Ring network
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A ring network is a network topology in which each node connects to exactly two other nodes, forming a circular pathway for signals: a ring. Data travels from node to node, with each node handling every packet.
Because a ring topology provides only one pathway between any two nodes, 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. FDDI networks overcome this vulnerability by sending data on a clockwise and a counterclockwise ring: in the event of a break data is wrapped back onto the complementary ring before it reaches the end of the cable, maintaining a path to every node along the resulting "C-Ring". 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 Multistation Access Unit to imitate a ring at the datalink layer.
Many ring networks add a "counter-rotating ring" to form a redundant topologies. Such "dual ring" networks include Spatial Reuse Protocol, fiber distributed data interface, and Resilient Packet Ring.
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[edit] Advantages
- Very orderly network where every device has access to the token and the opportunity to transmit
- Performs better than a star topology under heavy network load
- Can create much larger network using Token Ring
- Does not require network server to manage the connectivity between the computers
[edit] Disadvantages
- One malfunctioning workstation or bad port in the MAU can create problems for the entire network
- Moves, adds and changes of devices can affect the network
- Network adapter cards and MAU's are much more expensive than Ethernet cards and hubs
- Much slower than an Ethernet network under normal load
[edit] Misconceptions
- "Token Ring is an example of a ring topology." 802.5 (Token Ring) networks do not use a ring topology at layer 1. As explained above, IBM Token Ring (802.5) networks imitate a ring at layer 2 but use a physical star at layer 1.
- "Rings prevent collisions." The term "ring" only refers to the layout of the cables. It is true that there are no collisions on an IBM Token Ring, but this is because of the layer 2 Media Access Control method, not the physical topology (which again is a star, not a ring.) Token passing, not rings, prevent collisions.
- "Token passing happens on rings." Token passing is a way of managing access to the cable, implemented at the MAC sublayer of layer 2. Ring topology is the cable layout at layer one. It is possible to do token passing on a bus (802.4) a star (802.5) or a ring (FDDI). Token passing is not restricted to rings.
