欢迎来到麦多课文档分享! | 帮助中心 海量文档,免费浏览,给你所需,享你所想!
麦多课文档分享
全部分类
  • 标准规范>
  • 教学课件>
  • 考试资料>
  • 办公文档>
  • 学术论文>
  • 行业资料>
  • 易语言源码>
  • ImageVerifierCode 换一换
    首页 麦多课文档分享 > 资源分类 > PDF文档下载
    分享到微信 分享到微博 分享到QQ空间

    ITU-T V 21-1988 300 BITS PER SECOND DUPLEX MODEM STANDARDIZED FOR USE IN THE GENERAL SWITCHED TELEPHONE NETWORK《公用电话交换网中使用的标准化300bit s的双工调制解调器-电话网络上的数据交流 第XVII研究组》.pdf

    • 资源ID:804247       资源大小:56.35KB        全文页数:7页
    • 资源格式: PDF        下载积分:10000积分
    快捷下载 游客一键下载
    账号登录下载
    微信登录下载
    二维码
    微信扫一扫登录
    下载资源需要10000积分(如需开发票,请勿充值!)
    邮箱/手机:
    温馨提示:
    如需开发票,请勿充值!快捷下载时,用户名和密码都是您填写的邮箱或者手机号,方便查询和重复下载(系统自动生成)。
    如需开发票,请勿充值!如填写123,账号就是123,密码也是123。
    支付方式: 支付宝扫码支付    微信扫码支付   
    验证码:   换一换

    加入VIP,交流精品资源
     
    账号:
    密码:
    验证码:   换一换
      忘记密码?
        
    友情提示
    2、PDF文件下载后,可能会被浏览器默认打开,此种情况可以点击浏览器菜单,保存网页到桌面,就可以正常下载了。
    3、本站不支持迅雷下载,请使用电脑自带的IE浏览器,或者360浏览器、谷歌浏览器下载即可。
    4、本站资源下载后的文档和图纸-无水印,预览文档经过压缩,下载后原文更清晰。
    5、试题试卷类文档,如果标题没有明确说明有答案则都视为没有答案,请知晓。

    ITU-T V 21-1988 300 BITS PER SECOND DUPLEX MODEM STANDARDIZED FOR USE IN THE GENERAL SWITCHED TELEPHONE NETWORK《公用电话交换网中使用的标准化300bit s的双工调制解调器-电话网络上的数据交流 第XVII研究组》.pdf

    1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 6 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU$!4!G0G0#/-5.)#!4)/./6%2G0G04(%G0G04%,%0(/.%G0G0.%47/2+G0G0“)43G0G00%2G0G03%#/.$G0G0$50,%8G0G0-/$%-34!.$!2$):%$G0G0 amended at Mar del Plata, 1968,and at Geneva, 1972, 1976 and 1980,and at Malaga-Torremolinos

    2、, 1984)Note - The modem, designed for use on connections set up by switching in the general telephone network, canobviously be used on leased lines.A system of data transmission at a low data signalling rate, such that data could be transmitted over a telephonecircuit operated alternatively for tele

    3、phone calls and data transmissions, using simple input/output equipment and easyoperating procedures, would be economical.The data signalling rate must be such as to allow the use of current types of data sources and sinks, especiallyelectromechanical devices.The system for data transmission will be

    4、 duplex, either for simultaneous two-way data transmission or for thetransmission of signals sent in the backward direction for error-control purposes. The transmission must be such that usecan be made of normal telephone circuits, and this applies both to the bandwidth available and to the restrict

    5、ionsimposed by signalling in the telephone networks.The two correspondents are brought into contact by a telephone call, and the circuit is put into the data-transmission position:a) manually by agreement between the operators, orb) automatically.For these reasons, the CCITTunanimously declares the

    6、following view1 Data transmission may take place at low data signalling rates on telephone calls set up on switched telephonecircuits (or on leased telephone circuits).2 The communication circuit for data transmission is a duplex circuit whereby data transmission in bothdirections simultaneously is

    7、possible at 300 bit/s or less.The modulation is a binary modulation obtained by frequency shift, resulting in a modulation rate being equalto the data signalling rate.Note - Attention is drawn to the fact that there may be in operation some old-type V.21 modems for which themaximum data signalling r

