Add item for requirements document.

index.md

@@ -52,6 +52,33 @@ Radiator was developed by Australian-based *Open System Consultants (OSC)* 1998-
 
 *Radiator Software Oy* is the sole manufacturer of Radiator AAA Server software. *Radiator Software* sells Radiator licences globally and you can buy a licence directly from the Radiator team. Radiator licences are also sold through various distribution partners all over the world.
 
+### What do I need to know if plan to start using RADIUS or change from another product to Radiator? {#requirements-document}
+
+It's good to create a requirements document describing what you need Radiator to do. The requirements include at least the following information:
+
+#### 1. RADIUS clients
+- The list of **client devices** that will be sending RADIUS requests to Radiator
+- The associated **device types** for all client devices
+
+#### 2. Authentication methods
+- The **authentication** required for your users, together with any **user groups**
+- The **authentication method** required for your users and/or groups - ie. LDAP, SQL, etc.
+
+#### 3. Authorisation
+- The **authorisation** required for your users, user groups, or devices. For example, checking if user or device belongs to certain group or is listed on the allow or deny lists.
+- RADIUS **reply attributes**, Change-of-Authorisation (CoA) messages, etc. which need to be sent to the client devices. If vendor-specific RADIUS attributes (VSA) are used, the RADIUS dictionary or detailed information of such attributes.
+- Any **additional functionality** which needs to be done, such as IP address allocation, VLAN assignment, etc.
+
+#### 4. Accounting and logging
+- Any **accounting** processing that is needed and where the accounting data should be stored
+- What **logging** you require for user authentication, user accounting, server log, etc.
+
+#### 5. Other requirements
+- Any **special requirements** that can't be met with normal Radiator configuration (ie. hooks, scripting)
+- Any other **integration with external systems**
+- Expected **amount of requests** or users.
+
+This is a basic list and there are probably other requirements that you are aware of.
 
 ## Features {#features}