We have seen that the Internet is really a collection of independently owned and operated networks. The concept of networks was previously dominated by the telephone model. It had a central switching exchange and all information ran through this exchange. The telegraph network also used centralized switching. Like the telephone switching system, it, too, had telegraph lines that connected the switching centers. The telegraph-switching center was called a message switch. These message-switching centers were originally manually operated copy and relay centers. Later, paper tape with automatic punches and, finally, computers replaced the manual switching centers. It became clear that some mechanism was needed to distinguish between the message content and the control characters that were used by the computer to recognize the beginning and end of the message.

Message switching with its telegraphy history was message integrity oriented. Each message was carefully acknowledged. Losing messages was not acceptable. This formed the basis for reliable message transfer.

About the time the Internet was taking shape, the X.25 network protocol was being developed. One might say that the X.25 protocol is the successor to message switching. It was essentially designed with the Telco model in mind. It was intended to make money by charging for packets, just as the message-switching system was designed to charge for each message. The goal was to provide end-to-end message integrity.

A further impetus to the development of X.25 was the deregulation of the telephone equipment market brought about by the Carterphone decision of 1968.