1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T X.147TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 1(04/2004) SERIES X: DATA NETWORKS AND OPEN SYSTEM COMMUNICATIONS Public data networks Network aspects Frame relay network availability Amendment 1: Specification of availability objective val
2、ues ITU-T Recommendation X.147 (2003) Amendment 1 ITU-T X-SERIES RECOMMENDATIONS DATA NETWORKS AND OPEN SYSTEM COMMUNICATIONS PUBLIC DATA NETWORKS Services and facilities X.1X.19 Interfaces X.20X.49 Transmission, signalling and switching X.50X.89 Network aspects X.90X.149 Maintenance X.150X.179 Admi
3、nistrative arrangements X.180X.199 OPEN SYSTEMS INTERCONNECTION Model and notation X.200X.209 Service definitions X.210X.219 Connection-mode protocol specifications X.220X.229 Connectionless-mode protocol specifications X.230X.239 PICS proformas X.240X.259 Protocol Identification X.260X.269 Security
4、 Protocols X.270X.279 Layer Managed Objects X.280X.289 Conformance testing X.290X.299 INTERWORKING BETWEEN NETWORKS General X.300X.349 Satellite data transmission systems X.350X.369 IP-based networks X.370X.399 MESSAGE HANDLING SYSTEMS X.400X.499 DIRECTORY X.500X.599 OSI NETWORKING AND SYSTEM ASPECT
5、S Networking X.600X.629 Efficiency X.630X.639 Quality of service X.640X.649 Naming, Addressing and Registration X.650X.679 Abstract Syntax Notation One (ASN.1) X.680X.699 OSI MANAGEMENT Systems Management framework and architecture X.700X.709 Management Communication Service and Protocol X.710X.719
6、Structure of Management Information X.720X.729 Management functions and ODMA functions X.730X.799 SECURITY X.800X.849 OSI APPLICATIONS Commitment, Concurrency and Recovery X.850X.859 Transaction processing X.860X.879 Remote operations X.880X.899 OPEN DISTRIBUTED PROCESSING X.900X.999 For further det
7、ails, please refer to the list of ITU-T Recommendations. ITU-T Rec. X.147 (2003)/Amd.1 (04/2004) i ITU-T Recommendation X.147 Frame relay network availability Amendment 1 Specification of availability objective values Source Amendment 1 to ITU-T Recommendation X.147 (2003) was approved on 29 April 2
8、004 by ITU-T Study Group 17 (2001-2004) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. X.147 (2003)/Amd.1 (04/2004) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardiza
9、tion Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which me
10、ets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts
11、 purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is
12、 voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ an
13、d the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may inv
14、olve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Rec
15、ommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database.
16、 ITU 2004 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. X.147 (2003)/Amd.1 (04/2004) iii CONTENTS Page 1) Clause 2 1 2) Clause 8 1 3) New Appendix II 4 ITU-T Rec. X.147 (2003)/Amd.1 (04/2004) 1 ITU
17、-T Recommendation X.147 Frame relay network availability Amendment 1 Specification of availability objective values 1) Clause 2 Add the following references alphanumerically to clause 2: ITU-T Recommendation G.827 (2003), Availability performance parameters and objectives for end-to-end internationa
18、l constant bit-rate digital paths. ITU-T Recommendation X.111 (2003), Principles for the routing of international frame relay traffic. 2) Clause 8 Replace the existing clause 8 with the following: 8 Availability performance objectives This clause specifies performance objectives for the Availability
19、 Ratio and MTBSO parameters for the following connection portion types: Access Circuit Section; National Network Portion; International Transit Network Portion; International Interoperator Portion. The network portion objectives define long-term performance of a frame relay virtual connection. It is
20、 recognized that some frame relay virtual connections might not meet the long-term objectives when the assessment is made over a shorter period, e.g., one month. The recommended period for assessing long-term performance is one year. A single set of objectives is specified which are worst-case and w
21、hich are applicable to each individual connection portion. All values are provisional and they need not be met by networks until they are revised (up or down) based on real operational experience. The end-to-end availability performance of an international Frame Relay virtual connection can be calcu
