Network Working Group M. Civanlar
Request for Comments: 2862 G. Cash
Category: Standards Track AT&T
June 2000
Network Working Group M. Civanlar
Request for Comments: 2862 G. Cash
Category: Standards Track AT&T
June 2000
RTP Payload Format for Real-Time Pointers
实时指针的RTP有效负载格式
Status of this Memo
本备忘录的状况
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
本文件规定了互联网社区的互联网标准跟踪协议，并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态，请参考当前版本的“互联网官方协议标准”（STD 1）。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2000). All Rights Reserved.
版权所有（C）互联网协会（2000年）。版权所有。
Abstract
摘要
This document describes an RTP [1] payload format for transporting the coordinates of a dynamic pointer that may be used during a presentation. Although a mouse can be used as the pointer, this payload format is not intended and may not have all functionalities needed to implement a general mouse event transmission mechanism.
本文档描述了一种RTP[1]有效载荷格式，用于传输演示过程中可能使用的动态指针的坐标。尽管鼠标可用作指针，但此有效负载格式并不适用，也可能不具备实现通用鼠标事件传输机制所需的所有功能。
In most presentations, significant information is conveyed through the use of viewgraphs and a pointer. This makes accurate transmission of them vital in remote conferencing applications. Using regular video of a presenter's display for this purpose is problematic because, while the viewgraphs require a high spatial resolution, the pointer movements need to be sampled and transmitted at a high temporal resolution so that the presenter's pointing actions can be displayed synchronously with the corresponding audio and video signals. In many instances, this synchronization carries vital information. As an example, consider a speaker pointing at two alternatives on a viewgraph in sequence and saying "this one is better than this". To satisfy both high spatial and high temporal resolution requirements, at least S-VHS quality video may need to be used. Codecs that can compress S-VHS video effectively in real-time are expensive for this purpose, and transmitting such video uncompressed requires very high bandwidths.
在大多数演示中，重要信息是通过使用视图图和指针来传达的。这使得它们的准确传输在远程会议应用程序中至关重要。为此目的使用演讲者显示器的常规视频是有问题的，因为尽管视图图需要高空间分辨率，但指针移动需要以高时间分辨率进行采样和传输，以便演讲者的指向动作可以与相应的音频和视频信号同步显示。在许多情况下，这种同步携带重要信息。作为一个例子，考虑一个演讲者在一个视点上按顺序选择两个备选方案，并说“这个比这个更好”。为了满足高空间和高时间分辨率要求，可能需要使用至少S-VHS质量的视频。为此，能够实时有效压缩S-VHS视频的编解码器价格昂贵，并且传输未压缩的此类视频需要非常高的带宽。
A much simpler and economical system can be designed by capturing and transmitting the pointer coordinates separately [2]. The pointer coordinates with respect to a displayed viewgraph can easily be obtained in electronic presentation systems. For presentations prepared for optical systems, such as transparencies for overhead projectors, an arrangement where the viewgraph is captured in a frame buffer on a computer can be used to associate the pointer coordinates with the displayed viewgraph. For capturing transparencies, printed material, or even three dimensional objects, a document camera and a personal computer or workstation based video capture card can be used. This arrangement can handle electronic viewgraphs by feeding the video output of the computer that displays them to the video capture card through an appropriate converter also. A side benefit of this is that it allows using a presenter's own computer to transmit electronic viewgraphs without connecting it to, for example, an intranet. The captured image is then displayed along with the capturing computer's mouse pointer on the presenter's display using a projector. The presenter moves the pointer on the display using a regular or maybe a wireless mouse whose location can easily be captured by appropriate software running on the capturing computer.
