1、 Rec. ITU-R F.1703 1 RECOMMENDATION ITU-R F.1703 Availability objectives for real digital fixed wireless links used in 27 500 km hypothetical reference paths and connections (Question ITU-R 102/9) (2005) Scope This Recommendation provides updated information on availability objectives for real digit
2、al fixed wireless links used in 27 500 km hypothetical reference paths taking into account ITU-T Recommendation G.827 (approved in 2003). It is the only Recommendation defining availability objectives for all real digital fixed wireless links. Recommendations ITU-R F.1492 and ITU-R F.1493 are supers
3、eded by this Recommendation. The applicability of Recommendations ITU-R F.557, ITU-R F.695, ITU-R F.696 and ITU-R F.697 is limited to systems designed prior to the approval of this Recommendation. Examples of the application of the Recommendation are given in Annex 1. Definition of the events, deriv
4、ed from ITU-T Recommendation G.827, is given in Annex 2. The ITU Radiocommunication Assembly, considering a) that ITU-R has specified the error performance objectives for real digital fixed wireless links used in 27 500 km hypothetical reference paths (HRPs) and connections (see Recommendation ITU-R
5、 F.1668); b) that ITU-T has specified the availability parameters and objectives for end-to-end and path element of international constant bit-rate digital paths at or above the primary rate (see ITU-T Recommendation G.827); c) that digital fixed wireless systems play an important role in the intern
6、ational path; d) that it is necessary for the availability of fixed wireless systems to be compliant with the availability objectives specified in ITU-T Recommendation G.827; e) that any real path, link or connection for digital data transmission may be realized using a linear and/or redundant topol
7、ogy, depending on the needs of network providers; f) that digital fixed wireless systems may be used in intermediate and terminating countries of an international path; g) that for the purposes of this Recommendation, the national portion of the 27 500 km HRP can be subdivided into three basic secti
8、ons (see Fig. 1); 2 Rec. ITU-R F.1703 1703-01LFIGURE 1Basic sections of the national portion of the HRPPathend-point(PEP)Localexchange(LE)Note 1Terminalinternationalcentre(TIC)AccessportionShort haulportionLong haulportionNote 1 Depending on the country network architecture, this centre may coincide
9、 with a primary centre (PC), secondary centre (SC) or tertiary centre (TC) (see ITU-T Recommendation G.801).Access: Access network section, including the connections between PEP and the corresponding local access switching centre/cross connector LE. It corresponds to the PAE.Short haul: Short haul n
10、etwork portion, including the connections between a local access switching centre/cross connector, LE, and a PC, SC or TC (depending on the network architecture).Long haul: Long haul network portion, including the connections between a PC, SC or TIC (depending on the network architecture) and the co
11、rresponding international gateway (IG).Note 2 TIC, PAE and NPCE are defined in ITU-T Recommendation M.1010.Nationalpath coreelement(NPCE)Pathaccesselement(PAE)h) that for the path elements of a constant bit-rate digital path at or above the primary rate, ITU-T Recommendation G.827 specifies fixed-bl
12、ock allocation plus distance-based allocations for the availability objectives; j) that there is a need to establish the availability objectives for real digital radio links in order to allow the proper engineering of fixed wireless links; k) that unavailability of fixed wireless systems may be due
13、to propagation effects, equipment failure, human intervention, interference or other causes; l) that the availability objectives, availability ratio (AR) and mean time between outage (Mo) or its reciprocal, outage intensity (OI) are needed for design purposes, recommends 1 that availability objectiv
14、es applicable to any real digital fixed wireless link forming part of the international portion or belonging to the long-haul network portion of the national portion of an international constant bit-rate digital path and connection should be fixed-block plus distance-based allocated; 2 that availabi
15、lity objectives applicable to any real digital radio link belonging to the access and short-haul network portions of the national portion of an international constant bit-rate digital path and connection should be fixed block-based (i.e. length independent); Rec. ITU-R F.1703 3 3 that the availabili
16、ty objectives applicable to each direction of a fixed wireless link of length, Llink, can be derived from the values given in Tables 1, 2, 3 and 4 by means of equations (1) and (2) for the AR and Mo, or the reciprocal of Mo defined as OI objectives, respectively; +=jRlinkjCLLBAR 1 (1) jRlinkjELLDOIM
17、o+=1/1 (2) where: the value of j is: for international portion: 1 for Lmin7 500 km for section of national portion: 5 for access network 6 for short haul 7 for long haul LR:reference length LR= 2 500 km. The lower limit of Llinkused to scale the objectives is Lmin= 50 km. The values of Bj, Cj, Djand
