System Technical Description

Fiber Optic Telecommunications involves the transmission of digital information in the form of laser light pulses via glass fibers (refer to Figure B1). About the thickness of a human hair, each glass fiber has an immense data carrying capacity, and when bundled together in protective sheathing, about the diameter of a pencil, the optical fiber cable is capable of carrying more information than copper cable the diameter of a utility pole.

Digital Signal Transmission Through a Pair of Optical Fibers.

Unrepeatered Submarine Fiber Optic Systems represent the latest in fiber optic telecommunications technology, enabling the transmission of broadband communications over extended distances with the greatest possible system security and minimal operational and maintenance costs. A typical unrepeatered fiber optic system (schematically shown in Figure B2) consists of two primary components:

• Terrestrial Plant – Comprising the outside plant system elements from the beach vault, where the marine cable is spliced with the terrestrial cable, to the interconnect with the local interexchange carriers (i.e. demarc point). These elements include the beach vault, the land fiber optic cable carried through underground conduit or overhead pole line attachments, and the Submarine Line Termination Equipment located in the co-location facility at the demarc.
• Marine Plant – Comprising system elements connecting the sequential landing points. Primarily the marine fiber optic cable, other elements include the cable armouring, clamshell cable protectors, conduit seaward of the vaults where necessary, and vault clamps. All plant elements are specifically designed and tested to meet the rigorous demands of operation in deep oceanic environments.

Schematic of a Unrepeatered Fiber Optic Telecommunications System.

The Kodiak Kenai Fiber Link, including its interfaces at the Terminal Stations, will be a part of the international network with reliability, performance, and operation standards conforming to the internationally accepted specifications of ITU-T and ANSI (i.e. Characteristics of Repeaterless Optical Fibre Submarine Cable Systems: ITU-T G.973).

At start-up, the KKFL System will provide synchronous digital transmission facilities for a minimum of 25-years, operating at a monochromatic wavelength (λN) of 1550 nanometers without any submarine amplification or active components (Unrepeated). Each terminal station will be equipped with an initial capacity of 2.5 Gbit/s operating over a “Point to Point” or a “Collapsed Ring” architecture.

Collapsed Ring protection refers to the use of two dedicated OC-48 or STM16 SONET/SDH ADM channels equipped to operate in parallel over two dedicated fiber pairs (refer to Figure B3). In the unlikely event that there is a component failure in one of the fiber segments, the duplicate system will continue transmission until the fault is resolved.

Phase 1- Collapsed Ring System Architecture.

To insure the utmost system reliability a final segment, the Phase II route, will be installed between Narrow Cape, Kodiak Island and Seward. This redundant loop insures system integrity even in the improbable event of a catastrophic segment failure. Should an entire cable segment fail, the system’s traffic will be rerouted back through the remaining active segments as illustrated in Figure B4. Completion of the loop will be obtained through the use of other carriers’ (e.g. AT&T Alascom’s or Alaska Fiber Star’s) terrestrial fiber backhaul from Seward to Anchorage.

The Phase II route length approaches the practical limit of unrepeatered system technology. Because of this, two additional elements have been engineered into this segment. First, the cable will be built with pure silica optical fibers that are optically clearer than standard fibers and will transmit with lower loss. Secondly, a Remote Optically Pumped Amplifier (ROPA) will be incorporated to boost transmission. The ROPA is a piece of Erbium-doped fiber inserted in the cable at some tens of kilometers from the receive station. A ROPA pump located in the terminal station excites the Erbium fiber thereby amplifying the transmitted signal into the receiver at 10db greater than possible without the pump. All marine components are passive and are therefore considered part of an unrepeatered system.

Figure B4. Addition of Phase II and a Redundant Ring Architecture.

System Capacity
As presented earlier, the overall system capacity will be configured to operate at an OC-48 (2.5 Gb/s) level over 2 fiber pairs. This represents the most cost effective approach to meeting the current needs of the Kodiak and Kenai areas. Current estimates project a need for 3 DS-3’s with a latent demand of possibly an additional 2 DS-3’s. Referring to Appendix C, it can be seen that an OC-48 is equivalent to 55 DS-3’s, and therefore, only 14% of the initial lit capacity will be required to meet the current demand.

While today’s capacity is sufficient it is safe to assume that technological demands on bandwidth, economic growth, and a further dependence on the internet will someday outgrow the current capacity. In anticipation of this need, KKCC will install a four (4) fiber pair submarine fiber optic cable in each segment. This will allow for growth by expanding the operation to Wavelength Division Multiplex (WDM) equipment and special consideration for designs capable of 640 Gb/s or 14,222 DS-3’s.

For the foreseeable future, this ultimate capacity will never be met because the extra fiber pairs will be reserved for spares, or allocated for more specialized applications. However, it is clear that a single fiber pair will meet the needs of Kodiak and the Kenai Peninsula for years.