通过分别捕获和传输指针坐标，可以设计出更简单、更经济的系统[2]。在电子演示系统中，可以很容易地获得相对于显示的视图图形的指针坐标。对于为光学系统准备的演示文稿，如高架投影仪的透明胶片，可以使用在计算机上的帧缓冲区中捕获viewgraph的安排，将指针坐标与显示的viewgraph相关联。为了拍摄透明胶片、印刷品甚至三维物体，可以使用文档摄像机和个人计算机或基于工作站的视频采集卡。该装置还可以通过适当的转换器将显示电子视图的计算机的视频输出馈送至视频捕获卡，从而处理电子视图。这样做的一个附带好处是，它允许使用演示者自己的计算机传输电子视图，而无需将其连接到（例如）内部网。然后使用投影仪将捕获的图像与捕获计算机的鼠标指针一起显示在演示者的显示器上。演示者使用常规鼠标或无线鼠标移动显示器上的指针，该鼠标的位置可以通过捕获计算机上运行的适当软件轻松捕获。
This document describes an RTP payload format to transmit the pointer coordinates captured in one of the ways described above using RTP. Although, a mouse can be used as the pointer, this payload format is not intended and may not have all functionalities needed to implement a general mouse event transmission mechanism.
本文档描述了一种RTP有效负载格式，用于传输使用RTP以上述方式之一捕获的指针坐标。尽管鼠标可用作指针，但此有效负载格式并非目的，可能不具备实现通用鼠标事件传输机制所需的所有功能。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [3].
本文件中的关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[3]中所述进行解释。
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 |M| PT | sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: contributing source (CSRC) identifiers :
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
|L|M|R| | x-coordinate | | PIN | y-coordinate |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
MBZ MBZ
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 |M| PT | sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: contributing source (CSRC) identifiers :
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
|L|M|R| | x-coordinate | | PIN | y-coordinate |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
MBZ MBZ
Figure 1 - An RTP packet for Real-Time Pointer
图1-实时指针的RTP数据包
Fig. 1 shows an RTP packet carrying real-time pointer coordinates. This payload format does not have a payload specific header.
图1示出了携带实时指针坐标的RTP分组。此有效负载格式没有特定于有效负载的标头。
2.1. RTP Header Usage:
2.1. RTP头使用：
Payload Type (PT): The assignment of an RTP payload type for this new packet format is outside the scope of this document, and will not be specified here. It is expected that the RTP profile for a particular class of applications will assign a payload type for this encoding, or if that is not done then a payload type in the dynamic range shall be chosen.
有效负载类型（PT）：此新数据包格式的RTP有效负载类型的分配不在本文档的范围内，此处将不指定。预计特定类别应用的RTP配置文件将为此编码分配有效负载类型，或者如果未分配有效负载类型，则应选择动态范围内的有效负载类型。
Marker (M) bit: Set to one if the pointer icon is changed in this packet.
标记（M）位：如果此数据包中的指针图标更改，则设置为1。
Extension (X) bit: Defined by the RTP profile used.
扩展（X）位：由使用的RTP配置文件定义。
Sequence Number: Set as described in RFC1889 [1].
序列号：按RFC1889[1]所述设置。
Timestamp: The sampling time for the pointer location measured by a 90kHz clock.
时间戳：指针位置的采样时间，由90kHz时钟测量。
SSRC: Set as described in RFC1889 [1].
SSRC：设置如RFC1889[1]所述。
CC and CSRC fields are used as described in RFC 1889 [1].
CC和CSC字段的使用如RFC 1889[1]所述。
RTCP SHOULD be used as defined in RFC 1889 [1].
RTCP应按照RFC 1889[1]中的定义使用。
2.2. Payload:
2.2. 有效载荷：
The pointer's x and y coordinates are measured from the upper left corner of the associated display window. They are represented as a fraction of the corresponding edge length of the display window using 12 bits, positive, fixed point numbers between 0 and (1 - 2^-12).
指针的x和y坐标是从相关显示窗口的左上角测量的。使用0和（1-2^-12）之间的12位正定点数字，将它们表示为显示窗口相应边缘长度的一部分。
L (left), R (right) and/or M (middle) bits are pointer special effects flags. Their use is application dependent and MUST be established out-of-band. Applications MAY ignore these bits.
L（左）、R（右）和/或M（中间）位是指针特效标志。它们的使用取决于应用程序，必须在带外建立。应用程序可能会忽略这些位。
PIN: Pointer Icon Number (3 bits) selects a pointer icon. The association between the PIN numbers and the icon pictures MUST be established out-of-band. PIN = 0 represents a default pointer icon. Applications which only support a single pointer icon SHOULD set the PIN field to zero. Applications MAY ignore non-zero PIN values on reception, and display a default icon.
