|                           timestamp                           |
    |                             48000                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           synchronization source (SSRC) identifier            |
    |                            0x5234a8                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |F|   block PT  |     timestamp offset      |   block length    |
    |1|     98      |            16383          |         4         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |F|   block PT  |     timestamp offset      |   block length    |
    |1|     97      |            16383          |         8         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |F|   Block PT  |
    |0|     97      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  event=ring   |0|0| volume=0  |     duration=28383            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | modulation=0    |0| volume=63 |     duration=16383            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 0|     frequency=0       |0 0 0 0|    frequency=0        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | modulation=0    |0| volume=5  |     duration=12000            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 0|     frequency=440     |0 0 0 0|    frequency=480      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
圖4：一個(gè)組合了話音和事件的RTP數(shù)據(jù)包
      可選參數(shù)：“events”參數(shù)列出了實(shí)現(xiàn)支持的事件。表中的多個(gè)事件元素由逗號(hào)分隔。
每個(gè)元素是單個(gè)整數(shù)或由連字符分開的兩個(gè)整數(shù)。參數(shù)間不允許空白。整數(shù)指出了實(shí)現(xiàn)支持
的事件號(hào)。所有的實(shí)現(xiàn)都必須支持事件0～15，所以如果執(zhí)行只支持這些事件的話，參數(shù)表
就可以省略。
      “rate”參數(shù)描述了采樣速率，以赫茲為單位。數(shù)值可寫為浮點(diǎn)或整數(shù)形式。若忽略
不寫，則為默認(rèn)值8000 Hz。
      編碼考慮：這種類型只定義為通過(guò)RTP[1]傳送。
      安全考慮：見(jiàn)本文中的“安全考慮“部分（第7節(jié)）。
      互操作性考慮：無(wú)
     已發(fā)行規(guī)范：本文
      使用該媒體的應(yīng)用：電話事件音頻子類型支持在Internet上傳輸電話系統(tǒng)事件。
      附加信息：
          1．幻數(shù)：N/A
          2．文件擴(kuò)展名：N/A
          3．Macintosh 的文件類型代碼：N/A
6．2 audio/tone
      MIME媒體類型名：audio
      MIME子類型名：tone
      必需參數(shù)：無(wú)
      可選參數(shù)：“rate”描述了取樣品的速率，以赫茲為單位。數(shù)值可寫為浮點(diǎn)或整數(shù)形式。
若忽略不寫，則為默認(rèn)值8000 Hz。
      編碼考慮：只定義為通過(guò)RTP [1]傳輸。
      安全考慮：見(jiàn)本文中的“安全考慮“部分（第7節(jié)）。
互操作性考慮：無(wú)
       已發(fā)行規(guī)范：本文
      使用該媒體的應(yīng)用：電話音音頻子類型支持純合成話音的傳輸，例如那些常用于當(dāng)前
電話系統(tǒng)中表示呼叫進(jìn)程的電話音。
      附加信息：
           1．幻數(shù)：N/A
           2．文件擴(kuò)展名：N/A
           3．Macintosh 的文件類型代碼：N/A
7．安全考慮
    使用本規(guī)范定義的負(fù)載格式的RTP數(shù)據(jù)包在安全考慮上要依照RTP規(guī)范(RFC 1889 
[1])，及任何合適的RTP框架（如RFC 1890 [19]）。這意味著媒體數(shù)據(jù)流的機(jī)密性要通過(guò)加
密來(lái)實(shí)現(xiàn)。因?yàn)樨?fù)載格式的數(shù)據(jù)壓縮應(yīng)用于端到端場(chǎng)合，所以加密可在壓縮之后進(jìn)行，這樣
兩種操作間就不會(huì)有沖突。
    這種負(fù)載類型不會(huì)引起接收端包處理過(guò)程中在計(jì)算復(fù)雜性方面明顯的不一致性，從而避
免了潛在的拒絕服務(wù)。
    在早期網(wǎng)絡(luò)采用帶內(nèi)信令且缺乏相應(yīng)的信號(hào)音濾波器，3.14小節(jié)中介紹的話音可以用于
收費(fèi)欺詐。
    附加安全考慮在RFC 2198 [6]中描述。
8. IANA考慮
    本文定義了兩種新的RTP負(fù)載格式，電話事件和電話音，以及相關(guān)的MIME類型，即
audio/event和audio/tone。
    在audio/event類型中，附加的事件必須由IANA注冊(cè)。注冊(cè)要得到當(dāng)前IETF視聽(tīng)傳輸
工作組主席的正式批準(zhǔn)，或者如果AVT組已經(jīng)關(guān)閉，也可由傳輸領(lǐng)域主管任命的一個(gè)專家
正式批準(zhǔn)。新事件的含義必須以RFC文檔或者由其它標(biāo)準(zhǔn)化團(tuán)體（如ITU-T）的等價(jià)標(biāo)準(zhǔn)
化文檔形式發(fā)行。
鳴謝
    對(duì)Megaco工作組的建議表示萬(wàn)分感激。具體建議和意見(jiàn)由Fred Burg,，Steve Casner， 
Fatih Erdin， Bill Foster， Mike Fox，Gunnar Hellstrom，Terry Lyons，Steve Magnell,，Vern 
Paxson and Colin Perkins提供。
作者地址
   Henning Schulzrinne
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue
   New York, NY 10027
   USA
   EMail:  schulzrinne@cs.columbia.edu
   Scott Petrack
   MetaTel
   45 Rumford Avenue
   Waltham, MA 02453
   USA
   EMail:  scott.petrack@metatel.com
參考書目
   [1]  Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
        "RTP:  A Transport Protocol for Real-Time Applications", RFC
        1889, January 1996.

