NetworkDesign: Difference between revisions

The idea behind arianne's network protocol is to use a single stream of UDP packets tobetween comunicatethe server and clients, to allow the differentclients. kindDifferent kinds of actionsin-game weactions create different types of messages that are then interpreted at the opposite peerside in to meaningful data.

The Networknetwork designsystem is based on Messages being transmitted using UDP Packets. There are two types of streams,data stream; one isfrom the Server to the Client and another one thatfrom isthe Client to the Server.

Each message is self contained in a SINGLE UDP Packet. There is no mechanism for recovery of lost or repeated messages.

<b>Each UDP Packet is composed of:</b>

* <i>Protocol version ( 1 byte )

* Type of Message ( 1 byte )

* Client ID ( 4 bytes )

* Rest of Message ( up to 1494 bytes )</i>

Each message is containedheld in one or more UDP Packets, and the UDP Packet format is as follows: <br>

The following<b>1st UDP PacketsPacket areis composed of:</b>

* <i>Total number of packets (1 byte)

* Position of this message (1 byte)

* Signature of the message (1 byte)

Receiving the message is a bit more complex. First we need to determine that we are running a compatible version of the protocol by comparing the protocol version with the expected version in the message. Once we have agreed that the protocol is compatible we read the type of message and we ask athe Message Factory ( "Java Design Patterns" ) to build an object of that type with the corespondingcorresponding data. Once the message is build we simply store it in a queue of incoming messages waiting to be processed.

* Reading a message from the network

* Sending a message to the network

* Finalizing the manager

The read operation is a blocking type operation so we have two options, either Polling and Blocking. We choose Blocking because we don't want to waste CPU time Polling the network for messages, we just want to sleep until messages are available. Hence we create a Thread to read from the Network, let's call it Network Manager Read.

To writeWriting messages to the network so we can safelybe codesimply it simplycoded as a method of Network Manager, as write is an operation that is non blocking by nature.

The Network Manager opens a Socket from which it will receive all the messages from the network,. and toIt wherewill it willalso write all the outbound messages to the network from this same socket. Note: Both write and read use the same Socket. (

As you can see, messages are stored in a list when they are received,. henceHence access to the list ismust be synchronized.

Now lets get back to the interface as exposed to other objects. The Write method is immediate, just call it with the message to send, making sure that you have correctly filled SourceAddress and ClientID,. andThe itmessage will then be sent to the Client.

It is important to notice that as the transport is based on UDP there areis no guaranteesguarantee that the message is correctly sent. This situation is inpart of the protocol itself.

The Read method is blocking, when you call the Read method it either returns a message from the queue or if the queue is empty the thread blocks (sleeps) until one arrives.

That is the basic idea of the Network Manager; however, the manager gets a bit more complex as a result of the need to support Server to Client messages that are bigger than one UDP package,. Note that the manager just sends the stream of packets once, and doesn't confirm if any of the messages are received. Please refer to UDP Packet Format for more info about it.

To communicate, the Client and Server of Marauroa use a stream of UDP packets. The message system belongs to the marauroa.common.net package, so refer to the code for a detailed knowledge of the system.

The login Message is sent from the Client to the Server to request the right to access to the game. The message is composed of a username and password. The Username is a string that is already registered on the Server as the name of a user account,. and passwordPassword is a string that is associated with that account. If the username/password combination is correct then the Server must send a Login ACK Message to indicate to the Client that the message has been correctly processed. On the contraryHowever, if the username/password is wrong the Server will send a Login NACK (Not ACKnoledge).

The Server Info Message is sendsent from the Server to the Client to tell the Client about what Server is running, and details on how to inform the Server administrator of any problems (e.g. their email address).

The Choose Character ACK Message is sent from the Server to the Client to notify the Client that the character has been chosen. The message is composed of: the object.ID of the character

!!==Message S2C Action ACK==

The Perception message is a message sent from the Server to the Client to notify the Client about changes to the objects that exist near it. The message is based on the idea explained in Delta perceptionPerception document.

* A type that can be DELTA or TOTAL

* A string indicating the name of the zone the perception is related to.

* A time stamp value that will be just one unit bigger than the previous perception

* A List of RPObject that contains added object

* A List of RPObject that contains modified added object attributes

* A List of RPObject that contains modified deleted object attributes

* A List of RPObject that contains deleted object

* A RPObject that describedescribes the things the rest of players don't see about OUR own object.

The TransferREQ message is a message sent from the Server to the Client to notify the Client about the request of the server's desire to send content useful for the game where play will happen.

The message is composed of: An array of TransferContent objects containing all the name of each resource, its timestamp and if the resource is cacheable or not.

==Versioning and port numbering==