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The Fiber Distributed Data Interface (FDDI) is a network technology that uses fiber-optic cable as a transmission medium and dual counter-rotating rings to provide data delivery and fault tolerance. FDDI was developed as a way to combine the high-speed capabilities of fiber-optic cable and the fault tolerance of IBM’s Token Ring technologies. An FDDI network is based on a standard introduced by the ANSI X3T9.5 committee in 1986. It defines a high speed (at 100Mbps), token-passing network using fiber-optic cable. In 1994, the standard was updated to include copper cable (called CDDI, or Copper Distributed Data Interface). FDDI was slow to be adopted, but has found its niche as a reliable, high-speed technology for backbones and high-bandwidth applications that demand reliability.

FDDI is similar to Token Ring in that it uses token passing for permission to transmit. Instead of a single ring, however, FDDI uses two rings that counterrotate. That is, the token is passed clockwise in one ring and counterclockwise in the other. If a failure occurs, the counter-rotating rings can join together forming a ring around the fault, thus isolating the fault and allowing communications to continue.

Additionally, stations on an FDDI network can be categorized as either dual-attached stations (DAS) or single-attached stations (SAS). DASes are attached to both rings, whereas SASes are attached to only one of the rings. DASes are much more fault tolerant than SASes.

Remote Access Protocols

remote access protocol manages the connection between a remote computer and a remote access server. These are the primary remote access protocols that are in use today:

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