ETSI EN 300 903 V8.1.1 (2000-11)
Digital cellular telecommunications system (Phase 2+) (GSM); Transmission planning aspects of the speech service in the GSM Public Land Mobile Network (PLMN) system (GSM 03.50 version 8.1.1 Release 1999)
Digital cellular telecommunications system (Phase 2+) (GSM); Transmission planning aspects of the speech service in the GSM Public Land Mobile Network (PLMN) system (GSM 03.50 version 8.1.1 Release 1999)
REN/SMG-110350Q8R1
Digitalni celični telekomunikacijski sistem (faza 2+) – Vidiki načrtovanja oddajanja govorne storitve v javnem kopenskem mobilnem omrežju (PLMN) sistema GSM (GSM 03.50, različica 8.1.1, izdaja 1999)
General Information
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2+) (GSM); Transmission planning aspects of the speech service in the GSM Public Land Mobile Network (PLMN) system (GSM 03.50 version 8.1.1 Release 1999)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 300 903 Version 8.1.1SIST EN 300 903 V8.1.1:2003en01-december-2003SIST EN 300 903 V8.1.1:2003SLOVENSKI
STANDARD
FOR MOBILE COMMUNICATIONSR
ETSI ETSI EN 300 903 V8.1.1 (2000-11)2(GSM 03.50 version 8.1.1 Release 1999)
Reference REN/SMG-110350Q8R1 Keywords Digital cellular telecommunications system, Global System for Mobile communications (GSM) ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE
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ETSI ETSI EN 300 903 V8.1.1 (2000-11)3(GSM 03.50 version 8.1.1 Release 1999) Contents Intellectual Property Rights.7 Foreword.7 1 Scope.8 1.1 References.8 1.2 Abbreviations.10 1.3 Introduction.10 2 Network configurations.11 2.1 General.11 2.2 Model of the PLMN.11 2.3 Interfaces.11 2.4 Configurations of connections.12 2.4.1 General configurations of connections.12 2.4.2 Reference configurations to illustrate delay and echo control issues.12 2.5 4-wire circuits in the PLMN.12 3 Transmission performance.13 3.1 Overall Loss/Loudness ratings.13 3.1.1 Connections with handset MSs.14 3.1.2 Connections with handsfree MSs.14 3.1.3 Connections with headset MSs.14 3.2 Stability Loss.15 3.3 Delay.15 3.3.1 General.15 3.3.2 Sources of delay.15 3.3.2.1 Elements of the PLMN that cause delay.15 3.3.2.2 Elements of the PSTN that cause delay.16 3.3.3 Effects of delay.16 3.3.4 Allocation of delay to the PLMN.16 3.3.4.1 Allocation of delay to the PLMN when using a full rate system.16 3.3.4.2 Allocation of delay to the PLMN when using a half rate system.16 3.3.5 Delay of various network configurations.17 3.3.5.1 National and international connections with no echo control in the PSTN (reference configurations A).17 3.3.5.2 National and international connections with echo control in the PSTN (reference configurations B).17 3.3.5.3 Connections where re-routeing leads to a significant increase in transmission path length (reference configurations C).17 3.3.6 Delay related requirements on the MS.17 3.3.6.1 Full rate MS.17 3.3.6.2 Half rate MS.17 3.3.6.3 Handsfree MS.17 3.4 Echo.18 3.4.1 General.18 3.4.2 Electrical echo control in the PLMN (Reference configurations A).18 3.4.3 Acoustic echo control in the PLMN.18 3.4.3.1 Acoustic echo control in a handsfree MS.19 3.4.3.2 Acoustic echo control in a handset MS.19 3.4.3.3 Acoustic echo control in a headset MS.19 3.4.4 Interaction between tandem echo control devices (reference configurations B & C).19 3.5 Clipping.19 3.5.1 General.19 3.5.2 Properties of voice switches in the PLMN.19 3.5.3 Problems of tandem voice switching.20 3.6 Idle channel noise (handset and headset MS).20 3.6.1 Sending.20 3.6.2 Receiving.20 SIST EN 300 903 V8.1.1:2003
