WAP Development Issues

Push Not Supported
The WAP WSP specification defines the WSP push operation and a WSP push PDU (Protocol Data Unit). A push operation is not specified for the HTTP protocol, used by the WAP Gateway server to communicate with content hosts. To support pushes, the server has to provide an application interface to allow server based applications to generate a push to a mobile client. The support of pushes on the client side depends on the capabilities of the handsets to handle pushed content. The Nokia OTA configuration proposal to the WAP Forum describes the use of a connectionless push over the SMS bearer, to transfer the configuration data to the handset.

 

Wireless Telephony Application Not Defined
The so-called Wireless Telephony Application (WTA) has been discussed by the WAP Forum but not yet defined or likely to be defined anytime soon. The WTA gives WAP some of the features that SIM Application Toolkit incorporates such as access to phone report and call handling.

 

Lack of Cookies for Session Management
There are no "cookies" for session management, i.e. to hold the session together. Cookies are used on the fixed Internet to identify the web browser and thereby assist in providing customised and streamlined services. Instead, some WAP applications use indexes in the URL as an alternative.

 

The cookie information is transmitted via HTTP headers. Because WAP WSP is based on HTTP headers, it should be possible to transmit cookie information to the clients. The problem may be the clients itself, which may currently not support the handling of cookie HTTP header information or to save this information to a persistent storage in the mobile phone.

 

Premature Encryption Endpoint
The Wireless Transport Layer Security defines encryption between the Mobile Station and the WAP Gateway. The "endpoint" of the encrypted WTLS data is the WAP Gateway proxy server. To have a secure connection to a content host (e.g. banking server) the gateway proxy server has to establish secure (https) connections to this hosts. In this case the proxy server has access to the decrypted data received via WTLS from the mobile station or from the content host via https.

 

Small Downloadable Unit Size
WAP incorporates no compression techniques for the textual content, although the WML markup commands are compressed. Additionally, the "deck" - the smallest unit of downloadable information in Wireless MarkUp Language - is limited to a maximum of 1400 bytes. This means that applications need to be specifically designed to be very code efficient by using templates and variables and keeping information on the server and using the cache on the phone.

 

WML byte code converting defines a (maybe inefficient) compression technique by string tables. With this technique duplicate strings in the WMLC bytecode are avoided. This reduces the size of the data to transfer to the mobile client. The WSP SDU size of 1400 bytes is a default value. An increased size may be negotiated by a mobile client within the WSP capabilities. The WAP transport layer (WTP) is able to handle greater SDU sizes than 1400 bytes too, by using SAR (Segmentation and Re-assembly).

 

WDP Datagram Protocol
The September 1999 London meeting of the WAP Forum included a decision from the SMS Experts Group that the single common standardized interface between the SMS Center and the WAP Gateway would be a subset of SMPP (Short Message Peer to Peer Protocol). A PDU (Protocol Data Unit) set has been added to SMPP version 3.4 for this purpose. There will be no SMPP specific legacy- in other words, SMS Center manufacturers that do not support SMPP can evolve their SMS Center external interface to support the new SMPP commands for connecting to WAP Gateways.

 

Basically, this is a victory for Logica, the creators of SMPP, who spun control of the protocol off in 1999 to an "independent" SMPP Forum (see www.smpp.org). The wording of this resolution was careful to avoid mention of the political battle between the pro-SMPP companies such as Logica and those opposed to it such as CMG. Basically, the US carriers insisted upon SMPP and swung the vote.

 

WAP Version 1.2
WAP version 1.2 is expected to be finalized as a specification in late 1999 and first available in spring 2000. It will support Push services (proactive delivery of information from a WAP Gateway to a WAP terminal), User Profiles, WDP Tunneling, WMLscript, CryptoLibrary, Wireless Telephony Application, Wireless Application Environment enhancements and other features.

As such, WAP version 1.2 may be the first version of the protocol that is actually workable in terms of delivering easy to use and innovative non-voice mobile services.

Clearly, as the WAP specifications evolve, some of these issues will be resolved. However, programmers need to be aware of them when they commence WAP application design.

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