1、Technical Report No. 58January 1999A Test Plan for Investigatingthe Crosstalk Potential ofDigital Modems Conforming toITU-T Recommendation V.90Prepared by T1A1.7Working Group onSignal Processing andNetwork Performancefor Voiceband ServicesCopyright 1999 by Alliance for Telecommunications IndustrySol
2、utionsAll rights reserved.Committee T1 is sponsored by the Alliance for Telecommunications Industry Solutions (ATIS) and accredited by the American National Standards Institute (ANSI)No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without th
3、e prior written permission of the publisher.A Technical Report onA Test Plan for Investigating the Crosstalk Potential of DigitalModems Conforming to ITU-T Recommendation V.90AbstractThis Technical Report contains a test plan which can be used to investigate thepotential for crosstalk induced into a
4、djacent voiceband service subscriber loopsby digital modems conforming to ITU-T Recommendation V.90 operating with thepower level of the encoded analog signal in excess of that permitted by FCC Part68. Thresholds of harm to the public network as well as rationale for thethresholds are provided.Docum
5、ent T1A1.7/98-027r3Prepared byT1A1.7Working Group on Signal Processing andNetwork Performance for Voiceband ServicesiForewordThis T1 Technical Report was initiated in the T1A1.7 Working Group on SignalProcessing and Network Performance for Voiceband Services.When modems conforming to ITU-T Recommend
6、ation V.90 were developed,discussion was initiated throughout the industry regarding the continued need forthe FCC maximum power constraint on encoded analog signals, other than voice,input into the public network. If the V.90 digital modem was permitted to transmitat some level in excess of the FCC
7、 maximum, it was purported that the modemcould achieve downstream data rates closer to the theoretical maximum of 56kbit/s. In October 1996, Working Group T1A1.7 determined that V.90 modemswere bound by the FCC power constraint. An unknown factor attendant to theincreased power levels is the potenti
8、al for harm to the network in the form ofimpaired performance to other voiceband services in subscriber cable pairsadjacent to those carrying V.90 signals. Preliminary testing conducted inDecember 1997 was not considered of sufficient depth upon which to base adecision regarding the need for the con
9、straint in this application or the advisabilityof support for waiver consideration.This Technical Report contains a test plan that can be used to evaluate thepotential for network harm in the form of crosstalk.Suggestions for improvement of the Technical Report are welcome and should besent to the A
10、lliance for Telecommunications Industry Solutions - Committee T1Secretariat, 1200 G Street N.W., Suite 500, Washington, D.C. 20005.At the time this report was completed, T1A1.7 had the following members:D.J. Atkinson Ricky B. Grams John RoquetChuck Balogh Eric Hauch Glenn J. ScheydDick Bobilin Ralph
11、 E. Jensen Ernest SchmidtLorence F. Brown Michael Kalb Dan ThomasE. Mel C Celi Gary Knippelmier Pat TweedyGregory Cermak Mustafa Kocaturk Stephen VoranAntony Crossman Gary Koerner Arthur WebsterChuck Dvorak Barry Lerich Bernard WorneGeorge Fawcett, Jr. A. C. Morton William R. WycoffMichael Floyd Tom
12、 Oshidari Sangamesh VinayagamurtySuhas S. Gandhi Mark E. Perkins J. A. ZebarthTom Geary Max J. Roesch, Jr.iiiiiContents1 Introduction12 Scope13 Purpose.24 References25 Definitions36 PCM Modem Crosstalk Test Plan36.1 Operating Configuration.36.2 Subscriber Loop Cable Information46.3 Test Equipment .5
13、6.4 Connection 56.5 Test Steps .57 Criteria for harm 77.1 General77.2 Rationale for Thresholds of Harm 87.2.1 Rationale for Service Threshold 87.2.2 Rationale for Voiceband Data Rate Threshold 87.3 Thresholds of Harm .87.3.1 Threshold for Service Interference 87.3.2 Threshold for Voiceband Data Rate
14、 Signal Interference9iv1A Test Plan for Investigating the Crosstalk Potential ofDigital Modems Conforming to ITU-T Recommendation V.901 IntroductionParts 68.308 (h) (1) iv and 68.308 (h) (2) v, FCC Rules and Regulations 1,constrain the maximum power from registered terminal equipment connecting tosu
15、brate services and 1.544 Mbit/s digital services. If such equipment generatessignals in digital form that are intended for eventual conversion into voicebandanalog signals other than voice, the maximum equivalent power of the encodedanalog signal is limited to -12 dBm averaged over any 3 second time
16、 interval.Modems conforming to ITU-T Recommendation V.90 2 are considered to besuch equipment. The V.90 digital modems are usually used in modem serversthat connect individual subscribers using companion analog modems to Internetservice providers (ISP) or to corporate data networks. Adherence to thi
17、s powerconstraint limits the downstream1connect rate of the modems to a rate less thanthe theoretical maximum of 56 kbit/s. For the application addressed in this testplan, the upstream connect rate is equivalent to that described in ITU-TRecommendation V.34 3. Note that other conditions on the chann
