没有可用数据连接的Google Cloud Messaging

Question

Can Google Cloud Messaging deliver a notification with "zero-byte payload" to a phone that's capable of receiving voice calls and SMS, but for whatever reason has no working data connectivity at the moment?

By "zero byte", I mean that the phone would be aware that a GCM notification having no payload was sent to it by a specific sender, and could fire off an intent to that effect.

Real-world example: A burglar alarm gets triggered, and sends two push messages to the homeowner -- a zero-byte message whose meaning is implied entirely from the fact that it was sent at all, implies "something bad is happening", and can (presumably) be delivered even when data connectivity is blocked or unavailable because it (presumably) rides over the same transport layer used for SMS, and a longer push notification sent a few seconds later with additional meta-information about the situation that might only work if there's working data connectivity at the moment (so the phone could be notified, and fetch the payload from a server after establishing a conventional data session).

I've read Google's docs, but it seems like they've intentionally bent over backwards to say nothing about GCM's physical transport layer.

Answer 1

I would have to say "No" on that, since GCM (and pretty much everything Google does) is TCP/UDP/IP-based, there's no way it can get delivered to your phone if your phone doesn't have an active data (3G/4G/WiFi) connection.

Since the phone wouldn't have an IP-address, GCM couldn't deliver the message.

From GCM Architectural Overview :

• It uses an existing connection for Google services.

Answer 2

• No. There is no zero length message if you are using the GCM. GCM needs to aleast contain some information on what service will be recieving this message.
• Notice GCM=> Google CLOUD Message . Can't be cloud if you aren't connected.
• GCM is a server-push. Servers can't push to client if they aren't reachable.