Network Protocol

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).

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 or 0x00
 /*05*/  u8     user_len;             // length of USER. 0xc0 or 0x00
 /*06*/  u8     item_len;             // length of ITEM. 0x08 or 0x00
 /*07*/  u8     event_len;            // length of EVENT. 0x00, or 0x18 or greater

 /*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. There is a prefix record "GLOBAL" for non-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.

Links

• Wiimms mkw-ana (tool)
• Discussion at mariokartwii.com
• Wiimmfi-Project (Project to create own MKWii servers)

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