NDD / A-Book Order Flow

How to Read This Diagram

This diagram shows the complete lifecycle of a single client order in an NDD/A-book environment. Each box represents a processing stage; arrows show the direction of data flow.

The Client Platform submits the order, which passes through the broker's Gateway for validation (margin check, lot size, symbol verification). The Liquidity Bridge translates the order into FIX protocol and forwards it to the Price Aggregator, which selects the best available quote from the connected LP pool.

The selected Liquidity Provider receives the order and responds with either a fill or rejection. On fill, the confirmation flows back through the same chain to the client platform.

Key Observations

• The broker never takes the opposite side of the trade -- the LP is always the counterparty.
• Total latency is the sum of all stages: typically 30-120ms depending on infrastructure and LP response times.
• If the LP rejects the order (e.g., price moved beyond tolerance), the bridge may attempt a second LP or return a requote to the client.
• In a well-configured NDD setup, this entire process is automated with no manual intervention.

Where Things Can Go Wrong

Common failure points include: bridge misconfiguration causing order timeouts, aggregator selecting stale quotes, LP last-look rejection during volatile markets, and network latency spikes between bridge and LP. Each stage introduces potential slippage or delay.