ETSI ETSI EN 300 903 V8.1.1 (2000-11)4(GSM 03.50 version 8.1.1 Release 1999) 3.7 Noise contrast.20 3.7.1 General.20 3.7.2 Elements of a PLMN which can cause noise contrast impairment.21 3.7.3 Reduction of noise contrast.21 3.7.3.1 Reduction of noise contrast by limiting the noise received by the microphone.21 3.7.3.1.1 Headset MS.21 3.7.3.1.2 Handset MS.22 3.7.3.1.3 Handsfree MS.22 3.7.3.2 Reduction of noise contrast by insertion of comfort noise.22 3.7.4 Consequence of the introduction of high comfort noise levels on other voice-operated devices.22 3.8 Sensitivity/frequency characteristics.22 3.8.1 Headset and Handset MSs.22 3.8.1.1 Sending.22 3.8.1.2 Receiving.23 3.8.2 Handsfree MS.23 3.8.2.1 Sending.23 3.8.2.2 Receiving.24 3.9 Distortion (handset and headset MS).24 3.9.1 Sending.24 3.9.2 Receiving.25 3.10 Sidetone (handset and headset MS).26 3.10.1 Sidetone loss.26 3.10.2 Sidetone distortion.26 3.11 Out-of-band signals.26 3.11.1 Discrimination against out-of-band input signals.26 3.11.1.1 Handset and headset MS.26 3.11.1.2 Handsfree MS.26 3.11.2 Spurious out-of-band signals.27 3.11.2.1 Handset and headset MS.27 3.11.2.2 Handsfree MS.27 3.12 Requirements for information tones.27 3.13 Crosstalk.27 3.13.1 Near and far end crosstalk.27 3.13.2 Go/return crosstalk.27 3.14 MS Ambient Noise Rejection.28 3.14.1 Full-Rate, (TCH-FS) MS Ambient Noise Rejection (handset MS).28 3.14.2 Full-Rate, (TCH-FS) MS Ambient Noise Rejection (handsfree MS).28 3.14.3 Half-Rate, (TCH-HS) MS and Dual-Rate (TCH-FS and TCH-HS) MS Ambient Noise Rejection.28 Annex A (informative): Considerations on the Acoustic Interface of the Mobile Station.37 A.1 Handsfree MS.37 A.2 Handset MS.37 A.3 Headset MS.37 A.4 Inter-reaction with DTX.37 Annex B (normative): Test considerations.38 B.1 Test signals.38 B.1.1 Sinusoidal signals.38 B.1.2 Artificial voice.38 B.2 Test signal levels.38 B.2.1 Sending.38 B.2.1.1 Handset and headset MSs.38 B.2.1.2 Office type Handsfree MS.38 B.2.1.3 Car type Handsfree MS.39 B.2.2 Receiving.39 B.3 Test rooms.39 B.3.1 Anechoic room.39 SIST EN 300 903 V8.1.1:2003
ETSI ETSI EN 300 903 V8.1.1 (2000-11)5(GSM 03.50 version 8.1.1 Release 1999) B.4 Test arrangement.40 B.4.1 Electro-acoustic equipment.40 B.4.2 Test arrangement for handsfree MS.41 B.4.2.1 Office type handsfree MS.41 B.4.2.2 Car type handsfree MS.41 B.4.2.3 Use of HATS for testing the receive characteristics of the car type handsfree MS.42 B.4.2.3.1 Equalization of HATS.42 B.4.2.3.2 Combination of ear signals.43 Annex C (normative): Transmission requirements testing.44 C.1 Loudness ratings.44 C.1.1 Sending Loudness Rating (SLR) – Handset MS.44 C.1.2 Sending Loudness Rating (SLR) – Handsfree MS.44 C.1.3 Receiving Loudness Rating (RLR) – Handset MS.44 C.1.4 Receiving Loudness Rating (RLR) - Handsfree MS.45 C.2 Idle Channel Noise.45 C.2.1 Sending.45 C.2.2 Receiving.45 C.3 Sensitivity/frequency characteristics.45 C.3.1 Sending - Handset MS.45 C.3.2 Sending – Handsfree MS.46 C.3.3 Receiving - Handset.46 C.3.4 Receiving - Handsfree.47 C.4 Distortion.47 C.4.1 Sending.47 C.4.2 Receiving.47 C.5 Variation of gain with input level.48 C.5.1 Sending.48 C.5.2 Receiving.48 C.6 Sidetone.48 C.6.1 Talker sidetone (STMR).48 C.6.2 Listener sidetone (LSTR).48 C.7 Sidetone distortion.49 C.8 Out-of-band signals.49 C.8.1 Discrimination against out-of-band input signal for handset and headset MS.49 C.8.2 Spurious out-of-band signals for handset and headset MS.49 C.8.3 Discrimination against out-of-band signals for handsfree MS.49 C.8.4 Spurious out-of-band emissions for handsfree MS.49 C.9 Acoustic echo loss.50 C.9.1 Acoustic echo loss – Handset MS.50 C.9.2 Acoustic echo loss – Handsfree MS.50 C.10 Delay for handsfree MS.51 C.10.1 Uplink.51 C.10.2 Downlink.51 C.10.3 Result.51 C.11 Ambient noise rejection.52 C.11.1 Full-Rate, (TCH-FS) MS Ambient Noise Rejection (handset MS).53 C.11.2 Full-Rate, (TCH-FS) MS Ambient Noise Rejection (handsfree MS).53 C.11.3 Half-Rate, (TCH-HS) MS and Dual-Rate (TCH-FS and TCH-HS) MS Ambient Noise Rejection.53 SIST EN 300 903 V8.1.1:2003
ETSI ETSI EN 300 903 V8.1.1 (2000-11)6(GSM 03.50 version 8.1.1 Release 1999) Annex D (normative): MS delay requirement definition.54 D.1 Full rate MS delay requirement definition.54 D.2 Half rate MS delay requirement definition.55 Annex E (informative): Adaptive gain control.56 Annex F (informative): Change Request History.57 History.58
