1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU E.454 SERIES E: TELEPHONE NETWORK AND ISDN Quality of service, network management and traffic engineering - Network management - Checking the quality of the international telephone service (1 0196) Transmissi
2、on performance metrics based on Error Correction Mode (ECM) facsimile ITU-T Recommendation E.454 (Previously CCIT Recommendation) ITU-T E-SERIES RECOMMENDATIONS TELEPHONE NETWORK AND ISDN OPERATION, NUMBERING, ROUTING AND MOBILE SERVICES INTERNATIONAL OPERATION E.100-E.229 OPERATIONAL PROVISIONS REL
3、ATING TO CHARGING AND ACCOUNTING IN E.230-E.299 THE INTERNATIONAL TELEPHONE SERVICE UTILIZATION OF THE INTERNATIONAL TELEPHONE NETWORK FOR NON- E.300-E.329 TE LEP HONY AP PLI CATI0 NS ISDN PROVISIONS CONCERNING USERS E.330-E.399 QUALITY OF SERVICE, NETWORK MANAGEMENT AND TRAFFIC ENGINEERING I NETWOR
4、K MANAGEMENT E.400-E.489 International service statistics E.400-E.409 II International network management E.410-E.419 H TRAFFIC ENGINEERING E.490-E.799 Measurement and recording of traffic (1 Forecasting of traffic E.490-ES05 E.506-E.509 II Determination of the number of circuits in manual operation
5、 E. 5 1 O-E. 5 1 9 Determination of the number of circuits in automatic and semi-automatic operation E.520-ES39 Definitions E.600-E.699 Grade of service E.540-E.599 ISDN traffic engineering E.700-E.749 Mobile network traffic engineering E.750-E.799 E.800-E.899 QUALITY OF TELECOMMUNICATION SERVICES:
6、CONCEPTS, MODELS, OBJECTIVES AND DEPENDABILITY PLANNING Terms and definitions related to the quality of telecommunication services E.800-E.809 Models for telecommunication services E.810-E.844 Objectives for quality of service and related concepts of telecommunication E.845-E.859 services Use of qua
7、lity of service objectives for planning of telecommunication networks Field data collection and evaluation on the performance of equipment, networks and services E.860-E.879 E.880-E.899 For further details, please refer to ITU-T List of Recommendations. ITU-T RECOMMENDATION E.454 TRANSMISSION PERFOR
8、MANCE METRICS BASED ON ERROR CORRECTION MODE (ECM) FACSIMILE Summary The purpose of this Recommendation is to define transmission performance metrics based on Error Correction Mode (ECM) facsimile. Performance parameters defined in Recommendations E.45 1, E.452 and E.453 have been modified to accomm
9、odate the error correction and partial page characteristics of ECM facsimile. Performance parameters for ECM that will help infer the image quality for non-ECM transmissions have also been defined. The parameters defined in this Recommendation are intended for use when intrusive text techniques are
10、employed. Source ITU-T Recommendation E.454 was prepared by ITU-T Study Group 2 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 8th of October 1996. FOREWORD U (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunica
11、tions. The ITU Telecommunication Standardization Sector (RU-T) is a permanent organ of the U. The U-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunic
12、ation Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC R
13、esolution No. 1 (Helsinki, March 1-12, 1993). In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate bot
14、h a telecommunication administration and a recognized operating agency. O ITU 1997 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. 1
15、1 Recommendation E.454 (10196) CONTENTS Summary References Definitions . Abbreviations . Introduction Frame size for ECM-based test calls . Facsimile call cut-off performance Modem speed reductions and transaction time Image quality metrics . Recommendation E.454 (10/96) Page 1 1 2 2 3 3 3 4 5 . 111
16、 STD-ITU-T RECMN E-454-ENGL L77b W 48b2571 Ob2b253 773 Recommendation E.454 TRANSMISSION PERFORMANCE METRICS BASED ON ERROR CORRECTION MODE (ECM) FACSIMILE (Geneva, 1996) 1 Summary The purpose of this Recommendation is to define transmission performance metrics based on Error Correction Mode (ECM) f
17、acsimile. Performance parameters defined in Recommendations E.45 1, E.452 and E.453 have been modified to accommodate the error correction and Partial Page characteristics of ECM facsimile. Performance parameters for ECM that will help estimate the image quality for non-ECM transmissions have also b
18、een defined. The parameters defined in this Recommendation are intended for use when intrusive test techniques are employed. These metrics may be extended for use with non-intrusive test methodologies. ECM metrics for operation using V.34 modulation and the options for G3 terminals to operate at 64
19、kbit/s defined in Annex Fm.4 and Annex CIT.30 are for further study. The various parameters relating to Group 3 Facsimile terminal characteristics have been selected in order to provide a common basis for the measurement of the transmission performance of networks. The metrics defined in this Recomm
20、endation are not appropriate for the evaluation of the performance of facsimile terminals. 2 References The following Recommendations contain material that is either relevant to or provides background for this Recommendation. ITU-T Recommendation T.4 (1996), Standardization of group 3 facsimile appa
21、ratus for document transmission . ITU-T Recommendation T.30 ( 1996), Procedures for document facsimile transmission in the general switched telephone network. ITU-T Recommendation T.22 ( 1993), Standardized test charts for document facsimile transmissions. ITU-T Recommendation F. 182 (1993), Operati
22、onal provisions for the international public facsimile service between subscribers stations with group 3 facsimile machines (telefax 3). ITU-T Recommendation E.450 (1 993), Facsimile quality of service on PSTN - General aspects. ITU-T Recommendation E.45 1 ( 1993), Facsimile call cut-ofperformance.
