Bob Clements remembers the details of Fibernet: Fibernet started out under the name “CheapNet.” It was BBN's first local area network, and came into existence in the context of Chaosnet at MIT and Ethernet from DEC/Intel/Xerox. Both of those required (at that time) quite a complex and expensive controller and network (analog) interface to talk to the shared coaxial cable. BBN decided to try to make a cheaper local network with one important “sexy” feature.
The “Cheap” feature consisted of using the fastest off-the-shelf serial interface we could find to send and receive packets. This turned out to be the Signetics 2652-1 “speed selected” HDLC USART chip to carry HDLC packets with their inherent addressing bytes and CRC error detection. This ran at 2 Mbps. IP packets were minimally encapsulated in HDLC frames.
The CheapNet fiber infrastructure was installed across all of the multi-building BBN Cambridge campus. It supported dumb terminals, Jericho workstations, and central timesharing machines.
The “sexy” feature was the idea of carrying the packets over a fiber optic link rather than a copper link. This was done using a fiber transmitter/receiver pair from Hewlett-Packard. The salient feature of these devices was that they [could] handle silence on the link. All other transceivers we found at the time would put out noise if there was no transmitter sending on the fiber at a given time. The HP units would be quiet in the absence of transmissions. This allowed the CDMA/CD concept to work as if the fiber system was an Ethernet.
The whole concept of fiber optics was new at that time. The idea of a network which could not be tapped by electronic eavesdropping was brand new. This was used to promote BBN's status as a leading-edge network and security house. On more than one occasion, a client from the armed services (particularly the Navy) was brought into a data closet at BBN and shown the CheapNet infrastructure. The demonstrator would begin typing out a long filefrom one of the timesharing systems onto a local glass TTY. Then he would unscrew the fiber connection from the local hub. He would point out the pretty red light, and then point out that the terminal had stopped printing (not mentioning that all other users on the floor had also lost their network connection). Then he would reconnect the fiber and show that the printing had resumed. This generally impressed the visitor, who was unlikely to be aware of the robustness of the TCP/IP protocols.