============================================================ Question 1/XVII - Supplement to the vocabulary for data transmissions (Continuation of Question 1/XVII, 1985-1988) (Concerns Study Groups I, II, VII, VIII, XI, XV, XVIII) Continue the preparation of definitions of terms which arise during the study of all Questions entrusted to Study Group XVII (see Annex 2 hereunder and Recommendation V.7). Annex 1 (to Question 1/XVII) Organization for study of definitions organizes: definitions work within Study Group XVII and with other Study Groups. coordinates: with the CCITT Secretariat and other international standards bodies such as ISO in definitions work. represents: Study Group XVII in definitions work of the Joint Study Committee CMV (CCITT/CCIR) as required. provides: compatible definitions in English, Spanish and French through assistance of the Collaborators on Definitions. prepares: CCITT contributions listing draft definitions obtained from the Representatives on Definitions for review and approval by Study Group XVII. presents: reports to the Study Group to obtain approval of definitions prepared by the Working Parties, Sub-Working Parties or Rapporteur's Groups. ============================================== assist: the Special Rapporteur as required. translate: draft definitions into the three working languages of the CCITT. ============================================== prepare: draft definitions of terms developed within the Working Parties, Sub-Working Parties or Rapporteur's Groups. obtain: agreement of Working Groups on draft definitions and forward terms and definitions to the Special Rapporteur. Note - Where Working Group Representatives on Definitions have not been established, the Chairman of the Working Group will transmit draft definitions to the Special Rapporteur. ============================================== examine: contributions on definitions prepared by the Special Rapporteur's Group on Definitions. inform: the Special Rapporteur well in advance of presentations of Definitions Reports to the Study Group if changes are desired. ============================================== Annex 2 (to Question 1/XVII) The following terms are proposed for further study: a) essential facilities; b) optional facilities; c) amplitude hit; d) phase hit; e) frequency shift; f) asymmetrical duplex; g) burst duplex; h) break-in duplex; i) pseudo duplex. ============================================================ Question 2/XVII - Measurements on telephone-type circuits used for data transmission systems between subscribers (Continuation of Question 2/XVII, 1985-1988) (Concerns Study Groups II, IV and VIII) It would be difficult and probably undesirable to establish a rigid test specification, but nevertheless some guiding principles can be given for further tests. 1. Preliminary laboratory tests The recommendations given below apply to systems which have already been subjected to the normal laboratory tests applied to new transmission systems. 2. Arrangement of the test connection It is possible to set up the test connection on a point-to-point basis or in the form of a loop. The former arrangement most closely resembles the practical case but there are serious difficulties involved in transporting equipment and personnel. A satisfactory form of loop testing can be achieved by connecting the transmitting apparatus to a distant point by means of a high-quality circuit producing no noise or attenuation in the test conditions. The return circuit to the receiving apparatus can be set up in a variety of ways as detailed later. 3. Measurement of group delay distortion Further measurement of group delay distortion between subscribers is desirable, and administrations are encouraged to report any such tests that are made. It would be very helpful to the designers of data modems to have statistical information on overall subscriber-to-subscriber group delay distortion. The results of any test the administrations are able to make would be a help in the future study of this problem. On the other hand, Recommendation G.114 specifies the propagation time between subscribers, and Recommendation G.133 on limits of the group delay distortion on a chain of international circuits. 4. Transmission loss A nominal range of losses in subscriber-to-subscriber connections might be 5 to 30 dB at the reference frequency (800 or 1 000 Hz), perhaps assuming up to 35 dB loss at the carrier and characteristic frequencies recommended. Studies and, where necessary, tests should be made from which statistical conclusions could be drawn for national, international and intercontinental connections. These might be expressed in terms of the loss at the reference frequency, plus the slope over the frequency band of interest, and would form the basis of a study on equalization. Note - See Supplements Nos. 14 to 17, Green Book, Volume VIII. 5. Data signalling rate It is recommended that a data signalling rate be selected from those which are preferred or permitted by Study Group XVII (see also Recommendations V.5 and V.6). Study Group XVII expressed the opinion that four preferred rates can be stated, namely 600, 1200, 2400 and 4800 bit/s, for use over telephone connections established on the switched network. On point-to-point circuits, the preferred rates would be 600, 1200, 2400, 4800 and 9600 bit/s. 6. Signal level It is recommended that the tests should be made at the signal level which is proposed in Recommendation V.2. Additional tests should be carried out at levels 6 dB above and below the level proposed. A reduced level test would be useful to determine whether the amount of margin for random circuit noise is available. However, a high level test (6 dB above the specified level) should not be made on international telephone-type circuits. 