Internet Engineering Task Force (IETF) J. Elwell
Request for Comments: 5876 Siemens Enterprise Communications
Updates: 3325 April 2010
Category: Informational
ISSN: 2070-1721
Internet Engineering Task Force (IETF) J. Elwell
Request for Comments: 5876 Siemens Enterprise Communications
Updates: 3325 April 2010
Category: Informational
ISSN: 2070-1721
Updates to Asserted Identity in the Session Initiation Protocol (SIP)
更新会话启动协议（SIP）中断言的标识
Abstract
摘要
The Session Initiation Protocol (SIP) has a mechanism for conveying the identity of the originator of a request by means of the P-Asserted-Identity and P-Preferred-Identity header fields. These header fields are specified for use in requests using a number of SIP methods, in particular the INVITE method. However, RFC 3325 does not specify the insertion of the P-Asserted-Identity header field by a trusted User Agent Client (UAC), does not specify the use of P-Asserted-Identity and P-Preferred-Identity header fields with certain SIP methods such as UPDATE, REGISTER, MESSAGE, and PUBLISH, and does not specify how to handle an unexpected number of URIs or unexpected URI schemes in these header fields. This document extends RFC 3325 to cover these situations.
会话发起协议（SIP）具有通过P-Asserted-identity和P-Preferred-identity报头字段传递请求的发起人的身份的机制。这些头字段指定用于使用许多SIP方法（特别是INVITE方法）的请求中。但是，RFC 3325未指定受信任用户代理客户端（UAC）插入P-Asserted-Identity标头字段，未指定P-Asserted-Identity和P-Preferred-Identity标头字段与某些SIP方法（如更新、注册、消息和发布）的使用，并且没有指定如何处理这些标头字段中意外数量的URI或意外URI方案。本文件扩展了RFC 3325以涵盖这些情况。
Status of This Memo
关于下段备忘
This document is not an Internet Standards Track specification; it is published for informational purposes.
本文件不是互联网标准跟踪规范；它是为了提供信息而发布的。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。并非IESG批准的所有文件都适用于任何级别的互联网标准；见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5876.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc5876.
Copyright Notice
版权公告
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2010 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction ....................................................2
2. Terminology .....................................................4
3. Discussion ......................................................4
3.1. Inclusion of P-Asserted-Identity by a UAC ..................4
3.2. Inclusion of P-Asserted-Identity in Any Request ............5
3.3. Dialog Implications ........................................6
4. Behaviour .......................................................6
4.1. UAC Behaviour ..............................................7
4.2. Proxy Behaviour ............................................7
4.3. Registrar Behaviour ........................................7
4.4. UAS Behaviour ..............................................8
4.5. General Handling ...........................................8
5. Security Considerations .........................................9
6. Acknowledgements ...............................................10
7. References .....................................................10
7.1. Normative References ......................................10
7.2. Informative References ....................................11
1. Introduction ....................................................2
2. Terminology .....................................................4
3. Discussion ......................................................4
3.1. Inclusion of P-Asserted-Identity by a UAC ..................4
3.2. Inclusion of P-Asserted-Identity in Any Request ............5
3.3. Dialog Implications ........................................6
4. Behaviour .......................................................6
4.1. UAC Behaviour ..............................................7
4.2. Proxy Behaviour ............................................7
4.3. Registrar Behaviour ........................................7
4.4. UAS Behaviour ..............................................8
4.5. General Handling ...........................................8
5. Security Considerations .........................................9
6. Acknowledgements ...............................................10
7. References .....................................................10
7.1. Normative References ......................................10
7.2. Informative References ....................................11
The Session Initiation Protocol (SIP) is specified in RFC 3261 [RFC3261]. RFC 3325 [RFC3325] specifies a mechanism for conveying the asserted identity of the originator of a SIP request within a Trust Domain. This is achieved by means of the P-Asserted-Identity header field, which is specified for use in requests using a number of SIP methods, in particular the INVITE method. In addition, the P-Preferred-Identity header field can be used to indicate a preference for which identity should be asserted when there is a choice.