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.
   [3]  International Telecommunication Union, "Procedures for starting
        sessions of data transmission over the public switched telephone
        network," Recommendation V.8, Telecommunication Standardization
        Sector of ITU, Geneva, Switzerland, Feb. 1998.
   [4]  R. Kocen and T. Hatala, "Voice over frame relay implementation
        agreement", Implementation Agreement FRF.11, Frame Relay Forum,
        Foster City, California, Jan. 1997.
  [5]  International Telecommunication Union, "Multifrequency push-
        button signal reception," Recommendation Q.24, Telecommunication
        Standardization Sector of ITU, Geneva, Switzerland, 1988.
   [6]  Perkins, C., Kouvelas, I., Hodson, O., Hardman, V., Handley, M.,
        Bolot, J., Vega-Garcia, A. and S. Fosse-Parisis, "RTP Payload
        for Redundant Audio Data", RFC 2198, September 1997.
   [7]  Handley M. and V. Jacobson, "SDP: Session Description Protocol",
        RFC 2327, April 1998.
   [8]  International Telecommunication Union, "Automatic answering
        equipment and general procedures for automatic calling equipment
        on the general switched telephone network including procedures
        for disabling of echo control devices for both manually and
        automatically established calls," Recommendation V.25,
        Telecommunication Standardization Sector of ITU, Geneva,
        Switzerland, Oct. 1996.
   [9]  International Telecommunication Union, "Procedures for document
        facsimile transmission in the general switched telephone
        network," Recommendation T.30, Telecommunication Standardization
        Sector of ITU, Geneva, Switzerland, July 1996.
   [10] International Telecommunication Union, "Echo cancellers,"
        Recommendation G.165, Telecommunication Standardization Sector
        of ITU, Geneva, Switzerland, Mar. 1993.
   [11] International Telecommunication Union, "A modem operating at
        data signaling rates of up to 33 600 bit/s for use on the
        general switched telephone network and on leased point-to-point
        2-wire telephone-type circuits," Recommendation V.34,
        Telecommunication Standardization Sector of ITU, Geneva,
        Switzerland, Feb. 1998.
   [12] International Telecommunication Union, "Procedures for the
        identification and selection of common modes of operation
        between data circuit-terminating equipments (DCEs) and between
        data terminal equipments (DTEs) over the public switched
        telephone network and on leased point-to-point telephone-type
        circuits," Recommendation V.8bis, Telecommunication
        Standardization Sector of ITU, Geneva, Switzerland, Sept. 1998.

   [13] International Telecommunication Union, "Application of tones and
        recorded announcements in telephone services," Recommendation
        E.182, Telecommunication Standardization Sector of ITU, Geneva,
        Switzerland, Mar. 1998.
   [14] Bellcore, "Functional criteria for digital loop carrier
        systems," Technical Requirement TR-NWT-000057, Telcordia
        (formerly Bellcore), Morristown, New Jersey, Jan. 1993.
   [15] J. G. van Bosse, Signaling in Telecommunications Networks
        Telecommunications and Signal Processing, New York, New York:
        Wiley, 1998.
   [16] International Telecommunication Union, "AAL type 2 service
        specific convergence sublayer for trunking," Recommendation
        I.366.2, Telecommunication Standardization Sector of ITU,
        Geneva, Switzerland, Feb. 1999.
   [17] International Telecommunication Union, "Various tones used in
        national networks," Recommendation Supplement 2 to
        Recommendation E.180, Telecommunication Standardization Sector
        of ITU, Geneva, Switzerland, Jan. 1994.
   [18] International Telecommunication Union, "Technical
        characteristics of tones for telephone service," Recommendation
        Supplement 2 to Recommendation E.180, Telecommunication
        Standardization Sector of ITU, Geneva, Switzerland, Jan. 1994.
   [19] Schulzrinne, H., "RTP Profile for Audio and Video Conferences
        with Minimal Control", RFC 1890, January 1996.
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致謝
   Funding for the RFC Editor function is currently provided by the Internet Society.

RFC 2833——RTP Payload for DTMF Digits,                          用于DTMF數(shù)字信號(hào)、電話音
Telephony Tones and Telephony Signals                     和電話信號(hào)的RTP負(fù)載格式


1
RFC文檔中文翻譯計(jì)劃