18、el between asubscribers modem and a V.90 modem server may also affect the connect rate,but that subject is beyond the scope of this technical report.There has been discussion throughout the industry regarding the continued needfor the FCC maximum signal power constraint. Information submitted to ITU
19、-TStudy Group 15 4 provided a theoretical calculation based on the crosstalkmodel of ANSI T1.413 5 to support the premise that the FCC power constraint isnot necessary for the V.90 application.2If the maximum power constraint is to beretained in FCC Part 68, then, to permit the V.90 modem to attain
20、connect ratescloser to the theoretical maximum, the possibility of a waiver of the maximumpower constraint for this modem application, may be worthy of consideration.Preliminary testing reported to T1A1.7 6 was not considered of sufficient depthupon which to base a decision regarding the need for th
21、e constraint in thisapplication, or the advisability of support for waiver consideration.2 ScopeThis Technical Report contains a test plan which can be used to investigate thepotential for crosstalk induced into adjacent voiceband service subscriber loopsby modems conforming to ITU-T Recommendation
22、V.90 operating with the powerlevel of the encoded analog signal in excess of that permitted by FCC Part 68.The focus of the test plan is (1) to determine the level of crosstalk generated byV.90 modems and determine if the detected level of crosstalk would impair voiceservices carried on subscriber l
23、oops in the same cable binder group as loops1For the purposes of this test plan, “downstream“ refers to the direction from the V.90 modemserver to the analog modem test site, and “upstream“ refers to the direction from the analog modemtest site to the V.90 modem server.2The calculation assumed 49 V.
24、90 disturbers transmitting at 6 dBm in a single cable binder groupand concluded that the incremental noise due to crosstalk to the 50th pair would be 76.7 dBm or13.3 dBrn.Technical Report No. 582carrying V.90 modem traffic, and (2) to investigate the mutual effect on themodem throughput by other lik
25、e modem traffic in the same cable binder group.Additionally, this technical report provides thresholds of harm which can be usedto evaluate test results obtained through the execution of the test plan. Therationale associated with the selection of the thresholds of harm has also beenprovided for com
26、pleteness.3 PurposeThis Technical Report presents a methodology for determining the potentialimpact on other services of V.90 modems transmitting in excess of the FCCmandated power constraint of 12 dBm signal power of the encoded analogsignal. The thresholds of harm presented in this document are in
27、tended aspass/fail criteria for tests conducted in the execution of the plan. Should aparticular set of equipment undergoing tests in accordance with this plan pass allspecified tests, the documented results would provide support for consideration ofa recommendation for waiver of the FCC power const
28、raint for the server modemof that particular modem pair.It is further noted that the thresholds of harm presented in this document are nota recommendation for change of the applicable provisions of FCC Part 68. Nordoes this Technical Report suggest that passing of the tests by one modemmanufacturer
29、provides sufficient justification to recommend modification of FCCPart 68 or to recommend a blanket waiver for all V.90 equipment.4 References1. Code of Federal Regulations (CFR), Title 47, Part 308, Connection ofTerminal Equipment to the Telephone Network, National Archives andRecords Administratio
30、n, October 1, 1997.32. ITU-T Recommendation V.90, A digital modem and analogue modem pair foruse on the public telephone network (PSTN) at data signalling rates of up to56,000 bit/s downstream and up to 33,600 bit/s upstream.43. ITU-T Recommendation V.34, A modem operating at data signalling rates o
31、fup to 33,600 bit/s for use on the general switched telephone network and onleased point-to-point 2-wire telephone-type circuits.44. PCM97-029, submitted at the ITU-T Q23/15 V.pcm Rapporteur meeting,Dublin, Ireland, July 7-11, 1997.55. ANSI T1.413-1995, Asymmetric Digital Subscriber Line (ADSL) Meta
32、llicInterface.46. Contribution T1A1.7/98-004, PCM Modem Output Signal Testing, March 17,1998.63Available from U. S. Government Printing Office via GPO Access online,http:/frwebgate.access.gpo.gov.4Available from American National Standards Institute, 11 West 42nd Street, New York, NY 10036.5Availabl
33、e from David Moon, General DataComm, P. O. Box 1299, Middlebury, CT 06762-1299.Technical Report No. 5837. ANSI T1.413-1998, Asymmetric Digital Subscriber Line (ADSL) MetallicInterface (revision of ANSI T1.413-1995).65 DefinitionsPCM modem the term “PCM modem“ was used to denote the digital modemof t
