the details of a new Synchronous Digital Hierarchy; (b) that the technology of the new Synchronous Digital Hierarchy permits flexible rearrangements of channels and convenient insertion or removal of channels of varying bandwidth at various points of a network; (c) that a comprehensive overhead capacity provided in the new Synchronous Digital Hierarchy facilitates improved provisioning, maintenance and administration methods as well as rapid restoral of network links that have failed; (d) that some administrations will be introducing the new Synchronous Digital Hierarchy into their existing networks as well as establishing entirely new synchronous networks; the following should be studied: 1. How should the new Synchronous Digital Hierarchy be utilized in existing digital networks to benefit from the advanced capabilities? 2. What are the general principles for establishing new advanced digital networks using the new Synchronous Digital Hierarchy which will provide for efficient growth and capacity for new services including broadband ISDN? ============================================================ Questions 5 to 9/XVIII - Quality of Service and performance of digital networks including ISDNs Preamble to Questions 5 to 9/XVIII These Questions are concerned with studies related to the general performance of digital networks, including ISDNs. In particular, studies should embrace all of the network performance characteristics that are observable at the ISDN user-network interface, encompassing transmission, switching and signalling related performance aspects. Due account should be taken of the progress made on this matter within Study Group XVIII during the previous study period and of the work of other CCITT Study Groups on other aspects of performance; in particular Study Groups II, VII, XI, XV, XII and CCIR Study Group 4 and Study Group 9. The role of Study Group XVIII will therefore consist of coordination of areas where relevant detailed study is being undertaken in the specialist Study Groups. In the areas where detailed study is not being undertaken, the role of Study Group XVIII should be to give direction as required, and if necessary, progress the detailed study to completion. Considering (a) that there is a need to establish performance requirements for ISDNs, taking account, for example, of broadband aspects (including Asynchronous Transfer Mode), integration of mobile services, private network issues and multipoint and broadcast services; (b) that network performance requirements will influence the design of systems (e.g., signalling systems, transmission systems); (c) that general principles that govern the study of network performance and Quality of Service are defined in Recommendation I.350; (d) that certain performance objectives already studied need to be expanded to cover bit rates other than those already the subject of Recommendations (e.g., for broadband services, etc.); (e) that there is a need to further clearly distinguish between the network performance, and the Quality of Service of telecommunication services offered to customers; (f) that there is a need to establish a set of performance objectives catering for a wide variety of services on fully integrated networks; the following Questions 5 to 9/XVIII should be studied: ============================================================ Question 5/XVIII - General aspects of Quality of Service and network in digital networks, including ISDNs Note - To be studied in close consultation with Study Group II and other related Study Groups. 1. What general Quality of Service parameters for telecommunication services should be recommended and how should they be structured? 2. What digital network performance parameters (including availability) should be recommended for ISDN connection types and how should they be structured? 3. How do the Quality of Service parameters of an ISDN telecommunication service relate to the network performance parameters of ISDN connection types(s) which support that service? 4. How does the performance of the equipment in the customer installation interact with the network performance to influence the Quality of Service of telecommunication services? Account should be taken of standards set by other bodies? 5. What are the performance considerations resulting from the integration of mobile networks into the ISDN? 6. Do particular services (e.g., audiovisual, broadcast, multipoint, and multimedia services) require particular consideration, and if so, in what way? 7. Where are the boundaries in an international ISDN connection at which performance can be measured and allocated among the network entities? Note - These apportionment boundaries will be used in answering Questions 6, 8, and 9. 8. What are the performance significant reference events that can be observed at those boundaries and can be used in defining a comprehensive set of ISDN performance parameters? Note - These reference events will be used in answering Questions 6, 8, and 9. 9. How do the specific ISDN performance parameters defined under Questions 6, 7, 8, and 9 fit this general model (I.350)? 10. What are the appropriate parameters for Quality of Service and network performance in a B-ISDN, taking account of the following: a) that B-ISDN will build on the very high bandwidth and low error properties of many available transmission systems; b) that Asynchronous Transfer Mode and other possible B-ISDN transfer modes introduce the possibility of impairment mechanisms (e.g., cell loss due to congestion) which, if not controlled, may mask the inherent high performance capabilities of the transmission facilities; c) that these transfer modes may impact the manner in which network impairments are perceived by the end user? 11. What performance related guidance can be given to the other concerned groups concerning the development of B-ISDN architecture and protocols? 