7. Sampling of test circuits The system performance texts using the 511-bit pseudo-random test pattern standardized in Recommendation V.52 should be carried out on a selection of samples totalling not less than the quantities shown in the following table: + + Data signalling rate Leased circuits Switched circuits + + + 600 2 107 bits 4 107 bits 1200 4 107 bits 8 107 bits 2400 and above 8 107 bits 2 108 bits + + For the leased circuits, the samples chosen should be representative of the facilities likely to be frequently used in practice. For the switched circuits, the tests should include at least 25 different connections which are representative of the facilities likely to be experienced in practice. The tests should be restricted to the business hours of normal working days and the samples should be representative both of the working day and the different attenuation conditions which may be experienced in practice. Tests should also be made on long and complicated circuits. No special maintenance should be carried out on circuits. For higher data signalling rates than 2400 bit/s, suitable test patterns longer than 511-bit shall be considered for comparative line test. For parallel data transmission systems a suitable test pattern needs to be defined. 8. Error record It was agreed that there are two possible forms in which the error statistics might be recorded: i) a complete fault statement including the exact position of all faults. Such raw material could be used for a variety of statistical studies necessary for the overall design of a data transmission system; ii) a simplified fault record indicating totals for a number of predetermined parameters which could be easily obtained during the testing process. It was agreed that the complete fault statement was preferable for general assessment and essential for the evaluation of the error detection part of the system. The simplified record will be valuable for the comparison of different data transmission systems and line facilities. 9. Presentation of results It is recommended that for all tests the following statistics should be recorded: i) block-error rate for given block sizes; ii) number of erroneous bits within erroneous blocks; iii) error burst length (a burst being regarded as constituted by errors separated by 10 or more error free elements); iv) structure of error bursts or error distribution; v) average element-error rate. 10. Information concerning connections used for test It is desirable that characteristics of the connection used for data tests should be obtained by monitoring and by measurement. For example, if the transmission of data causes any unwanted operation of signalling equipment with a consequential adverse effect on the stability of the connection, this should be recorded. Similarly it should be recorded if the reception of the test message is adversely influenced by warning tones, metering signals, etc. The presence and extent of switch noise, dial impulses and random impulse noise should be noted. The level of the signals at the receiving apparatus, the level of white noise and, if possible, noise bursts, attenuation distortion and phase distortion, should also be recorded. 11. Statistics of the public switched telephone network In the study of the data transmission characteristics to be standardized for data signalling rates in excess of 1200 bit/s on the general switched telephone network it is desirable that the results should be capable of application in the maximum number of situations. In order to achieve this, Study Group XVII should be in possession of as much information as possible concerning the properties and technical limitations of public switched telephone networks and international links. Therefore, it would be very helpful if administrations could obtain and submit as a contribution as many statistics as possible in order to further the studies. Much of this information will be valuable in studying other Questions of Study Group XVII. Subjects on which information would be of interest are enumerated below. Many relevant contributions on specific subjects have been made previously to either Study Group XVII or other Study Groups in which case it will only be necessary to give the appropriate reference. Information on the following would be