A ring network is a
network topology
Network topology is the arrangement of the elements ( links, nodes, etc.) of a communication network. Network topology can be used to define or describe the arrangement of various types of telecommunication networks, including command and contr ...
in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node – a ring. Data travels from node to node, with each node along the way handling every packet.
Rings can be unidirectional, with all traffic travelling either clockwise or anticlockwise around the ring, or bidirectional (as in
SONET/SDH
Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting ...
). Because a unidirectional ring topology provides only one pathway between any two nodes, unidirectional ring networks may be disrupted by the failure of a single link.
A node failure or cable break might isolate every node attached to the ring. In response, some ring networks add a "counter-rotating ring" (C-Ring) to form a redundant topology: in the event of a break, data are wrapped back onto the complementary ring before reaching the end of the cable, maintaining a path to every node along the resulting C-Ring. Such "dual ring" networks include the
ITU-T
The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...
's
PSTN
The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other el ...
telephony systems network
Signalling System No. 7 (SS7),
Spatial Reuse Protocol,
Fiber Distributed Data Interface (FDDI), and
Resilient Packet Ring.
IEEE 802.5 networks – also known as IBM Token Ring networks – avoid the weakness of a ring topology altogether: they actually use a ''star'' topology at the ''physical'' layer and a
media access unit (MAU) to ''imitate'' a ring at the ''datalink'' layer.
All
Signalling System No. 7 (SS7), and some SONET/SDH rings have two sets of bidirectional links between nodes. This allows mai