12. How should the performances of digital sections be specified? ============================================================ Question 6/XVIII - Network performance objectives for ISDN circuit mode information transfer Note - Specific reference should be made to Recommendation G.821. 1. What speed, accuracy, and dependability performance parameters should be recommended for circuit mode information transfer through ISDNs? Note - The digital network performance objectives recommended should be generally applicable to all services. 2. What methodologies can be used to relate performance at 64 kbit/s rate to performance at higher bit rates? Note - The methodology may be transmission media dependent, therefore close liaison with other concerned Study Groups is required. 3. What reference connections should be used in the consideration of values for these parameters? Note - Specific reference should be made to Recommendation G.801. 4. What values and measurement conditions should be recommended for circuit mode information transfer performance through ISDNs? 5. How does the distribution of error bursts influence the performance objectives? 6. What rules should be adopted for apportioning the overall values to the constituent parts of the connections? Note - Specific reference should be made to Recommendation G.921. 7. What are the implications of the circuit mode information transfer performance requirements on broadband ISDN performance requirements? 8. What guidance can be given to the other competent Study Groups regarding use of the recommended values? ============================================================ Question 7/XVIII - Performance objectives for timing and controlled slips (synchronization), jitter, wander and propagation delay 1. What further Recommendations should be made regarding the performance objectives for timing and frequency tolerance, controlled slip, jitter, wander and propagation delay of the transmission path in digital networks including networks employing the Synchronous Digital Hierarchy and including 64 kbit/s and broadband ISDNs? 2. What further improvement can be made to the definition of Maximum Time Interval Error (MTIE) so as to include the statistical characteristics of clocks? 3. What is the need for synchronization at higher bit rates to cater for broadband services? 4. What further consideration should be given to the problem of jitter, and wander in order to refine the network performance objectives, specifically, how should the accumulation of jitter be controlled? Note - Specific reference should be made to Recommendation G.921. 5. What consideration needs to be given to the effect of variations in cross-network delay, including waiting-time jitter, in ATM circuits? 6. What will be the effects on jitter/wander and MTIE of the inclusion of international and domestic satellite links in the network? ============================================================ Question 8/XVIII - Network performance objectives for ISDN connection processing and packet mode information transfer Note - Specific references should be made to Recommendations I.352, X.135 and X.136, E.713 and E.721. 1. What network performance parameters should be recommended for connection processing performance on connections through ISDNs? Note - Items such as blocking, connection processing delays, connection failure, etc., should be covered by this study. 2. What network performance parameters should be recommended for packet mode information transfer through ISDNs? Note - Items such as data packet delay, throughput capacity, etc., should be covered by this study. 3. What reference connections should be used in the consideration of values for these parameters? 4. What values and measurement conditions should be recommended for connection processing and for packet mode information transfer performance through ISDNs? Note - To be studied in close liaison with Study Groups II and VII. 5. What guidance can be given to the other competent Study Groups regarding compliance with the recommended values? Note - In due course, other transfer modes (e.g., additional packet mode, Asynchronous Transfer Mode) should be considered under this Question. ============================================================ Question 9/XVIII - Performance objectives for ISDN availability Note 1 - Consideration should be given to Recommendation X.137 and the E.800Series. Note 2 - To be studied in close consultation with Study Group II and other related Study Groups. 1. What definitions of "availability" and models for its calculation are appropriate for ISDNs, including broadband aspects? Note - Quotation marks are used to indicate that the term "availability" is taken to have wider applicability than implied by the definition in Recommendation G.106. 2. What levels of connection processing performance, packet performance, and circuit performance will be used in determining the "availability" of an ISDN connection? Note - Specific reference should be made to the work done on Questions 5 and 7. 3. What "availability" parameters should be recommended for ISDNs? Note - These parameters will be measured at connection element boundaries. 4. What reference connections should be used in the consideration of values for these parameters? 5. What values and measurement conditions should be recommended for "availability" performance on connections through ISDNs? 