useful: i) inband signalling systems, their limitations and percentage usage. If any obsolescent systems are to be replaced in the future, such information would be useful; ii) presence of echo suppressors within a country and any disabling features they contain. Possibilities of simultaneous, backward channel operation; iii) subscriber-to-subscriber loss over as much as possible of the available bandwidth. The information might be relative to the loss at 800 or 1 000 Hz plus the slope over the frequency band, or the actual loss at a number of discrete frequencies covering the band, the latter being preferable as the former can give pessimistic results; iv) group delay distortion between subscribers; v) phase jitter; vi) presence of sudden changes of phase or amplitude or short line breaks and the frequency of occurrence; vii) impulsive noises not included in vi) above; viii) signal/listener echo ratios; ix) signal/background noise ratios including information about special noise sources, e.g. PCM systems; x) any non-linearity giving rise to harmonics and intermodulation products; xi) probability of successful connections with regard to data transfer considering the limits set for the error rate and distortion (e.g. Recommendation V.50); xii) new problems which would affect modem operation. It is appreciated that the above list of subjects is a formidable one but any information that can be obtained on any of the aspects will be useful. 12. Interruption of the connection used for the test It was agreed that in the event of the connection used for the test being interrupted for a period exceeding 300 milliseconds, it should be considered that the connection was "out of service" during such an interval; such periods are to be ignored when the test results are evaluated, but will be indicated in the test record (duration, time of occurrence and, if possible, the cause). 13. System description It is recommended that the performance results should be accompanied by a brief description of the basic characteristics of the data transmission system undergoing test. In addition, a short explanation of the method of testing used would be advisable. 14. The results of this test are of interest for Study Groups IV and VIII which are to be kept informed by the CCITT Secretariat. ============================================================ Question 3/XVII - Modems for the transmission of data and other digital signals on the General Switched Telephone Network (GSTN) and on two- wire telephone-type leased circuits (Continuation of Question 3/XVII, 1985-1988: revised wording) (Concerns Study Group VIII) 1. Study of modems for signalling rates above 9600 bit/s including the study of what performance advantage might be achieved through different modes of operation (e.g. duplex, asymmetrical duplex, and half duplex). 2. Study of the characteristics, other than error control, needed by modems to be used on cellular radio services. 3. Study of modems for the simultaneous transmission of voice and data signals. 4. Study of points arising from the implementation of existing V-Series modems for use on the General Switched Telephone Network (GSTN) and on two-wire telephone-type leased circuits. Note - With the development of new modem technology the measuring methods for test parameters and the relevant performance parameters shall be studied in accordance with the updating of Recommendation V.56. ============================================================ Question 4/XVII - Modems for the transmission of data and other digital signals on four-wire telephone-type leased circuits (Continuation of Question 4/XVII, 1985-1988; revised title and wording) 1. Study of modems for signalling rates above 14400 bit/s. 2. Study of points arising from the implementation of existing V-Series modems for use on four-wire leased telephone-type circuits. ============================================================ Question 5/XVII - Error control in modems (New Question) The study of the LAPM protocol specified in Recommendation V.42. Specifically to study the provision of: 1) Data Compression, 2) Forward Error Correction, 3) Statistical Multiplexing, 4) End-to-end transmission of interface state information, 5) Control-function to control-function information exchange, 6) Rate negotiation, 7) Operation with modems not operating in the duplex mode, 8) Multiple frame reject, 9) Character format indication/negotiation, 10) Preservation of framing/parity errors, 11) Encryption, 12) ISDN Compatibility. ============================================================ Question 6/XVII - Characteristics of a device used to interface a DTE to digital channels other than ISDN (New Question) Considering (a) that there is an increasing need for leased circuits with data signalling rates of 64 kbit/s and multiples thereof; (b) that most applications at these data signalling rates do not require more interchange circuits than the data and timing circuits; (c) that PCM transmission paths capable of conveying 64 kbit/s or multiples thereof