A brief history of the UUID (2017)

Apollo’s answer was the their Network Computing System (NCS). When Apollo began to approach standardizing the principles of NCS as the Network Computing Architecture (NCA), it became clear that the existing UID design was insufficient. NCA UUIDs had a 48-bit timestamp, 16 reserved bits, an 8-bit indicator for network address family, and a 56-bit host ID.

Source: segment.com