ETSI ETSI EN 300 903 V8.1.1 (2000-11)7(GSM 03.50 version 8.1.1 Release 1999) Intellectual Property Rights IPRs essential or potentially essential to the present document may have been declared to ETSI. The information pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web server (http://www.etsi.org/ipr). Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Foreword This European Standard (Telecommunications series) has been produced by ETSI Technical Committee Special Mobile Group (SMG). The present document describes the transmission planning aspects pertaining to the speech service within the digital cellular telecommunications system (Phase 2+). The contents of the present document is subject to continuing work within SMG and may change following formal SMG approval. Should SMG modify the contents of the present document it will be re-released with an identifying change of release date and an increase in version number as follows: Version 8.x.y where: 8 indicates Release 1999 of GSM Phase 2+. x the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates, etc. y the third digit is incremented when editorial only changes have been incorporated in the specification.
National transposition dates Date of adoption of this EN: 24 November 2000 Date of latest announcement of this EN (doa): 28 February 2001 Date of latest publication of new National Standard or endorsement of this EN (dop/e):
31 August 2001 Date of withdrawal of any conflicting National Standard (dow): 31 August 2001
ETSI ETSI EN 300 903 V8.1.1 (2000-11)8(GSM 03.50 version 8.1.1 Release 1999) 1 Scope The present document describes the transmission planning aspects pertaining to the speech service in the GSM PLMN system. Due to technical and economic factors, there cannot be full compliance with the general characteristics of international telephone connections and circuits recommended by the ITU-T. The present document gives guidance as to the precautions, measures and minimum requirements needed for successful interworking of the PLMN with the national and international PSTN. The present document identifies a number of routeing and network configurations. The objective is to reach a quality as close as possible to ITU-T standards in order to safeguard the performance seen by PSTN customers. 1.1 References The following documents contain provisions which, through reference in this text, constitute provisions of the present document. • References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific. • For a specific reference, subsequent revisions do not apply. • For a non-specific reference, the latest version applies. • A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the same number. • For this Release 1999 document, references to GSM documents are for Release 1999 versions (version 8.x.y). [1] GSM 01.04: "Digital cellular telecommunications system (Phase 2+); Abbreviations and acronyms". [2] GSM 03.04: "Digital cellular telecommunications system (Phase 2+); Signalling requirements relating to routeing of calls to mobile subscribers". [3] GSM 06.01: "Digital cellular telecommunications system (Phase 2+); Full rate speech processing functions". [4] GSM 06.10: "Digital cellular telecommunications system (Phase 2+); Full rate speech; Transcoding". [5] GSM 06.11: "Digital cellular telecommunications system (Phase 2+); Full rate speech; Substitution and muting of lost frames for full rate speech channels". [6] GSM 06.12: "Digital cellular telecommunications system (Phase 2+); Full rate speech; Comfort noise aspect for full rate speech traffic channels". [7] GSM 06.31: "Digital cellular telecommunications system (Phase 2+); Full rate speech; Discontinuous Transmission (DTX) for full rate speech traffic channels". [8] GSM 06.32: "Digital cellular telecommunications system (Phase 2+); Voice Activity Detection (VAD)". [9] GSM 06.02: "Digital cellular telecommunications system (Phase 2+); Half rate speech; Half rate speech processing functions". [10] GSM 06.20: "Digital cellular telecommunications system (Phase 2+); Half rate speech; Half rate speech transcoding". [11] GSM 06.21: "Digital cellular telecommunications system (Phase 2+); Half rate speech; Substitution and muting of lost frames for half rate speech traffic channels". SIST EN 300 903 V8.1.1:2003