are internationally available; (d) that Recommendations V.36 and V.37 already specify DCEs for data signalling rates of up to 144 kbit/s using analogue transmission paths according to Recommendations of the H-Series; (e) that ISO 4902 and ISO 4903 specify DCE/DTE interface connectors which are, by their nature, not restricted to data signalling rates of 64 kbit/s or 144 kbit/s; (f) that Recommendations V.36 and V.37 already address an optional PCM interface; a study should be made of the characteristics of a device interfacing a DTE to existing PCM transmission paths. The study shall comprise: -control of remote loops according to Recommendation V.54, -rate adaption techniques for 48 kbit/s and 56 kbit/s, -definition of scramblers, -definition and allocation of framing for G-Series interfaces, -definition of characteristics of interface connectors for G-Series interfaces in close cooperation with ISO/IEC. ============================================================ Question 8/XVII - Measuring criteria for telephone-type circuits appropriate to their use for transmission of data signals (Continuation of Question 8/XVII, 1985-1988); (Concerns Study Groups IV, XII and XV-Q.26/XV) Considering that the transmission characteristics of leased telephone- type circuits are described in the following Recommendations: (a) ordinary telephone-type circuits (M.1040/H.12.A); (b) special quality leased circuits with basic bandwidth conditioning (M.1025/H.12.B); (c) special quality leased circuits with special bandwidth conditioning (M.1020/H.12.C), 1. the following line parameters and the measuring techniques to measure these parameters, arising from these Recommendations, should be studied from a data transmission point of view: a) Bandwidth characteristics: i) Ordinary telephone-type circuits: - overall loss frequency distortion. ii) Special quality leased circuits with basic bandwidth conditioning: -overall loss frequency distortion, -group delay distortion. b) Interface characteristics: i) Ordinary telephone-type circuits: -nominal overall loss. ii) Both types of special quality leased circuits: -nominal overall loss. c) Transmission system characteristics: i) Ordinary telephone-type circuits: -random circuit noise. ii) Both types of special quality leased circuits: -random circuit noise (Note 2), -impulsive noise, -phase jitter, -single tone interference, -quantizing noise (Note 2), -harmonic distortion (intermodulation distortion) (Note 2). d) Additionally the study should include the following transmission system characteristics of both types of special quality leased circuits: -short breaks in transmission (drop-outs), -phase hits, -amplitude hits, -low frequency phase jitter. e) Points of study for telephone-type circuits: -The study of the appropriate measuring criteria for the impairments to data signals caused by the introduction of ADPCMs, A/D converters and a/u law converters to the telephone network. 2. In addition, the following issues also require further study: a) Are there any special requirements for the operation of two- wire, duplex modems operating at data signalling rates above 1200 bit/s? b) What is the effect on data transmission between V-Series modems if, by some chance, all of the transmission characteristics of circuits leased for data transmission are at their lower limit (as specified in Recommendation H.12.A, B or C/M.1040, 1025 or 1020 respectively)? c) How might a "Figure of Merit" or some measuring technique be defined to insure the operation of V-Series modems to the performance specified in Recommendation V.53? d) How should the bandwidth and transmission system parameters (such as random circuit noise) be allocated in the case of simple multipoint circuits? e) What guidance should be given to the Study Groups deliberating the appropriate number of quantizing distortion units to be assigned to 32 kbit/s ADPCMs to ensure that adequate consideration is given to the satisfactory performance of V-Series modems? Note 1 - Study Group XVII's attention is called to the following questions from Joint Study Group CMBD which arose from the statement of Study Group XVII that transmission interruption longer than 5-15 ms could result in a service interruption of a duration of up to 1 second: a) Do these transmission interruptions cause disconnection of the established connection? b) If not, what frequency of such interruptions is acceptable for data transmission? Note 2 - In order to enhance the probability of the satisfactory operation of certain V-Series modems at data signalling rates higher than 4800 bit/s, the following are some of the transmission system characteristics that require further study: -random circuit noise (possibly given as a signal/noise ratio); -quantizing noise (possibly using a single frequency tone source); -harmonic distortion (possibly measured as second and third order intermodulation distortion products). Question 9/XVII - Network Management Continuation of Question 9/XVII, 1985-1988; revised title and wording) (Concerns Study Group