Spectrum 2 is an XMPP transport/gateway and XMPP server. It allows XMPP users to communicate with their friends who are using one of the supported networks. It supports a wide range of different networks such as ICQ, XMPP (Jabber, GTalk), AIM, MSN, Facebook, Twitter, Gadu-Gadu, IRC and SIMPLE. Spectrum is written in C++ and uses the Swiften XMPP library and different libraries for legacy networks. Spectrum 2 is open source and released under the GNU GPL2+ license.

h2. Gateway mode and server mode

h3. Gateway mode

Gateway mode represents the classic way how XMPP gateway works. You have to configure an external XMPP server (like Prosody or Ejabberd) to serve the subdomain you want to use for Spectrum 2 (for example "icq.domain.tld"). Spectrum 2 in gateway mode then connects the XMPP server as its component and users are able to find out "icq.domain.tld" in Service Discovery, register it and use it.

*Advantages:*

* Users can use more legacy networks using single XMPP account (and using single TCP connection).

* It's easy to extend existing XMPP servers using gateway mode.

*Disadvantages:*

* Passwords are stored (even in encrypted form) on server.

* Roster (contact list) synchronization can be problematic, because it depends on the client user uses. This can be improved by usage of Remote Roster protoXEP.