通过 SIP 的第 3 方呼叫控制
我正在尝试使用 SIP 进行第 3 方呼叫控制。我不确定这是否可能，所以希望有人能启发我。
我有以下场景。在内部网络上，有多个电话分机。 Alice 有一部物理 SIP 电话，办公室里的所有其他人也有一部。
我想要做的（对于初学者来说）是允许以下操作：有人呼叫 Alice。她没有拿起物理 SIP 电话，而是单击计算机屏幕上的某个按钮（假设有一个标记为Answer）。这会迫使物理电话摘机（例如，它现在处于扬声器状态），并且她正在与给她打电话的人通话。
这可以做到吗？任何代码项目，尤其是 C# 项目，都将受到欢迎。
我已经使用 TAPI 完成了此类工作，效果非常好，但 TAPI 是一项即将消亡的技术（没有 64 位等效技术），因此我正在寻找替代方案。
I am trying to use SIP to do 3rd party Call Control. I am not sure that it's possible, so hopefully someone can enlighten me.
I have the following scenario. On an internal network, there are several phone extensions. Alice has a physical SIP phone, so do all the other people in the office.
What I want to do (for starters), is to allow the following: someone calls Alice. Instead of picking up the physical SIP phone, she instead clicks on some button (let's say one marked Answer) on her computer screen. That forces the physical phone off hook (e.g. it's now on speaker) and she is talking to whoever called her.
Can this be done? Any code projects, especially in c#, would be welcome.
I've done this type of thing with TAPI and it worked out pretty well, but TAPI is a dying technology (there is no 64-bit equivalent), so I am looking for a replacement.
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让您知道 Alice 的电话已被拿起的 SIP 机制是一个事件通知，记录在 RFC 中3265 会话发起协议 (SIP) 特定事件通知 和 INVITE 相关通知的特定事件包为 RFC 4235 用于会话发起协议 (SIP) 的 INVITE 发起的对话事件包。
简而言之，SIP 事件在订阅/通知的基础上工作，其中一个 SIP 用户代理可以订阅通知服务器，以获取有关不同用户代理上发生的事件的通知。不幸的是，对 SIP 事件的支持并不是那么广泛，即使支持也可能有点不稳定，Asterisk 对于用于生成非常奇怪的 NOTIFY 请求的示例。
The SIP mechanism to let you know that Alice's phone was picked up is an event notification which is documented in RFC 3265 Session Initiation Protocol (SIP)-Specific Event Notification and the specific event package for INVITE relatedd notifications is RFC 4235 An INVITE-Initiated Dialog Event Package for the Session Initiation Protocol (SIP).
In short SIP events work on a subscribe/notify basis where one SIP user agent can subscribe to a notification server for notifications about events that happen on a different useragent. Unfortunately support for SIP events is not that widepread and even when it is supported can be a bit flakey, Asterisk for example used to generate very strange NOTIFY requests.
RFC 3725 中解释了 SIP 的 3pcc（最佳实践）。
另一种可能性（不使用 3pcc）是 Alice 的软件电话以比她的物理 SIP 电话更高的优先级进行注册。对 Alice 记录地址的呼叫将转至她的软件电话，该软件电话可以将呼叫（即呼叫转接/盲转）转接到 SIP 电话。
(Best practices) for 3pcc for SIP are explained in RFC 3725.
Another possibility (that doesn't use 3pcc) is for Alice's softphone to REGISTER with a higher preference than her physical SIP phone. Calls to Alice's Address of Record will go to her softphone, which can REFER the call (so call forwarding/blind transfer) to the SIP phone.