Communication is facilitated by the Network News Transfer Protocol (NNTP) which allows connection to Usenet servers and data transfer over the internet. Similar to another early (yet still used) protocol SMTP which is used for email messages, NNTP allows both server-server and client-server communication. This means that newsgroups can be replicated from server to server which gives the Usenet network the ability to maintain a level of robust data persistence as a result of built-in data redundancy. However, most users will access using only the client-server commands of NNTP and in almost all cases will use a GUI for browsing as opposed to command line based client-server communication specified in the NNTP protocol.