会话启动协议（SIP）在RFC 3261[RFC3261]中规定。RFC 3325[RFC3325]指定了一种机制，用于在信任域内传递SIP请求的发起人的断言身份。这是通过P-Asserted-Identity报头字段实现的，该字段指定用于使用许多SIP方法（尤其是INVITE方法）的请求中。此外，P-Preferred-Identity报头字段可用于指示当有选择时应声明哪个标识的首选项。
RFC 3325 does not specify the insertion of the P-Asserted-Identity header field by a User Agent Client (UAC) in the same Trust Domain as the first proxy. Also, RFC 3325 does not specify the use of the P-Asserted-Identity and P-Preferred-Identity header fields with certain SIP methods such as UPDATE [RFC3311], REGISTER, MESSAGE [RFC3428], and PUBLISH [RFC3903]. This document extends RFC 3325 by allowing inclusion of the P-Asserted-Identity header field by a UAC in the same Trust Domain as the first proxy and allowing use of P-Asserted-Identity and P-Preferred-Identity header fields in any request except ACK and CANCEL. The reason for these two exceptions is that ACK and CANCEL requests cannot be challenged for digest authentication.
RFC 3325未指定用户代理客户端（UAC）在与第一个代理相同的信任域中插入P-Asserted-Identity头字段。此外，RFC 3325未指定P-Asserted-Identity和P-Preferred-Identity标头字段与某些SIP方法的使用，如更新[RFC3311]、注册、消息[RFC3428]和发布[RFC3903]。本文档扩展了RFC 3325，允许UAC在与第一个代理相同的信任域中包含P-Asserted-Identity标头字段，并允许在除ACK和CANCEL之外的任何请求中使用P-Asserted-Identity和P-Preferred-Identity标头字段。这两个异常的原因是ACK和CANCEL请求不能被质疑进行摘要身份验证。
RFC 3325 allows the P-Asserted-Identity and P-Preferred-Identity header fields each to contain at most two URIs, where one is a SIP or SIPS URI [RFC3261] and the other is a TEL URI [RFC3966]. This may be unduly restrictive in the future, for example, if there is a need to allow other URI schemes, if there is a need to allow both a SIP and a SIPS URI, or if there is a need to allow more than one URI with the same scheme (e.g., a SIP URI based on a telephone number and a SIP URI that is not based on a telephone number). This document therefore provides forwards compatibility by mandating tolerance to the receipt of unexpected URIs.
RFC 3325允许P-Asserted-Identity和P-Preferred-Identity头字段各自最多包含两个URI，其中一个是SIP或SIPS URI[RFC3261]，另一个是TEL URI[RFC3966]。例如，如果需要允许其他URI方案，如果需要同时允许SIP和SIPS URI，或者如果需要允许具有相同方案的多个URI（例如，基于电话号码的SIP URI和不基于电话号码的SIP URI），则这在将来可能是过度限制的。因此，本文档通过强制允许接收意外URI来提供向前兼容性。
This document does not alter the fact that the asserted identity mechanism has limited applicability, i.e., within a Trust Domain. For general applicability, including operation outside a Trust Domain (e.g., over the public Internet) or between different Trust Domains, a different mechanism is needed. RFC 4474 [RFC4474] specifies the Identity header field, in conjunction with the From header field, to provide authenticated identity in such circumstances. RFC 4916 [RFC4916] specifies the use of RFC 4474 in mid-dialog requests, in particular, in requests in the reverse direction to the dialog-forming request as a means of providing authenticated connected identity.
本文件不改变以下事实：断言的身份机制的适用性有限，即在信任域内。对于一般适用性，包括信任域之外（例如，通过公共互联网）或不同信任域之间的操作，需要不同的机制。RFC 4474[RFC4474]指定标识标头字段，与From标头字段一起，在这种情况下提供经过身份验证的标识。RFC 4916[RFC4916]指定在中间对话请求中使用RFC 4474，特别是在与对话形成请求相反方向的请求中，作为提供认证连接身份的手段。
RFC 3325 is unclear on the use of P-Asserted-Identity in responses. In contrast to requests, there is no means in SIP to challenge a User Agent Server (UAS) to provide SIP digest authentication in a response. As a result, there is currently no standardised mechanism whereby a proxy can authenticate a UAS. Since authenticating the source of a message is a prerequisite for asserting an identity, this document does not specify the use of the P-Asserted-Identity header field in responses. This may be the subject of a future update to RFC 3325. Also, this document does not specify the use of the P-Preferred-Identity header field in responses, as this would serve no purpose in the absence of the ability for a proxy to insert the P-Asserted-Identity header field.
