On the BlackBerry device, the transfer of messages has a higher priority than other types of I/O communication, such as socket and HTTP connections. Therefore, if the device is not in a sufficient wireless coverage area or the wireless network is busy and is unable to transmit data, pending messages will be transferred first once network communication is restored.
This can pose an issue when using the BlackBerry Simulator. Unlike the device, where the wireless network handles message and data transmission, the BlackBerry Simulator relies on the following two different applications:
The Email Server Simulator (ESS), which handles the transfer of messages.
The BlackBerry Mobile Data System™ (MDS) (BlackBerry MDS™) Simulator, which handles HTTP and socket communication.
If the ESS is not running, messages sent from the device will pend until they can be delivered. This can halt other socket or HTTP connections until the message has been delivered, even if the BlackBerry MDS Simulator is running.
Verify that both the ESS and BlackBerry MDS Simulator are running if your application needs to send messages and use data connections.