User`s guide

30 DC 900-1339H
FMP Programmer’s Guide
of frames when the line mode option is set to one of the asynchronous settings (see
Chapter 4 for more information on these option settings).
2.1.2.1 Structured Asynchronous Frame
A structured asynchronous frame is similar to a BSC frame containing one message.
The diagram below shows the structured asynchronous text frame which is identical to
a normal BSC 3780 frame without leading SYN or trailing PAD characters. The frame
begins with an STX (or SOH) character and ends with an ETX character. Each text
block is followed by a BCC character (usually LRC-8) that is a redundancy check of the
characters in the entire block starting with the first character following SOH or STX
and ending with the ETX character.
The London International Financial Futures Exchange (LIFFE) is an example of a mar-
ket feed using a structured asynchronous frame.
2.1.2.2 Unstructured Asynchronous Frame
The most common method of broadcasting information on an asynchronous line is to
use an unstructured frame. In this format, no start-of-text or end-of-text characters are
broadcast. Characters are received as one continuous stream of information. On some
feeds, a terminating character (TC) can be used to signify the end of a received block as
shown below:
FMP uses the terminating character to divide messages into separate buffers before
sending them to the client. If your feed does not specify a distinct character for message
termination, a common recurring character (such as a carriage return or line feed) can
be used as a message break.
STX text message ETX BCC
text message TC