RFC 3325不清楚在响应中使用P-Asserted-Identity。与请求不同的是，SIP中没有任何方法可以挑战用户代理服务器（UAS）在响应中提供SIP摘要身份验证。因此，目前还没有标准化的机制，代理可以据此对UAS进行身份验证。由于验证消息源是断言标识的先决条件，因此本文档不指定在响应中使用P-Asserted-identity头字段。这可能是RFC 3325未来更新的主题。此外，本文档未规定在响应中使用P-Preferred-Identity标头字段，因为在代理无法插入P-Asserted-Identity标头字段的情况下，这没有任何用途。
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 [RFC2119].
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照[RFC2119]中所述进行解释。
This document uses the concepts of Trust Domain and Spec(T), as specified in section 2.3 of RFC 3324 [RFC3324].
本文件使用了RFC 3324[RFC3324]第2.3节规定的信任域和规范（T）的概念。
RFC 3325 does not include procedures for a UAC to include the P-Asserted-Identity header field in a request. This can be meaningful if the UAC is in the same Trust Domain as the first downstream SIP entity. Examples of types of UACs that are often suitable for inclusion in a Trust Domain are:
RFC 3325不包括UAC在请求中包含P-Asserted-Identity标头字段的过程。如果UAC与第一个下游SIP实体位于同一信任域中，则这可能是有意义的。通常适合包含在信任域中的UAC类型示例如下：
o Public Switched Telephone Network (PSTN) gateways;
o 公共交换电话网（PSTN）网关；
o media servers;
o 媒体服务器；
o application servers (or Back-to-Back User Agents (B2BUAs)) that act as URI list servers [RFC5363];
o 充当URI列表服务器的应用服务器（或背靠背用户代理（B2BUA））[RFC5363]；
o application servers (or B2BUAs) that perform third party call control.
o 执行第三方呼叫控制的应用程序服务器（或B2BUA）。
In the particular case of a PSTN gateway, the PSTN gateway might be able to assert an identity received from the PSTN, the proxy itself having no means to authenticate such an identity. Likewise, in the case of certain application server or B2BUA arrangements, the application server or B2BUA may be in a position to assert an identity of a user on the other side of that application server or B2BUA.
在PSTN网关的特定情况下，PSTN网关可能能够断言从PSTN接收到的身份，而代理本身没有手段认证这样的身份。类似地，在某些应用服务器或B2BUA布置的情况下，应用服务器或B2BUA可以处于在该应用服务器或B2BUA的另一侧断言用户的身份的位置。
In accordance with RFC 3325, nodes within a Trust Domain must behave in accordance with a Spec(T), and this principle needs to be applied between a UAC and its proxy as part of the condition to consider the UAC to be within the same Trust Domain. The normal proxy procedures of RFC 3325 ensure that the header field is removed or replaced if the first proxy considers the UAC to be outside the Trust Domain.
根据RFC 3325，信任域内的节点必须按照规范（T）来执行，并且这一原理需要在UAC与其代理之间应用，作为考虑UAC在同一信任域内的条件的一部分。RFC 3325的正常代理程序确保，如果第一个代理认为UAC在信任域之外，则删除或替换头字段。
This update to RFC 3325 clarifies that a UAC may include a P-Asserted-Identity header field in a request in certain circumstances.
RFC 3325的更新澄清了在某些情况下，UAC可能在请求中包含P-Asserted-Identity头字段。
There are several use cases that would benefit from the use of the P-Asserted-Identity header field in an UPDATE request. These use cases apply within a Trust Domain where the use of asserted identity is appropriate (see RFC 3325).
在更新请求中使用P-Asserted-Identity报头字段将有几个用例受益。这些用例适用于适当使用断言标识的信任域（参见RFC 3325）。
In one example, an established call passes through a gateway to the PSTN. The gateway becomes aware that the remote party in the PSTN has changed, e.g., due to call transfer. By including the P-Asserted-Identity header field in an UPDATE request, the gateway can convey the identity of the new remote party to the peer SIP User Agent (UA).
