Network Protocol

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Revision as of 23:46, 12 June 2015 by MrBean35000vr (talk | contribs) (→‎Main records ("RACE" records): Fixed malformed hyperlink.)
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This page describes the network protocol used by Mario Kart Wii.


In Progress
This article is managed by Wiimm and Leseratte and will grow slowly. Feel free to edit typos and grammatical or speech issues. If you have additional information, please complete this page.


Introduction

The analysis of the data is done with the tool mkw-ana. So the naming of mkw-ana for objects (records, stages, ...) is used here. Because of the very early phase of the analysis, names and structures may completely change.

You can discuss this topic at Wii-Homebrew.com (English and German) or at mariokartwii.com (English).

Terms and definition

Template:MKWii Network Terms

General description

The Mario Kart Wii traffic starts with some name resolutions. Then it will use TCP connection to the servers and UDP packets for the player to player data transfer.

First it connects the Wiimmfi server (N-server). In a room or while racing, all Wiis communicate directly to each other. In a race, only some alive records are send to a N-server.

Connecting the Wiimmfi-Server(s)

When entering the Mario Kart WFC, the Wii started with DNS queries to find out the IP addresses of the following servers:

  • gpcm.gs.nintendowifi.net
  • gpsp.gs.nintendowifi.net
  • gamestats.gs.nintendowifi.net
  • gamestats2.gs.nintendowifi.net
  • mariokartwii.available.gs.nintendowifi.net
  • mariokartwii.natneg1.gs.nintendowifi.net
  • mariokartwii.natneg2.gs.nintendowifi.net
  • mariokartwii.natneg3.gs.nintendowifi.net
  • mariokartwii.master.gs.nintendowifi.net
  • mariokartwii.gamestats.gs.nintendowifi.net
  • mariokartwii.gamestats2.gs.nintendowifi.net
  • mariokartwii.ms19.gs.nintendowifi.net
  • naswii.nintendowifi.net

("nintendowifi.net" replaced with "wiimmfi.de" for the Wiimmfi server)

Then it starts the communication with nintendos servers and the first packet goes to mariokartwii.available.gs.nintendowifi.net.

More Details about the servers

Point to point communication

The Wii uses a frequency of 59.94Hz (based on NTSC, about 1/60s) as time base. All clients send a status packet to one of the other clients every second pulse (~1/30s). When there are for example 3 clients A, B and C, then A sends first a packet to B and then, 1/30s later, a packet to C, and again 1/30s later, the next packet to B. This means, that the individual status update is only done every 1/15s. This update time is reduced to 11/30s (~1/3s), when there are 12 clients in a race. And that's the reason for the many lagging effects when playing with many players.

The average packet length is about 220 bytes, so the total traffic is about 6.6 KB/s (52.8 KBit/s) in both directions, independent of the number of clients.

Main records ("RACE" records)

Each UDP packet can be split in records. Records are logical units.

A race packet consists of records. The main race header has 8 bytes.

typedef struct header_t
{
 /*00*/  u8	header_len;           // always 0x10 (length of checksum record + length of this header)
 /*01*/  u8     raceheader1_len;      // length of the first race header. 0x28 or 0x00
 /*02*/  u8     raceheader2_len;      // length of the 2nd race header. 0x28 or 0x00
 /*03*/  u8     room_select_len;      // length of the ROOM or SELECT record. 0x04 (for room), 0x38 (for select), probably 0x3b for both, or 0x00

 /*04*/  u8     racedata_len;         // length of RACEDATA. 0x40 (for 1 player), 0x80 (for 2 players) or 0x00
 /*05*/  u8     user_len;             // length of USER. 0xc0 or 0x00
 /*06*/  u8     item_len;             // length of ITEM. 0x08 (for 1 player), 0x10 (for 2 players) or 0x00
 /*07*/  u8     event_len;            // length of EVENT. 0x00, or >= 0x18

 /*08*/
}
__attribute__ ((packed)) header_t;

RACE records are send from every client to all other clients during a race including the race preparation. Each clients send every 1/30s one record to one other client.