22、lated by simply multiplying the availability values for each portion. 8.1 Availability ratio The Availability Ratio objective for each connection portion type is specified in Table 1. Availability objectives for specific virtual connections may be calculated by using the formulas given in 8.3 and ap
23、plying the method specified in 8.4. Specific examples for calculating the end-to-end objective of a virtual connection are given in Appendix II. 2 ITU-T Rec. X.147 (2003)/Amd.1 (04/2004) Table 1/X.147 Objectives for availability ratio Connection portion or section Availability ratio objective Access
24、 Circuit Section (Notes 1 and 2) (in accordance with ITU-T Rec. G.827) See 8.3 National Network Switching Portion (Notes 3 and 4) 99.98% International Transit Network Portion (Notes 3 and 4) 99.98% International Interoperator Portion (Notes 1 and 2) (in accordance with ITU-T Rec. G.827) See 8.3 NOTE
25、 1 The Availability Ratio objectives of an Access Circuit Section and an International Interoperator Portion, of a given length, are calculated using guidelines based on the availability of objective formulas specified in ITU-T Rec. G.827. These formulas, adapted for Frame Relay, are given in 8.3. I
26、n the case of the Access Circuit Section, the achieved availability may be also impacted by geographical and climatic extremes. NOTE 2 ITU-T Rec. G.827 defines availability performance parameters and objectives for end-to-end international constant bit-rate digital paths. NOTE 3 All Network Portion
27、or Section Availability objectives are provisional and need not be met by networks until they are revised (up or down) based on real operational experience. NOTE 4 It is recognized that over short-term periods, e.g., one month, the performance of an individual virtual connection might not meet the o
28、bjective. However, network operators should endeavour to ensure that in the long term, the availability of an individual virtual connection meets the objective. 8.2 Mean time between outages The MTBO objective for each connection portion type is specified in Table 2. Table 2/X.147 Objectives for mea
29、n time between service outages Connection portion or section MTBSO objective Access Circuit Section (Notes 1, 2 and 3) 1200 hours National Network Portion (Note 4) 1200 hours International Transit Network Portion (Note 4) 1200 hours International Interoperator Portion (Notes 1 and 2) 1200 hours NOTE
30、 1 The MTBSO values for the Access Circuit Section and the International Interoperator Portion are consistent with the Outage Intensity objectives defined in ITU-T Rec. G.827. NOTE 2 ITU-T Rec. G.827 defines availability performance parameters and objectives for end-to-end international constant bit
31、-rate digital paths. NOTE 3 ITU-T Rec. G.827 defines a performance objective for Outage Intensity. Outage Intensity is the reciprocal of MTBO when the MTBO is expressed as a fraction of the long-term assessment period (usually taken to be one year). NOTE 4 The MTBSO objectives specified for the Nati
32、onal and International Transit Network Portions are provisional and need not be met by networks until they are revised (up or down) based on real operational experience. 8.3 Formulas for availability objectives for access circuit sections and international interoperator portions The lengths of the a
33、ccess circuit sections and international interoperator portions of an international Frame Relay virtual connection have a major impact on the availability of a virtual connection. The formulas provided in this clause are based on the concepts specified in ITU-T Rec. G.827 (2003). It should also be n
34、oted that despite these formulas and the specification of objectives for the access circuit section and the national network switching portion, the only commitment of Frame Relay ITU-T Rec. X.147 (2003)/Amd.1 (04/2004) 3 network operators is to the availability objective of the national portion, tha
35、t is to say, the concatenation of the availability objectives for the access circuit section and the national network (switching) portion. 8.3.1 Length Except for Access Circuit Section or International Interoperator Portions carried on undersea cables, the lengths refer to the actual route lengths