在一个示例中，已建立的呼叫通过网关传递到PSTN。网关意识到PSTN中的远程方已经改变，例如，由于呼叫转移。通过在更新请求中包括P-Asserted-Identity报头字段，网关可以将新远程方的身份传送给对等SIP用户代理（UA）。
Note that the (re-)INVITE method could be used in this situation. However, this forces an offer-answer exchange, which typically is not required in this situation. Also, it involves three messages rather than two.
请注意，（重新）INVITE方法可以在这种情况下使用。但是，这会强制进行要约-应答交换，在这种情况下通常不需要这样做。此外，它涉及三条信息，而不是两条。
In another example, a B2BUA that provides third party call control (3PCC) [RFC3725] wishes to join two calls together, one of which is still waiting to be answered and potentially is forked to different UAs. At this point in time, it is not possible to trigger the normal offer-answer exchange between the two joined parties, because of the mismatch between a single dialog on the one side and potentially multiple early dialogs on the other side, so this action must wait until one of the called UAs answers. However, it would be useful to give an early indication to each user concerned of the identity of the user to which they will become connected when the call is answered. In other words, it would provide the new calling UA with the identity of the new called user and provide the new called UA(s) with the identity of the new calling user. This can be achieved by the B2BUA sending an UPDATE request with a P-Asserted-Identity header field on the dialogs concerned.
在另一个示例中，提供第三方呼叫控制（3PCC）[RFC3725]的B2BUA希望将两个呼叫合并在一起，其中一个呼叫仍在等待应答，并且可能被分岔到不同的UAs。此时，不可能触发两个加入方之间的正常要约-应答交换，因为一方的单个对话框与另一方可能的多个早期对话框之间不匹配，因此此操作必须等待一个被调用的UAs应答。然而，在电话应答时，尽早向每个相关用户指示他们将连接到的用户的身份是有用的。换句话说，它将向新的主叫UA提供新的被叫用户的身份，并向新的被叫UA提供新的主叫用户的身份。这可以通过B2BUA在相关对话框上发送带有P-Asserted-Identity头字段的更新请求来实现。
Within a Trust Domain, a P-Asserted-Identity header field could advantageously be used in a REGISTER request between an edge proxy that has authenticated the source of the request and the registrar.
在信任域内，P-Asserted-Identity报头字段可有利地用于已认证请求源的边缘代理和注册器之间的注册请求中。
Within a Trust Domain, a P-Asserted-Identity header field could advantageously be used in a MESSAGE request to assert the source of a page-mode instant message. This would complement its use in an INVITE request to assert the source of an instant-message session or any other form of session. Similarly, between a UAC and first proxy that are not within the same Trust Domain, a P-Preferred-Identity header field could be used in a MESSAGE request to express a preference when the user has several identities.
在信任域内，P-Asserted-Identity报头字段可有利地用于消息请求中以断言页面模式即时消息的源。这将补充其在INVITE请求中的使用，以断言即时消息会话或任何其他形式的会话的源。类似地，在不在同一信任域内的UAC和第一个代理之间，当用户具有多个身份时，可以在消息请求中使用P-Preferred-Identity头字段来表示偏好。
Within a Trust Domain, a P-Asserted-Identity header field could advantageously be used in a PUBLISH request to assert the source of published state information. This would complement its use in SUBSCRIBE and NOTIFY requests. Similarly, between a UAC and first proxy that are not within the same Trust Domain, a P-Preferred-Identity header field could be used in a PUBLISH request to express a preference when the user has several identities.
在信任域内，P-Asserted-Identity报头字段可以有利地用于发布请求中，以断言发布状态信息的源。这将补充它在订阅和通知请求中的使用。类似地，在不在同一信任域内的UAC和第一个代理之间，可以在发布请求中使用P-Preferred-Identity头字段来表示用户具有多个身份时的偏好。
Thus, there are several examples where P-Asserted-Identity could be used in requests with methods for which there is no provision in RFC 3325. This leaves a few methods for which use cases are less obvious, but the inclusion of P-Asserted-Identity would not cause any harm. In any requests, the header field would simply assert the source of that request, whether or not this is of any use to the UAS. Inclusion of P-Asserted-Identity in a request requires that the original asserter of an identity be able to authenticate the source of the request. This implies the ability to challenge a request for SIP digest authentication, which is not possible with ACK and CANCEL requests. Therefore, ACK and CANCEL requests need to be excluded.
