1、G9 Page 1 Recommendation T/Tph 44 micosia 1990 (CAC) RELIABILITY OF DIGITAL LEASED CIRCUITS Recommendation proposed by the “Telephone Operation and Tariffs” Working Group T/WG 2 (Tph) Text of the Recommendation adopted by the “Telecommimications” Commission: “The European Conference of Postal and Te
2、lecommunications Administrations, considering - the need, for commercial reasons, to provide the user with information on the performance of digital international leased circuits for private use, - the efforts made by administrations, for the rational management of their circuits and the need to ens
3、ure customers requirements correspond to the actual technical capability of the networks, - that digital international leased circuits are provided and maintained to standards, procedures and organization as defined in the CCITT-M Recommendations, - that such data can as a rule be obtained by observ
4、ing the reliability performance of existing digital international leased circuits in the service area of CEPT by means of the methods of statistical and probability calculations, - that the observation and evaluation procedures used must be applied in a uniform, coordinated and repeatable manner, -
5、that CCITT Recommendation M.1016 is of special importance in this respect, - that in consideration of these aspects, an average availability performance figure of 99.42% has been established and published for analogue international leased circuits throughout CEPT (cf. CEPT Recommendation T/Tph - tha
6、t the use of digital systems in national and international transmission line networks is expected to result in higher avaiiability standards for digital international leased circuits than for analogue international leased circuits, - that during the period from 1 January to 31 March 1988 the availab
7、ility performance of 111 digital international leased circuits of 64 kbit/s between the Federal Republic of Germany, Austria, Belgium, France, the Netherlands, the United Kingdom, Sweden and Switzerland was observed and evaluated, - that the performance figure of 99.13% was determined from measureme
8、nts on 57 circuits where information from the two control stations was available, - that a more reliable data base was considered necessary in order to obtain results which represented the average availability standard expected for digital international leased circuits of 64 kbit/s throughout CEPT,
9、- that, therefore, a second observation was agreed to be carried out during the period from 1 January to 31 March 1989 on 206 circuits of 64 kbit/s between the Federal Republic of Germany, Austria, Belgium, Denmark, France, Italy, Sweden, Switzerland and the United Kingdom, - that a new availability
10、 figure of 99.19% was established, - that this figure will certainly improve as and when the digital networks of CEPT-member countries grow and the O 41 E), O operational conditions are adapted accordingly, recommends that Administrations are invited to make the following information available to th
11、eir customers : 1. A list of the relevant CCITT-M Recommendations, which constitute the basis of international arrangements and 2. The average performance of digital international leased circuits between CEPT-member countries has been standards (see Annex A). observed and evaluated respectively duri
12、ng a series of tests over a 2-year period (Note I). Edition of July 10, 1990 -I r CEPT T/TPH*44*E 90 W 232b4L4 00102b3 4 T/Tph 44 E Page 2 3. Mean values concerning the current performance of intra-CEPT digital international leased circuits have been established over two three-month observation peri
13、ods as follows: Mean Downtime per circuit Mean Time to Restore Service Mean Time between Failures 17.57 hours 8.44 hours 42.86 days 99.19% Mean Service Availability per circuit 4. This data will be up-dated when Administrations agree bilaterally that a significant change of the figures has taken pla
14、ce. Administrations keep such up-dated data concerning their individual trafic relations available for their customers (CCITT Recommendation M. 1016 refers). 5. The performance of any individual digital international leased circuit may vary considerably from the mean values stated above. The effecti
15、ve availability values will tend to the mean values if the measurement period exceeds three months. 6. Digital international leased circuits with a high degree of utilization tend to have a lower service availability than those of lower utilization because the customer observes more closely the form
16、er which results in an increasing number of fault reports. 7. Failures occuring on customer equipment are not included in the recording of circuit failures. Therefore, a failure on a digital international leased circuit should not be reported until the customer has verified that his equipment, as we
17、ll as that of the distant terminal, is working correctly. 8. If the information provided on the basis of this Recommendation fails to meet users requirements. Adininistra- tions will give additional information about additional ways of improving the performance of the service and any associated char
18、ges. 9. In principle it is not possible to take advantage of the information provided to customers on the basis of this Recommendation in order to claim refunds. Only CCITT Recommendation D. 1 or the special contract clauses will be applied in the case of refkds. Note 1. The availability established
19、 on the basis of this method corresponds to the average service availability as perceived by the customer. (b Edition of July 10, 19,9-.- - - CEPT T/TPH*44*E 90 2326434 0030264 b W - - Edition of July 10, 1990 I T/Tph 44 E Page 3 Annex A LIST OF CCITT RECOMMENDATIONS RELEVANT TO THE INVESTIGATION OF
20、 THE AVAILABILlTY PERFORMANCE OF DIGITAL INTERNATIONAL LEASED CIRCUITS 1. M. 1016 Assessment of the service availability performance of international leased circuits. 2. M.1370 Setting up and lining up of international data transmission systems operating in the range 48 kbit/s to 64 kbit/s. 3. M.101
21、2 Circuit control station for leased and special circuits. 4. M.1013 Siib-control for leased and special circuits. 5. M.93 Exchange of contact point information for the maintenance of international services and the internation- al network. 6. M. 140 Designation of international circuits, groups, digital blocks, etc. 7. M. 1045 Preliminary exchange of information for the provision of international leased circuits. 8. M.821 Error performance of an international digital connection forming part of an integrated services digital network.
