Other common protocols besides HTTP?

Question

I usually pass data between my web servers (in different locations) using HTTP requests (sometimes using SSL if it's sensitive). I was wondering if there were any lighter protocols that I might be able to swap HTTP(S) for that would also support public/private keys like SSH or something.

I used PHP sockets to build a SMTP client before so I wouldn't mind doing that if required.

Answer 1

There are lots and lots and lots of protocols. Lots. Start here for a list. http://en.wikipedia.org/wiki/Internet_Protocol_Suite

SFTP is fun for passing data around. It works well. You'll find that it's not much better than HTTP, however, because HTTP is pretty simple. http://en.wikipedia.org/wiki/SSH_file_transfer_protocol

SMTP would work. http://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol

SNMP can be made to work. http://en.wikipedia.org/wiki/Simple_Network_Management_Protocol You have to really push the envelope.

All of these, however, involve TCP/IP sockets, which involve a fair amount of overhead because of the negotiation for a connection and the acknowledgement of packets.

If you want real fun with very low overhead, use UDP.
http://en.wikipedia.org/wiki/User_Datagram_Protocol

You might want to use Reliable UDP if you're worried about messages getting dropped. http://en.wikipedia.org/wiki/Reliable_User_Datagram_Protocol

Answer 2

I'd like to mention XMPP in addition to protocols already listed in other answers.

It's lightweight, and it is used in some "realtime" communication systems (for example, in GTalk).