    8、ate is 200 bit/s.3 For channel No. 1, the nominal mean frequency is 1080 Hz.For channel No. 2, it is 1750 Hz.The frequency deviation is 100 Hz. In each channel, the higher characteristic frequency (FA) corresponds to abinary 0._1)See Note under 2 of this Recommendation.2 Fascicle VIII.1 - Rec. V.21T

    9、he characteristic frequencies2)as measured at the modulator output must not differ by more than 6 Hz fromthe nominal figures.A maximum drift frequency of 6 Hz is assumed for the line. Hence the demodulation equipment must toleratedrifts of 12 Hz between the frequencies received and their nominal val

    10、ues.4 Data may be transmitted by synchronous or asynchronous procedures. With synchronous operation, themodem will not have to provide the signals which would be necessary to maintain synchronism when transmission is notproceeding.5 When echo control device disabling is required, it is recommended t

    11、hat the procedures specified inRecommendation V.25 be followed.6 The maximum power output of the modem into the line shall not exceed 1 mW.The power level of the modem should be adjusted to make allowance for loss between this equipment and thepoint of entry to an international circuit, so that the

    12、corresponding nominal level of the signal at the international circuitinput shall not exceed - 13 dBm0 (see Recommendation V.2, 2).7 a) When both channels are used for simultaneous both-way data transmission, channel No. 1 is used fortransmission of the callers data (i.e. the person making the telep

    13、hone call) towards the called station, while channel No.2 is used for transmission in the other direction.b) When one channel is used for data transmission and the other is used for transmission of check signals,service signals, etc., only, it is channel No. 1 which is used for transmission from the

    14、 calling to the called stationregardless of the direction in which the data are transmitted.c) The procedure for the assignment of the channels described under a) and b) above applies in the case ofthe general service of data transmission, making it possible to transmit data or check signal, service

    15、 signal, etc.,bilaterally between any two subscribers. In special cases which do not come under this rule, the procedure of assignmentof the channels is determined by the prior agreement between the correspondents, bearing in mind the requirementproper to each service.8 Interchange circuits8.1 List

    16、of interchange circuits essential for the modems when used on the general switched telephone network or non switched leased telephone circuits (see Table 1 /V.21)The configurations of interchange circuits are those essential for the particular switched network or leasedcircuit requirement indicated.

    17、 Where one or more of such requirements are provided in a modern, then all of theappropriate interchange circuit facilities should be provided._2)The nominal characteristic frequencies;channel No. 1 (FA= 1180 Hz and Fz= 980 Hz);channel No. 2 (FA= 1850 Hz and Fz= 1650 Hz).Fascicle VIII.1 - Rec. V.21

    18、3TABLE 1/V.21Note 1 - All essential interchange circuits and any others which are provided shall comply with the functional and operationalrequirements of Recommendation V.24. All interchange circuits indicated by X shall be properly terminated in the data terminalequipment and in the data circuit-t

    19、erminating equipment in accordance with the appropriate Recommendation for electricalcharacteristics (see 9).Note 2 - Circuit 105 is not required when alternate voice/data service is used on non-switched leased point-to-point circuits.Note 3 - The circuit shall be capable of operation as circuit 108

    20、/1 - connect data set to line or circuit 108/2 - data terminalready depending on its use.Note 4 - In the leased point-to-point case, where alternate voice/data service is to be provided, circuit 108/2 may be usedoptionally.8.2 Response times of circuits 106 and 1098.2.1 Definitions8.2.1.1 Circuit 10

    21、9 response times are the times that elapse between the connection or removal of a tone to or from themodem receive line terminals and the appearance of the corresponding ON or OFF condition on circuit 109.The test tone should have a frequency corresponding to the characteristic frequency of binary 1

    22、 and be derivedfrom a source with an impedance equal to the nominal input impedance of the modem under test.The level of the test tone should fall into the level range between 1 dB above the actual threshold, of thereceived line signal detector and the maximum admissible level of the received signal

    23、. At all levels within this range themeasured response times shall be within the specified limits.8.2.1.2 Circuit 106 response times are the times from the connection of an ON or OFF condition on:- circuit 105 (where it is provided) to the appearance of the corresponding OFF or ON condition on circu