ETSI ETSI EN 300 903 V8.1.1 (2000-11)9(GSM 03.50 version 8.1.1 Release 1999) [12] GSM 06.22: "Digital cellular telecommunications system (Phase 2+); Half rate speech; Comfort noise aspects for half rate speech traffic channels". [13] GSM 06.41: "Digital cellular telecommunications system (Phase 2+); Half rate speech; Discontinuous Transmission (DTX) for half rate speech traffic channels". [14] GSM 06.42: "Digital cellular telecommunications system (Phase 2+); Half rate speech; Voice Activity Detection (VAD) for half rate speech traffic channels". [15] I-ETS 300 245-2: "Integrated Services Digital Network (ISDN): Technical characteristics of telephony terminals: Part 2: PCM A-Law handset telephony". [16] ITU-T Recommendation G.103 (1998): "Hypothetical reference connections". [17] ITU-T Recommendation G.111 (1993): "Loudness ratings (LRs) in an international connection". [18] ITU-T Recommendation G.113 (1993): "Transmission impairments". [19] ITU-T Recommendation G.114 (1993): "Mean one-way propagation time". [20] ITU-T Recommendation G.121 (1993): "Loudness ratings (LRs) of national systems". [21] ITU-T Recommendation G.122 (1993): "Influence of national systems on stability, talker echo, and listener echo in international connections". [22] ITU-T Recommendation G.131 (1988): "Stability and echo". [23] ITU-T Recommendation G.165 (1993): "Echo cancellers". [24] ITU-T Recommendation G.223 (1988): "Assumptions for the calculation of noise on hypothetical reference circuits for telephony". [25] ITU-T Recommendation G.703 (1991): "Physical/electrical characteristics of hierarchical digital interfaces". [26] ITU-T Recommendation G.711 (1988): "Pulse code modulation (PCM) of voice frequencies". [27] ITU-T Recommendation G.712 (1992): "Transmission performance characteristics of pulse code modulation". [28] ITU-T Recommendation G.167 (1993): "Acoustic Echo Controllers". [29] ITU-T Recommendation M.1020 (1993): "Characteristics of special quality international leased circuits with special bandwidth conditions". [30] ITU-T Recommendation M.1025 (1993): "Characteristics of special quality international leased circuits with basic bandwidth conditioning". [31] ITU-T Recommendation M.1030 (1988): "Characteristics of ordinary quality international leased circuits forming part of private switched telephone networks". [32] ITU-T Recommendations M.1040 (1988): "Characteristics of ordinary quality international leased circuits". [33] ITU-T Recommendation O.132 (1988): "Specification for a quantizing distortion measuring apparatus using a sinusoidal test signal". [34] ITU-T Recommendation P.11 (1993): "Effect of transmission impairments". [35] ITU-T Recommendation P.34 (1993): "Transmission characteristics of hands-free telephones". [36] ITU-T Recommendation P.38 (1993): "Transmission characteristics of operator telephone systems (OTS)". [37] ITU-T Recommendation P.50 (1993): "Artificial voices". [38] ITU-T Recommendation P.51 (1993): "Artificial mouths". SIST EN 300 903 V8.1.1:2003
ETSI ETSI EN 300 903 V8.1.1 (2000-11)10(GSM 03.50 version 8.1.1 Release 1999) [39] ITU-T Recommendation P.64 (1993): "Determination of sensitivity/frequency characteristics of local telephone". [40] ITU-T Recommendation P.76 (1988): "Determination of loudness ratings; fundamental principles". [41] ITU-T Recommendation P.79 (1993): "Calculation of loudness ratings". [42] ITU-T Recommendation Q.35 (1988): "Technical characteristics of tones for the telephone service". [43] ITU-T Recommendation Q.551 (1994): "Transmission characteristics of digital exchanges". [44] ITU-T Blue Book (1988): "Volume V, Supplement 13: Noise spectra". [45] ISO 3 (1973): "Preferred numbers – series of preferred numbers". [46] ITU-T Recommendation P.57 (1996): "Artificial Ears". [47] ITU-T Recommendation P.58 (1993): "Head and Torso Simulator for Telephonometry". [48] I-ETS 300 245-3: "Integrated Services Digital Network (ISDN): Technical characteristics of telephony terminal: Part 3: PCM A-law loudspeaking and handsfree telephony". 