-------------------
SERVER ARCHITECTURE
-------------------

1. INTRODUCTION
2. RO REVIEW
3. EATHENA MODEL
4. TMW SERVER
5. TCP - UDP
6. SECURITY
7. DATABASE
8. REGISTRATION


1. INTRODUCTION

One of the most important thing in a online game is the architecture of the
server system, which reflects in performances (lag and denial of service),
scalability, fault tolerance. In this article we will examine the pre-existing
model and we will evaluate a way to improve it and to add custom features.


2. RO REVIEW

Let's start by taking as reference the current server system used to play
Ragnarok Online on the euRO server. (www.euro-ro.com)
RO works by using 4 kinds of server:

 - Login Server (L): takes care of verifying accounts with username-password
   system, allows also encrypted login.

 - Char Server (C): saves every player status (stats, items, equipment, skills
   and so on.

 - Map Server (M): the real game server, work as interconnection between
   clients, manage chat, monster AI, damage calculations and everything you can
   see in game.

 - Inter Server (I): probably manages the messages between the other type of
   servers.

In euRO there are 1 login server, 1 char server, 1 inter server and 14 map
servers.


3. EATHENA MODEL

The eAthena system mirrors the way used by official RO servers. eAthena
implements 3 servers: login, char and map. It is allowed to have more than one
map server at a time. Every server communicates with all the others.


4. TMW SERVER

The basic idea of TMW server architecture mainly is the same as the one used by
eAthena. Since the login and char server don't have heavy traffic they could be
melt togheter.

        C       M
          \   /
        C - L - M
          /   \
        C       M
        
The login server manages new connections and stores all the informations about
the player. The map server is pretty the same as the eAthena one. The login
server manages also connections to a new map server when changing map.        


5. TCP - UDP

RO is TCP based, mainly because you use the mouse to move the player. When you
want to reach a point on the map, you click on it and the client send a packet
to the server with destination coordinates. The server replies with an
agreement if there's a path to that way. Using this way you don't need high
speed nor a lot of packets, so TCP it's pretty enough.

With our custom server we want to achieve pixel movements, by that we mean that
the player is not always positioned in the center of the tile, but will have
fine coordinates.

Asking the server if every destination coordinates is walkable means a lot of
traffic from and to the server and probably will result in lag. Using UDP will
probably help avoiding this problem.

An idea could be using the system used for racing games where speed is
fundamental. When you press a key to move, the client sends a packet with
starting coordinates, direction and client time. When you release the key (or
change direction) the client sends another packet with current coordinates and
client time. According to the player speed the server check if the coordinates
are right, if not reply with a packet with the correct position.


6. SECURITY

Solutions to keep the server working and avoid unfair players.

 - DoS attack:
        * Account activation.
        * Limit number of accounts to 1 per email address.
        
 - Cheating/Botting:
        * First of all just keep every calculation done by the server.


7. DATABASE

Player data should be stored using databases, probably MySQL. This way player
infos could be easily accessed trough web.


8. REGISTRATION

Still to decide if we want to use a dialog (client registration) or to use a
web based interface (web registration).