6. What rules should be adopted for apportioning the overall values to the constituent parts of the connections? Note - Specific reference should be made to Recommendation G.921. 7. What guidance can be given to the other competent Study Groups regarding use of the recommended values? Note - The study should take account of the following: a) that circuit mode connections can be completed over many alternative routes through the network; b) that the failure of any one route or link does not prevent the connection from being established; c) that traffic load will vary in time, thus impacting the accessibility of a particular route or link; d) that an end-user will not be able to distinguish these two conditions; e) that a failure of the access line will, in general, make the connection unavailable; f) that many of the same observations apply to packet mode connections as well. ============================================================ Question 10/XVIII - Impact of signal processing on ISDN Considering (a) the existing Recommendations on coding; (b) that the present ISDN is based on 64 kbit/s capabilities; (c) that Study Group XV is studying further coding and signal processing techniques; (d) that there is a need for encryption for some services; the following should be studied: 1. What is the impact of new and existing types of signal processing, encoding and encryption methods on the network capabilities of ISDNs (e.g., switching and signalling, selection/rejection, etc.) for example: 1.1 7 kHz audio encoding within 64 kbit/s, 32 kbit/s ADPCM encoding, and lower rate encoding; 1.2 speech packetization; 1.3 encoding for audiovisual services (e.g., visual telephony, videoconferencing, audiographic and Telematic teleconferencing etc.)? Note 1 - To be studied in cooperation with Study Group XV. Note 2 - With reference to Recommendation G.722 (7 kHz audio encoding within 64 kbit/s), the study should specify how the ISDN can utilize such method of coding for intra-ISDN applications, with due consideration for interworking with the PSTN and Recommendation G.711 encoding. ============================================================ Question 11/XVIII - Interworking of ISDNs with other networks, including compatibility checking and terminal selection Considering (a) the present Recommendations dealing with interworking; (b) the need to extend these to take account of further interworking situations including those associated with addition packet mode bearer services (APMBS) and ISDNs incorporating broadband capabilities; (c) the present Recommendations dealing with terminal compatibility and terminal selection; the following should be studied: 1. What new and/or revised Recommendations should be prepared for interworking of ISDNs (including, for example, those incorporating APMBS) with: -PSTN; -PSPDN; -CSPDN; -ISDN; -telex networks; -private networks (including satellite based private networks); -ISDN incorporating broadband capabilities; -special networks providing intelligent network services; -mobile services networks (including satellite based mobile services networks)? 2. What new or revised Recommendations are required for terminal selection and terminal compatibility checking? Note 1 - Studies should include the identification of routing issues associated with interworking as an input to the study of routing in other Study Groups. Note 2 - The work on mobile networks carried out by other Study Groups should be taken into consideration. Note 3 - Account should be taken of operation and maintenance issues associated with interworking as an input to the studies of O & M in other Study Groups. ============================================================ Question 12/XVIII - Interworking between networks using different digital hierarchies - Layer 1 functionality Considering (a) that I.500-Series Recommendations specify the general principles on interworking between networks including ISDN and other networks; (b) that Recommendations I.511 and G.802 specify, in particular, the Layer 1 functions necessary for interworking between networks including those incorporating different standards and hierarchies; (c) that Layer 1 broadband aspects of ISDN described in Recommendation I.121 including the possible impacts of ATM need further consideration for interworking; (d) the existence of synchronous digital hierarchy and its relevant frame formats and functions specified in Recommendations G.707, G.708 and G.709 along with the likely long-term existence of equipment based on the existing different asynchronous hierarchies and standards; the following should be studied: 1. What new or revised Recommendations are requested for interworking between networks using different hierarchies? ============================================================ Question 13/XVIII - Network capabilities for the support of broadband services in ISDNs Considering (a) that Recommendation I.121 provides the framework for the support of broadband services in an ISDN and that a status report (annexed to relevant Questions) has been prepared on broadband ISDN; (b) that Study Group I is defining services; (c) most kinds of information-related activity involves a mixture of multi-media requirements; (d) ISDN will incorporate both broadband and 64 kbit/s based capabilities; (e) that Study Group XVIII will consider broadband services and will support Study Group I by giving advice on the network capabilities available for the provision of broadband services in ISDNs; (f) other Study Groups may initiate studies on specific aspects