23、ITU-T Recommendation E.452 ( 1993), Facsimile modem speed reduction and transaction time. “U-T Recommendation E.453 (1994), Facsimile image quality as corrupted by transmission- induced scan line errors. ITU-T Recommendation E.456 ( 1994), Test transactions for facsimile transmission performance. IT
24、U-T Recommendation E.457 (1996), Facsimile measurement methodologies. Recommendation E.454 (10/96) 1 3 Definitions For the purposes of this Recommendation, the definitions given in Recommendations E.450, E.45 1, E.452, E.453 and E.456 are applicable. 4 Abbreviations For the purposes of this Recommen
25、dation, the following abbreviations are used. ARQ CFR CPE CRP CTC CTR DCS ECM EOM EOP EOR ERR FCD FCS FTT HDLC MCF MPS PP PPR PPS PSTN RCP RNR RFt RTC RTN RTP 2 Automatic Repeat Request Confirmation to Receive Customer Premises Equipment Command Repeat Continue To Correct Response to Continue to Cor
26、rect Digital Command Signal Error Correction Mode End of Message End of Procedure End of Retransmission Response to End of Retransmission Facsimile Coded Data Frame Check Sequence Failure to Train High-Level Data Link Control Message Confirmation Multipage Signal Partial Page Partial Page Request Pa
27、rtial Page Signal Public Switched Telephone Network Return to Control Partial Page Receiver Not Ready Receiver Ready Return To Control Retrain Negative Retrain Positive Recommendation E.454 (10/96) 5 Introduction The purpose of this Recommendation is to define transmission performance metrics based
28、on Error Correction Mode (ECM) facsimile. ECM facsimile has been defined in Annex AIT.4 and Annex AiT.30. The error correction is based on half-duplex page selective repeat ARQ (automatic repeat request) technique. An HDLC frame structure is utilized for all binary coded facsimile message procedures
29、. The basic HDLC structure consists of a number of frames each of which is subdivided into a number of fields. These fields provide for frame labelling and error checking. A facsimile page is divided into Partial Pages (PPs)consisting of up to 256 Facsimile Coded Data (FCD) frames and three Return t
30、o Control Partial Page (RCP) frames. Each FCD frame has a frame number field as well as a Frame Check Sequence (FCS). Two options are recognized for the FCD frames: The Facsimile Data Field may have a length of either 256 or 64 Octets. The last PP may have less than 256 FCD frames and the last frame
31、 (including RTC) may have less than 256 or 64 octets. The choice of 256- or 64-octet frame size is made by the transmitter and communicated to the receiver via the DCS command (bit 28). The transmitter sends one of a set of PPS messages at the end of a Partial Page. When an errored frame is declared
32、 by the receiver, it transmits a Partial Page Request (PPR) to the transmitter to indicate that the frames specified in the associated facsimile information field need to be retransmitted. When the PPR is received, the transmitting station retransmits the requested frames. If the PPR is received fou
33、r times in the same block, either the End of Retransmission (EOR) for end of Retransmission or Continue to Correct (CTC) is sent for continuing the transmission. In the following clauses, the facsimile performance parameters for ECM facsimile are discussed. ECM facsimile performance can be used to d
34、erive an estimate of the image quality of non-ECM facsimile and we specify how this could be accomplished. 6 Frame size for ECM-based test calls Test calls for ECM facsimile can use either the 256- or 64-octet frame size. It is recommended that the 256-octet frame size be chosen if the test calls ar
35、e intended to evaluate: rn 256-octet ECM transmissions and/or; 0 error-free page image quality metric only for non-ECM facsimile (from ECM facsimile). The 256-octet choice means that 256 x 8 x 256 = 524 288 bits of facsimile coded data can be transmitted in one Partial Page or block. A Partial Page
36、of this size is sufficient to accommodate a T.22 Test Chart No. 4 (or the older T.21 Test Chart No. 2). This is helpful because ECM metrics defined in clause 9 b) and 9 c) closely correspond to the error-free page metrics defined in E.453 for non-ECM facsimile. The 64-octet frame size may be used if