    24、it106;- circuit 109 (where circuit 105 is not provided) to the appearance of the corresponding ON or OFFcondition on circuit 106.Interchange circuitGeneral switched telephonenetwork including terminalsequipped for manual calling,Non-switched leasedtelephone circuits(Note 1)Number Designationmanual a

    25、nswering, automaticcalling, automatic answering(Note 1)Point-to-point Multipoint102103Signal ground or common returnTransmitted dataXXXXXX104105106Received dataRequest to sendReady for sendingX-XXX (Note 2)XXXX107108/1108/2109Data set readyConnect data set to lineData terminal readyData channel rece

    26、ived line signal detectorXX (Note 3)X (Note 3)XXXX (Note 4)XXX-X125126Calling indicatorSelect transmit frequencyX-X4 Fascicle VIII.1 - Rec. V.218.2.2 Response timesTABLE 2/V.21Note 1 - These times are used on leased point-to-point networks without alternate voice data facilities and on leased multip

    27、ointfacilities.Note 2 - These times are used in the general switched network service and on leased point-to-point circuits with alternate voicedata.8.3 Threshold of data channel received line signal detectorLevel of received line signal at received line signal terminals of modem for all types of con

    28、nection, i.e. generalswitched telephone network or non-switched leased telephone circuit:greater than -43 dBm circuit 109 ONless than -48 dBm circuit 109 OFFThe condition of circuit 109 for levels between -43 dBm and -48 dBm is not specified except that the signaldetector shall exhibit a hysteresis

    29、action such that the level at which the OFF to ON transition occurs shall be at least2 dB greater than for the ON to OFF transition.Where transmission conditions are known on switched or leased circuits, Administrations should be permittedat the time of modem installation to change these response le

    30、vels of the received line signal detector to less sensitivevalues (e.g. -33 dBm and -38 dBm respectively).8.4 Fault condition of interchange circuitsSee Recommendation V.28, 7 for association of the receiver failure detection types).8.4.1 The DTE should interpret a fault condition on circuit 107 as

    31、an OFF condition using failure detection type 1.8.4.2 The DCE should interpret a fault condition on circuits 105 and 108 as an OFF condition using failure detectiontype 1.8.4.3 All other circuits not referred to above may use failure detection type 0 or 1.9 Electrical characteristics of interchange

    32、circuitsUse of electrical characteristics conforming to Recommendation V.28 is recommended together with theconnector and pin assignment plan specified by ISO 2110.Circuit 106OFF to ONON to OFF20-50 ms (see Note 1) 400-1000 ms (see Note 2) 2msCircuit 109OFF to ONON to OFF 20 ms (see Note 1) 300-700

    33、ms (see Note 2)20-80 msFascicle VIII.1 - Rec. V.21 5Note - Manufacturers may wish to note that the long-term objective is to replace electrical characteristicsspecified in Recommendation V.28, and that Study Group XVII has agreed that the work shall proceed to develop amore efficient, all-balanced,

    34、interface for the V-Series application which minimises the number of interchange circuits.10 The following information is provided to assist equipment manufacturers:a) The nominal range of attenuations in subscriber-to-subscriber connections is from 5 to 30 dB at the reference frequency (800 or 1000 Hz), assuming up to 35 dB attenuation at the frequency 1750 Hz.b) The data modem should have no adjustment for send level or receive sensitivity under the control of the operator.Reference1 CCITT Recommendation Echo suppressors, Vol. III, Rec. G.164.


    注意事项

    本文(ITU-T V 21-1988 300 BITS PER SECOND DUPLEX MODEM STANDARDIZED FOR USE IN THE GENERAL SWITCHED TELEPHONE NETWORK《公用电话交换网中使用的标准化300bit s的双工调制解调器-电话网络上的数据交流 第XVII研究组》.pdf)为本站会员(eastlab115)主动上传,麦多课文档分享仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对上载内容本身不做任何修改或编辑。 若此文所含内容侵犯了您的版权或隐私,请立即通知麦多课文档分享(点击联系客服),我们立即给予删除!




    关于我们 - 网站声明 - 网站地图 - 资源地图 - 友情链接 - 网站客服 - 联系我们

    copyright@ 2008-2019 麦多课文库(www.mydoc123.com)网站版权所有
    备案/许可证编号:苏ICP备17064731号-1 

    收起
    展开