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Time Features

Time Features. Authors:. Date: 2009-05-11. Abstract. This presentation provides some background on the reason why time distribution is useful to WAVE. Original reasons for including timing information.

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Time Features

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  1. Time Features Authors: Date: 2009-05-11 Justin McNew, Kapsch TrafficCom

  2. Abstract This presentation provides some background on the reason why time distribution is useful to WAVE Justin McNew, Kapsch TrafficCom

  3. Original reasons for including timing information • WAVE environment utilizes a multi-channel operation scheme that includes channel switching for the most basic devices • Devices may switch to one of six service channels (North American frequency allocation) to exchange data with a service provider (channel intervals must be synchronized) • Guard interval is 2 ms (implies at least microsecond granularity is required) • Devices without a time reference can utilize the timing advertisement to know when to switch to another channel (to switch synchronously) • Timing advertisement approach is most efficient for WAVE because it can be combined with a service advertisement (instead of multiple frames) Justin McNew, Kapsch TrafficCom

  4. Additional Background • The Timestamp has always been part of 802.11p’s advertisement frame • WAVE Action Frame, Quick Beacon, and now the Timing Advertisement • The Timestamp provides the most accurate means of conveying time because it is accurate to a few microseconds • WAVE originally relied on a higher layer function to provide the TSF Timer Offset Estimate (TTOE) • TTOE is the difference between UTC and the Timestamp • It is included in the same frame that can be used to advertise some specific features from the service provider (using the VSIE with a IEEE 1609 specific OUI) • Timing is useful for a number of other IEEE 1609 applications and functions such as message lifetimes and higher layer security features • Mechanism cannot rely on periodic beacons due to scalability limitations in a highly mobile environment Justin McNew, Kapsch TrafficCom

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