文章目录
含义
“408” ; Request Timeout
如果从事务处理层收到超时错误，就会将这个错误，翻译成408（请求超时）错误。说明在传输层出了问题。
8.1.3.1 Transaction Layer Errors
In some cases, the response returned by the transaction layer will not be a SIP message, but rather a transaction layer error. When a timeout error is received from the transaction layer, it MUST be treated as if a 408 (Request Timeout) status code has been received. If a fatal transport error is reported by the transport layer (generally, due to fatal ICMP errors in UDP or connection failures in TCP), the condition MUST be treated as a 503 (Service Unavailable) status code.
如果是其他严重的传输错误，比如UDP上的严重的ICMP错误，或者TCP上的连接错误，就需要使用503状态码。
遇到的情况
网络将Register消息的IP分片包丢掉一个导致重组不起来
上层返回408 超时错误。IP重组的timer 比SIP协议的超时时间长。