FAST implementation

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Imported from previous forum

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Hello Every one,

I was reading the documents provided for FAST implementation.can anyone suggest me how to detect the start of the FAST message.and what is the significant of the preamble. In the preamble, what exactly the sequence number represents? is it same as tag 34 value? if it is then how we are getting this value at the time of fast message decoding? is it done by decoding the FAST message through the specific template?

Thanks

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I was reading the documents provided for FAST implementation.can anyone suggest me how to detect the start of the FAST message
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A simple answer to that part of your message is “no” if you ever get lost in a stream of FAST data there is no guaranteed way to recover.

That being said, many FAST feeds are sent via Multicast (packet based) rather than TCP (stream based). For these feeds the beginning of a packet marks the beginning of a message.

and what is the significant of the preamble.
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The preamble is an exchange-specific extension to the FAST protocol. In theory it can be used to avoid decoding messages that the receiver has already seen and/or to detect missing messages when using an unreliable protocol.

In the preamble, what exactly the sequence number represents? is it same as tag 34 value? if it is then how we are getting this value at the time of fast message decoding? is it done by decoding the FAST message through the specific template?
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I’m going to duck this question except to say that the data in the preamble is not tied to any tag or field. It is also not FAST encoded. The preamble is a wrapper around a FAST encoded message – in this case the wrapper contains data before the message but not after it.

Thanks
Hope this helps.

Dale Wilson
Principal Software Engineer
Object Computing, Inc.
Lead developer of QuickFAST