1、ITU-T RECMN*E.452 93 4862593 0583130 083 w INTERNATIONAL TELECOMM U N ICA1 ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU ON UNION E.452 (03/93) TELEPHONE NETWORK AND ISDN QUALITY OF SERVICE, NETWORK MANAGEMENT AND TRAFFIC ENGINEERING FACSIMILE MODEM SPEED REDUCTIONS AND TRANSACTION TIME ITU-
2、T Recommendation E.452 (Previously “CCITT Recommendation”) ITU-T RECMNaE.452 93 4862573 0583333 TIT FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and ta
3、riff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produ
4、ce Recommendations on these topics. ITU-T Recommendation E.452 was prepared by the ITU-T Study Group II (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCIT ceased to exist
5、 as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no c
6、hange has been made in the text to references containing the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication admini
7、stration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including ph
8、otocopying and microfilm, without permission in writing from the ITU. ITU-T RECMN*E.452 93 m 48b2.591 0583332 956 CONTENTS Page Introduction 1 Definitions. . 1 2.1 2 2.2 2 2.4 Transaction time metrics . 3 Remarks 3 Modem speed reductions measured on a transaction basis . Modem speed reduction measur
9、ed on a page basis 2.3 Transaction efficiency rating 2 Recommendation E.452 (03/93) i ITU-T RECflN*E*452 93 W 4862591 0583333 892 Recommendation E.452 FACSIMILE MODEM SPEED REDUCTIONS AND TRANSACTION TIME (Helsinki, 1993) 1 Introduction Facsimile modem speed reductions and increased transaction time
10、 are important parameters when measuring the performance of networks carrying group 3 facsimile. The purpose of this Recommendation is to develop modem speed and transaction time metrics that can be used to describe the performance of transmission networks with respect to group 3 facsimile. At prese
11、nt, only the performance parameters are defined. In future values for these parameters from international network measurements will be provided. Group 3 facsimile machines are capable of transmitting image data using a wide range of transmission speeds. Currently approved speeds are: S1- 2400bps S2-
12、 4800bps 53- 7200bps S4- 9600bps S5 - 12 O00 bps S6-14400bps During the initial exchange of DIS and DCS signals, the originating and terminating terminals exchange data regarding the maximum speeds at which they can transmit and receive. Initial transmission attempts are made at the agreed upon spee
13、d (Si). Note that in some cases, terminals may be set by the user to use a speed below the maximum speed of the terminal and Si will be taken as the speed of the initial TCF as indicated by the DCS message (see Note). NOTE - When measuring performance using test, transactions, modem speed reductions
14、 are most easily detected by an examination of the V.21 protocol messages exchanged between the terminals. In some cases, where transactions occur between machines from the same manufacturer, the modem speedinformation is not carried in the DISIDCS messages. For these cases, the modem speed informat
15、ion will be carried in the proprietary NSF/NSS messages, and may not be easily decoded. Protocol data can be collected by using external fax protocol monitors. Modem speed reductions from Si can take place prior to the sending of any pages in response to failure to train (FlT) messages. FTTs are sen
16、t by the receiving terminal when it declares that the reception of TCF was unsatisfactory. Modem speed reductions can also take place between pages. This is often due to the receipt of an RTP or RTN message causing the originating terminal to return to phase B. 2 Definitions The following definition
17、s apply where test transactions are exchanged between a pair of transmitting and receiving test terminals using a fixed number of standard test pages. Application of these metrics in instances where the data is collected by monitoring actual facsimile traffic, is for further study. 1 2.1 The followi
18、ng metrics represent modem speed reduction data on a transaction basis. Measured parameters are expressed as a percentage of the number of completed transactions (T,). calls without modem speed reduction (CI): This is the number of completed transactions where all pages were sent Modem speed reducti
19、ons measured on a transaction basis at Si. Represented as a percentage of the number of completed transactions: %CI = CI/T, * 100 calls with some modem speed reductions (Cr): This is the number of completed transactions that had one or more pages sent at a speed less than Si. Represented as a percen
20、tage of the number of completed transactions: %Cr = cp, * 100 calls with modem speed reduction during initial phase B (CB): This is the number of completed transactions that had all pages sent at a speed less than Si. Represented as a percentage of the number of completed transactions: This paramete
21、r may also be expressed as a percentage of all calls with some modem speed reduction (CBr): %CBr = CB/c, * 100 2.2 The following metrics expresses modem speed reduction on a page basis. number of pages at speed S, (Ns,) for S, = Si, Si-1, Si4 etc.: This is the number of pages sent at each of the pos
22、sible speeds. This performance parameter can be expressed as a percentage of the total number of pages associated with completed transaction (NJ. Modem speed reduction measured on a page basis %Nsi,sn = NstJN, * 100 2.3 Transaction efficiency rating The following metric expresses the impact of modem
23、 speed reductions on a transaction. Information regarding the number of pages transmitted at different speeds is combined to produce a single metric that represents an efficiency rating for the transaction. For a single transaction the efficiency rating is given by: %E, = 100 - (l/Nf * CNsn * (Si -
24、Sn)/Si) * 100) An efficiency rating can be calculated for all completed transactions: %E, = (C%E,)/T, 2 Recommendation E.452 (03/93) ITU-T RECMNUE.452 93 M 4862591 0583135 665 2.4 Transaction time metrics The impact of modem speed reductions can be measured by examining transaction times. transactio
25、n time for completed transactions without modem speed reductions below Si (Trl): This is the average transaction time for all completed transactions without any modem speed reductions. transaction time for all completed transactions with modem speed reductions below Si (T,z): This is the average tra
26、nsaction time for all completed transactions that had modem speed reductions below Si. transaction time for all completed transactions regardless of modem reductions (Tr3): transaction time for all completed transactions. This is the average The impact of modem speed reduction on transaction time (T
27、r4) can be presented as follows: Tr4 = Tr3/Trl * 100 3 Remarks a) All transaction based metrics other than CB can be measured by an examination of transaction times from terminal provided reports. CB requires facsimile protocol information. b) The page based metric S, requires facsimile protocol inf
28、ormation. c) The frequency of modem speed reductions will be conditional on Si. For example, when Si = 14 400 bps there might be more speed reductions than if Si = 4800 bps., d) The frequency of modem speed reductions may vary with CPE. This is because criteria for returning FTT, RTP and RTN are man
29、ufacturer specific and are in some cases set by the user. Also, the performance of the modem internal to the fax machine may vary by manufacturer. e) All meirks, except for the page based metric, apply to both ECM and non-ECM transaction. The question of a page or partial page based metric for ECM t
30、ransaction requires further study. f) In general, only pages that are part of successfully completed transactions are included when measuring modem speed reductions. However, modem speed reduction data for transactions that suffered cut-Offs can be useful when troubleshooting facsimile call cut-Offs
31、. g) The presence of modem speed reductions can be detected by examining transaction times provided as part of CPE generated transaction reports. Because page transmission times are long compared to the protocol message transmission time, it is possible to distinguish increased transaction time due to modem speed reductions from an increase due to some inefficiency in the protocol signaling. Recommendation E.452 (03193) 3
