Hitachi, Ltd.

Yoshiaki Ikoma

Shinji Sakano

Hideaki Tsushima

Yasushi Sawada

Masaki Miyagami

A medium-scale IP telecommunications network is configured in a low-cost optical network with good reliability and expandability. A physical configuration example has a center node-and eight local nodes-through-connected in one OADM ring--. The logical configuration is a star configuration with the central node-at its origin with all traffic passing through the center node-. The local nodes-through-are connected to the central node-by wavelength-unit optical channels or optical paths &#x3bb;through &#x3bb;. Channels are added as required. Initially, for example, the center node-and the local node-are connected by &#x3bb;, but &#x3bb;can added when the need arises. Since the logical star network is limited to approximately two add/drop optical channels at local nodes, costs are reduced by using inexpensive filters (e.g., dielectric interference film filters or fiber Bragg reflectors) that are capable of extracting only the specific wavelength of the optical channel. High reliability is provided through the use of optical switches for correction of fiber transmission path failures.

Optical network

To ensure transmission in a flexible optical network system, a digital test signal generation/comparison circuit is incorporated in an electrical signal processing portion of a transponder. The optical network system provides transparent wavelength-division multiplex service regardless of the signal type in client optical signals. Prior to connecting a client optical line to the optical system, a selective insertion unit and a selective extraction unit enable quality assessment of the client optical line.

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Yokohama, Japan

Yoshiaki Ikoma