Financial Information eXchange Protocol (FIX)

The Financial Information eXchange (FIX) protocol is an electronic communications protocol initiated in 1992 for international real-time exchange of information related to the securities transactions and markets. With trillions of dollars traded annually on the NASDAQ alone, financial service entities are investing heavily in optimizing electronic trading and employing Direct Market Access (DMA) to increase their speed to financial markets. Managing the delivery of trading applications and keeping latency low increasingly requires an understanding of the FIX protocol.
The FIX protocol is a technical specification for electronic communication of trade-related messages. It is a self-describing protocol in many ways similar to other self-describing protocols such as the newer XML; XML representation of Business content of FIX messages is known as FIXML.
FIX Session is layered on TCP (Transmission Control Protocol). FIX is more popular than FIXML in Securities Trading because FIXML messages are much larger in size due to XML tags.

FIX format

The message fields are delimited using the ASCII 01 <start of header> character. They are composed of a header, a body, and a trailer.
Up to FIX.4.4 the first three fields in all FIX messages are (header) must contain the 8 (BeginString), 9 (BodyLength), and 35 (MsgType) tags.
From FIXT.1.1 / FIX.5.0, the first five or six fields are
8 (BeginString), 9 (BodyLength), 35 (MsgType), 49 (SenderCompID), 56 (TargetCompID) and 1128 (ApplVerID – if present must be in 6th position)‏
The last field of FIX Message Checksum and its of the form ^10=NNN^ where ^ is SOH delimiter character and NNN is three digit checksum.
Header+Body+Trailer: FIX Content
Example of a FIX message : Execution Report
8=FIX.4.2 | 9=67 | 35=8 | 49=PHLX | 56=PERS | 11=ATOMNOCCC9990900 | 52=20071123-05:30:00.000 | 20=3 | 150=E | 39=E | 55=MSFT | 167=CS | 54=1 | 38=15 | 40=2 | 44=15 | 58=PHLX EQUITY TESTING | 59=0 | 47=C | 32=0 | 31=0 | 151=15 | 14=0 | 6=0 | 10=102 |
(In the above FIXMessage Body length 9 is incorrect and checksum 10 may be incorrect)‏
Body Order / Trade Details Info Trailer Security Check thru Signature and CheckSum.