因此，有几个例子表明，P-Asserted-Identity可以在请求中使用RFC3325中没有规定的方法。这就留下了一些用例不太明显的方法，但是包含P-Asserted-Identity不会造成任何伤害。在任何请求中，header字段都将简单地断言该请求的源，无论这对UAS是否有用。在请求中包含P-Asserted-Identity需要身份的原始断言者能够对请求的源进行身份验证。这意味着能够质询SIP摘要身份验证请求，这在ACK和CANCEL请求中是不可能的。因此，需要排除ACK和CANCEL请求。
Similarly, there are examples where P-Preferred-Identity could be used in requests with methods for which there is no provision in RFC 3325 or any other RFC (with the exception of ACK and CANCEL).
类似地，也有一些示例，其中P-Preferred-Identity可用于具有RFC 3325或任何其他RFC（ACK和CANCEL除外）中没有规定的方法的请求中。
This update to RFC 3325 allows a P-Asserted-Identity or P-Preferred-Identity header field to be included in any request except ACK and CANCEL.
RFC 3325的此更新允许在任何请求中包括P-Asserted-Identity或P-Preferred-Identity头字段，ACK和CANCEL除外。
A P-Asserted-Identity header field in a received request asserts the identity of the source of that request and says nothing about the source of subsequent received requests claiming to relate to the same dialog. The recipient can make its own deductions about the source of subsequent requests not containing a P-Asserted-Identity header field. This document does not change RFC 3325 in this respect.
接收到的请求中的P-Asserted-Identity头字段断言该请求的源的标识，并且不说明声称与同一对话框相关的后续接收到的请求的源。接收方可以对不包含P-Asserted-Identity标头字段的后续请求的来源进行自己的推断。本文件在这方面不改变RFC 3325。
This document updates RFC 3325 by allowing a P-Asserted-Identity header field to be included by a UAC within the same Trust Domain and by allowing a P-Asserted-Identity or P-Preferred-Identity header field to appear in any request except ACK or CANCEL.
本文档通过允许UAC在同一信任域中包含P-Asserted-Identity标头字段，并允许P-Asserted-Identity或P-Preferred-Identity标头字段出现在除ACK或CANCEL之外的任何请求中，来更新RFC 3325。
A UAC MAY include a P-Asserted-Identity header field in any request except ACK and CANCEL to report the identity of the user on behalf of which the UAC is acting and whose identity the UAC is in a position to assert. A UAC SHOULD do so only in cases where it believes it is in the same Trust Domain as the SIP entity to which it sends the request and where it is connected to that SIP entity in accordance with the security requirements of RFC 3325. A UAC SHOULD NOT do so in other circumstances and might instead use the P-Preferred-Identity header field. A UAC MUST NOT include both header fields.
UAC可以在除ACK和CANCEL之外的任何请求中包括P-Asserted-Identity报头字段，以报告UAC代表的用户的身份以及UAC能够断言的用户身份。UAC应仅在其认为其与向其发送请求的SIP实体位于同一信任域，并且根据RFC 3325的安全要求连接到该SIP实体的情况下这样做。UAC不应在其他情况下这样做，而可以使用P-Preferred-Identity标头字段。UAC不能同时包含两个标题字段。
A UAC MAY include a P-Preferred-Identity header field in any request except ACK or CANCEL.
UAC可以在除ACK或CANCEL之外的任何请求中包括P-PREFERED-Identity头字段。
Inclusion of a P-Asserted-Identity or P-Preferred-Identity header field in a request is not limited to the methods allowed in RFC 3325.
在请求中包含P-Asserted-Identity或P-Preferred-Identity头字段不限于RFC 3325中允许的方法。
If a proxy receives a request containing a P-Asserted-Identity header field from a UAC within the Trust Domain, it MUST behave as it would for a request from any other node within the Trust Domain, in accordance with the rules of RFC 3325 for a proxy.
如果代理从信任域内的UAC接收到包含P-Asserted-Identity标头字段的请求，则它必须按照RFC 3325关于代理的规则，与来自信任域内任何其他节点的请求的行为相同。
Note that this implies that the proxy must have authenticated the sender of the request in accordance with the Spec(T) in force for the Trust Domain and determined that the sender is indeed part of the Trust Domain.
