问题背景
CUCM上注册的话机通过SIP trunk外呼失败
以下是典型的案例
通过SIP trunk下的配置检查SIP trunk 状态，显示为503.
根据CUCM error message guide
For Remote=503, possible reasons include
1) route/sip trunk for originating side doesn't exist on remote peer;
2) route/sip trunk for originating side does exist on the remote peer but the port is either used for a SIP phone or a different sip trunk;
3) the remote peer has limited resources and may not be able to handle new calls.
需要检查语音网关的SIP 服务状态
Show sip service
Show voice sip license status
正常状态显示为UP，不正常状态显示为down
但是实际是有语音的license安装在CUBE上的。通过show version 查看IOS版本，原因是因为命中了如下bug
发生的条件：
License Usage Report (RUM) Acknowledgement not received before ACK deadline (presented in 'show license status').
https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvz89043
解决办法
1.根据BUG的workaround 跟新ACK到语音网关上
2.升级到Known Fixed Releases 来避免此类问题的发生。
