Cambridge Ring (computer network)
The Cambridge Ring was a pioneering token ring local area network (LAN) technology developed at Cambridge University in England during the late 1970s. It served as an important precursor to the IEEE 802.5 token ring standard, though the two are not directly compatible.
The network used a slotted ring topology, with a number of repeaters connected in a ring via twisted-pair cables. Data was transmitted in small packets called "minipackets" which circulated around the ring. Each minipacket contained a source address, destination address, data, and some control bits.
Unlike early Ethernet implementations, the Cambridge Ring offered guaranteed bandwidth and deterministic access, as a station could only transmit when it possessed a free slot (identified by a token) in the ring. This made it suitable for time-sensitive applications such as real-time process control and voice communication, which were difficult to support reliably on collision-based networks.
The Cambridge Ring operated at a relatively low data rate, initially at 10 Mbit/s and later increased to 16 Mbit/s. Despite its technological advantages, it did not achieve widespread commercial success, primarily due to the emergence of Ethernet and the subsequent development of faster Ethernet standards. The cost of implementing and maintaining Cambridge Ring networks was also higher than Ethernet, further limiting its adoption.
Key features of the Cambridge Ring included:
- Slotted Ring: Data was transmitted in small, fixed-size packets within defined slots.
- Token-based Access: Nodes transmitted data only when possessing a free slot (token), preventing collisions.
- Acknowledgement Mechanism: The destination station set an "A bit" in the returning minipacket to confirm successful reception.
- Deterministic Performance: Guaranteed bandwidth and bounded access times made it suitable for real-time applications.
- Early Implementation of Quality of Service (QoS): The ring's architecture allowed for prioritization of certain types of traffic.
The Cambridge Ring, while not widely adopted commercially, made significant contributions to the field of computer networking. It influenced the development of later token ring standards and highlighted the importance of deterministic access and guaranteed bandwidth in LAN technologies. Its concepts and innovations have had a lasting impact on network design.