The entire suite provided routing and packet delivery, as well as higher-level functions such as a reliable byte stream, along with numerous applications.
It was primarily designed by Robert Metcalfe, David Boggs, Charles P. Thacker, Butler Lampson and John Shoch.
PUP also includes a simple echo protocol at the internetwork layer, similar to IP's ping, but operating at a lower level.
PUP showed that internetworking ideas were feasible, influenced the design work on TCP/IP, and laid a foundation for the later XNS protocols.
During design discussions, the Xerox attendees kept pointing out flaws in the ideas that were suggested, until one of the Stanford researchers blurted out, "You guys have already done this, haven’t you?
One version of RIP served as one of the initial so-called interior gateway protocols for the growing Internet, before the arrival of the more modern OSPF and IS-IS.
PUP's 8-bit network and 8-bit host could scale to at most 64k machines, before an inter-network bridge or gateway would be needed.
For this reason, a successor, the Xerox Networking System (XNS), was developed by the Xerox Office Systems Division using many of the ideas of PUP and a globally-unique, 48-bit host identifier (which became the MAC address in DIX v2 and later IEEE 802.3) to solve these problems:[5]