A push-based implementation in which the application pushes out the information whenever an update is available solves many of these problems. The issue of low bandwidth can be addressed through downloads in the background, as is typically done in today’s mobile email applications. In the absence of presence information, however—that is, the ability to determine whether the user is on his home network or roaming—push implementations also become ineffective because the application must poll clients constantly.  

To work around these problems, the mobile industry devised a simple, if somewhat blunt, approach that uses SMS alerts. In this implementation, the end-user receives notification via SMS that some new data arrived, and asks whether the end-user wishes to proceed with retrieval of that data. If he or she does, then he or she must retrieve the information manually.

Fig 1: Modified “Push” Service Based on SMS Alerts over GPRS

This approach fails to deliver on the desired user experience of always-on, real-time connectivity. In slightly enhanced versions of this mode, application providers deploy modified push implementations in which SMS is used to wake up the mobile client and sync it with the application. But such implementations use the operator’s bandwidth-constrained signalling channels for traffic and do not produce revenue. These implementations also require that corporate applications become aware of the myriad mobile data bearers and be written to deal with client-specific differences in the handling of SMS.  

Deploying Always-on Push  

The key to deploying genuine push services, therefore, lies in enabling applications to detect a subscriber’s presence on the network and send information if—and only if there is data to send, regardless of the user’s device or location.  From the moment the mobile subscriber’s terminal (be it a mobile phone or a PDA) initiates a GPRS session, a PDP context is established. Using protocols like RADIUS, the user is authenticated onto the network and is interrogated for the list of applications authorised to receive presence information about the subscriber. Once established, the application server must be notified of the user’s presence so that, whenever new data for that user is received at the corporate application server, it can be pushed automatically to the appropriate mobile device.  

In developing such a solution, many technical and operational challenges need to be addressed. An application needs to know the relationship between the user’s identity and user’s IP address, as well as information on the user’s location (that is, roaming or not roaming) and access network (policies may differ based on whether the subscriber is on a 2.5G, 3G, or Wi-FI network). A major challenge in implementing such a solution for the corporate subscriber is the complexities associated with multiple schemes used for corporate IP addressing and the ways to deal with private overlapping addresses. For the corporate user, the mobile operator does not always have the control of the IP address. Unfortunately, the typical standard presence servers in an operator’s network are not useful: they are not optimised for LAN-based applications and cannot deal with the vast security and address implications associated with corporate applications. A usable push solution needs something simple that integrates with a corporation’s addressing and security schemes.

The ideal network-based push service solution must integrate presence detection with simplified address binding. It also must provide flexible policy- and rules-based management. The best point to implement such a solution is the “service control point” in the mobile service core network. Megisto’s implementation of an advanced service control point, the Mobile Service Delivery System (MSDS) combined with Megisto’s Simple Dynamic Push capability, incorporates all the required elements of this ideal solution. Simple Dynamic Push capability can manage the presence notifications between the corporate application (or any presence database) and the user’s device over the operator’s network. Simple Dynamic Push capability maintains and tracks key information it receives from the MSDS, including the subscriber’s telephone number, assigned IP address, access network identity, and access network type.

Smart applications can make use of the network characteristics   supplied along with presence notification to enhance the content delivery. For example, when the subscriber is connected via a relatively low bandwidth network (example GPRS) the application can push abbreviated information to the client (example mail headers).  However, when the application is notified that the subscriber has moved to a high bandwidth access network (for example, when the subscriber roams into a Wi-FI hot spot) the application can download large amount of rich content (for example, mail body containing graphics etc. that consume a lot of bandwidth). Applications developed for mobile environments have to be aware of the characteristics of the different types of mobile environments that exist and modify their behavior dynamically to provide the user with a satisfying experience and achieve success.

This push capability also must work with the capabilities that already exist on client devices. Within thick clients, a connector framework is required to associate incoming push messages with a specific application. Because terminals are becoming more programmable—especially those targeted at the professional subscriber—this lightweight push connector is easy to deploy. In addition, the ability to make use of the push model of application content delivery on standard terminals is receiving significant interest within the wireless application development forums. For example, in the Java world, J2ME/MIDP created a powerful framework to develop applications based on the push paradigm. The application developer can take advantage of the Push Registry supplied by the J2ME engine on the mobile device. This registry helps in notifying the client application whenever a connection is set up with the mobile device, for example, whenever a network-initiated connection is set up. In addition, Java has programming constructs by which application developers can listen on a TCP or a datagram socket while they wait for pushed data. The socket paradigm for application development is a well-understood and popular method among network application developers. In addition, the push paradigm is under serious consideration in various standards bodies like the Internet Engineering Task Force (IETF).  

Summary