Doc: update multiplayer documentation with latest changes (#9552)

Although several places were fixed during the PR making the change,
not all made it in this document.

While at it, removed all kinds of Markdown warnings by an excessive
usage of spacebar in this document.

1 files changed, 160 insertions, 178 deletions

diff --git a/docs/multiplayer.md b/docs/multiplayer.md
index c7e1839cf..6ef14c4e7 100644
--- a/docs/multiplayer.md
+++ b/docs/multiplayer.md
@@ -1,225 +1,207 @@
 # Multiplayer manual for OpenTTD
 
-Last updated:    2011-02-16
-
-
 ## Table of contents
 
 - 1.0) [Starting a server](#10-starting-a-server)
 - 2.0) [Connecting to a server](#20-connecting-to-a-server)
-    - 2.1) [Connecting to a server over the console](#21-connecting-to-a-server-over-the-console)
+  - 2.1) [Connecting to a server over the console](#21-connecting-to-a-server-over-the-console)
 - 3.0) [Playing internet games](#30-playing-internet-games)
 - 4.0) [Tips for servers](#40-tips-for-servers)
-    - 4.1)[Imposing landscaping limits](#41-imposing-landscaping-limits)
+  - 4.1)[Imposing landscaping limits](#41-imposing-landscaping-limits)
 - 5.0) [Some useful things](#50-some-useful-things)
 - 6.0) [Troubleshooting](#60-troubleshooting)
 
 
 ## 1.0) Starting a server
 
- - Make sure that you have your firewall of the computer as well as possible
-   routers or modems of the server configured such that:
-    - port 3979 is free for both UDP and TCP connections in- and outgoing
-    - port 3978 is free outbound for UDP in order to advertise with the master
-     server (if desired). Otherwise you'll have to tell players your IP.
-    - port 3977 if use of the admin interface is desired (see admin_network.txt)
- - Click "multiplayer" on the startup screen
- - Click "start server"
- - Type in a game name
- - Select the type of game ('LAN/Internet' or 'Internet (advertise)'. With the
-   last one other people are able to see you online. Else they need your IP and
-   port to join)
- - Click "start game", "load game" or "load scenario"
- - Start playing
-
+- Click on "Multiplayer" in the Start Menu.
+- Click on "Start Server".
+- Give your server a name.
+- Select the visibility of your server:
+  - "Public": your server will be publicly listed.
+  - "Invite Only": only players who have the invite code for your server can
+    join.
+  - "Local": only players on your local network can join.
+- (optional) Set a password for your server.
+- Click "New Game", "Load Game", or "Play Scenario".
+- Start playing.
 
 ## 2.0) Connecting to a server
 
- - Click "multiplayer" on the startup screen
- - If you want to connect to any network game in your LAN click on 'LAN', then
-   on 'Find Server'
- - If you want to see which servers all online on the Internet, click on
-   'Internet' and 'Find Server'
- - If there were more than one server
-    - select one in the list below the buttons
-    - click on 'join game'
- - If you want to play and you have the ip or hostname of the game server you
-   want connect to.
-    - click add server
-    - type in the ip address or hostname
-    - if you want to add a port use :<port>
- - If you want to play and you have the invite code of the game server you
-   want connect to.
-    - click add server
-    - type in the invite code
- - Now you can select a company and press: "Join company", to help that company
-    - Or you can press "Spectate game", to spectate the game
-    - Or you can press "New company", and start your own company (if there are
-   slots free)
- - You see a progressbar how far you are with joining the server.
- - Happy playing
+- Click on "Multiplayer" in the Start Menu.
+- There are three ways to join a server:
+  - If you want to connect to a local server, click "Search LAN".
+  - If you want to connect to a public game, click "Search internet".
+  - If the server-owner shared an invite code with you:
+    - Click "Add Server".
+    - Fill in the invite code, which always starts with a `+`.
+    - Click "OK".
+- Click on the server you want to join.
+- Click "Join Game".
+- If the server has a password, it will ask you for this.
+- You see a progressbar how far you are with joining the server.
+- Happy playing.
 
 ## 2.1) Connecting to a server over the console
 
- - Open the console and type in the following command:
-    connect `<ip/host>:<port>#<company-no>`
-
+- Open the console and type `connect` for help how to connect via the console.
 
