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102 lines
5.1 KiB
Plaintext
102 lines
5.1 KiB
Plaintext
Lossless UDP:
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A network protocol over UDP to transfer data without any loss.
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Problems with conventional UDP:
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-Packet loss.
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-Packet mixup.
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-No flow control.
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Draft of Proposed protocol:
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Connexion example:
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Alice wants to connect to Bob (Connection handshake):
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Alice generates a random 4 byte number.
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Alice puts it in the handshake packet (handshake_id1).
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Alice starts sending handshake packets to Bob (send 10 packets over 5 seconds if no response connection fails.)
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Bob receives the packet.
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Bob copies the handshake packet he got from alice but caternates a random 4 byte number to it (handshake_id2)
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Alice receives the packet, checks if handshake_id1 matches the one she sent.
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If it does she starts sending SYNC packets with sent_packetnum = handshake_id2 and recv_packetnum = handshake_id1.
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Bob receives the packet,
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if (handshake_id2) matches Bob adds Alice to his connections list and starts sending SYNC packets to alice.
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Alice receives the SYNC packets and starts sending them too.
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Connection is now established.
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Alice wants to send packets to Bob:
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Alice sends packets to bob.
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If bob receives the packets, his next SYNC packets reflect it.
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Alice receives the SYNC packets which confirms that bob received them
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Alice clears the packets from her buffer.
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If bob does not receive any packets, but receives a SYNC packet with a larger sent_packetnum than his recv_packetnum:
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bobs SYNC packets become request packets.
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The packet id of the missing packet(s) are added to the end of the SYNC packet.
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Alice resends the packets whose numbers appear at the end of the request packet.
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If bob receives some packets but some are missing
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bobs SYNC packets become request packets.
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The packet id of the missing packet(s) are added to the end of the SYNC packet.
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Alice resends the packets whose numbers appear at the end of the request packet.
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Alice and bob disconnect suddenly:
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Alice stops receiving SYNC packets from bob.
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Bob stops receiving SYNC packets from Alice.
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Connexion times out if no data is received for 5 seconds.
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Packet handling:
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The client receives a SYNC packet:
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He checks if the packet is valid(sent_packetnum and counter make sense)
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If the packet is valid:
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If the client was currently trying to establish a connection.
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If the handshake was done:
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Start sending SYNC packets.
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Add +1 to the counter of the SYNC packets we send.
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Check to see if any packets were dropped when sending them to us (compare sent_packetnum with the number of packets we recieved.)
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If some were, The next SYNC packets we send will be request packets requesting the missing packets.
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Check if the other client received what we sent him (compare recv_packetnum with the number of packets we sent) and clear them from the buffer.
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If the packet is a request packet.
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Send the packets he requested.
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The client receives a Connection handshake packet(not initiating connection):
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If handshake_id2 is zero:
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use the handshake_id1 in the packet as the handshake_id2 of the response.
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use our random handshake_id1 as handshake_id1.
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send the response packet.
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The client receives a Connection handshake packet(initiating connection):
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check if handshake_id1 matches what we sent.
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If it does start sending SYNC packets with sent_packetnum as handshake_id2
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The client receives a data packet:
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Put the packet in the proper place in the receive buffer using packet_num as the reference.
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If all the previous packets have been received correctly set recv_packetnum equal to packet_num
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Keep track of the percent of packets dropped, if it is too high, lower the send rate. If it is low, increase it.
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Have a send packets buffer that we can write to and a recieved packets buffer that we can read from.
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Protocol:
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Connection handshake packets:
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[byte with value: 16 (10 in hex)][4 byte (handshake_id1)][4 bytes (handshake_id2)]
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SYNC packets:
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[byte with value: 17 (11 in hex)][byte (counter)][4 byte (recv_packetnum)][4 byte (sent_packetnum)][sequence of requested packet ids[4 bytes each](not present in keep alive)]
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data packets:
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[byte with value: 18 (12 in hex)][4 byte (packet_num)][data (arbitrary size)]
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