36、or the air-route distance multiplied by a routing factor, whichever is smaller. The routing factor is as follows: if the air-route distance is less than 1000 km, then the routing factor is 1.5; if the air-route distance is larger than 1000 km and less than 1200 km, then the calculated route length i
37、s taken to be 1500 km; if the air-route distance is larger or equal to 1200 km, then the routing factor is 1.25. For an Access Circuit Section or an International Interoperator Portion carried on an undersea cable, the actual cable route length is used. The length value of an Access Circuit Section
38、is denoted by LACS, and the length of an International Interoperator Portion is denoted by LIIOP. NOTE If the length of an Access Circuit Section or an International Interoperator Portion is greater than 10 500 km, its length, for the purpose of calculating its availability objective, is taken to be
39、 10 500 km. 8.3.2 Availability objectives Availability objectives for the Access Circuit Section and the International Interoperator Portion are determined by the following equations which are consistent with the guidelines specified in ITU-T Rec. G.827: For an Access Circuit Section or an Internati
40、onal Interoperator Portion: AR = 1 k x where: x = 0.0005 and k = 1 + integer part of (L/100) with L being either LACSor LIIOPas appropriate. The National Portion availability objective is: A = 1 (0.0002 + k x) where: x = 0.0005 and k = 1 + integer part of (LACS/100). NOTE The National Portion availa
41、bility objective may alternatively be estimated as the product of the Access Circuit Section and National Network Portion availability objectives. 8.4 Method of concatenation for calculating availability objective for a frame relay virtual connection The end-to-end availability objective of an inter
42、national frame relay virtual connection is calculated as follows: Define the following parameters: ACO is the Availability objective of the Originating Access Circuit Section; ACD is the Availability objective of the Destination Access Circuit Section; 4 ITU-T Rec. X.147 (2003)/Amd.1 (04/2004) NNO i
43、s the Availability objective of the Originating National Network Portion; NND is the Availability objective of the Destination National Network Portion; ITNkis the Availability objective of the International Transit Network Portion (k); IIPkis the Availability objective of the International Interope
44、rator Portion (k). Assume that international frame relay virtual connection transits through three transit networks ITN1, ITN2and ITN3.The end-to-end availability of an international frame relay virtual connection is given by: Availability Ratio = ACO NNO IIP1 ITN1IIP2ITN2 IIP3 ITN3 IIP4 NND ACD NOT
45、E 1 ITU-T Rec. X.111 recommends a maximum of 3 transit networks on any international connection. NOTE 2 In the case where less than 3 International Transit Network portions are employed to establish the frame relay connection, the appropriate terms in the expression (ITN1 IIP2 ITN2 IIP3 ITN3 IIP4) a
46、re set to unity as required. 3) New Appendix II Add new Appendix II as follows: Appendix II Example calculations of end-to-end availability objectives II.1 Illustrative example 1 Assume that both access circuit sections have a 1000 km route length (an access circuit of 1000 km is representative of a
47、n extreme case). Using the formulas in 8.3, the availability objective of each Access Circuit Section is calculated to be 99.45%. For the example where two international transit networks are required to establish the end-to-end connection, three International Interoperator Portions are required. Ass
48、ume that the International Interoperator Portions have route lengths of 1000 km, 6000 km and 3300 km. Using the formulas in 8.3, the availability objectives of the International Interoperator Portions are calculated to be 99.45%, 96.95%, and 98.30%, respectively. From Table 1 the Availability object
49、ive for each Network Portion is 99.98%. Hence the end-to-end availability objective is: (0.9945 0.9998 0.9945 0.9998 0.9695 0.9998 0.9830 0.9998 0.9945) = 0.9366 = 93.66% II.2 Illustrative example 2 Assume that both access circuits are less than 100 km route length. Using the formulas in 8.3, the availability objective for each Access Circuit Section is calculated to be 99.95%. For the example where two international transit networks are required to e
