Due to the configuration of ppp multilink protocol, most of the equipment will create the virtual-template and then add this interface into the ppp mp, such as ppp mp virtual-template 1, but any way some of the equipment, if configure only this the link will not able to be changed into up state.
Using only "ppp mp virtual-template 1" command on the AR28-09 is not enough for configures the ppp multilink in this case, we should add another command which is "ppp mp" also, then this protocol can be work normally.
Normally, every process and the link protocol should be work now, and then we take more concentrate in this case. At last I contact to my team leader to analyst this configuration again at last the configuration can be solved.
The configuration on the router of every type or every version should be the same, so everyone can configure the command correctly without the common error which could not be happen.