问题
Which port and protocol does Google Cloud Messaging (GCM) use?
We experience some times that messages doesnt get through, and have noticed that it depends on which network we sitting on.
回答1:
The device accesses the GCM servers on ports 5228-5230.
Note: If your organization has a firewall that restricts the traffic to or from the Internet, you'll need to configure it to allow connectivity with GCM. The ports to open are: 5228, 5229, and 5230. GCM typically only uses 5228, but it sometimes uses 5229 and 5230. GCM doesn't provide specific IPs. It changes IPs frequently. We recommend against using ACLs but if you must use them, take a broad approach such as the method suggested in this support link.
This is relevant if your device is connected to the internet via WiFi.
Here is the link to the relevant GCM documentation: https://developers.google.com/cloud-messaging/http
来源：https://stackoverflow.com/questions/15571576/which-port-and-protocol-does-google-cloud-messaging-gcm-use