OTA Downloads

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Answer:

SAR (or WTP-SAR) stands for Segmentation and Reassembly. It's an optional feature of the Wireless Transaction Protocol (WTP) within WAP. SAR defines a method for a WAP gateway to break a large message (a JAR file you're downloading, for instance) into small chunks (the segmentation) and for the phone to piece it back together (the reassembly).

Not all phones use SAR, but most will access web servers through a WAP gateway. Nokia uses SAR, while Motorola uses features of HTTP 1.1 to retrieve small chunks of a file one at a time and then reassemble it.

One problem that arises with WAP gateways concerns MIME types returned by the web server. If a user requests a JAD or JAR file and the server returns the wrong MIME type, the gateway and subsequently the phone will handle the transfer incorrectly. To ensure proper downloading of MIDlets, use the following MIME types:

text/vnd.sun.j2me.app-descriptor	jad
application/java-archive 		jar

Resources

For a (very) detailed description of SAR, you can download the WTP specifications from http://www.wapforum.org/what/technical.htm

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