How do push notifications work?

[reocam_448003255267488]

I have a RLN16-410 NVR and so far I have not been doing any push notifications or anything like that. I've just been using it view the cameras and record. But I wanted to play around with push notifications but I have no idea how they work.

I have the android app loaded on an old tablet that has no phone number and no cellular service capability; it is wi-fi only. Can that work or does a push notification require a cellular phone that has a phone number active? I just don't understand how the push works.

[joseph_1979]

@reocam_448003255267488

Push Message Notification works on both WIFI and Cellular and works only on Android and IoS.

1 When you run the Reolink client for the first time, it will register to the push message service provided by Google FCM (Android) or Apple APNS (IoS).

2 The push service FCM/APNS generates a unique token to identify the device+application and returns this token to the application. Note that the google/apple services running on the smartphone will update the FCM/APNS with the source Public IP of the smartphone.

3 When you enable push notification on a camera, the application transmits the token together with the UID of the camera to the token maintainer hosted by Amazon.

4 The token maintainer checks if the UID is already available. If not a record is created with UID as the index and token added as a field in the record. If
the record exists, the new token is added.

5 When the camera detects an object and the push notification is enabled, a message containing the UID is forwarded to pushx.reolink.com ( will hit the server mentioned above -- you can check its IPs with nslookup -q pushx.reolink.com). The application workflow requires a push notification to warn all registered devices/apps.

6 The push provider (Reolink message handler running on AWS) reads the database using the UID as the pointer to the registered tokens. Note that a camera can be enabled from a number of smartphones, each of which has its own token.

7 The push provider (Reolink message handler running on AWS) sends push notification requests to the push service (FCM or APNS) for each token.

8 The push service (FCM or APNS) broadcasts the notification messages to all registered devices using the source Public IP. So if the IP is assigned to a mobile operator then the push message is sent over the mobile packet data i.e. FCM -----> Internet ----> IP core of mobile operator - PGW - SGW/MME - eNodeB - smartphone (assuming 4G). If your smartphone is connected to WIFI then we have Google FCM -----> Internet ------> ISP IP core ---------> GPON OLT (assuming fibre to the home) ------>GPON ONT at your home ------> router at your home ---(NAT Public to Private IP)------- smartphone connected to WIFI.

And if you need to know how media is conveyed between camera and client then read my explanation at https://community.reolink.com/topic/87/how-does-the-reolink-uid-actually-work/2?post_id=22657&_=1739217026299

Hope that now you have a clear picture of how things work.

[reocam_448003255267488]

Wow, that is a great explanation and I appreciate it, but unfortunately that is a little above my ability to understand. So if you don't mind dumbing it down a little let's take my situation for example. I have an android device on my LAN and both the device and the NVR are on the same subnet behind a hardware firewall. The push notifications work and I see in my logs that it is sending a packet to Amazon AWS for every push notification and to the same address.
What I don't understand is how is that notification coming back from AWS into my LAN and going to the device? Or is it sending both a packet to AWS and also sending a packet directly via the LAN to the device?

Also, I don't know if it matters or not, but the android device does not have a Google account at all on it.

[joseph_1979]

@reocam_448003255267488

Your Android smartphone which is connected to your home WIFI has Google services running on it which continuously update the Google FCM with its IP. So when the Google FCM receives the push message request from Reolink message handler server (AWS), it knows where to send it...to the IP of your smartphone. Consider the IP as your home address which is unique in the world. This is at high level as there is NAT at your router but this is beyond your understanding.

[reocam_448003255267488]

OK, after reading your linked post I "think" I might be beginning to almost understand this.
So for the purposes of oversimplification and understanding I'm just going to talk about my particular setup which is an NVR and 1 wifi only tablet and 1 cellular capable phone, both are android. Also none of my devices have google accounts on them at all.

1. The NVR has a UID which is like a specific serial/user number. It registers this UID and the IP address of where it is located out on the internet with reolink/AWS so that there's an entry in a list.

2. When you log in to the NVR with an android app the NVR keeps a list of these logged in apps and their UIDs so that it can send a push to them when needed.

3. When you install the android app on your device and log in to the NVR that device gets its own UID.

4. When an event happens the NVR sends out a "push" notification to AWS (amazon) via the internet along with the UID of the client it wants to send the push to. (I was blocking my NVR from going out to the internet in my router so that's why that was not working.)

5. AWS looks up the UID in it's database and sends the push to the IP address it has on file for that client.

I know this is way dumbed down but am I getting it kinda right? If so then what I don't understand is how my wifi only device is getting the push? My hardware firewall router should be blocking any incoming new traffic.

Also I had UID disabled on my NVR but still the wifi tablet was getting the push. The cellular device did get the push but only when on wifi. If I shut off wifi then it got nothing cellular. After reading your article I turned UID on in the NVR and bam, cellular worked.