37、 the intent is to evaluate: rn 64-octet ECM transmissions and/or; rn a more fine-grained assessment of Image quality metrics for non-ECM facsimile (from ECM facsimile) including an approximate evaluation of Severely Errored pages. 7 Facsimile call cut-off performance Recommendation E.45 1 defines pe
38、rformance parameters for facsimile call cut-Offs. Most of the definitions in clause 3E.451 apply to cut-off performance of ECM facsimile without any modifications and others require some modification: Recommendation E.454 (10/96) 3 a) A pre-message phase B failure is considered to have occurred if p
39、rior to the transmission of the first page, either the originating or the terminating facsimile terminal goes on-hook prior to the reception of CFR message by the originating terminal. A post-message phase B failure is considered to have occurred if a phase B failure occurs after the transmission of
40、 any Partial Page. A phase C/phase D failure at any Partial Page is considered to have occurred: b) if a valid post message response (MCF, PPR, CTR, ERR, RNR) is not received in response to PPS-NULL, PPS-EOM, PPS-MPS, PPS-EOP, PPS-PRI-Q; CTC, EOR- NULL, EOR-EOM, EOR-MPS, EOR-EOP, EOR-PRI-Q; RR, and
41、CRP; if the transmitter aborts the transmission after receiving PPR for the fourth time; if the timer T5 (which is reset at the beginning of the receipt of the first RNR from the receiver and has a limit of 60 f 5 s) elapses. Facsimile call cut-off ratios for test calls have been defined in Recommen
42、dation E.451. In clause 2E.45 1, the conditions that apply to test calls have been established. These conditions apply to test calls in the ECM mode also. The size of the ECM test transactions shall be the same as for non-ECM transactions as specified in Recommendation E.456. One key performance par
43、ameter for cut-off ratios defined in Recommendation E.45 1 is shown here: %CN = (%/T)*100 Where FN is the number of N-Partial Page test transactions ( Recommendation E.456) where there was a phase B, C or D failure, and T is the total number of test transactions that satisfy all the requirements sta
44、ted in clause 2E.45 1. (N is chosen to be 5 for the 256-octet frame size and 20 for the 64-octet frame size.) Facsimile cut-off ratios for m Partial Pages (1 I m 5 N) is: %c, = (F,/T)*oo Where F, is the number of transactions that had a phase B, C or D failure at the m Partial Page. Other metrics as
45、sociated with cut-Offs for ECM transmission follow the definitions in E.45 1. Note the following difference between the call cut-off performance of ECM and non-ECM transmissions. For ECM transmissions, the modems must train more often if there are PPRs and associated frame retransmissions. Therefore
46、, there are more chances for call cut-Offs if the network impairments are such that the training sequences are affected. 8 Performance parameters for modem speed reduction and transaction time for non-ECM transmissions have been defined in Recommendation E.452. There are some differences in the mann
47、er in which speed reductions take place for ECM transmissions when compared to non-ECM transmissions: Modem speed reductions and transaction time e For both ECM and non-ECM transmissions, speed reductions can take place during Phase B negotiations. In this case, speed reductions take place until a C
48、FR is transmitted by the receiver to the transmitter confirming that the TCF has been received at an acceptable error level. e For ECM transmissions, additional speed reductions can take place if four PPRs have been received in the same block and the transmitter chooses to fall back in speed. This i
49、s similar 4 Recommendation E.454 (10/96) STD-ITU-T RECMN E.454-ENGL Lb .I LlAb257L ObZb257 337 to but different from the speed fallback in non-ECM transmissions that may occur in response to RTP or RTN responses from the receiver. A key performance parameter is the percentage of calls without modem speed reduction from the initial agreed upon speed Si (see clause 1E.452): a) %CI =CI/TC*lOO where Tc is the total number of completed test calls. b) Partial Page based metrics can be defined by the number of Partial Pages at speed Sn(NsJ for Sn = Si, Si-1, Si-2, etc. This parameter