of broadband ISDN with Study Group XVIII giving guidance for their work; (g) that strong coordination of activities in the broadband field will still be necessary early in this study period, at least until there is a consensus on a number of basic assumptions and parameters; the following should be studied: 1. What new and/or revised Recommendations and what guidance to other Study Groups is required concerning network capabilities for the support of broadband services in ISDNs? Note 1 - The study will include the following, e.g.: 1.bit rates for services; 2.multipoint and broadcast operation and multimedia applications; 3.description of broadband services and network capabilities using the methodology contained in Recommendation I.130; 4.signalling and control functions; 5.numbering; 6.maintenance; 7.user-network interface capabilities. 2. What network capabilities are needed in ISDN during the evolutionary period from 64 kbit/s based networks to networks with broadband capabilities? 3. What are the implications on network functions (interfaces, signalling procedures, protocol definitions, etc.) for offering simultaneous, mixed-media capabilities in a broadband ISDN environment? Note 2 - Under this Question general guiding principles for the work of broadband aspects of ISDN should be further established. Note 3 - The study should be conducted in close relation to Question 2/XVIII. ============================================================ Question 14/XVIII - ISDN network capabilities for the support of additional and/or new services Considering (a) existing Recommendations on services supported by (64 kbit/s) ISDN; (b) the studies to be carried out by other Study Groups on additional and/or improved services; (c) that Study Group XVIII has to define any additional network capabilities needed to support these services; the following should be studied: 1. What new and/or revised Recommendations are required for additional network capabilities of (64 kbit/s) ISDNs for the support of new or improved services? 2. What use can be made of existing network capabilities to support new and/or improved services (all services aspects, including billing capabilities) including: -multiservices operation/multimedia application; -still image transfer; -in-call modification; -OSI services? Note - The study of these Questions should cover service areas (utilizing the method for the characterization of services and network capabilities contained in Recommendation I.130) such as: -audiovisual; -teleaction on D Channel; -intelligent networks; -value added networks; -mobile networks; -maintenance and management; -universal personal telecommunications; -7 kHz services and associated capabilities; -supplementary services associated with the above. ============================================================ Question 15/XVIII - ISDN packet mode bearer services - service and user- network interface aspects Considering (a) that Recommendation I.232 describes the packet mode bearer services supported by an ISDN; (b) that Recommendation X.31 already defines the support of X.25 based packet mode terminals by the ISDN; (c) that Recommendation I.122 contains a framework for the definition of additional packet mode bearer services; (d) that Recommendation I.122 defines four possible additional packet mode bearer services; (e) that a wide range of data applications should be supported by the ISDN; the following should be studied: 1. What are the detailed service and network requirements and characteristics required of the additional packet mode bearer services? 2. Which of the potential bearer services currently defined in Recommendation I.122 best meet the service requirements and which of these potential bearer services should be the basis for future Recommendations and/or amendments to existing Recommendations? 3. What enhancements/additions, if any, are required to Recommendation I.232? Note - This study should include the application of supplementary services to additional packet mode bearer services. ============================================================ Question 16/XVIII - ISDN architecture and functional principles, characterization methods and reference configurations (including user- network interfaces) Considering (a) existing Recommendations on network functional principles, architectures, reference configurations, models and methodologies; (b) that there is a need to develop further and/or enhanced Recommendations on these aspects taking account of new network capabilities and services; the following should be studied: 1. What enhancements if any need to be made to the characterization methods of ISDN services and network capabilities? 2. What new and enhanced Recommendations are required to take account of the architectural and functional modelling aspects of: 2.1further capabilities of the (64 kbit/s) ISDN; 2.2network management and control functions; 2.3 functional interfacing with private networks (including mixed public/private network applications); 2.4functional integration of mobile services networks with the ISDN; 2.5intelligent networks; 2.6universal personal telecommunications; 2.7B-ISDN (including broadcast multipoint and multimedia applications? 