Message Waiting Indication学习笔记

1 MWI是电话网络的一个通用特性。通常是一个可听或可见的提示符，表示消息正在等待。譬如，播放一个特别的拨号音(电话网络中称为message-waiting dial tone)，或者点亮一颗灯，或者在电话上显示图标或者文本，或者几种的组合。

2 当一个subscriber User Agent订阅一个账号的消息，那么当这个账号的状态发生变化时，User Agent(这儿应该是UAS吧)都会通知该subscriber。当任何subscriptions或者notifications被发

送之前，每一个相关的User Agent都必须配置好他们的messaging notifier(s)，或者在合适的SIP Proxy上配置，或者动态请求caller preferences和registered callee capabilities。

3 Message Summary和Message Waiting Indicator subcribe的时间可以是数分钟，也可以是数周，不过最好是数小时或数天。

4 Notification的消息体是基于文本的，以一个状态行开始，然后每一个消息上下文类别(voice-class,fax-class,mutimedia-class等)都以一个summary开始。

5 某些情况下，详细的消息概要是不能用的，那么允许messaging systems或者messaging gateways使用传统的boolean message waiting notification：

  Messages-Waiting: yes  

6

If the Request-URI or To header in a message-summary subscription corresponds to a group or collection of 

individual messaging   accounts, the notifier MUST specify to which account the message-   summary body corresponds.  Note that the account URI MUST NOT be  

 delimited with angle brackets ("<" and ">").      Message-Account: sip:alice@example.com   In the example that follows, more than boolean message summary  

 information is available to the User Agent.  There are two new and   four old fax messages.      Fax-Message: 2/4   After the summary, the format can optionally list a 

summary count of   urgent messages.  In the next example there are one new and three old   voice messages, none of the new messages are urgent, but one of the   

old messages is.  All counters have a maximum value of 4,294,967,295   ((2^32) - 1).  Notifiers MUST NOT generate a request with a larger   value.  Subscribers MUST 

treat a larger value as 2^32-1.      Voice-Message: 1/3 (0/1)   Optionally, after the summary counts, the messaging systems MAY   append RFC 2822 style message 

headers [9], which further describe   newly added messages.  Message headers MUST NOT be included in an   initial NOTIFY, as new messages could be essentially 

unbounded in   size.  Message headers included in subsequent notifications MUST only   correspond to messages added since the previous notification for that   

subscription.  A messaging system which includes message headers in a   NOTIFY MUST provide an administrator configurable mechanism to select   which headers are 

sent.  Headers likely for inclusion are To, From,   Date, Subject, and Message-ID.  Note that the formatting of these   headers in this body is identical to that of SIP

 extension-headers,   not the (similar) format defined in RFC 2822.   Implementations which generate large notifications are reminded to   follow the message size 

restrictions for unreliable transports   articulated in Section 18.1.1 of SIP [1].   Mapping local message state to new/old message status and urgency is   an 

implementation issue of the messaging system.  However, the

messaging notifier MUST NOT consider a message "old" merely because   it generated a notification, as this could prevent another   subscription from accurately 

receiving message-summary notifications.   Likewise, the messaging system MAY use any suitable algorithm to   determine that a message is "urgent".   Messaging 

systems MAY use any algorithm for determining the   appropriate message-context-class for a specific message.  Systems   which use Internet Mail SHOULD use the 

contents of the Message-   Context header [7] (defined in RFC 3458) if present as a hint to make   a context determination.  Note that a composed messaging system 

does   not need to support a given context in order to generate   notifications identified with that context.