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Working Document for the RSSPWG

A Review of Error Performance & Availability

in meeting

International Obligations based upon ITU Recommendations.

Abstract

Following discussions at the 6th FLCC Policy meeting on the 10th September 2001, concerns were raised that the Minimum Path Length Study Report (August 2001) and its conclusions, would not enable operators to meet theirinternational obligations in terminating traffic. At this meeting a presentation was made on UK Link Length Policy factors and the technical considerations that would affect availability and performance. This working document tries to review the whole issue of error performance and availabilty issues against the ITU-T Recommendation G.826 and G.828 Error Performance Objectives (EPO) in conjunction withthe latest draft revision of the radio link performance of ITU-R Recommendation P.530 for Propagation data and prediction methods required for the design of terrestial line-of-sight systems.

Background

The International Telecommunications Union (ITU) specify the performance objectives for long distance communications links in a series of recommendations produced by the ITU TelecommunicationStandardization Sector (ITU-T). The “G” series of these recommendations specify the performance requirements for a 27,500km Hypothetical Reference Path (HRP).

In particular, ITU-T Recommendations G.821 [1], G.826 [2], G.827 [3] and G.828 [4] specify the performance required from an international digital HRP and G.829 [5] specifies that required from Synchronous Digital Hierarchy (SDH) multiplexand regenerator sections. ITU-T Recommendations G.821, G.826, G.827 and G.828 only specify the end-to-end performance of an HRP and apply irrespective of the physical transport mechanism (e.g. optical fibre, digital radio relay, metallic cable etc.).

The ITU-T G Recommendations cannot be used directly when designing a digital radio system and therefore the ITU Radiocommunications Sector (ITU-R)have used the ITU-T G Recommendations to produce a series of ITU-R Recommendations (the “F” series) which specify the performance required from digital radio links if they are to meet the overall HRP performance objectives.

ITU-R F series Recommendations, based on ITU-T Rec. G.821 (Error performance of an international digital connection forming part of an integrated services digital network),have been used for many years to specify the error performance objectives for digital radio links and specify the required error performance in terms of Bit Error Ratios (BER). ITU-T Rec. G.821 has now been superseded by ITU-T Rec. G.826 (1999) (Error performance parameters and objectives for international, constant bit rate digital paths at or above the primary rate) and ITU-T Rec. G.828 (2000)(Error performance parameters and objectives for international, constant bit rate synchronous digital paths) and new ITU-R error performance objectives based on these and applicable to digital radio links have been produced. These new recommendations specify error performance in terms of error blocks rather than on BER values.

ITU-T Rec. G.826 applies to both Plesiochronous Digital Hierarchy(PDH) and Synchronous Digital Hierarchy (SDH) systems. ITU-T Rec. G.828 only applies to Synchronous Digital Hierarchy (SDH) systems. The performance requirements in ITU-T Rec. G.828 are more stringent than those in ITU-T Rec. G.826 and compliance with ITU-T Rec. G.828 will, in most cases, also ensure compliance with ITU-T Rec. G.821 and ITU-T Rec. G.826. It should be noted that ITU-T Rec. G.828only applies to equipment designed after 10th March 2000 (the date ITU-T Rec. G.828 was adopted by the ITU). Performance objectives for paths using equipment designed prior to this date are given in ITU-T Rec. G.826.

A key ITU-R Recommendation in this context is ITU-R F.1491 (Error performance objectives for real digital radio links used in the national portion of a 27,500km hypothetical...
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