Мобильная и беспроводная связь

Mobile Application Development with SMS and the SIM Toolkit Scott B. Guthery Mary J. Cronin. 

The USAT Interpreter Some would argue that application downloading to the SIM is a bridge too far. Certainly some big operators, notably the Vodafone Group, have stepped back from this way of coupling the GSM phone into IT applications. Although downloaded applications can do a lot, there are three primary drawbacks. First, downloaded applications occupy precious space in the EEPROM of the SIM. You’d better be sure that they are used frequently enough—and generate enough revenue when they are used to justify the SIM real estate they demand. Second, downloaded applications are hard to manage. Not only does the network operator have to be sure that the code is squeaky clean, but the process of getting them to the SIM and activating them once they are there has to be airtight from a security point of view. A downloaded application doesn’t have to even touch the edge of the virtual machine’s sandbox to set up the occasional call to Siberia Tel and Tel. There is also the central database of keeping track of the different applications on the SIMs of the subscribers. Third, and perhaps most problematic, is the issue of the human interface. No matter whose application it is, the subscriber can’t figure out how to use it will call their network operator. It doesn’t take very many of these calls coupled with the expense of training all the call center people on all the applications before the spreadsheet for downloaded applications turns red. In 1998, Across Wireless (now Sonera SmartTrust) came up with an elegant solution to these problems that still harnessed the full capability of the proactive SIM. They installed a microbrowser on the SIM that could interpret downloaded mark-up language pages. The analog was to World Wide Web browsers but the emphasis was on tickling the SAT API rather than the content of the pages themselves. The Across Wireless microbrowser addressed the shortcomings of full-bore application download as follows. First, the downloaded pages were thrown away after they were interpreted so that they didn’t burn up EEPROM space. Second, mark-up languages were much simpler than procedural languages so they could be checked automatically for deviant behavior. Third, publication of a style manual and quick manual checks when the application was certified could standardize and homogenize the human interface and thereby minimize the number of calls to customer service. The Across Wireless microbrowser approach got a very favorable reception in the marketplace and in mid-2000 Vodafone proposed that microbrowser technology be standardized. In the meantime the SIM manufacturers, seeing the success of Across, had come up with their own microbrowser based on a Gemplus prototype.

Some More SIM Toolkit History A critical element of making this connection is being able to tell the difference between an SMS message that is intended to be read by the subscriber and an SMS message that is meant to be treated as input to a SIM-based application. In the early 1990s Swisscom solved this problem with a system called NATELsicap that enabled them to update options and routing tables on subscribers’ SIMs with the use of SMS messages. A Sicap message modified the SMS header with a bit that said that this message was to be given to the Swisscom application on the SIM rather than stored in the SMS messages file. As we saw in Chapter 3, the Sicap bit was subsequently folded into the standard Data Coding Scheme (DCS) field. Initially, “sicap” stood for “SIm Card Application Platform,” but as the general utility of this technique became recognized and the number of services supported by this platform grew, particularly in the area of prepaid services, the definition of the acronym changed to “Solutions for Innovative Communications Applications.” As of 2001, Sicap is a freestanding commercial enterprise and even has own Web site www.sicap.com. At about the same time, the ETSI SMG9 standards committee was extracting itself from a run-in with the European Commission. SMG9 had been trying to define a standard way of undoing the locking of a SIM to a particular handset. SIM locking is done so that a handset whose purchase price is subsidized by a network operator can’t be used with another operator’s SIM. The process of unlocking a SIM using OTA commands is called “unlatching.” When the European Commission got wind of SMG9’s effort to standardize what appeared to them to be uncompetitive behavior, they were, as we say, not pleased. In a very deft piece of downfield running, SMG9 morphed unlatching into a general-purpose programming interface on the SIM that could be used for unlatching but certainly was intended to be used for much more user-friendly applications. The initial enthusiasm for downloading applications to the SIM, although driven by some very elegant technical innovations such as the SIM Toolkit API discussed in Chapter 7, was soon dampened by the daunting task of securely loading applications onto the SIM and then administering those applications. As a result, there was a bit of a retreat to the original NATELsicap model of having a fixed program on the SIM to which one sends messages that are acted on and then discarded. In 1998 a Swedish company named Across Wireless made the leap between the Swisscom NATELsicap model of mobile applications and the way that the World Wide Web works. Rather than creating proprietary SMS messages that are sent to the SIM, why not express the messages as HTML pages and think of the NATELsicap client on the SIM as a microbrowser? In a sense, this is carrying Kristian Woodsend’s original idea of a SIM Toolkit one step further. Kristian defined a standard, fixed set of commands to be implemented on the handset so that applications could be written on the SIM that didn’t require any new software to be installed in the handset. A natural next step taken by Across Wireless was to define a fixed set of commands to be implemented on the SIM so that applications could be written back on network servers that didn’t require any new software to be installed in the SIM. What goes around, comes around. This is exactly the NATELsicap approach. In big iron computing, commands that are interpreted by a fixed program are called byte codes and the fixed program that interprets these commands is called, imaginatively, a byte code interpreter or, more grandiosely, a virtual machine. The only difference between the downloaded program version of SIM Toolkit applications that ran into administrative problems and the Across Wireless microbrowser version of SIM Toolkit applications is whether or not the byte codes remain on the SIM after they have been interpreted. It is little wonder then that the Across Wireless provided an attractive alternative approach where the downloaded program approach failed. It was exactly the installing of the byte codes on the SIM that caused the network operators big time headaches and sleepless nights. The Across Wireless solution provided all the flexibility and utility of general-purpose application development without the problems of SIM installation...

Далее см. раздел 10, стр. 182--184. К сожалению про S@T ни слова (описывается другой браузер).