The Wireless Messaging API (WMA) reference implementation supports short message service (SMS) text and binary messages, but leaves the implementation of the hot area of multimedia messaging untouched. This article will demonstrate how to build a Multimedia Messaging Service (MMS) client using J2ME so you can get started writing new applications using this technology. By doing your own J2ME client implementation, you can bypass carrier lock-in of the content server or Multimedia Messaging Service Center (MMSC), as well as build your own server-side MMS applications, which you couldn't do before outside of the carrier network.
Software Requirements
A number of software requirements are needed to test the MMS client application. To run the basic emulation environment, make sure you have Sun's Wireless Toolkit 2.1 and JDK 1.4.2 or higher, both downloadable at http://java.sun.com. Download and compile the latest source code for the MMS Client and tools, available at http://sourceforge.net/projects/jvending. Next, set up either a Web or application server to act as the content server for the multimedia messages. Finally, you'll need to download the Nokia Mobile Internet Toolkit 4.0 from www.forum.nokia.com.
MMS Notification and Retrieval
The push registry maintains a list of inbound connections to mobile devices. It's one of the most exciting and least used features of the MIDP 2.0 spec. Under MIDP 1.0, a network-based application needed to constantly establish a connection and poll an application server for events. This ate up airtime and cost the user money, making network-based J2ME applications infeasible in many cases.
You can register inbound connections in the push registry by adding the connection information to the JAD file or by explicitly invoking the registerConnection static method on the PushRegistry class. In the J2SE world, registration is equivalent to opening a ServerSocket connection and waiting for a connection. The snippet below shows how we can register the connections in the JAD.
MIDlet-Push-1: serversocket://:1236, org.jvending.messaging.mmclient.MmsMidlet, *
MIDlet-Push-2: datagram://:1235, org.jvending.messaging.mmclient.MmsMidlet, *
MIDlet-Push-3: sms://:1234, org.jvending.messaging.mmclient.MmsMidlet, *
Why would you need to register so many push connections? There are a number of different ways to push the message notification, depending on the carrier network. You may need to set up push interfaces to cover push-over TCP (serversocket), WDP/UDP (datagram), and SMS. For instance, if we have an active GPRS or CSD connection, the server application may decide to send the MMS notification on the datagram connection, without failing over to the SMS connection. This means our MMS message is effectively lost.
Let's show how notification works in a carrier environment. Prior to the recipient MMS user agent retrieving an MMS message, the network must notify the user agent that the message is awaiting retrieval. There are a number of different ways for this notification to take place. The most common are SMS or WDP/UDP. If the user does not have a data session established, the notification will come over an SMS bearer. If a session has been established, the server just needs to push the request to the device over WDP/UDP (WAP 1.2+) or TCP (WAP 2.0).
