Prestel
In 1983, the Prestel messaging service known as “Prestel Mailbox” was launched, initially hosted on the computer known as "Enterprise", and later available from all IRC computers by means of a centralised messaging computer known as "Pandora". This facility extended the original day one concept of “Response Frames” whereby an end user could send a message back to the IP who owned the page via special pages, for example to order goods or services. The user’s name, address, telephone number, and date could be added automatically to the message when the IP set up the response frame by means of codes which triggered extraction of key data from the users account held on the IRC computer. Initially response frames were ingathered by an IP from each IRC individually, but later the facility to collect messages from all IRCs at the UDC from where they could be ingathered centrally was implemented, and with the introduction of Mailbox, they could be retrieved from any IRC.
IPv6
Devices on the Internet are assigned a unique IP address for identification and location definition. With the rapid growth of the Internet after commercialization in the 1990s, it became evident that far more addresses would be needed to connect devices than the IPv4 address space had available. By 1998, the Internet Engineering Task Force (IETF) had formalized the successor protocol. IPv6 uses a 128-bit address, theoretically allowing 2, or approximately addresses. The actual number is slightly smaller, as multiple ranges are reserved for special use or completely excluded from use. The total number of possible IPv6 addresses is more than times as many as IPv4, which uses 32-bit addresses and provides approximately 4.3 billion addresses. The two protocols are not designed to be interoperable, complicating the transition to IPv6. However, several IPv6 transition mechanisms have been devised to permit communication between IPv4 and IPv6 hosts.