请注意，这意味着代理必须根据对信任域有效的规范（T）对请求的发送者进行身份验证，并确定发送者确实是信任域的一部分。
If a proxy receives a request (other than ACK or CANCEL) containing a P-Asserted-Identity or P-Preferred-Identity header field, it MUST behave in accordance with the rules of RFC 3325 for a proxy, even if the method is not one for which RFC 3325 specifies use of that header field.
如果代理收到包含P-Asserted-Identity或P-Preferred-Identity头字段的请求（ACK或CANCEL除外），则其行为必须符合RFC 3325对代理的规则，即使该方法不是RFC 3325指定使用该头字段的方法。
If a registrar receives a REGISTER request containing a P-Asserted-Identity header field, it MUST disregard the asserted identity unless it is received from a node within the Trust Domain. If the node is within the Trust Domain (the node having been authenticated by some means), the registrar MAY use this as evidence that the registering UA has been authenticated and is represented by the identity asserted in the header field.
如果注册器接收到包含P-Asserted-Identity头字段的注册请求，它必须忽略断言的标识，除非它是从信任域内的节点接收到的。如果该节点在信任域内（该节点已经通过某种方式进行了认证），则注册官可以使用该节点作为注册UA已经过认证的证据，并且由在报头字段中断言的标识表示。
If a UAS receives any request (other than ACK or CANCEL) containing a P-Asserted-Identity header field, it MUST behave in accordance with the rules of RFC 3325 for a UAS, even if the method is not one for which RFC 3325 specifies use of that header field.
如果UAS接收到包含P-Asserted-Identity标头字段的任何请求（ACK或CANCEL除外），则其行为必须符合适用于UAS的RFC 3325规则，即使该方法不是RFC 3325指定使用该标头字段的方法。
An entity receiving a P-Asserted-Identity or P-Preferred-Identity header field can expect the number of URIs and the combination of URI schemes in the header field to be in accordance with RFC 3325, any updates to RFC 3325, or any Spec(T) that states otherwise. If an entity receives a request containing a P-Asserted-Identity or P-Preferred-Identity header field containing an unexpected number of URIs or unexpected URI schemes, it MUST act as follows:
接收P-Asserted-Identity或P-Preferred-Identity报头字段的实体可以期望报头字段中的URI数量和URI方案组合符合RFC 3325、RFC 3325的任何更新或其他规定的任何规范（T）。如果实体接收到包含P-Asserted-Identity或P-Preferred-Identity标头字段的请求，该字段包含意外数量的URI或意外URI方案，则该实体必须按如下方式操作：
o ignore any URI with an unexpected URI scheme;
o 忽略具有意外URI方案的任何URI；
o ignore any URI for which the expected maximum number of URIs with the same scheme occurred earlier in the header field; and
o 忽略头字段中较早出现具有相同方案的预期最大URI数的任何URI；和
o ignore any URI whose scheme is not expected to occur in combination with a scheme that occurred earlier in the header field.
o 忽略其方案预期不会与头字段中较早出现的方案组合出现的任何URI。
In the absence of a Spec(T) determining otherwise, this document does not change the RFC 3325 requirement that allows each of these header fields to contain at most two URIs, where one is a SIP or SIPS URI and the other is a TEL URI, but future updates to this document may relax that requirement. In the absence of such a relaxation or a Spec(T) determining otherwise, the RFC 3325 requirement means that an entity receiving a request containing a P-Asserted-Identity or P-Preferred-Identity header field must act as follows:
在没有规范（T）另有规定的情况下，本文档不会更改RFC 3325要求，该要求允许这些标题字段中的每个字段最多包含两个URI，其中一个是SIP或SIPS URI，另一个是TEL URI，但本文档的未来更新可能会放宽该要求。在没有此类放宽或规范（T）另有规定的情况下，RFC 3325要求意味着接收包含P-Asserted-Identity或P-Preferred-Identity标头字段的请求的实体必须按照以下方式行事：
o ignore any URI with a scheme other than SIP, SIPS, or TEL;
o 忽略任何具有SIP、SIPS或TEL以外方案的URI；
o ignore a second or subsequent SIP URI, a second or subsequent SIPS URI, or a second or subsequent TEL URI; and
o 忽略第二或后续SIP URI、第二或后续SIPS URI或第二或后续TEL URI；和
o ignore a SIP URI if a SIPS URI occurred earlier in the header field and vice versa.
o 如果SIPS URI较早出现在标头字段中，则忽略SIP URI，反之亦然。
A proxy MUST NOT forward a URI when forwarding a request if that URI is to be ignored in accordance with the requirement above.
