This article was initially published in French, and it got some interest, so we started to translate the whole series in English. If you can read French, you can follow the whole series there: http://www.goffi.org/tag/parlons_xmpp
In the software development field, and much in the libre software, group’s discussions are really common, mostly with IRC (Internet Relay chat).
This venerable protocol do what we ask it and XMPP is strongly inspired by it. Let’s see that closely.
Group’s discussions used nowadays are called MUC (Multi-User Chat) and are defined by XEP-0045. This one standardizes and extends the first solution called Groupchat. As all that comes from IRC, I’ll explain as they come the major differences between them.
It is possible to acces a chat room located on any server from any server (again, while it is not explicitly prohibited). Chat rooms do, as the users, have a jid, which has the pattern chat_room_name@service. For example, that of Salut à Toi is email@example.com: “sat” is the chat room’s name, “chat.jabberfr.org” the service.
The resource is used for occupants of the chat room: firstname.lastname@example.org/goffi corresponds to the occupant “goffi” in the chat room email@example.com. Ah little detail that I forgot in previous articles: everything is unicode in XMPP, including jid. So you can use arabic or russian nickname. But beware: some unicode characters are strongly similar, therefore it is possible to get 2 words graphically similar mixed up, we name it “homoglyphs”. For example “ｇοｆｆⅰ” looks like “goffi” but it uses different characters. This issue is mentioned in a unicode technical report: http://www.unicode.org/reports/tr36/. Also, do not rely exclusively on a nickname to identify someone (espcially that it is possible that it can be reused by someone else between two sessions).
The nickname is linked to the chat room and not to the service. You can have a nick “toto” in a chat room and “titi” in another one, and someone else can have “titi” on a third chat room. This is a big difference with IRC where we have only one nickname on a server that will be used in every chat room (channel on IRC).
To go in or go out a chat room, or to change nickname, we send an available (or not) presence directly to firstname.lastname@example.org/desired_nick, but this is normaly managed by your client.
It is also possible to write directly to all chat room’s occupants (under the hood this is a “groupchat” message that is sent to the chat room’s bare jid), or to have a private chat with a member (we write to the full jid of the recipient).
A chat room can be public or hidden (it will not appear in the chat room list), not anonymous or semi-anonymous (in the first case everyone can see the occupant’s real jid, in the second case only moderators and administrators can), persistent or temporary, open or accessible only by white list or can be protected by password, moderated or not.
All those parameters are normally defined at the creation of the chat room, or they can be modified after with the suitable option of your client (on Gajim: right click on chat room tab => Manage Room => Configure Room). According to the service you use, you can configure more or less things, for example limit the occupant’s maximal number.
A feature often implemented is the history or “back log”: when you get in a chat room, the service sends you the last X messages, allowing you to understand the context of the current conversation.
Also, if a public archive of the chat room is kept (we say “logged” chat room), the service must warn you (it’s mandatory in the XEP), this is another good point compared to IRC. For sure, one has to remember that anyone in the room can keep a log and could publish it without your consent.
So far, so good, but a great strength of IRC is its simplicity: no need to create an account, you just have to pick a nick (unique), with a server, and that’s it! So, you won’t be disapointed, XMPP has exactly the same thing with connections called “anonymous”. No anonymity in terms of Tor here, but rather the possibility to get a temporary account, with a jid more or less random, for the connection time. This comes built-in but it must often be explicitly enabled in the server configuration, and most of the time, anonymous connections are limited to the local network, no communication with other servers (to avoid spam).
If you want to chat as with IRC in a simple and intuitive way, and if you like the console, I would strongly recommend Poezio which is an excellent XMPP client that is easy to use: initially, without changing the configuration, you will be anonymously connected to the MUC service of Poezio. It is inspired by Irssi/Weechat and use the same commands (and more generally those of IRC). Below the welcome message, without changing the configuration, we see the anonymous jid assigned for the session time.
Well this episode is long enough, but I am not finished with MUC, therefore we will talk about it next time, probably with transports.