Edit: The basic packet structure for a conquer online server includes the following header:
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Offset 0: Length of the packet (ushort)
Offset 2: Packet Identity (ushort)
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and then the data that follows it:
Offset 4: Normally the identity of the client.
Offset 8: Normally the subtype of the packet.
Offset 12: Normally the first value. (goes on from there)
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Most people packet sniff. There are a few packet sniffers already released here.