VII) Considering (a) that the management/maintenance of data networks can be accomplished by administrations, RPOAs, and users, and that management/maintenance principles must be harmonized to: i) offer optimum network management and testing facilities to the administrations, RPOAs and users; ii) define consistent network management and testing facilities, (b) that ISO/IEC JTC 1/SC 21, SC 6 and CCITT are developing standards for OSI management for interconnection of different systems and networks with diverse architectures; (c) that there exists a large installed base of V-Series DCEs with network management capability implemented with diverse architectures; (d) that it is desirable to provide system management to devices in multiple-protocol, non-homogeneous networks; (e) that Recommendation V.230 specifies the electrical character- istics for a new physical interface for V-Series DCEs that will offer a migration path to the ISDN; (f) that Recommendation V.54 defines loop test devices for modems; (g) that Recommendation V.25bis defines a serial automatic calling and answering procedure on the GSTN supported by the DTE/DCE V.24 interface, the following should be studied: an OSI network management protocol for use between a V-Series DCE and a network management system as well as the means to communicate this information between the two. This should be provided in such a way as to assure a nondisruptive separation of the management information and the user data. A methodology must therefore be specified that would provide management information with a communications path between the management system and the managed DCE. In particular, the following points should be considered: 1. What principles are required for the network management and testing facilities to be consistent with the overall CCITT ISO-IEC activities on network management? 2. What general functional requirements for management must be defined? 3. How do the OSI management applications apply to V-Series DCEs and what additional network management aspects should be studied? 4. How can V.230 be used to provide a network management information path? 5. How can existing V-Series DCEs with diverse management architectures be accommodated? 6. How can multiple separate DCEs be managed from a system manager in non- homogeneous networks independently of diverse user protocols? 7. How can the work be harmonized with points of study under Questions 14/XVII and 23/XVII? ============================================================ Question 11/XVII - Support of DTEs (TE2s) with V-Series type interfaces on an ISDN, and interworking of DTEs with modems on PSTNs with TE2s and TE1s on ISDNs (Continuation of Questions 11 and 24/XVII, 1985-1988) (Of interest to Study Groups IV, VII, VIII, XI, XVIII) Considering (a) that ISDNs will offer the universal interfaces to connect subscriber terminals according to the reference configurations described in Recommendation I.411; (b) that, during the evolution of ISDN, there will exist, for an indefinite period, DTEs with V-Series type interfaces which have to be connected to the ISDN; (c) that, during this evolution of ISDN, there will exist a need for some terminals on ISDNs (TE1s and adapted TE2s) to interwork with DTEs connected (with modems) to PSTNs and with DTEs connected to non-ISDN digital networks; (d) that Recommendation V.110 describes procedures for adapting TE2s to an ISDN 64 kbit/s B channel (or 8, 16 or 32 kbit/s sub-rate channels); (e) that Recommendation V.120 describes procedures for adapting TE2s to ISDN B and H channels, etc., using an HDLC-based protocol; (f) that 3.1 kHz bearer capability provides for the connection of modem- equipped TE2s to an ISDN B channel with a terminal adaptor which includes the CODEC function; (g) that Recommendation I.122 describes the additional packet mode bearer service (APMBS) on which it is desirable to support existing DTEs with V-Series type interfaces; (h) that the D channel signalling protocol is described in Recommendations I.430, I.431, I.441/Q.921 and I.451/Q.931; (i) that the I.500-Series includes the requirements to interworking between ISDNs and existing networks; (j) that Recommendation T.90 describes a protocol that may be used by TE1s, What procedures/protocols should be recommended for the adaption to ISDNs of DTEs with V-Series type interfaces and what interworking functions should be defined for the connection of modem-equipped DTEs on a PSTN with terminals on an ISDN, a PDN or other digital network? The following are some of the points that should be considered: 1. continuation of the study, associated with Recommendations V.110 and V.120, of the functionality required for the adaption of existing DTEs to ISDNs; 2. continuation of the study of multi-modem configurations, for use in interworking functions, that automatically adapt to the characteristics of the calling/called modem; 3. continuation of the study of alternate voice/data service using DTE adaption procedures described in Recommendations V.110 and V.120 in association with the 64 kbit/s bearer channel as well as using modem- equipped DTEs in association with the 3.1 kHz bearer channel; 4. what are the appropriate means of multiplexing, both deterministic (see e.g., I.460 and I.430) and statistical, the output of several TE2s onto a single ISDN bearer channel? 