Issue title: What does the port firewall coming from GCM server?
 Issue body: I have a problem with port firewall for receiving notification from GCM server.
My network use allow policy for configurated firewall, so I try to config follow this 
http://esupport.trendmicro.com/solution/en-US/1060693.aspx.
I hope it worked but it not.

I search in many way to solve, but I couldn’t make head or tail of it.

 Comments: 
 Comment 0: The GCM needs the following connections:
- port: 5228, host: mtalk.google.com
- port: 443, host: android.googleapis.com 
 Comment 1: Great thank, Finally I got it. > <
 Comment 2: UPDATE: GCM is also using:
- port: 443, host: android.client.google.com
 Comment 3: this is about devices receiving push notifications.. My server is blocking attempt to initiate push request to GCM server...What ip/port I should open to send push notification request to GCM? 
{'source': 'GithubIssues', 'repo_name_with_owner': 'google/gcm', 'issue_id': 108252348, 'repo_stars': 946.0}