Chapter 2: General Guidelines (Baby-Friendly Explanation)

What This Chapter Talks About

Chapter 2 lays the ground rules for developers like you. It teaches how your terminal will send and receive messages to/from NSE’s system. Think of it as the "language" your terminal needs to speak to communicate properly.

Key Concepts for Your Terminal

1. Message Structure Basics
   • Every message you send to NSE or receive from NSE has two parts:
     1. Message Header: Like the envelope of a letter, it contains information about the message type and where it’s going.
     2. Message Data: Like the letter itself, it contains the actual information (e.g., order details, market updates).
2. Transaction Codes
   • Every action (like placing an order, logging in) has a unique number called a transaction code.
     • Example: A "Logon Request" has a transaction code like 2300.
3. Data Types
   • Data in messages uses specific types:
     • CHAR: For text (e.g., symbols like "RELIANCE").
     • LONG: For numbers (e.g., prices).
     • DOUBLE: For very large or precise numbers (e.g., timestamps).
   • Each type has a specific size (e.g., CHAR = 1 byte, LONG = 4 bytes).
4. Endian-ness (Twiddling)
   • Computers have two ways of storing numbers: big-endian (used by NSE) and little-endian (used by some systems).
   • If your system uses little-endian, you need to "twiddle" (reverse) the bytes before sending numbers to NSE.

Guidelines for Designers

When designing your terminal:

1. Logon Message Order:
   • NSE expects messages in a strict order during login (explained in Chapter 3). If you mess up the order, your terminal can’t connect.
2. Price and Quantity Scaling:
   • NSE handles prices in paisa, not rupees.
     • Multiply price by 100 before sending it (e.g., ₹250.75 becomes 25075).
     • Divide by 100 when receiving price data from NSE.
   • Quantities are scaled by (100,000 x 100). Handle them carefully.
3. No Host-End Inquiries:
   • Your terminal cannot ask the NSE system for additional information beyond what’s described in the protocol.

Guidelines for Programmers

When coding:

1. Set Reserved Fields to Zero:
   • Some fields are marked as "reserved" in the protocol. Always set these fields to 0 or null when sending messages.