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Purpose: This document describes how to use the Huffman-encoded data feed intended for wireless devices. WSDOT encourages developers to use the data stream for new applications. WSDOT will consider distributing third party products as long as the products are no cost to the public.

History: This data stream was proposed by 3Com Palm Computing Inc. The Palm VII organizer has a built-in wireless interface that provides communication to the Internet. Most wireless service providers charge by the amount of data transmitted or received. To lower costs to the end user, 3Com Palm Computing proposed a new data stream for wireless devices. The new stream is a highly-compressed version of the WebFlow data currently provided at webflow.wsdot.wa.gov. The new wireless data stream is typically less than 200 bytes.

Features: The new data stream is written into files named "WirelessXXX.DAT", where XXX is a version number such as "001". The station format of a particular version will never be changed. Software designers may choose to hard-code the "WirelessXXX.STA" database directly into their executables. The version number contained in a "WirelessXXX.DAT" file is the number of the most current version of the database. By comparing the internal version number with the XXX in the file name, the application can determine if the data file is for an obsolete data stream. WSDOT will generate the old data streams for some period of time (maybe a few months), then drop support for the old versions. The "WirelessXXX" data files are available at: http://images.wsdot.wa.gov/nwflow/wireless/.

Decoding: Rather than explain Huffman encoding, WSDOT is providing a "C"-code file file that shows how to decode the wireless data files. 3Com Palm Computing Inc. wrote the original code. This version is considered to be in the Public Domain.

Relationship: WSDOT was approached by 3Com Palm Computing Inc. with the idea of a compressed data stream. WSDOT agreed to provide the data to the Public as long as the data format was non-proprietary. WSDOT did not develop the algorithm for the compression or the application for the Palm VII. WSDOT encourages other developers to use the data for any type of device that connects to the Internet.

Data Contents: The wireless data files contain a version number that relates to the latest version available, the time/date of the data, and a Huffman-encoded data stream that contains a code that represents the traffic condition for each station contained in the station database (.STA). WSDOT recommends using the ".c" file provided as a guide for decoding the data. Developers need to test their product against the WSDOT internet maps and/or WebFlow to ensure that their applications report a correct representation of the WSDOT data.

Agreement: WSDOT intends to provide the wireless data as long as it provides benefit to the public. WSDOT provides no guaranty that the data will be available at any time in the future. Our servers and data-links are known to have failures and down time. Users of the data are warned that disruptions will occur. WSDOT assumes no liability for the availability, accuracy or use of this data. Developers must inform users of their software of the source and nature of the data stream. WSDOT will not provide end user support for third party applications. WSDOT will not provide developer support other then this document and the "Huffman.c" source-code file. Errors in the "Huffman.c" file or this document maybe reported to Michael Forbis (WSDOT) at forbism@wsdot.wa.gov.