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The following section describes the MDP 3.0 message and packet structure with event based messaging.  

MDP Packet Structure

The encoded FIX transmission is sent in a packet structured as follows:

  • Packet header - contains packet sequence number, sending time
  • Message Size - field indicating size of message
  • Message header - contains message size, templateID, schemaID, and version
  • FIX Message - contains FIX header and FIX message
  • MDP Message - contains message header and FIX updates such as book updates and trades


Each packet sent on all feeds (Incremental, Market Recovery, Instrument Definition, and TCP Replay) contains a packet sequence number and a timestamp. The packet number is unique to each packet sent and each channel has its own separate set of sequence numbers that increment sequentially with each packet and are reset weekly.

Packet and Message Headers

MDP 3.0 uses the concept of sequencing and recovery by packet instead of by message. Packets may contain a single or multiple MDP messages.   

Each packet is prefixed with:

  • Sequence Number
  • Sending Time (nanosecond precision)

Each MDP message includes:

  • Message Size
  • Template ID

MDP Packet Structure Examples

The following section provides examples of MDP packet structures. 

One Packet, One Event

The following example shows the packet structure for single event in one packet.

1 packet, multi events

One Packet, Two Events

The following example shows the packet structures for two events in one packet.

1 packet, 2 events new

One Event, Multiple Packets

The following example shows the packet structures for one event in multiple packets.

1 event multi packets new