SIST ETS 300 727 E1:2003

• Abstract:

  This draft European Telecommunication Standard (ETS) defines a frame substitution and muting procedure which shall be used by the Receive (RX) Discontinuous Transmission (DTX) handler when one or more lost speech or Silence Descriptor (SID) frames are received from the Radio Sub System (RSS). The requirements of this ETS are mandatory for implementation in all GSM Base Station Systems (BSS)s and Mobile Stations (MS)s capable of supporting the enhanced full-rate speech traffic channel. It is not mandatory to follow the bit exact implementation outlined in this specification and the corresponding C-source code.

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.070.50 - Global System for Mobile Communication (GSM)
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Mandate: T-172
• Ref Project: ETSI ETS 300 727 ed.1 (1997-04) - Digital cellular telecommunications system; Substitution and muting of lost frames for Enhanced Full Rate (EFR) speech traffic channels (GSM 06.61 version 5.1.2)

SIST ETS 300 727 E1:2003 is the Slovenian adoption of ETS 300 727 Edition 1, a European Telecommunication Standard from ETSI for the Global System for Mobile communications (GSM). It specifies how Enhanced Full Rate (EFR) speech traffic channels should handle lost speech frames and Silence Descriptor (SID) frames by substitution and muting, so that GSM Base Station Systems (BSS) and Mobile Stations (MS) behave consistently when frames are missing.

What does SIST ETS 300 727 E1:2003 specify?

SIST ETS 300 727 E1:2003 specifies the frame substitution and muting procedure used by the Receive (RX) Discontinuous Transmission (DTX) handler when one or more lost speech or SID frames are received from the Radio Sub System (RSS). In practice, this is the behaviour that helps conceal frame loss and control how audio fades when the channel quality drops.

The requirements apply to GSM BSS and MS that support the enhanced full-rate speech traffic channel. The document also states that a bit exact implementation and the corresponding C-source code are not mandatory, as long as the required behaviour is met.

The document is organized into:

• Scope
• Normative references
• Definitions and abbreviations
• General
• Requirements
• Example solution

What are the key requirements of SIST ETS 300 727 E1:2003?

The core requirement is that lost-frame handling must prevent unpleasant audio effects and progressively reduce output when repeated errors occur. The standard separates lost speech frames from lost SID frames, because they are handled differently.

Error detection and bad frame indication

The RSS sets the Bad Frame Indication (BFI) flag when it detects an error using its CRC-based checks and other error detection mechanisms. The Transcoding Rate Adaptation Unit (TRAU) also derives a Bad Sub-block Indication obtained from A-bis CRC checks (BSI_Abis). If either indicator is set, the speech decoder shall use substitution handling rather than normal decoding. In practice, implementers need to react to channel quality indications, not just to missing packets.

Lost speech frames

For lost speech frames, the decoder shall substitute the missing frame with repetition or extrapolation of previous good speech frame(s). The aim is to make the output level fall gradually toward silence instead of producing harsh noise. This is the main concealment behaviour for voice quality.

First lost SID frame

A single lost SID frame shall be replaced by the last valid SID frame, and the valid SID frame procedure from GSM 06.81 is then applied. In practice, this preserves comfort noise behaviour when only one SID frame is missing.

Subsequent lost SID frames

For the second lost SID frame, the comfort noise shall be muted with a gradual level decrease of -3 dB per frame until the decoder output is silenced. If more SID frames are lost, that muted output is maintained. This is what makes repeated loss audible as silence rather than unstable noise.

Example implementation behaviour

Clause 6 gives an example solution based on a seven-state machine. It uses the current BFI and the previous-frame indicator PrevBFI to control how aggressively the codec attenuates the signal. As the state rises, the channel is treated as worse and the gains are reduced more strongly.

Signal shaping during concealment

The example solution limits the LTP-gain and fixed codebook gain using past subframe values and a 5-point median operation. It also updates the predictive fixed codebook gain memory, shifts past LSFs toward their mean, and replaces the LTP-lag with the value from the fourth subframe of the previous frame. In practice, these rules help keep the concealed speech stable instead of producing sudden artifacts.

What terms does SIST ETS 300 727 E1:2003 define?

• BFI (Bad Frame Indication) - The flag used by the RSS to mark a received frame as bad.
• BSI_Abis (Bad Sub-block Indication obtained from A-bis CRC checks) - A flag derived in the TRAU from CRC checks on speech sub-blocks.
• PrevBFI (Bad Frame Indication of Previous frame) - A previous-frame status used to steer concealment decisions.
• RSS (Radio Sub System) - The part of the system that reports bad speech or SID frames.
• RX (Receive) - The receive side of the DTX handler.
• DTX (Discontinuous transmission) - The mechanism that reduces transmission activity and supports speech handling during silence.
• SID (SIlence Descriptor frame) - A frame that carries comfort-noise information.
• median5 (5-point median operation) - The operation that sorts five values and selects the middle one.

Who uses SIST ETS 300 727 E1:2003?

SIST ETS 300 727 E1:2003 is used by GSM equipment designers, codec implementers, and system integrators working on EFR speech paths. It matters for BSS and MS vendors, and for teams handling DTX, transcoding, and radio-link error concealment. Quality and test engineers use it to check that lost-frame handling, muting, and comfort-noise behaviour match the required GSM behaviour.

What changed in SIST ETS 300 727 E1:2003 from the previous edition?

