FIX Protocol Session or Admin messages tutorial

FIX Protocol Session or Admin messages tutorial

I have been working in FIX protocol for almost 5 years when I started working on FIX protocol I looked upon internet for some good tutorial which could supplement or complement lengthy FIX protocol specification there was nothing at that time so when I started my blog I thought to write about my own experience in FIX protocol as short, clear and concise tutorial format. Since I like question answer type of knowledge sharing too I have written some blog post on FIX protocol Interview questions you may find it interesting.

In today’s FIX tutorial we are going to have a look on FIX protocol session level messages. As you guys may know all FIX messages can be broadly classified in two categories Admin messages also called session level messages and Application messages which include Trade, pre trade and post trades messages.  Understanding of how FIX session works is very important because until you know the fundamental of FIX Sequence number, how does FIX session gets connected , what are the sequence of messages that flows between Sender Fix Engine and receiver FIX engine you won’t be able to quickly identify any problem related to FIX protocol.  FIX specification is very clear about what should FIX engine do on various FIX session connection / disconnection scenario.

Just to revise as per FIX protocol first Sender FIX Engine and receiver FIX engine connects to each other on TCP/IP protocol on specified IP and Port via leased line , Radianz link , Virtual Private network(VPN) or via internet. Once TCP Socket level connectivity established Sender application sends Logon (fix tag 35=A MsgType=A) with agreed SenderCompID (fix tag 49) and TargetCompID (fix tag 56). Receiver FIX engine receives this message and authenticate Sender FIX Engine client based upon SenderCompID (fix tag 49) and TargetCompID (fix tag 56) ,if client is authenticated successfully then receiver fix engine replies with same sends Logon (fix tag 35=A) message and connection is successfully established and then both FIX engine will send Heartbeat messages (fix tag 35=0) at specified  heartbeat interval to keep connection alive. In case receiver FIX engine is not able to authenticate client it will send a Logout message (fix tag 35=5) and connection will be terminated though socket connection will still be there. Receiver FIX engine can also send Logout message (fix tag 35=5) if it receives fix message with sequence number lower than it is expecting.