1、 STDOITU-R RECMN F-574-4-ENGL 1777 m 4855212 0530938 009 m Rec. ITU-R F.594-4 19 RECOMMENDATION ITU-R F.594-4 ERROR PERFORMANCE OBJECTIVES OF THE HYPOTHETICAL CONNECTIONS AT A BIT RATE BELOW THE PRIMARY RATE AND FORMING PART OR ALL OF THE HIGH GRADE PORTION OF AN INTEGRATED SERVICES DIGITAL NETWORK
2、REFERENCE DIGITAL PATH FOR RADIO-RELAY SYSTEMS PROVIDING (Question ITU-R 13419) (1982-1986- 1990- 1991- 1997) The ITU Radiocommunication Assembly, considering that the error performance objectives of digital radio-relay systems should be defined; that the definition of the allowable error performanc
3、e of the hypothetical reference digital path (HRDP) is that propagation and other effects suggest that the error performance should be stated statistically as a fraction a b) necessary for the design and construction of radio-relay systems; c) of time: d) that a bit-error measurement requires a cert
4、ain duration of time which depends on the magnitude of the error ratio; e) that the effect of error burst phenomena and jitter may need to be taken into account; 0 that during normal operation, periods of high bit error ratio will occur which will cause short interruptions (see Note 8); g) that the
5、error performance objectives for an international digital connection operating at a bit rate below the primary rate and forming part of an integrated services digital network (ISDN) have been specified by the ITU-T (see ITU-T Recommendation G.82 1); h) that Recommendations ITU-R F. 1092 and ITU-R F.
6、 1 189, based on ITU-T Recommendation G.826, give error performance objectives for constant bit rate digital path at or above the primary rate carried by digital radio-relay systems which may form part of the international and national portions, respectively, of a 27500 km hypothetical reference pat
7、h; j) that the HRDP defined in Recommendation ITU-R F.556 corresponds to the “high-grade performance” specified in ITU-T Recommendation G.821 and for which the ITU-T has established a rule of apportionment of the total impairment allowance, recommends 1 respectively) HRDP specified in Recommendation
8、 ITU-R F.556 (see Note 1); 2 that fading, interference and all other sources of performance degradation are taken into account in establishing the values given below; 3 that error performance should be assessed in terms of the events errored seconds (ES) and severely errored seconds (SES) and the pa
9、rameters errored second ratio (ESR) and severely errored second ratio (SESR) as defined in Recommendation ITU-T G.821 (see Note 2); 4 5 6 performance requirements for digital radio-relay systems applied to the HRDP. NOTE 1 - N is less than 24 in the 1.544 Mbit/s based hierarchy and less than 32 in t
10、he 2.048 Mbit/s based hierarchy, that the following performance objectives are stated for each direction of the N x 64 kbit/s (1 I N 24 (or 32 that the ESR should not exceed 0.0032 in any month; that the SESR should not exceed 0.00054 in any month; that Annex 1 should be used for guidance on factors
11、 which need to be taken into account in determining COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN F-594-4-ENGL 3997 W 4855232 0530939 T45 W 20 Rec. ITU-R F.594-4 NOTE 2 - Error performance events and parameters are de
12、fined in the ITU-T Recommendation G.821, as follows: - - ES : 1s period in which one or more bits are in error. SES: Is period which has a bit error ratio 2 1 x - ESR: ratio of ES to total seconds in available time during a fixed measurement interval. - NOTE 3 - The output bit stream from a digital
13、radio-relay system may suffer from jitter. The effect of jitter on the error performance of digital radio-relay systems requires further study. The general issues of jitter are addressed by the ITU-T. NOTE 4 - This Recommendation relates to the HRDP. The values given are for use by the system design
14、er, and it is not intended that they should be quoted in specifications of equipment or used for acceptance tests. NOTE 5 - Contributions from multiplex equipment are not included on the basis that they are negligible in comparison with the contribution from transmission systems (see ITU-T Recommend
15、ation G.821). NOTE6-The Recommendation applies only when the system is considered to be available in accordance with Recommendation ITU-R F.557 and includes SESs which persist for periods of less than 10 consecutive seconds. Periods of SESs which persist for 10 consecutive seconds duration or longer
16、 are taken into account by Recommen- dation ITU-R F.557. NOTE 7 -The limits given in $ 5 are based upon the 10 s unavailability criteria given in Recommendation ITU-R F.557, and therefore will not necessarily include all forms of degradations in performance due to adverse propagation. Degradations d
17、ue to adverse propagation which persist for 10 s or longer will be limited by the requirements of Recommendation ITU-R F.557. NOTE 8 - Adverse propagation conditions can result in a decrease andor distortion of the wanted signal as well as an increase in the level of interfering signals. NOTE 9 - Th
18、e requirements are intended to meet the relevant performance objectives of ITU-T Recommen- dations G.821 and G.921 under all normally envisaged operating conditions. SESR: ratio of SES to total seconds in available time during a fixed measurement interval. ANNEX 1 Factors to be taken into account wh
19、en determining performance requirements for digital radio-relay systems applied to the HRDP This Annex considers factors which need to be taken into account in determining performance requirements for digital radio-relay systems applied to the HRDP. 1 SESR objective In ITU-T Recommendation G.821 the
20、 ITU-T states that: - - for a 27 500 km hypothetical reference connection (HRX) the SESR should not exceed 0.002 in any month; the SESR of the 25 O00 km high grade portion of the HRX should not exceed 0.0004 in any month. In addition, an allowance of 0.0005 is given to a 2 500 km HRDP for radio-rela
21、y systems to take account of adverse propagation conditions. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesRec. ITU-R F.594-4 21 Therefore, for a 2 500 km HRDP, the SESR should not exceed 0.00054 (ie., 0.0005 + 0.00004, where 0.00004
22、 has been obtained by linearly scaling the 0.0004 objective allocated to the 25 O00 km high grade portion of the HRX). With advances in high speed data transmission services, some users may require higher transmission quality than specified above. In particular, users may become concerned with the f
23、requency and duration of circuit interruptions. Although it is difficult to predict the frequency of such breaks from a knowledge of the design of radio-relay systems, it may be appropriate to reduce the SESR objective by considering whether the additional ITU-T Recommendation G.821 allowance for ad
24、verse propagation may be discarded. If this is the case, it will be necessary to include advanced technology in the design of radio-relay systems to achieve such high performance without compromising the economics of the system. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services
