sipcode

连麦使用SIP协议，常见状态及错误码如下:

数值	含义	msg1
100	Trying, in calling, no response yet	中间状态，无需处理
180	Ringing, in calling, destination user received INVITE	中间状态，无需处理
200	OK, everything go well	成功
400	Bad request. The request is illegal.	失败
404	NOT Found, the destination user is not existed.	失败
408	Request timeout, could not find the destination in time.	失败
420	Bad extension, the destination user is not online	失败
477	Send fail, socket error, the network is disconnected.	失败
486	Busy Here, the callee is busy	失败
500	Server internal error	失败
504	Server timeout	失败