5. what should be the interworking requirements between V-Series auto- calling procedures (e.g., V.25bis) and ISDN access signalling protocols/procedures? 6. what are the appropriate functions that should be recommended for the adaption of existing TE2s with V-Series interfaces to ISDN channels for use with the new ISDN APMBS defined in Recommendation I.122? 7. what interworking functions are required for the interconnection of modem-equipped DTEs on the PSTN with a ISDN. This includes study of provisions for operation with network-independent clocks and multiple modem configurations with automatic modem type and rate identification capabilities? 8. what are the appropriate maintenance/testing methods to be applied in terminal adaption and interworking configurations? Note - The study of these points requires close coordination with Study Groups IV, VII, VIII, XI and XVIII. ============================================================ Question 12/XVII - Comparative tests of data communication equipments for use over telephone-type circuits (Continuation of Question 12/XVII, 1985-1988; revised wording) Study of points arising from the implementation and permanent updating of Recommendation V.56. Particular points for further study are: a) Parameters of the line characteristics simulator. The latest standard of the M- and H-Series Recommendations and other relevant standards must be observed and the values of the line characteristics simulator shall be adopted to these. b) Completion and updating of the test parameters As the modem technology becomes more sophisticated with the higher data signalling rates and new additional facilities (e.g. error control, data compression, etc.) these devices may be affected by parameters that are not clearly evident today. Information is continuously requested when new aspects that affect modem operation arise so that the standard test setup can be updated. ============================================================ Question 13/XVII - Interchange circuits (Continuation of Question 13/XVII, 1985-1988; revised wording) (Of interest to Study Groups VII, XVIII) 1. Study of points arising from the implementation of Recommendations V.10, V.11, V.24, V.25, V.25bis, V.28 and revision thereof as required. 2. Continuation of the study of the electrical characteristics of interchange circuits with a view to: a) defining techniques for monitoring power OFF and fault conditions in Recommendations V.10 and V.11; b) defining the parameters of the line signal at the physical interchange point (practical interface) and/or the remote end of the interconnecting cable in addition to or in place of the internal parameters presently defined in Recommendations V.10 and V.11. This will permit the removal of the statement "The parameters defined in this Recommendation are not necessarily measurable at the physical interchange point. This is for further study" which appears in both Recommendations V.10 and V.11; c) introducing characteristics for dynamic balance, common mode rejection; d) defining parameters for a new V-Series Recommendation (related to Recommendation V.11) for electrical characteristics of balanced multipoint interfaces. 3. Further studies for revised or new logical circuit definitions appropriate to Recommendation V.24, together with definition of the interaction between circuits and, in particular, the study of: a) definition of circuits for multiple speed select as used in appropriate modem Recommendations; b) redefinition of circuits to accommodate V.25bis serial autocall protocol; c) implications arising from implementation of error control functions in DCEs. 4. Timing considerations for several interworking arrangements. ============================================================ Question 14/XVII - Refinement and extension of Recommendation V.25bis functions and protocols (New Question, based on Question 13/XVII point 4, 1985-1988) a) Consideration of additional modem functions controllable through the interface (V.xy). This study should take into account the following: - Recommendation V.25bis; - results already worked out (see Annexes 1 and 2); -coordination with on-going work under Questions 9 and 23/XVII and general CCITT/ISO-IEC approach on management. b) Refinement of Recommendation V.25bis. -clarification of the optional or mandatory status of V.25bis protocol elements. -study leading to a description of V.25bis that allows protocol verification on compliance checking. ============================================================ Question 15/XVII - Data transmission over intercontinental switched telephone connections (Continuation of Question 15/XVII, 1985-1988) Considering (a) that approximately 55-60% of the intercontinental switched telephone