3. What new and enhanced reference configurations need to be developed: -for new access arrangements; -for the allocation of performance objectives to accommodate mobile access to the ISDN; -for network interworking; -to cater for BB-ISDN? 4. What extensions to the concept of digital sections are required to cater for new network capabilities? Note 1 - With reference to study item 2.3 the purpose of the study is to establish an overall network reference model to cover interactions of mixed public/private networks in order to: i) enable consistent service descriptions to be developed; and ii) provide guidance for the development of protocols. Note 2 - An architectural reference model and associated guidelines are needed which provide a uniform framework for: -identifying network functions for service call control; -grouping network functions to create functional entities; -identification of basic physical network entities/resources; -mapping functional entities onto physical entities/resources; -showing the relationship between network functions to support telecommunications services and those required for network management and operations. ============================================================ Question 17/XVIII - ISDN protocol reference model Considering (a) that CCITT Recommendation I.320 defines principles for modelling information flows in various ISDN configurations; (b) that there is a continuing need to model ISDN capabilities within a common framework or reference model which will facilitate the further development of ISDN protocols and associated architectures; the following should be studied: 1. What further methods of modelling and categorizing information flows and the corresponding layer service definitions in various ISDN configurations are required in Recommendation I.320 taking account of the needs of broadband services, improved (64 kbit/s) ISDN services new transfer modes, mobile services, interfaces to private networks, management and control functions, intelligent network services, universal personal telecommunications services and broadcast and multipoint modes of operation? 2. What further development of Recommendation I.320 is required? Note - In developing Recommendation I.320 account has been taken of the OSI layered model. In the further development of both the ISDN protocol reference model and the OSI layered model the continuing need for close alignment of the models is recognized. Studies should therefore be coordinated with Study Group VII and ISO. ============================================================ Question 18/XVIII - ISDN connection types Considering (a) the Recommendations on ISDN connection types and their corresponding reference configurations; (b) that the required range of services to be supported by an ISDN is likely to be expanded in the future and that the number of connection types required to support these services should be limited; (c) that continuous advances in technology may make it desirable to modify some values of attributes of ISDN connection types; (d) the need to develop reference configurations to describe network performance of ISDN connection types; (e) that further development of the connection type concept will be required to take account of the needs of interconnection with private networks, broadband capabilities (including broadcast and multipoint connection, mobile services, intelligent network services and universal personal telecommunications services); the following should be studied: 1. What modifications, if any, are required to the connection types specified in Recommendation I.340? 2. What additional ISDN connection types should be identified? 3. What enhancements are needed to the definition of ISDN connection types to cater for the evolution of ISDN (including new transfer modes) and implementation of change in service during progress of a call? 4. How should ISDN connection types be detailed to cater for non-uniform connections? 5. How should reference configurations for ISDN connection types be further developed taking into account the concepts contained in Recommendation I.340, e.g.: 1.in what level of detail should reference configurations address the topological considerations and other functionally related aspects of connections in order to provide a good basis for the development of HRXs; 2.are the number of ISCs and other network nodes reduced in the case of satellite based connections and, if so, in what manner and with what impact; 3.for satellites involved in the distribution of multipoint narrow and broadband services, what are appropriate new reference configurations and HRXs and how can existing ones be modified to take account of these capabilities? Note - In the studies for developing HRXs for particular network performance parameters, it will be necessary to ensure that these HRXs are derived from and consistent with the reference configurations available for the relevant connection types and which refer to the network performance parameters. ============================================================ Question 19/XVIII - Network capabilities for the integration of mobile services into the ISDN Considering (a) the existing CCITT Recommendations on digital mobile systems; (b) that CCIR are developing Recommendations on interfaces to implement mobile personal telecommunications services; (c) that a high degree of commonality between fixed and mobile user- network interfaces should be aimed for; (d) that the provision of universal personal telecommunications services will necessitate integration of mobile services and interworking of mobile networks with the ISDN; the following should be studied: 1. What principles should be established to provide for a functional integration of mobile networks into the ISDN? This study should include: 1.1 Network implication of new techniques to allow substantial penetration of mobile service (e.g. dynamic allocation of capacity). 1.2 To what extent should the digital mobile network use the resources of ISDNs? 