Network Protocol
Overview
This article describes the network protocol used by Mario Kart Wii.
Terminology
The following terms are used in this article.
| Term | Description |
|---|---|
| ARP | Address Resolution Protocol, a network routing protocol. |
| cfc | The console friend code. It is displayed as 16 digits in the format "XXXX-XXXX-XXXX-XXXX". |
| Client | A Wii system that takes part in the race. |
| fc, fc8 | The friend code of the first user of a client. Sometimes it is extended by ".1" or ".2" to identify the user of the client. A friend code is displayed as 12 digits using format "XXXX-XXXX-XXXX". |
| GPCM | The client server. |
| GPSP | The server that retrieves friends. |
| Guest | All non-host clients. |
| Home client | The observed client where the network traffic comes from. |
| Host | The client who has opened the room. |
| MASTER | The master matchmaking server. |
| Mii | The Mii avatar of a user. |
| MS | The matchmaking retrieving server. |
| N-server | One of Nintendo's servers. |
| NAS, NASWII | The login server. |
| NATNEG | The server that enables client to client connections behind firewalls. It stands for Network Address Translation NEGotiation. |
| Packet | A packet is a technical network packet. Mario Kart Wii uses ARP, TCP and UDP (including name resolution) packets. |
| Player | A player that takes part of the race, with a maximum of 12. Players are all users of all clients. |
| Player ID | An alternative name for Profile ID. |
| Profile ID, pid, fc4 | The Profile ID is a short version of the friend code with only the lowest 4 bytes (32 bit). It is used in the network protocols for identification. |
| TCP | Transmission Control Protocol, a network protocol. |
| Record | A packet can be split into logical records. Each record has its own meaning and its own data structure. |
| UPD | User Datagram Protocol, a network protocol. |
| User | A user of a client. Each client supports 1 or 2 users. The users of the client are numbered 1 and 2. |
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 p2p data transfer. First it connects the N-server (Wiimmfi server). In a room or while racing, all consoles communicate directly to each other. In a race, only some active records are send to an N-server.
Connecting to Servers
When connecting to the Nintendo Wi-Fi Connection, the console starts with DNS queries to locate 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
The Wiimmfi equivalents are the same servers with "nintendowifi.net" replaced with "wiimmfi.de". Then it starts the communication with the servers and the first packet goes to mariokartwii.available.gs.nintendowifi.net. More details about the servers can be found here.
Point to Point Communication
The Wii uses a frequency of 59.94Hz (NTSC) as time base. All clients send a status packet to one of the other clients every second pulse (around 1/30 seconds). For example, when there are three clients A, B and C, then A will send packets to B and C in turn every 1/30 seconds. This means that the individual status update is only done every 1/15 seconds. This update time is reduced to 11/30 seconds when there are 12 clients in a race. This is the main reason for lag when racing with many players. The average packet length is about 220 bytes, so the total traffic is about 8 KB/s in both directions, independent of the number of clients.
Main records ("RACE" records)
Each UDP packet can be split into records, which are logical units. Sometimes, a packet is prefixed by a SLOT record to reduce a client's needed upload bandwidth.
Header
After SLOT (if it exists), the main race header (16 bytes) is as follows.
| Offset | Type | Description |
|---|---|---|
| 0x00 | u32 | always 0x0000 0000 (start of checksum part) |
| 0x04 | u32 | Checksum record |
| 0x08 | u8 | always 0x10 (length of this header) |
| 0x09 | u8 | length of the first race header. 0x28 or 0x00 |
| 0x0a | u8 | length of the 2nd race header. 0x28 or 0x00 |
| 0x0b | u8 | length of the ROOM or SELECT record. 0x04 (for room), 0x38 (for select), or 0x00 |
| 0x0c | u8 | length of RACEDATA. 0x40 (for 1 player), 0x80 (for 2 players) or 0x00 |
| 0x0d | u8 | length of USER. 0xc0 or 0x00 |
| 0x0e | u8 | length of ITEM. 0x08 (for 1 player), 0x10 (for 2 players) or 0x00 |
| 0x0f | u8 | length of EVENT. 0x00, or >= 0x18 |
The CHECKSUM algorithm is described here. RACE records are sent from every client to all other clients during a race including the race preparation.
Packet Structure
The following table shows the packet structure and the different records.
| Name | Length | Description |
|---|---|---|
| HEADER | 0x10 | The packet header described above. |
| RACEHEADER_1 | 0x28 | Race header. |
| RACEHEADER_2 | 0x28 | Another race header. |
| ROOM | 0x04 | Room records are only sent in room events. The first byte decides the sub type:
|
| SELECT | 0x38 | This record is sent while selecting character and track. It is always placed before a USER record. One byte decides the phase.
|
| RACEDATA | 0x40 | Actual race data. May exist twice if there are two players on one console. |
| USER | 0xC0 | User information including a friend code and 2 Miis for both users of the client. |
| ITEM | 0x08 | Record indicating the item status. |
| EVENT | >= 0x18 | Record indicating the event status. |
Additional Records
The following table shows additional records.
| Name | Record ID | Length | Description |
|---|---|---|---|
| SLOT | 46fc.570x | 0x08 | The following message is related to the client slot "X". 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 a 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 five different extensions. Byte 0x08 describes the status type. One task is to select and advice client slots to clients. |
| NATNEG | fdfc | 0x14+N | NATNEG records. Only CONNECT_PING is sent peer-to-peer, all other records via the server. |
| QUIT | fefe.68 | 0x03 | This record is sent when a client quits a room or a race. It is not 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.
Global match
As soon as the client has found a room via MS, it sends a "Asking for entrance"-status message (same as in the room). When the room host is in the friend list, GPCM90-Messages are used. If the host is not in the friend list (more likely), STATUS-messages are being proxied by MS/MASTER.
Then, same as in the room, NATNEG and a few status messages are done. The wii then sends an empty record header (ANNOUNCE) to the host and starts sending packets containing an USER record.
During the VIEW phase (you are seeing the other players racing), race packets with only RACEHEADER_1 and EVENT are sent.
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.
Countdown
Before countdown, 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
Information:
Nintendo's Servers –
Friend Code –
Nick –
Dumping Network Traffic
Record Types:
HEADER –
ROOM –
SELECT –
USER
RACEHEADER_1 –
RACEHEADER_2 –
RACEDATA –
ITEM –
EVENT
NATNEG –
ANNOUNCE –
QUIT –
STATUS –
PARAM-STRING
Wiimmfi Extensions:
Online Status –
Connection Status –
Wiimmfi packets –
Server SV
Software:
Wiimms mkw-ana