1.2 Abbreviations For the purposes of the present document, the abbreviations given in GSM 01.04 and the following apply. ADC Analogue to Digital Converter ADPCM Adaptive Differential Pulse Code Modulation AEC Acoustic Echo Control BSC Base Station Controller (excluding transmission systems BTS Base Transceiver Station (excluding transmission systems) DAC Digital to Analogue Converter DMR Digital Mobile Radio DSI Digital Speech Interpolation EEC Electric Echo Control EL Echo Loss ERP Ear Reference Point FDM Frequency Division Multiplex ISC International Switching LE Local Exchange LSTR Listener Sidetone Rating MRP Mouth Reference Point OLR Overall Loudness Rating PCM Pulse Code Modulation POI Point of Interconnection (with PSTN) RLR Receiver Loudness Rating SLR Send Loudness Rating STMR Sidetone Masking Rating UPCMI 13-bit Uniform PCM Interface 1.3 Introduction Since the transmission quality and the conversational quality of the PLMN will in general be lower than the quality of the PSTN connection due to coding distortion, delay, etc., only some transmission aspects can be brought in line with ITU-T Recommendations. It is therefore necessary to improve the overall quality as much as possible by implementing proper routeing and network configurations. It should be recognized that the transmission plan for the GSM PLMN cannot lead to major changes in the PSTN. However, it is important to use the improvements in the evolving PSTN (e.g. digitalization, introduction of echo cancellers) in an effective way. SIST EN 300 903 V8.1.1:2003
ETSI ETSI EN 300 903 V8.1.1 (2000-11)11(GSM 03.50 version 8.1.1 Release 1999) The transmission requirements are in the first place based on international connections. When the quality is sufficient for international connections, it can be assumed that the national connections will have the same or better quality. In order to obtain a sufficient quality in the connection, it is preferable to have digital connectivity between the Base Station System (BSS) and the international exchange. The PLMN requirements are based on this assumption. When this situation cannot be provided, a lower quality must temporarily be accepted. The present document consists of two parts: one will deal with network configurations, the other with transmission performance. The part about network configurations gives information about the reference connections, on which the transmission plan is based. Furthermore, some guidelines are presented for improvement of the transmission quality in the evolving (digital) PSTN. The part about transmission performance gives mainly characteristics of the transmission between MS acoustic interface (MRP/ERP) and the interface between the PLMN and the PSTN (POI). For transmission aspects where it is impossible to give overall characteristics, it is in some cases necessary to make recommendations for individual parts of the equipment. Annex A considers the effects of the type of acoustic interfaces of the MS. 2 Network configurations 2.1 General The basic configuration for the interworking with the PSTN is shown in figure 1. 2.2 Model of the PLMN A more detailed model of the PLMN used for the consideration of transmission planning issues for speech is shown in figure 2. This model represents the main functions required and does not necessarily imply any particular physical realization. Routeing of calls is given in GSM 03.04. Any acoustic echo control is not specifically shown as it will be provided by analogue processing of digital processing or a combination of both techniques. 