A new SONET 2AGbps 4-fiber ring network system, named ITS-2400V, has been developed. The 4-fiber ring network is a self-healing type ring network that adopts the BLSR (Bidirectional Line Switched Ring) architecture referred to in the Bellcore specification GR-1230-CORE. The ITS-2400V, which adopts 4-fiber BLSR, can also adopt 2-fiber BLSR, linear chain, and point-to-point network application with mode selection on the F/W (Firm/Ware). The ITS-2400V has SONET OC-48 interfaces for the aggregate line and provides any combinations of asynchronous DS-3, SONET OC-12, OC-3, STS-1, and SDH STM-1 interfaces for the tributary. The ITS-2400V has many other features such as 200% add/drop capability, Standby Line Access (SLA), interlocking ring, software download, etc. The ITS-2400V, which has been successfully developed, is being rapidly introduced into the trunk line market in the USA.