18、 Ejare given in Tables 1, 2, 3 and 4. The parameter OI refers to the number of unavailability events per year, so its reciprocal Mo has to be multiplied by the number of seconds in a year to represent the effective mean time between the unavailability events that have occurred in a year expressed in
19、 seconds; 4 that availability objectives should be partitioned in order to take into account unavailability events due to propagation events, equipment failure, human intervention and other causes. The partitioning of objectives for the different unavailability causes is outside the scope of this Re
20、commendation; 5 that for the case when the link is composed of more than one hop, the objectives are applicable for the whole link. The scaling of the objectives for each individual hop is under the network operator responsibility (see Annex 1 for more information); 6 that the objectives for radio l
21、ink forming part of any path element composing the international portion (i.e. inter-country path core element (ICPCE) and international path core element (IPCE) should in any case not exceed the objectives defined in ITU-T Recommendation G.827 (see Annex 1 to this Recommendation for more informatio
22、n); 7 that the overall objectives for the national portion (i.e. obtained by adding the objectives of access network, short haul and long haul) implemented by fixed wireless systems should not exceed in any case the objectives defined in ITU-T Recommendation G.827 for the national portion element (s
23、ee Note 5). 4 Rec. ITU-R F.1703 NOTE 1 The international portion of a constant bit-rate digital path at or above the primary rate is composed of at least one ICPCE and/or one IPCE. NOTE 2 ICPCE is the path element (PE) carried on the highest order digital path across the border between two countries
24、. The ICPCE is the link between networks in different countries, considered as subnetworks. This PE is limited by the frontier stations (FSs) where the highest order inter-country path may be terminated. When the highest order inter-country path is not terminated in the FS, the ICPCE is limited by t
25、he supporting inter-country section access point. NOTE 3 IPCE is the PE used in a core network. The boundary of this PE depends on its application; for a transit country this PE is limited by the two FSs. For a terminating country, this element is limited by the IG and the FS. In particular this ele
26、ment should be delimited by the international switching centre (ISC) and the FS or by the TIC, which corresponds to the end of the international portion, and the FS. NOTE 4 The international portion of a path is composed by the ICPE and ICPCE, so the boundary of this element corresponds to the IPCE
27、(i.e. FS or TIC or ISC) and by the portion of ICPCE that crosses the border between two countries. NOTE 5 The national path element (NPE) is a PE used in a terminating country to connect the international portion and the PEP. The NPE includes both the PAE and the NPCE. NOTE 6 For the scope of this R
28、ecommendation the national portion corresponds to the NPE. NOTE 7 The TIC, the PAE and NPCE are defined in ITU-T Recommendation M.1010. (Note that the ISC and TIC may be in the same location.) NOTE 8 The criteria for entry to and exit from the unavailable state is defined in Annex A of ITU-T Recomme
29、ndation G.826. NOTE 9 The objectives for access portion of the network are assumed length independent, since typically these links are shorter than 50 km. NOTE 10 The objectives for access portion and short-haul portion are defined for a maximum length Lmax= 250 km. NOTE 11 The short-haul objectives
30、 for lengths greater than 2 500 km are not applicable. NOTE 12 The availability objectives and apportionment criteria for connections should be the same as for paths. NOTE 13 The criteria defining the entry to and exit from the unavailable state is defined in A.1 of Annex A of ITU-T Recommendation G
31、.826. NOTE 14 Further studies are invited to define what number of events, due to anomalous propagation conditions, can give rise to self-healing unavailability events, due to such events, usually much shorter than four hours mean time to restoration (MTTR) = four hours is defined in ITU-T Recommend
32、ation G.827 as a base for OI objectives), are not taken into account for OI objectives in ITU-T Recommendation G.827. Rec. ITU-R F.1703 5 NOTE 15 Further studies are invited to establish whether and to what extent the AR and the OI objectives can be improved. TABLE 1 Parameters for AR objectives for
33、 links forming part of an international portion of constant bit-rate digital path Length (km) Lmin Llink 250 250 Llink 2 500 2 500 Llink 7 500 Llink 7 500 B1C1B2C2B3C3B4C4International portion 1.9 1031.1 1043 1030 3 1030 3 1030 TABLE 2 Parameters for AR objectives for links forming part of a nationa
