這是一個沒有冗余的T140 RTP包的例子

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC=0  |M|   T140 PT   |       順序號               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      時間戳 (1000Hz)                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           同步源 (SSRC) 標識符                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+                      T.140 編碼數據                       +
|                                                           |
+                                               +---------------+
|                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

	
	這是一個攜帶冗余數據的RTP 包的例子

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |V=2|P|X| CC=0  |M|  "RED" PT   |   主序號                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      原始數據時間戳                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           同步源 (SSRC) 標識符                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |1|   T140 PT   |            "R" 時間戳位移  |      "R" 塊長度|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   T140 PT   |                                            |
   +-+-+-+-+-+-+-+-+                                            +
   |                                                           |
   +               "R" T.140 編碼冗余數據                      +
   |                                                           |
   +                                               +---------------+
   |                                               |            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
   |                "P" T.140 編碼原始數據                       |
   +                                                           +
   +                                               +---------------+
   |                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   
   附圖：RTP文本包的例子
5．安全性考慮
既然本負載格式的目的是在文本交談中攜帶文本，加密的安全性度量就變得十分重要。
文本傳輸的數量很少，這樣我們可以選擇任何加密方法來對T.140會話或者整個RTP包進
行加密。如果數據包中包含了冗余數據，要使用同RFC 2198一樣的安全性考慮。
6.  MIME Media Type Registrations

   本文檔描述了一種新的RTP負載名稱和相應的MIME類型，T140 (text/t140).
6.1  Registration of MIME media type text/t140
   MIME media type name: text
   MIME subtype name: t140
   必需參數: 無
   可選參數: 無
   編碼考慮: 按RFC 2793規定傳輸T140文本。
   安全性考慮：無
   互操作考慮: 無
   已發行規范: ITU-T建議T.140，RFC 2793.
   使用該媒體類型的應用:
     文本通信終端和文本會議工具。
   附加信息: 無
     Magic number(s): 無
     文件擴展: 無
     Macintosh文件類型碼: 無
   聯系辦法:
     Gunnar Hellstrom
     e-mail: gunnar.hellstrom@omnitor.se
   預期使用: COMMON
     Author                      / Change controller:
     Gunnar Hellstrom            | IETF avt WG
     gunnar.hellstrom@omnitor.se | c/o Steve Casner casner@cisco.com
鳴謝
感謝 Stephen Casner 和 Colin Perkins 在本文寫作時給予的細查和建議。
   	感謝Ericsson公司的Mickey Nasiri提供的實驗環境。
   	感謝Michele Mizarro驗證了負載格式的可用性。
作者地址
Gunnar Hellstrom
   	Omnitor AB
   	Alsnogatan 7, 4 tr
   	SE-116 41 Stockholm
   	Sweden
   	Phone: +46 708 204 288 / +46 8 556 002 03
   	Fax:   +46 8 556 002 06
   	EMail: gunnar.hellstrom@omnitor.se
參考
   [1]  ITU-T Recommendation T.140 (1998) - Text conversation protocol
        for multimedia application, with amendment 1, (2000).
   [2]  Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
        "RTP: A Transport Protocol for Real-Time Applications", RFC
        1889, January 1996.
   [3]  Perkins, C., Kouvelas, I., Hardman, V., Handley, M. and J.
        Bolot, "RTP Payload for Redundant Audio Data", RFC 2198,
        September 1997.
   [4]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.
   [5]  ISO/IEC 10646-1: (1993), Universal Multiple Octet Coded
        Character Set.
   [6]  Yergeau, F., "UTF-8, a transformation format of ISO 10646",  RFC
       2279, January 1998.
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致謝
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RFC2793—— RTP Payload for Text Conversation	用于文本交談的RTP負載


1
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