PubNub service includes an auto-reconnect message catch up mechanism to ensure that published messages are not lost. A subscribed client that experiences a network disconnect (e.g. a mobile device losing signal or switching from 3G to/from WiFi), is automatically reconnected to PubNub servers. Any messages published during the period of disconnect are delivered instantly to the subscribed client effectively catching up on short gaps (typically up to 20 minutes ). Note that the catchup mechanism works even if the subscribed client is assigned a new IP address upon reconnect since the mechanism is based on channel name and timestamp of the last message delivered to the client.
To guarantee recovery of messages across disconnect gaps longer than a few minutes, it is advised to use the Storage & Playback feature to retrieve stored messages by timetokens.