network trunks use satellite circuits; (b) that a very small but growing percentage of these trunks are derived from TASI and TDMA/DSI equipments; (c) that the traditional echo suppressors are being replaced with new echo cancellers, what is the overall data transmission performance that might be expected over intercontinental switched telephone network connections using existing V-Series modems? This study should include, inter alia, the following points: 1. the effects of echo, with variable delay, on the performance of V- Series modems including items such as: a) effect on circuit 109, etc. 2. the effects of TDMA/DSI, TASI and echo control devices (both echo suppressors and echo cancellers) on duplex and half-duplex data transmission, including items such as: a) circuit 105 to 106 delay intervals; b) effect on the training sequence of certain V-Series modems; c) effect of echo suppressors and echo cancellers, including the techniques of disabling the suppressors and/or cancellers, on two-wire duplex modem operating at data signalling rates of 2400 bit/s and greater. ============================================================ Question 22/XVII - Digital performance of data transmission services using V-Series modems over the telephone network (Continuation of Question 22/XVII, 1985-1988) (Concerns Study Groups IV, VII and XII) Considering (a) that the existing Recommendations V.50 and V.53 only provide signal quality and maintenance limits for modulation rates up to 1200 bauds; (b) that existing Recommendation V.52 describes the "Characteristics of distortion and error rate measuring apparatus for data transmission" at modulation rates up to 4800 bauds; (c) that the existing Recommendations V.50, V.52 and V.53 are based upon the use of the Recommendation V.28 electrical characteristics however, certain V-Series modems may also use the optional Recommendation V.10/V.11 electrical characteristics; (d) that Administrations offer data transmission service using V-Series modems on voice-band telephone-type circuits at data signalling rates up to 9600 bit/s per second (see Recommendation V.5 and V.6), there is an urgent need to study: How should Recommendations V.50, V.52 and V.53 be revised and/or updated? This study should include, inter alia, the following points: 1. Should the study of asynchronous and synchronous data transmission be separated, possibly into separate Recommendations? 2. Should the revised Recommendation(s) refer to both signal quality of interchange circuits and error-rate performance specifications, or should these characteristics be described in separate Recommendations? Note - It is expected that the primary study of the signal quality characteristics will be under Question 13/XVII. 3. Should the "V.50-Series" be reorganized better to reflect the organization of the performance and maintenance Recommendations? 4. What characteristics of asynchronous transmission systems require study? For example: a) further study of the limits of telegraph distortion expressed as degree of isochronous distortion at the DTE/DCE interface for various data signalling rates (expressed in bit/s) is required; b) further study of the limits for bit and block error rates at the DTE/DCE interface for various data signalling rates (expressed in bit/s). Note - As the bit error rate is dependent on the telegraph margin of the receiving apparatus, this margin may need to be specified at various values to take account of the different performance to be expected of mechanical and electrical apparatus. Similarly various values of block length appropriate to the system under test may need to be defined. 5. What characteristics of synchronous data transmission systems require study? For example: a) further study of the merits of measuring bit error vs. block error vs. error free seconds is required; b) further study of various test patterns, such as the 2047 or the 220-1 patterns is required; c) further study of isochronous jitter especially on the timing leads for tandem digital links is required. 6. What should be the duration of error rate performance tests to achieve a high degree of confidence in the test results? Note 1 - The study of this Question should take into account the work of Study Group VII in connection with their Questions 32, 33 and 34/VII. ============================================================ Question 23/XVII - General Data Communication Interface (Continuation of Question 23/XVII, 1985-1988; revised title and wording) Study of the characteristics of a DTE-DCE or DCE-DCE interface with physical characteristics based upon the S or T reference point in ISDN: a) points arising from the implementation of V.230, b) use of the BV1 channel described in V.230 for data transfer with rate adaptation, c) use of the BV2 and DV channel, described in V.230 for other purposes including modem control, loop control, automatic calling, network management, etc., d) definition of a terminal adapter to adapt V-Series DTEs conforming to V.24 and ISO 2110 to DCEs which implement the GDCI.