 ## 3.0) Playing internet games
 
- - Servers with a red dot behind it have a different version then you have. You
-   will not be able to join those servers.
+- Servers with a red dot behind it have a different version then you have. You
+  will not be able to join those servers.
+
+- Servers with a yellow dot behind it have NewGRFs that you do not have. You
+  will not be able to join those servers. However, via "NewGRF Settings" and
+  "Find missing content online" you might be able to download the needed
+  NewGRFs after which you can join the server.
+
+- It can happen that a connection is that slow, or you have that many clients
+  connected to your server, that your clients start to loose their connection.
+  Some things you can do about it:
+  - `[network] frame_freq`:
+    change it in console with: `set network.frame_freq <number>`
+    the number should be between the 0 and 10, not much higher. It indicates
+    the delay between clicking and showing up. The higher, the more you notice
+    it, but the less bandwidth you use.
+    A good value for Internet-games is 2 or 3.
+
+  - `[network] sync_freq`:
+    change it in console with: `set network.sync_freq <number>`
+    the number should be between the 50 and 1000, not much lower, not much
+    higher. It indicates the time between sync-frames. A sync-frame is a frame
+    which checks if all clients are still in sync. When the value it too high,
+    clients can desync in 1960, but the server detects it in 1970. Not really
+    handy. The lower the value, the more bandwidth it uses.
+
+   NB: changing `frame_freq` has more effect on the bandwidth then `sync_freq`.
 
- - Servers with a yellow dot behind it have NewGRFs that you do not have. You
-   will not be able to join those servers. However, via "NewGRF Settings" and
-   "Find missing content online" you might be able to download the needed
-   NewGRFs after which you can join the server.
-
- - It can happen that a connection is that slow, or you have that many clients
-   connected to your server, that your clients start to loose their connection.
-   Some things you can do about it:
-   - [network] frame_freq:
-     change it in console with: 'set network.frame_freq <number>'
-     the number should be between the 0 and 10, not much higher. It indicates
-     the delay between clicking and showing up. The higher, the more you notice
-     it, but the less bandwidth you use.
-     A good value for Internet-games is 2 or 3.
-
-   - [network] sync_freq:
-     change it in console with: 'set network.sync_freq <number>'
-     the number should be between the 50 and 1000, not much lower, not much
-     higher. It indicates the time between sync-frames. A sync-frame is a frame
-     which checks if all clients are still in sync. When the value it too high,
-     clients can desync in 1960, but the server detects it in 1970. Not really
-     handy. The lower the value, the more bandwidth it uses.
+## 4.0) Tips for servers
 
-   NB: changing frame_freq has more effect on the bandwidth then sync_freq.
+- You can launch a dedicated server by adding `-D` as parameter.
+- In UNIX like systems, you can fork your dedicated server by adding `-f` as
+  parameter.
+
+- You can automatically clean companies that do not have a client connected to
+  them, for, let's say, 3 years. You can do this via: `set autoclean_companies`
+  and `set autoclean_protected` and `set autoclean_unprotected`. Unprotected
+  removes a password from a company when it is not used for more then the
+  defined amount of months. `set autoclean_novehicles` can be used to remove
+  companies without any vehicles quickly.
+
+- You can also do this manually via the console: `reset_company`.
+
+- You can let your server automatically restart a map when, let's say,
+  year 2030 is reached. See `set restart_game_date` for detail.
+
+- If you want to be on the server-list, make your server public. You can do
+  this either from the Start Server window, via the in-game Online Players
+  window, or by typing in the console: `set server_game_type public`.
+
+- You can protect your server with a password via the console: `set server_pw`,
+  or via the Start Server menu.
+
+- When you have many clients connected to your server via Internet, watch your
+  bandwidth (if you have any limit on it, set by your ISP). One client uses
+  about 1.5 kilobytes per second up and down. To decrease this amount, setting
+  `frame_freq` to 1 will reduce it to roughly 1 kilobyte per second per client.
+
+- OpenTTD's default settings for maximum number of clients, and amount of data
+  from clients to process are chosen to not influence the normal playing of
+  people, but to prevent or at least make it less likely that someone can
+  perform a (distributed) denial-of-service attack on your server by causing
+  an out-of-memory event by flooding the server with data to send to all
+  clients. The major factor in this is the maximum number of clients; with
+  32 clients "only" sending one chat message causes 1024 messages to be
+  distributed in total, with 64 clients that already quadruples to 4096. Given
+  that upstream bandwidth is usually the limiting factor, a queue of packets
+  that need to be sent will be created.
+  To prevent clients from exploiting this "explosion" of packets to send we
+  limit the number of incoming data, resulting in effectively limiting the
+  amount of data that OpenTTD will send to the clients. Even with the default
+  limits it is possible to generate about 70.000 packets per second, or about
+  7 megabit per second of traffic.
+  Given that OpenTTD kicks clients after they have not reacted within about 9
+  seconds from sending a frame update packet it would be possible that OpenTTD
+  keeps about 600.000 packets in memory, using about 50 megabytes of memory.
+  Given that OpenTTD allows short bursts of packets, you can have slightly
+  more packets in memory in case of a distributed denial of service attack.
+  When increasing the amount of incoming data, or the maximum number of
+  clients the amount of memory OpenTTD needs in case of a distributed denial
+  of service attack is linearly related to the amount of incoming data and
+  quadratic to the amount of clients. In short, a rule of thumb for, the
+  maximum memory usage for packets is:
+  `#max_clients * #max_clients * bytes_per_frame * 10 KiB`.
 