34、l portion of constant bit-rate digital path element Access portion Short-haul portion Long-haul portion B5C5B6C6B7C70 5 1040 4 1043 103for 250 km Llink 2 500 km 1,9 103for Lmin Llink 250 km 0 for 250 km Llink 2 500 km 1.1 104for Lmin Llink 250 km TABLE 3 Parameters for OI objectives for links formin
35、g part of an international portion of constant bit-rate digital path Length (km) Lmin Llink 250 250 Llink 2 500 2 500 Llink 7 500 Llink 7 500 D1E1D2E22D3E3D4E4International portion 150 50 100 55 100 55 100 55 TABLE 4 Parameters for OI objectives for links forming part of a national portion of consta
36、nt bit-rate digital path element Access portion Short-haul portion Long-haul portion D5E5D6E6D7E70 100 0 120 100 for 250 km Llink 2 500 km 150 for Lmin Llink 250 km 55 for 250 km Llink 2 500 km 50 for Lmin Llink 250 km 6 Rec. ITU-R F.1703 Annex 1 Terminology and examples of evaluation for real link
37、1 Introduction This Annex gives further information on the meaning of terms related to the connection, on the relationship between the objectives given by ITU-T Recommendation G.827 and the objectives defined in this Recommendation and some examples of the evaluation of the objectives for a real rad
38、io link. 2 Definition and terminology The scope of this Recommendation is to define the availability objectives for a real radio link, but since in a telecommunication network the term “link” is quite general the clarification of the meaning of this term within the context of the current Recommendat
39、ion is given below. The definition of PE is given in ITU-T Recommendation G.827. An example of a path composed by several PEs is shown in Fig. 2. A radio link can be identified with a portion of the path and it can implement an IPCE (or a portion of it) and/or an ICPCE, as shown in Fig. 3, or can be
40、long to any portion of the network, as shown in Fig. 4. Moreover a link can be formed by several hops. 1703-02IB IB IBPEPCPFS FS FS FS PEPCPNPEIPCEIPCEICPCEIPCEICPCENPETerminating country Transit country 1 Terminating countryNational portion International portion National portionInternational path b
41、etween customer premises (Note 1)PEP: Path end pointIB: International borderNPE: National path elementCP: Customer premisesNote 1 This ICPCE crosses two international borders and is typically supported by a satellite or undersea transmission system.FIGURE 2Conceptual location of the elements of an i
42、nternational path between customer premisesTIC TICRec. ITU-R F.1703 7 1703-02FSIPCERadio linkRadio hopFIGURE 3Example of a radio link implementing a portion of IPCETIC1703-04Radio link L2Radio link L1Radio hopLE PC/SC/TCPEPAccess portion Short haul portion Long haul portionNational portionFIGURE 4Ex
43、ample of radio links used in access portion and short haul portion of NPEHistorically the terminology used in ITU-T Recommendation G.827 is derived from maintenance requirements for international paths, since availability is one of the main factors influencing the behaviour of radio path. In fact, i
44、n the past, error performance requirements were a negligible factor, so they were not considered. Nowadays, from the point of view of maintenance, error performance has the same importance as availability. Furthermore, performance and availability requirements are the fundamental requisites for the
45、design of links. Moreover, the error performance objectives defined in Recommendations ITU-R F.1668 and in ITU-T Recommendations G.826, G.828 and G.829 for plesiochronous digital hierarchy (PDH), synchronous digital hierarchy (SDH) and cell-based paths, are based on different elements of a path. In
46、particular the elements composing an SDH are the multiplex section (MS) and the regenerator section (RS), which are the basis for performance definitions. In order to clarify the relationship between error performance and availability objectives, the relationship between the SDH sections and PEs sho
47、uld be explained. Figures 5 and 6 show examples of a radio link implementing a portion of an IPCE and a part of a short-haul portion NPE and composed of SDH MS and RS. The objectives of this Recommendation are applicable to the radio link, while the objectives of Recommendation ITU-R F.1668 are 8 Re
48、c. ITU-R F.1703 applicable to the single SDH MS and RS implemented by radio. The subdivision of availability and performance objectives to each hop is outside the scope of this Recommendation and of Recommendation ITU-R F.1668. 1703-05FIGURE 5Example of a radio link implementing a portion of the IPC
49、ERadio linkRadio hopFSPEPNPEG.826 national portionG.826 international portionFSTICIGSDH RS SDH RS SDH RSSDH MS SDH MSIPCENational border1703-06FIGURE 6Example of a radio link implementing a portion of the NPERadio linkRadio hopPC/SC/TCPEPAccess portionNPEG.826 international portionTICIGLESDH RS SDH RS SDH RSSDH MS SDH MSShort haul Long haulFor the design of a radio link, besides the objectives, propagation effects should be considered carefully, since the relation between availability and per
