"This experiment also demonstrated that the existing ARPANET protocols were not suitable for running over different networks."

I'm learning computer networking on my own so I don't have anyone else to ask and couldn't find an explanation while searching, so some help is really appreciated.

I'm reading Computer Networks by Tanenbaum and Weatherall and am currently confused by this statement (the title).

The first paragraph talks about the experiment where a truck connected to a University in London successfully, with data packets sent through at least three different mediums (terrestrial radio, wires and satellite). Then, on the next paragraph it says "This experiment also demonstrated that the existing ARPANET protocols were not suitable for running over different networks.".

Did I miss something? If the experiment was successful then how did they know that the existing protocols were not suitable for different networks? I really got confused by this.

>In addition to helping the fledgling ARPANET grow, ARPA also funded re-search on the use of satellite networks and mobile packet radio networks. In onenow-famous demonstration, a big truck driving around in California used the pack-et radio network to send messages to SRI, which were then forwarded over the ARPANET to the East Coast, where they were then shipped to University College in London over the satellite network. This allowed a researcher in the truck to use a computer in London while driving around in California.

>This experiment also demonstrated that the existing ARPANET protocols werenot suitable for running over different networks. This observation led to more re-search on protocols, culminating with the invention of the TCP/IP protocols (Cerfand Kahn, 1974). TCP/IP was specifically designed to handle communication overinternetworks, something becoming increasingly important as more and more net-works were hooked up to the ARPANET.