Quick definition OUCH is NASDAQ's order entry protocol. Traders use OUCH to submit orders to NASDAQ and receive status updates (fills, rejections, cancellation confirmations). What it is OUCH is a binary protocol used by traders to interact with NASDAQ. A trading system connects to NASDAQ via OUCH and sends order messages. NASDAQ sends back responses. OUCH includes message types for: - Enter order (new order) - Cancel order (cancel a pending order) - Modify order (change size or price) - Order confirmation (order accepted) - Order executed (partial or full fill) - Order rejected (order not accepted) Why it matters OUCH is NASDAQ's native order entry protocol. Many professional trading systems use OUCH for direct market access (DMA) to NASDAQ. It is lower latency than using a broker's API. OUCH is also standardised, so trading systems can be built once and used across multiple instances of NASDAQ. OUCH versus FIX FIX is a universal order entry standard used across many venues. OUCH is NASDAQ-specific. OUCH is faster (lower latency) but works only with NASDAQ. FIX is slower but works with many venues. Professional traders typically use OUCH for NASDAQ and FIX for other venues (or both). Practical example A trading algorithm sends an OUCH message to NASDAQ: - Message type: "Enter Order" - Symbol: "AAPL" - Price: "150.00" - Size: "100,000" - Side: "Buy" NASDAQ responds with: - Message type: "Order Accepted" - Order ID: "#12345" The trading algorithm now knows the order has been accepted and has order ID #12345. Direct market access (DMA) Traders using OUCH typically have direct market access (DMA), which means they connect directly to NASDAQ without going through a broker. DMA is faster but requires infrastructure and funding. See also - ITCH (Interactive Transparent Clearing House) - FIX (Financial Information eXchange) - Order Submission - Direct Market Access (DMA)