如果要根据上述要求忽略URI，则代理在转发请求时不得转发该URI。
When a UAC or a proxy sends a request containing a P-Asserted-Identity header field to another node in the Trust Domain, if that other node complies with RFC 3325 but not with this specification, and if the method is not one for which RFC 3325 specifies use of the P-Asserted-Identity header field, and if the request also contains a Privacy header field with value 'id', as specified in RFC 3325, the other node might not handle the Privacy header field correctly. To prevent incorrect handling of the Privacy header field with value 'id', the Spec(T) in force for the Trust Domain SHOULD require all nodes to comply with this specification. If this is not the case, a UAC or a proxy SHOULD NOT include a P-Asserted-Identity header field in a request if the method is not one for which RFC 3325 specifies use of the P-Asserted-Identity header field and if the request also contains a Privacy header field with value 'id'.
当UAC或代理向信任域中的另一节点发送包含P-Asserted-Identity标头字段的请求时，如果该另一节点符合RFC 3325但不符合本规范，并且如果该方法不是RFC 3325指定使用P-Asserted-Identity标头字段的方法，并且，如果请求还包含RFC 3325中指定的值为“id”的隐私标头字段，则另一个节点可能无法正确处理隐私标头字段。为防止对值为“id”的隐私标头字段进行错误处理，对信任域生效的规范（T）应要求所有节点遵守此规范。如果不是这种情况，则UAC或代理不应在请求中包含P-Asserted-Identity标头字段，前提是该方法不是RFC 3325指定使用P-Asserted-Identity标头字段的方法，并且请求还包含值为“id”的隐私标头字段。
The use of asserted identity raises a number of security considerations, which are discussed fully in [RFC3325]. This document raises the following additional security considerations.
使用断言标识会引起许多安全注意事项，这些事项在[RFC3325]中有详细讨论。本文件提出了以下额外的安全注意事项。
When adding a P-Asserted-Identity header field to a message, an entity must have authenticated the source of the message by some means. One means is to challenge the sender of a message to provide SIP digest authentication. Responses cannot be challenged, and also ACK and CANCEL requests cannot be challenged. Therefore, this document limits the use of P-Asserted-Identity to requests other than ACK and CANCEL.
在向消息添加P-Asserted-Identity头字段时，实体必须通过某种方式对消息源进行了身份验证。一种方法是质询消息的发送方以提供SIP摘要身份验证。不能质询响应，也不能质询ACK和CANCEL请求。因此，本文档将P-Asserted-Identity的使用限制为ACK和CANCEL之外的请求。
When sending a request containing the P-Asserted-Identity header field and also the Privacy header field with value 'id' to a node within the Trust Domain, special considerations apply if that node does not support this specification. Section 4.5 makes a special provision for this case.
当向信任域内的节点发送包含P-Asserted-Identity标头字段和值为“id”的隐私标头字段的请求时，如果该节点不支持此规范，则需要特别注意。第4.5节对这种情况作了特别规定。
When receiving a request containing a P-Asserted-Identity header field, a proxy will trust the assertion only if the source is known to be within the Trust Domain and behaves in accordance with a Spec(T), which defines the security requirements. This applies regardless of the nature of the resource (UA or proxy). One example where a trusted source might be a UA is a PSTN gateway. In this case, the UA can assert an identity received from the PSTN, the proxy itself having no means to authenticate such an identity. A SIP entity must not trust an identity asserted by a source outside the Trust Domain. Typically, a UA under the control of an individual user (such as a desk phone or mobile phone) should not be considered part of a Trust Domain.
当接收到包含P-Asserted-Identity头字段的请求时，代理将仅在已知源位于信任域内并且其行为符合定义安全要求的规范（T）的情况下信任该断言。无论资源的性质如何（UA或代理），这都适用。可信源可能是UA的一个示例是PSTN网关。在这种情况下，UA可以断言从PSTN接收到的身份，而代理本身没有手段来验证这种身份。SIP实体不得信任由信任域之外的源声明的标识。通常，由个人用户（例如台式电话或移动电话）控制的UA不应被视为信任域的一部分。
When receiving a response from a node outside the Trust Domain, a proxy has no standardised SIP means to authenticate the source of the response. For this reason, this document does not specify the use of P-Asserted-Identity or P-Preferred-Identity in responses.