+### 4.1) Imposing landscaping limits
 
-## 4.0) Tips for servers
+- You can impose limits on companies by the following 4 settings:
+  - `terraform_per_64k_frames`
+  - `terraform_frame_burst`
+  - `clear_per_64k_frames`
+  - `clear_frame_burst`
 
- - You can launch a dedicated server by adding -D as parameter.
- - In UNIX like systems, you can fork your dedicated server by adding -f as
-   parameter.
-
- - You can automatically clean companies that do not have a client connected to
-   them, for, let's say, 3 years. You can do this via: 'set autoclean_companies'
-   and 'set autoclean_protected' and 'set autoclean_unprotected'. Unprotected
-   removes a password from a company when it is not used for more then the
-   defined amount of months. 'set autoclean_novehicles' can be used to remove
-   companies without any vehicles quickly.
-
- - You can also do this manually via the console: 'reset_company'.
-
- - You can let your server automatically restart a map when, let's say, year 2030
-   is reached. See 'set restart_game_date' for detail.
-
- - If you want to be on the server-list, make your server public. You can do
-   this either from the Start Server GUI, via the in-game Online Players GUI,
-   or by typing in the console:
-   'set server_game_type public'.
-
- - You can protect your server with a password via the console: 'set server_pw',
-   or via the Start Server menu.
-
- - When you have many clients connected to your server via Internet, watch your
-   bandwidth (if you have any limit on it, set by your ISP). One client uses
-   about 1.5 kilobytes per second up and down. To decrease this amount, setting
-   'frame_freq' to 1 will reduce it to roughly 1 kilobyte per second per client.
-
- - OpenTTD's default settings for maximum number of clients, and amount of data
-   from clients to process are chosen to not influence the normal playing of
-   people, but to prevent or at least make it less likely that someone can
-   perform a (distributed) denial-of-service attack on your server by causing
-   an out-of-memory event by flooding the server with data to send to all
-   clients. The major factor in this is the maximum number of clients; with
-   32 clients "only" sending one chat message causes 1024 messages to be
-   distributed in total, with 64 clients that already quadruples to 4096. Given
-   that upstream bandwidth is usually the limiting factor, a queue of packets
-   that need to be sent will be created.
-   To prevent clients from exploiting this "explosion" of packets to send we
-   limit the number of incoming data, resulting in effectively limiting the
-   amount of data that OpenTTD will send to the clients. Even with the default
-   limits it is possible to generate about 70.000 packets per second, or about
-   7 megabit per second of traffic.
-   Given that OpenTTD kicks clients after they have not reacted within about 9
-   seconds from sending a frame update packet it would be possible that OpenTTD
-   keeps about 600.000 packets in memory, using about 50 megabytes of memory.
-   Given that OpenTTD allows short bursts of packets, you can have slightly
-   more packets in memory in case of a distributed denial of service attack.
-   When increasing the amount of incoming data, or the maximum number of
-   clients the amount of memory OpenTTD needs in case of a distributed denial
-   of service attack is linearly related to the amount of incoming data and
-   quadratic to the amount of clients. In short, a rule of thumb for, the
-   maximum memory usage for packets is:
-       #max_clients * #max_clients * bytes_per_frame * 10 KiB.
+- Explaining `NNN_burst` and `NNN_per_64K_frames`
+  - `NNN_burst` defines 3 things, the maximum limit, the limit of a single
+    action, and the initial value for the limit assigned to a new company.
+    This setting is fairly simple and requires no math.
 
-### 4.1) Imposing landscaping limits
+    A value of 1 means a single tile can be affected by a single action.
+    This results in having to click 400 times when wanting to cover an area
+    of 20 x 20 tiles.
 
- - You can impose limits on companies by the following 4 settings:
-   - terraform_per_64k_frames
-   - terraform_frame_burst
-   - clear_per_64k_frames
-   - clear_frame_burst
+    The default value 4096 covers an area of 64 x 64 tiles.
 