SIST ETS 300 727 E1:2003 is the first edition of ETS 300 727 and corresponds to GSM technical specification GSM 06.61 version 5.1.2.

Which standards are used with SIST ETS 300 727 E1:2003?

• GSM 05.03 (ETS 300 575) - Provides channel coding rules that support the error-detection context.
• GSM 06.60 (ETS 300 726) - Gives the EFR speech transcoding reference used for related definitions.
• GSM 06.81 (ETS 300 729) - Provides the DTX procedure for EFR speech traffic channels, including the valid SID-frame behaviour referenced here.
• GSM 08.60 (ETS 300 737) - Covers inband control of remote transcoders and rate adaptors for EFR and full-rate traffic channels.

What does the SIST ETS 300 727 E1:2003 document contain?

The document contains a general description of bad-frame concealment, followed by requirements for speech-frame loss and SID-frame loss. It includes a seven-state example solution for bad-frame substitution, with a state machine shown in Figure 1. Clause 6 also gives equations and C-code-style logic for gain attenuation, median-based selection, LSF handling, and SID-frame muting. The example is meant to help implementers and test teams understand the intended behaviour without requiring a bit-exact implementation.

SLOVENSKI STANDARD
01-december-2003
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Digital cellular telecommunications system; Substitution and muting of lost frames for
Enhanced Full Rate (EFR) speech traffic channels (GSM 06.61 version 5.1.2)
Ta slovenski standard je istoveten z: ETS 300 727 Edition 1
ICS:
33.070.50 Globalni sistem za mobilno Global System for Mobile
telekomunikacijo (GSM) Communication (GSM)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 727
TELECOMMUNICATION April 1997
STANDARD
Source: ETSI TC-SMG Reference: DE/SMG-020661
ICS: 33.020
Key words: Digital cellular telecommunications system, Global System for Mobile communications (GSM)
R
GLOBAL SYSTEM FOR
MOBILE COMMUNICATIONS
Digital cellular telecommunications system;
Substitution and muting of lost frames for Enhanced
Full Rate (EFR) speech traffic channels
(GSM 06.61 version 5.1.2)
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE
Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
X.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: [e-mail]
Tel.: [phone] - Fax: [phone]
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1997. All rights reserved.

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ETS 300 727 (GSM 06.61 version 5.1.2): April 1997
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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ETS 300 727 (GSM 06.61 version 5.1.2): April 1997
Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Definitions and abbreviations .7
3.1 Definitions .7
3.2 Abbreviations .7
4 General.8
5 Requirements.9
5.1 Error detection .9
5.2 Lost speech frames .9
5.3 First lost SID frame.9
5.4 Subsequent lost SID frames.9
6 Example solution.9
6.1 Example solution for substitution and muting of lost speech frames.9
6.2 Example solution for substitution and muting of lost SID frames .11
History.12

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ETS 300 727 (GSM 06.61 version 5.1.2): April 1997
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ETS 300 727 (GSM 06.61 version 5.1.2): April 1997
Foreword
This European Telecommunication Standard (ETS) has been produced by the Special Mobile Group
(SMG) Technical Committee of the European Telecommunications Standards Institute (ETSI).
This ETS defines a frame substitution and muting procedure which is used by the Receive (RX)
Discontinuous Transmission (DTX) handler when one or more lost speech or Silence Descriptor (SID)
frames are received from the Radio Sub System (RSS) within the digital cellular telecommunications
system.
This ETS corresponds to GSM technical specification, GSM 06.61, version 5.1.2.
Transposition dates
Date of adoption: 28 February 1997
Date of latest announcement of this ETS (doa): 31 July 1997
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 January 1998
Date of withdrawal of any conflicting National Standard (dow): 31 January 1998

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ETS 300 727 (GSM 06.61 version 5.1.2): April 1997
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ETS 300 727 (GSM 06.61 version 5.1.2): April 1997
1 Scope
This European Telecommunication Standard (ETS) defines a frame substitution and muting procedure
which shall be used by the Receive (RX) Discontinuous Transmission (DTX) handler when one or more
lost speech or Silence Descriptor (SID) frames are received from the Radio Sub System (RSS).
The requirements of this ETS are mandatory for implementation in all GSM Base Station Systems (BSS)s
and Mobile Stations (MS)s capable of supporting the enhanced Full Rate speech traffic channel. It is not
mandatory to follow the bit exact implementation outlined in this ETS and the corresponding C-source
code.
2 Normative references
This ETS incorporates by dated and undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references, the
latest edition of the publication referred to applies.
[1] GSM 05.03 (ETS 300 575): "Digital cellular telecommunications system
(Phase 2); Channel coding".
[2] GSM 06.60 (ETS 300 726): "Digital cellular telecommunications system;
Enhanced Full Rate (EFR) speech transcoding".
[3] GSM 06.81 (ETS 300 729): "Digital cellular telecommunications system;
Discontinuous transmission (DTX) for Enhanced Full Rate (EFR) speech traffic
channels".
[4] GSM 08.60 (ETS 300 737): "Digital cellular telecommunications system
(Phase 2+); Inband control of remote transcoders and rate adaptors for
Enhanced Full Rate (EFR) and full rate traffic channels".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of this ETS, the following definition applies:
5-point median operation: Consists of sorting the 5 elements belonging to the set for which the median
operation is to be performed in an ascending order according to their values, and selecting the third
largest value of the sorted set as the median value.
Further definitions of terms used in this ETS can be found in
...