34、he pair of modems that was described in draft versions of ITU-TRecommendation V.90. Implementations of the PCM modem were proprietary. Inthis technical report, the term “PCM modem“ is not intended to be synonymouswith the term “V.90 modem“.Analog modem the analog modem of the pair of modems that is
35、described inITU-T Recommendation V.90.6 PCM Modem Crosstalk Test PlanContribution T1A1.7/98-004 reported the results of preliminary testing ofproprietary design 56 kbit/s modems, accomplished to try to determine if theoutput signal power in excess of 12 dBm from those modems results indetectable cro
36、sstalk impairment on adjacent subscriber lines. Tests wereconducted with up to six modems with output analog signal power of -6 dBm.T1A1.7 members, at the March 1998 meeting, did not believe that the testing wassufficient to warrant support of a waiver of the -12 dBm FCC Part 68 constraint onthe pow
37、er level of encoded analog signals input into the public network by thisapplication.This section contains a more rigorous test scenario.6.1 Operating ConfigurationThe connection between the V.90 modem server and the subscribers companionanalog modem may take any one of the three possible generic ope
38、ratingconfigurations shown in Figure 1, Figure 2, or Figure 3.Figure 1 Intra-office Connection6Available from Alliance for Telecommunications Industry Solutions - Committee T1 Secretariat,1200 G Street N.W., Suite 500, Washington, DC 20005.Technical Report No. 584Figure 2 Inter-office Connection (al
39、l digital trunking)Figure 3 Inter-office Connection (analog trunk segment)Figure 1 and Figure 2 assume that the network portion of the connection isalways digital, whereas Figure 3 assumes that some part of the network portionof the connection is analog.The designers of the V.90 modem indicate that
40、the pair of modems operating in aconfiguration equivalent to Figure 3 will not use the V.90 transmission schemeafter the handshaking process has completed. Rather, the V.90 modem pair willuse the V.34 scheme for both the transmitted and received signals over achannel that contains an analog carrier
41、system component. As a result, thisTechnical Report presumes that a V.90 modem will comply with all therequirements of FCC part 68 when operating in a connection equivalent to thatshown in Figure 3. Consequently, this technical report does not address aconnection configuration containing analog segm
42、ents other than the subscriberloop to the analog modem.6.2 Subscriber Loop Cable Information.Identify the cable to be used for testing.7Loops should be between 10 and 12 kft.Approximately 3 kft of the test cable should be paper-insulated cable with theremainder being plastic-insulated cable. It is p
43、referable that the test plan beexecuted using existing loop plant. If there are differences in the crosstalkproperties of the cable being used for testing from properly designed andmaintained existing loop plant, these differences should be taken into accountwhen evaluating the impact of the disturb
44、ers.1. Determine and record the pair-to-pair crosstalk coupling loss between thevarious combinations of pairs in a 25-pair binder group in the cable. If this isaccomplished empirically, a resistive termination should be used on the cablepairs, the tests should be conducted over the voiceband (0 4 kH
45、z), and the7Artificial cable cannot be used for this test.Technical Report No. 585test arrangement used should be identified.If the information is obtained from earlier research, the source should beidentified and the results should be included in the report of test planexecution.2. This test scenar
46、io should be conducted with 24 disturbers and one disturbedpair in the binder group. For the disturbed pair, select the pair that exhibits theworst-case crosstalk effect (i. e., the least coupling loss). Note that there are300 pair-to-pair combinations in a 25-pair cable.3. Connect the 24 disturber
47、cable pairs to directory number appearances on theserving switch.4. Measure the echo return loss of each connected cable pair. The connectionarrangement used to do this should be identified.6.3 Test EquipmentRecord the identification and limit specifications for all test measuring equipmentused in t
48、he execution of this test plan to demonstrate that no measured signalsare masked by test equipment limitations.6.4 Connection1. Connect analog test modems to the 24 disturbing pairs in the configuration ofeither Figure 1 or Figure 2.2. Verify translations for the connections between the V.90 server
49、trunks anddisturbing pair directory numbers to ensure no network loss pads are insertedin the connections. Arrange for translation modifications to remove padinsertion if necessary. If available, use test capabilities of the server modemto verify that no pads are inserted.6.5 Test Steps1. On the disturbed pair, dial the milliwatt supply in the serving switch; measureand record power at the analog modem test site to determine loop loss.Confirm that the measured loss is consistent with the loop length and that nopads have been inserted.2. On a disturbing pair, establi