- - Explaining 'per_64K_frames' and 'burst'
-    - 'burst' defines 3 things, the maximum limit, the limit of a single action,
-      and the initial value for the limit assigned to a new company.
-      This setting is fairly simple and requires no math.
+  - `NNN_per_64K_frames` defines the number of tiles added to each companies
+    limit per frame (however not past the possible maximum value,the
+    `NNN_burst`). 64k rather resembles the exact number of 65536 frames. So
+    setting this variable to 65536 means: `65536 / 65536 = 1 tile per frame`.
 
-      A value of 1 means a single tile can be affected by a single action.
-      This results in having to click 400 times when wanting to cover an area
-      of 20 x 20 tiles.
+    As a day consists of 74 frames, a company's limit is increased by 74
+    tiles during the course of a single day (2.22 seconds).
+    To achieve a 1 tile per day increase the following calculation is needed:
+    `1 / 74 (frames per day) * 65536 (per_64k_frames) = 885.62...`.
+    After rounding: a value of 886 means adding a bit over 1 tile per day.
 
-      The default value 4096 covers an area of 64 x 64 tiles.
+    There is still enough space to scale this value downwards:
+    decreasing this value to 127 results in a bit over 1 tile added to the
+    allowance per week (7 days).
 
-    - 'per_64k_frames' defines the number of tiles added to each companies limit
-      per frame (however not past the possible maximum value,the 'burst').
-      64k rather resembles the exact number of 65536 frames. So setting this
-      variable to 65536 means: 65536 / 65536 = 1 tile per frame.
-      As a day consists of 74 frames, a company's limit is increased by 74
-      tiles during the course of a single day (2.22 seconds).
+    To create a setup in which a company gets an initial allowance only,
+    set the value to 0 - no increase of the allowance per frame.
 
-      To achieve a 1 tile per day increase the following calculation is needed:
-      1 / 74 (frames per day) * 65536 (per_64k_frames) = 885.62...
-      after rounding: a value of 886 means adding a bit over 1 tile per day.
+- Even though construction actions include a clear tile action, they are not
+  affected by the above settings.
 
-      There is still enough space to scale this value downwards:
-      decreasing this value to 127 results in a bit over 1 tile added to the
-      allowance per week (7 days).
+## 5.0) Some useful things
 
-      To create a setup in which a company gets an initial allowance only,
-      set the value to 0 - no increase of the allowance per frame.
+- You can protect your company so nobody else can join uninvited. To do this,
+  set a password in your Company window.
 
- - Even though construction actions include a clear tile action, they are not
-   affected by the above settings.
+- You can chat with other players via ENTER or via SHIFT+T or via the Online
+  Players window
 
+- Servers can kick players, so don't make them use it!
 
-## 5.0) Some useful things
+## 6.0) Troubleshooting
 
- - You can protect your company so nobody else can join uninvited. To do this,
-   set a password in your Company Screen
+### My server does not show up in the serverlist
 
- - You can give other players some money via the ClientList (under the 'head'
-   in the mainbar).
+Check if the visibility of your server is set to `public`.
 
- - You can chat with other players via ENTER or via SHIFT+T or via the ClientList
+If it is, and your server still isn't showing up, start OpenTTD with
+`-d net=4` as extra argument. This will show debug message related to the
+network, including communication to/from the Game Coordinator.
 
- - Servers can now kick players, so don't make them use it!
+### My server warns a lot about getaddrinfo taking N seconds
 
+This could be a transient issue with your (local) DNS server, but if the
+problem persists there is likely a configuration issue in DNS resolving on
+your computer.
 
-## 6.0) Troubleshooting
+#### Running OpenTTD in a Docker container?
 
- - My advertising server does not show up in list at servers.openttd.org
-     Run openttd with the '-d net=2' parameter. That will show which incoming
-     communication is received, whether the replies from the master server or
-     communication from an admin tool reach the programme. See section 1
-     'Starting a server' further up for the ports and protocols used by OpenTTD.
-     The ports can be configured in the config file.
-
- - My advertising server warns a lot about getaddrinfo taking N seconds
-     This could be a transient issue with your (local) DNS server, but if the
-     problem persists there is likely a configuration issue in DNS resolving
-     on your computer. This seems to be a common configuration issue for
-     Docker instances, where the DNS resolving waits for a time out of usually
-     5 seconds.
+This is an issue with dual-stack Docker containers. If there is no default
+IPv6 resolver and IPv6 traffic is preferred, DNS requests will time out after
+5 seconds. To resolve this, use an IPv4 DNS server for your Docker container,
+for example by adding `--dns 1.1.1.1` to your `docker run` command.