1.3 How can the mobile network be used to provide access to ISDN services for customers irrespective of location (i.e. national and international roaming)? 1.4 Network implications in providing for mobile user authentication (and billing functions) and security (for voice and data services). Note 1 - The need for a new user-network interface and a new interface structure for the support of mobile services will be studied under Questions 14 and 18. Liaison with CCIR Study Group 8 will be required. Note 2 - The work on mobile networks carried out by other Study Groups should be taken into consideration. The work done in connection with Question 4/II should be taken into account. ============================================================ Question 20/XVIII - Layer 1 characteristics of ISDN interfaces and ISDN access Considering (a) existing Recommendations dealing with Layer 1 characteristics of ISDN interfaces; (b) ongoing studies related to the support of mobile and broadband services in ISDNs and to the network node interfaces taking account of the new Synchronous Digital Hierarchy; (c) there is a need to amend existing Recommendations and to define the Layer 1 characteristics of new interfaces; the following should be studied: 1. What Recommendations are required for Layer 1 characteristics of broadband ISDN user-network interfaces? 2. What revisions need to be made to existing Layer 1 user-network interface Recommendations (I.430/I.431)? 3. What extensions, if any, are needed for user-network interfaces to cater for mobile services? 4. What characteristics should be recommended for digital line systems on metallic pairs to be used in the local network (choice of options and enhancements to Recommendation G.961)? 5. What characteristics should be recommended for broadband ISDN customer access in local networks? 6. What new Recommendations are required for the characteristics of digital sections for subscriber access (Note 3)? 7. What additions need to be made, if any, to Recommendations on network interfaces to private networks including subscriber premises equipment, e.g. home electronic systems? Note 1 - In the course of preparation of Recommendations, the eventual requirements for conformance testing should be borne in mind. Note 2 - The Layer 1 specifications should take into account EMC and safety aspects being studied by Study Group V. Note 3 - The work on digital sections for subscriber access may require enhancement of the V-interface Recommendation G.512. Therefore close cooperation with Study Group XI is necessary. ============================================================ Question 21/XVIII - Vocabulary for ISDNs Considering (a) existing Recommendations on terminology; (b) the ongoing need to have a consistent vocabulary for digital networks and ISDNs; the following should be studied: 1. What further terms and definitions should be recommended for ISDNs and associated digital network aspects? Note 1 - Consistency with Recommendation G.701 should be maintained. Note 2 - Consistency with the IEV is desirable. Note 3 - Due consideration should be given to corresponding terms and definitions in all of the CCITT working languages. Note 4 - Alignment of vocabulary included in Recommendations I.430, I.431, G.960, G.961 with existing vocabulary Recommendations should be ensured. ============================================================ Question 22/XVIII - Broadband ISDN influence on principles for video coding Considering (a) that a CCITT Recommendation I.121 defines the basic principles for broadband ISDN and that a status report (annexed to relevant Questions) has been prepared on broadband aspects of ISDN; (b) that the characteristics of these broadband ISDN video services may differ significantly from pure distributive video services; (c) that CMTT have responsibility for producing Recommendations on video coding techniques for broadcast applications; (d) that CCITT have responsibility for producing Recommendations on video coding techniques for interactive services; (e) that it may be advantageous to use similar coding techniques for both interactive and distribution services; the following should be studied: 1. What new Recommendations are required to establish principles for the future development of video coding techniques for broadband ISDN video services applications? This should include: 1.1 the main characteristics of broadband ISDN which influence the choice of video coding techniques; 1.2 the capabilities for packetized video over Asynchronous Transfer Mode (ATM) networks and user-network interfaces. ============================================================ Question 23/XVIII - Guidelines for implementing ISDN field trials in developing countries Considering (a) the need, in particular for developing countries, for guidelines on field trials of ISDN systems and associated networks and terminals; (b) that administrations need to have a defined period together with a defined set of parameters for embarking on the field trial of ISDN capabilities and demand requirements; (c) the impact of ISDN on future network planning; the following points should be specially addressed: 1. What parameters influencing the field trial period for ISDN should be taken into account in drawing up guidelines? 2. What guidelines are required for the steps to be taken by administrations during the ISDN field trial period? 3. What guidelines are required for the trial methods and parameters influencing the said objectives? Note - This Question should be studied in consultation with other Study Groups, such as Study Groups II, IV, XI and XV.