The following table shows:

  • A name used by mkw-ana.
  • Data length
  • Description.
List of Records
Name Length Description
RACEHEADER_1 ? Race header
RACEHEADER_2 ? Another race header
ROOM 0x04 The first byte decides the sub type:
  • 0: unknown
  • 1: Send by host: Start an event (GP, Team, Ballon or Coin).
  • 2: unknown
  • 3: unknown
  • 4: Send a room message (online chat).

Room records are only sent in room events.

SELECT 0x38 This record is send while selecting driver and track. It is always placed before an USER record. One byte decides the phase:
  • 0: Prepare the race.
  • 1: Before first race: Driver selection. All races track selection by user.
  • 2: Track lottery. Before start of the lottery, the host sends to all clients the winning user and track.
RACEDATA ? Actual race data. May exist twice if there are two players on one console.
USER 0xc0 ? A user information including a FC and 2 Miis for both users of the client.
ITEM ? Record indicating the item status
EVENT ? Record indicating the event status

Additional records

The following table shows:

  • A name used by mkw-ana.
  • Value of the first 2-4 bytes (Record ID, big endian, hex).
  • Length of the record.
  • Description.
List of Records
Name Record ID Length Description
CHECKSUM 0000.0000 0x08 A checksum record used for the most data records.
SLOT 46fc.570x 0x08 The following message is related to client slot x (default: for the sender). This is mainly used in combination with ANNOUNCE and USER to tie information to specific client slots.

If a client has bandwidth problems, it can use another client as proxy to reduce its own traffic during the race. Such indirect packets are also prefixed by a SLOT record.

STATUS bb49.cc4d 0x14+N A status record with 5 different extensions. Byte 0x08 describes the status type. One task is to select and advice client slots to clients.
HANDSHAKE fdfc 0x14+N Different handshake records with different length. At the moment, an announce from Nintendo (with ip+port) and a little handshake between host and guest are known.
QUIT fefe.68 0x03 This Record is sent when a client quits a rooms or a race. This record isn't prefixed by a CHECKSUM-Record.

Stages

Here will be described what data is transmitted by the clients during the different stages of the game. Only peer-to-peer data will be mentioned here, not anything server-related.

Room

When a player wants to enter a friend room, he sends a "GMCP90"-Message type 1 (Ask for entrance, see server documentation for more details) via MASTER, this will either be answered with type 2 (access granted) or type 3 (denied, room full). When the host allows the new guest to enter, they start doing NATNEG to open a peer-to-peer-connection.

After NATNEG is done, the players start handshaking with a few FEXX-Status-Messages. After exchanging status messages, they send eachother an empty race packet ([ANNOUNCE]) to indicate the successful connection.

After that, the new player appears in the room and starts doing NATNEG with all the other players. Because NATNEG is very slow and does not run in threads (only one-by-one), only one player can join a room at the same time (others get 86420 after a timeout). This is the reason why starting a match takes a long time when the host starts a match as soon as everyone is in the room - all the peer to peer connections aren't set up yet - which are about 60 connections in a full room.

Event begin

At event begin, the host sends a ROOM-message to indicate the start of an event. The players select their characters and vehicle, and the track selection starts.

The track selection has three phases: Phase 1: SEL/PREPARE: You'll see the string "Preparing race ..." and wait until everyone is ready. Phase 2: SEL/WAITING: You'll see the track selection screen and can choose a track to drive, or you are waiting for others to complete their track choice. At this point, the engine class is already determined. Phase 3: SEL/LOTTERY: Everyone has chosen a track and the lottery begins. As soon as the lottery begins, the winning user and track is already know to all clients.

Count down

Before count down, the host sends a request "Ready for event?" to all clients. Until all clients have answered "ready!", you'll see the loading icon in the bottom right corner of the screen. If someone has a broken image or is in a CT room without having CTs, you'll all have to wait until he turns off his wii, as his console won't answer with "ready".

When the clients are syncronized and all ready for the event, the countdown and the race begins.

Finished

As soon as a player finishes, he sends his final time to all the other players. Now, the other players have 30 seconds left to complete the race (but a race has a minimum time of 2 minutes and a maximum time of 5 minutes). When the race is finished (either by everyone crossing the finish line, 5 minutes being over or the 30-seconds being reached, the phase "All finished" is activated. You'll see the rankings and the next race will begin.

Links


Template:MKWii Network Protocol mk8:MK8 Network Protocol