ETR 120 : 20001

Foreword
1 Scope
2 References
3 Definitions and abbreviations
   3.1 Definitions
   3.2 Abbreviations
4 Applicability of services
5 Realisation of service
6 Other users perception of the open channel operation
   6.1 Single timeslot open channel operation
   6.2 Distinction between group call and circuit mode data
7 Optimisation of the call set-up protocol
   7.1 Definition of performance parameters
8 Optimisation of the supplementary services involved at the
   set-up
   8.1 Definition of performance parameters
9 System performance parameters
   9.1 Modelling of the air interface protocol
10 Composition of annexes
Annex A (informative): Group voice call scenarios (TETRA 03.52)
      A.1 Procedures for message trunked systems
      A.2 Procedures for transmission trunked systems
      A.3 Procedures for quasi-transmission trunked systems
Annex B (informative): Supplementary Service stage 1: Access
        Priority (SS-AP) (TETRA 03.69)
      B.1 Scope
      B.2 Normative references
      B.3 Definitions and abbreviations (TETRA 01.04)
      B.4 Supplementary Service Access Priority (SS-AP)
          Stage 1 specification
Annex C (informative): Supplementary Service stage 1:
        Priority Call (SS-PC) (TETRA 03.70)
      C.1 Scope
      C.2 Normative references
      C.3 Definitions, symbols and abbreviations (if any)
      C.4 Supplementary Service Priority Call (SS-PC)
          Stage 1 specification
Annex D (informative): Supplementary Service stage 1:
        Pre-emptive Priority Call (SS-PPC) (TETRA 03.76)
      D.1 Scope
      D.2 Normative references
      D.3 Definitions and abbreviations (TETRA 01.04)
      D.4 Supplementary Service Pre-emptive Priority Call
          (SS-PPC) Stage 1 specification
Annex E (informative): Supplementary Service stage 1: Call
        Retention (SS-CRT) (TETRA 03.85)
      E.1 Scope
      E.2 Normative references
      E.3 Definitions and abbreviations
      E.4 Supplementary Service Call Retention (SS-CRT)
          stage 1 specification
Annex F (informative): Supplementary Service stage 1: Call
        Authorized by Dispatcher (SS-CAD) (TETRA 03.66)
      F.1 Scope
      F.2 Normative references
      F.3 Definitions and abbreviations (TETRA 01.04)
      F.4 Supplementary Service Call Authorized by Dispatcher
          (SS-CAD) Stage 1 specification
Annex G (informative): Supplementary Service stage 1: Late
        Entry (SS-LE) (TETRA 03.74)
      G.1 Scope
      G.2 Normative references
      G.3 Definitions and abbreviations (TETRA 01.04)
      G.4 Supplementary Service Late Entry (SS-LE)
          Stage 1 specification
Annex H (informative): Supplementary Service stage 1: Dynamic
        Group Number Assignment (SS-DGNA) (TETRA 03.83)
      H.1 Scope
      H.2 Normative references
      H.3 Definitions and abbreviations (TETRA 01.04)
      H.4 Supplementary Service Dynamic Group Number
          Assignment (SS-DGNA) Stage 1 specification
Annex J (informative): Supplementary Service stage 1:
        Transfer of Control (SS-TC) (TETRA 03.75)
      J.1 Scope
      J.2 Normative references
      J.3 Definitions and abbreviations (TETRA 01.04)
      J.4 Supplementary Service Transfer of Control (SS-TC)
          Stage 1 specification
History

Prepared to assist Electricity staff engaged in applying Engineering Recommendation G74 to evaluate short circuit current in transmission and distribution networks and in generating station auxiliary systems. Aim is to provide practical guidance through the provision of worked examples for typical networks highlighting where necessary the key features of the methodology and implications of the results on circuit breaker duties. Guidance on the fault infeed from induction motors is included.