2.3 Interfaces The main interfaces identified within the GSM specifications are shown in figure 1. For the purposes of the present document, the Air Interface and the Point of Interconnect (POI) are identified along with two other interfaces, Interface Z and a 13-bit Uniform PCM Interface (UPCMI). These interfaces are needed to define the PLMN transmission characteristics and the overall system requirements. The Air Interface is specified by GSM 05 series specifications and is required to achieve MS transportability. Analogue measurements can be made at this point by using the appropriate radio terminal equipment and speech transcoder. The losses and gains introduced by the test speech transcoder will need to be specified. The POI with the PSTN will generally be at the 2 048 kbits/s level at an interface, in accordance with ITU-T Recommendation G.703. At the point, which is considered to have a relative level of O dBr, the analogue signals will be represented by 8-bit A-law, according to ITU-T Recommendation G.711. Analogue measurements may be made at this point using a standard send and receive side, as defined in ITU-T Recommendations. Interface Z might be used in the case of direct MSC to MSC connections. Interface Z is of the same nature as the POI. The UPCMI is introduced for design purposes in order to separate the speech transcoder impairments from the basic audio impairments of the MS. SIST EN 300 903 V8.1.1:2003
ETSI ETSI EN 300 903 V8.1.1 (2000-11)12(GSM 03.50 version 8.1.1 Release 1999) 2.4 Configurations of connections 2.4.1 General configurations of connections Figure 3 shows a variety of configurations of connections. There are a number of PSTN features which should be avoided from such connections. These include: 1) echo control devices in the international network. If present, and not disabled, these devices will be in tandem with PLMN echo cancellers and may introduce degradation; 2) satellite routeings. The delay inherent in the connections when added to the PLMN delay, may result in conversational difficulties. Double satellite links are likely to cause severe difficulties and special precautions should be taken to avoid this situation under call forwarding arrangements; 3) Digital Speech Interpolation systems (DSI). There is likely to be an adverse interaction between DSI and DTX; 4) ADPCM. The distortion introduced by ADPCM on routes where PSTN echo control is not provided is likely to reduce the echo cancellation provided by the PLMN electric echo canceller; 5) significant differences in clock rates on non-synchronized digital network components. The resulting phase roll and slips are likely to degrade the performance of the PLMN echo canceller; 6) those analogue FDM routeings which exhibit phase roll. Any phase roll due to the absence of synchronization between the carrier frequencies on the two directions of transmission is likely to degrade the performance of the PLMN echo canceller; 7) tandem connections of sources of quantization distortion. The PLMN speech transcoder is estimated to be equivalent to 7 QDUs between uniform PCM interfaces (see ITU-T Recommendation G.113). It is recognized that on some connections it may not be feasible to avoid these features, but in many cases, especially if taken into account at the planning stage, this should be possible. 2.4.2 Reference configurations to illustrate delay and echo control issues Three basic reference configuration types shown in figures 4 to 6 are defined to illustrate delay and echo control issues. Intermediate echo control devices as shown in the figures are disabled by appropriate signalling between the MSC and ISC or MSC and MSC. Reference configurations A (see figure 4) represent national or international connections where there is no echo control device in the PSTN. These reference configurations include re-routeing configurations where the overall delay of the transmission path has not been extended. Reference configurations B (see figure 5) represent national or international connections where echo control is provided in the PSTN. These reference configurations include re-routeing configurations where the overall delay of the transmission path has not been extended. Reference configurations C (see figure 6) represent national or international connections where re-routeing has lead to an increase in the ov
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