The following is a comparison of instant messaging protocols. It contains basic general information about the protocols.
Table of instant messaging protocols
Note 1: In [email protected], the a.b.com part is known as the "hostmask" and can either be the server being connected from or a "cloak" granted by the server administrator; a more realistic example is [email protected]. The tilde generally indicates that the username provided by the IRC client on signon was not verified with the ident service.
Note 2: In [email protected]/home, the home part is a "resource", which distinguishes the same user when logged in from multiple locations, possibly simultaneously; a more realistic example is [email protected]/home
Note 3: Scalability issue: The protocol gets increasingly inefficient with the number of contacts.
Note 4: One-to-many/many-to-many communications primarily comprise presence information, publish/subscribe and groupchat distribution. Some technologies have the ability to distribute data by multicast, avoiding bottlenecks on the sending side caused by the number of recipients. Efficient distribution of presence is currently however a technological scalability issue for both XMPP and SIP/SIMPLE.
Note 5: There have been reports from users that the antispam filter is used to censor links to other IM programs and some websites.
Note 6: Serverless protocols don't have any central entities (usually companies) controlling the network. Serverless network consists only of clients. Such systems are usually extremely resistant to surveillance and censorship.