引脚：指针图标编号（3位）选择指针图标。PIN码和图标图片之间的关联必须在带外建立。PIN=0表示默认的指针图标。仅支持单指针图标的应用程序应将PIN字段设置为零。应用程序可能会忽略接收时的非零引脚值，并显示默认图标。
This document defines a new RTP payload name, "pointer," and associated MIME subtype, "video/pointer."
本文档定义了一个新的RTP有效负载名称“指针”，以及相关的MIME子类型“视频/指针”
MIME media type name: video
MIME媒体类型名称：视频
MIME subtype name: pointer
MIME子类型名称：指针
Required parameters: None
所需参数：无
Optional parameters: None
可选参数：无
Encoding considerations: Pointer video can be transmitted with RTP as specified in this document.
编码注意事项：指针视频可以按照本文件的规定使用RTP传输。
Security considerations: As described in this document.
安全注意事项：如本文件所述。
Interoperability considerations: None
互操作性注意事项：无
Published specification: this document.
已发布规范：本文件。
Applications which use this media type: Videoconferencing systems that transmit VUgraphs with a real-time pointer.
使用此媒体类型的应用程序：使用实时指针传输VuGraph的视频会议系统。
Additional information: None
其他信息：无
Magic number(s): None
幻数：无
File extension(s): None
Macintosh File Type Code(s): None
File extension(s): None
Macintosh File Type Code(s): None
Person & email address to contact for further information: M. Reha Civanlar e-mail: civanlar@research.att.com
联系人和电子邮件地址以获取更多信息：M.Reha Civanlar电子邮件：civanlar@research.att.com
Intended usage: COMMON Author/Change controller:
M. Reha Civanlar
e-mail: civanlar@research.att.com
Intended usage: COMMON Author/Change controller:
M. Reha Civanlar
e-mail: civanlar@research.att.com
RTP packets using the payload format defined in this specification are subject to the security considerations discussed in the RTP specification [1].
使用本规范中定义的有效负载格式的RTP数据包应遵守RTP规范[1]中讨论的安全注意事项。
This payload type does not exhibit any significant non-uniformity in the receiver side computational complexity for packet processing to cause a potential denial-of-service threat.
这种有效负载类型在数据包处理的接收方计算复杂性方面没有表现出任何显著的不均匀性，从而导致潜在的拒绝服务威胁。
[1] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A Transport Protocol for Real Time Applications", RFC 1889, January 1996.
[1] Schulzrinne，H.，Casner，S.，Frederick，R.和V.Jacobson，“RTP：实时应用的传输协议”，RFC 1889，1996年1月。
[2] M. R. Civanlar, G. L. Cash, "Networked Viewgraphs - NetVG" Proceedings of The 9th Int. Workshop on Packet Video, http://www.research.att.com/~mrc/PacketVideo99.html.
[2] M.R.Civanlar，G.L.Cash，“网络视图-NetVG”，第九届国际分组视频研讨会论文集，http://www.research.att.com/~mrc/PacketVideo99.html。
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[3] Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
M. Reha Civanlar AT&T Labs - Research 100 Schultz Drive, Room 3-205 Red Bank, NJ 07701, USA
M.Reha Civanlar AT&T实验室-美国新泽西州红银行Schultz大道100号3-205室，邮编07701
EMail: civanlar@research.att.com
EMail: civanlar@research.att.com
Glenn L. Cash AT&T Labs - Research 100 Schultz Drive, Room 3-213 Red Bank, NJ 07701, USA
Glenn L.Cash AT&T实验室-美国新泽西州红银行Schultz大道100号研究中心3-213室07701
EMail: glenn@research.att.com
EMail: glenn@research.att.com
Copyright (C) The Internet Society (2000). All Rights Reserved.
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Acknowledgement
确认
Funding for the RFC Editor function is currently provided by the Internet Society.
RFC编辑功能的资金目前由互联网协会提供。