当从信任域之外的节点接收响应时，代理没有标准化的SIP方法来验证响应源。因此，本文档未指定在响应中使用P-Asserted-Identity或P-Preferred-Identity。
Useful comments were received from Francois Audet, John-Luc Bakker, Jeroen van Bemmel, Hans Erik van Elburg, Vijay Gurbani, Cullen Jennings, Hadriel Kaplan, Paul Kyzivat, Jonathan Rosenberg, Thomas Stach, and Brett Tate during drafting and review.
在起草和审查期间，收到了弗朗索瓦·奥德特、约翰·吕克·巴克、杰伦·范贝梅尔、汉斯·埃里克·范埃尔伯格、维杰·古巴尼、卡伦·詹宁斯、哈德里尔·卡普兰、保罗·基齐瓦特、乔纳森·罗森伯格、托马斯·斯塔赫和布雷特·塔特的有用意见。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002.
[RFC3261]Rosenberg，J.，Schulzrinne，H.，Camarillo，G.，Johnston，A.，Peterson，J.，Sparks，R.，Handley，M.，和E.Schooler，“SIP：会话启动协议”，RFC 3261，2002年6月。
[RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP) UPDATE Method", RFC 3311, October 2002.
[RFC3311]Rosenberg，J.，“会话启动协议（SIP）更新方法”，RFC3311，2002年10月。
[RFC3324] Watson, M., "Short Term Requirements for Network Asserted Identity", RFC 3324, November 2002.
[RFC3324]Watson，M.，“网络断言身份的短期要求”，RFC 33242002年11月。
[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private Extensions to the Session Initiation Protocol (SIP) for Asserted Identity within Trusted Networks", RFC 3325, November 2002.
[RFC3325]Jennings，C.，Peterson，J.，和M.Watson，“在可信网络中声明身份的会话启动协议（SIP）的私有扩展”，RFC 33252002年11月。
[RFC3428] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and D. Gurle, "Session Initiation Protocol (SIP) Extension for Instant Messaging", RFC 3428, December 2002.
[RFC3428]Campbell，B.，Rosenberg，J.，Schulzrinne，H.，Huitema，C.，和D.Gurle，“即时消息的会话启动协议（SIP）扩展”，RFC 34282002年12月。
[RFC3903] Niemi, A., "Session Initiation Protocol (SIP) Extension for Event State Publication", RFC 3903, October 2004.
[RFC3903]Niemi，A.，“事件状态发布的会话启动协议（SIP）扩展”，RFC 3903，2004年10月。
[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966, December 2004.
[RFC3966]Schulzrinne，H.，“电话号码的电话URI”，RFC 3966，2004年12月。
[RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. Camarillo, "Best Current Practices for Third Party Call Control (3pcc) in the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, April 2004.
[RFC3725]Rosenberg，J.，Peterson，J.，Schulzrinne，H.，和G.Camarillo，“会话启动协议（SIP）中第三方呼叫控制（3pcc）的当前最佳实践”，BCP 85，RFC 37252004年4月。
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", RFC 4474, August 2006.
[RFC4474]Peterson，J.和C.Jennings，“会话启动协议（SIP）中身份验证管理的增强”，RFC 4474，2006年8月。
[RFC4916] Elwell, J., "Connected Identity in the Session Initiation Protocol (SIP)", RFC 4916, June 2007.
[RFC4916]Elwell，J.，“会话启动协议（SIP）中的连接身份”，RFC 4916，2007年6月。
[RFC5363] Camarillo, G. and A. Roach, "Framework and Security Considerations for Session Initiation Protocol (SIP) URI-List Services", RFC 5363, October 2008.
[RFC5363]Camarillo，G.和A.Roach，“会话启动协议（SIP）URI列表服务的框架和安全注意事项”，RFC 5363，2008年10月。
Author's Address
作者地址
John Elwell Siemens Enterprise Communications
西门子企业通信公司
Phone: +44 115 943 4989
EMail: john.elwell@siemens-enterprise.com
Phone: +44 115 943 4989
EMail: john.elwell@siemens-enterprise.com