Windows Azure and UDP ports
Windows Azure is a platform developed by Microsoft for the cloud that allows you to create applications and virtual machines. In the latter case, when creating a virtual machine with a Windows operating system, there is a limit on the opening of UDP ports which can cause problems with VoIP operators. The typical problem is that the VoIP gateways of the PBX do not register: in fact, it can be seen that the REGISTER requests come out of the PBX, but the operator’s responses never arrive, which are obviously blocked by Azure.
For this reason, it is necessary to manually configure and specify the UDP mappings for the SIP protocol of the platform endpoint one by one. In this regard, you can consult various resources on the net about it, for example: http://azure.microsoft.com/en-us/documentation/articles/virtual-machines-set-up-endpoints/
Note: There is probably also a limit (perhaps 100) on the number of configurable ports: this places a limit on the maximum number of simultaneous conversations that the PBX can perform