Special Report: Next Generation Internet Applications
Distinct differences exist between the construction of land-based and submarine cables. Land-based construction costs are heavily weighted by the costs of rights-of-way and trenching. In contrast, an expensive portion of submarine cable construction is the cost of deep-water submersible regenerators. Submarine cables operating at 580 Mbps require digital regenerators every 180 km at a cost of approximately $100,000 per regenerator. Cables spanning the Pacific Ocean from the United States to Japan are over 9600 km in length. The cost of regenerators quickly mounts in such systems. Newer cables like Trans Pacific Cable 5 (TPC-5) use all-optical submersible regenerators and operate at speeds of 1.2 Gbps and higher rates. Reprinted from the May 2001 issue of Lightwave Magazine. Source: Mark Sebastyn, Appian Communications Article: "Optical Ethernet: LAN Finally Meets WAN"
Land-based cables typically house tens or hundreds of fiber strands. Each pair of fiber represents a unique communications channel. Submarine cables rarely contain more than six fiber strands. At any time, only four strands are active, often referred to as "lit strands." Submarine cable designs dedicate two strands as hot standby, protection channels for rapid restoration in case of a regenerator or strand failure. Submarine cables hold the remaining pair as "cold spare" in case manufacturing defects or operational fatigue make one of the primary or protection strands inoperative after the cable is on the sea bottom.
The cost of the regenerators and associated power equipment needed to operate more than two primary and two protection strands becomes prohibitive. Introduction of DWDM and EDFA optical amplifiers to submarine cables increased their capacity immensely. New undersea cable systems operate with high-speed, 10 Gbps electronics, 16-channel DWDM, and SDH add-drop multiplexers. These DWDM submarine cables use EDFA submersible optical amplifiers that create 160 Gbps systems operating over two active strands of single mode fiber.[32] Like their predecessors, these high-speed, transcontinental systems use optical switching in the submersible regenerators and in the DWDM equipment located at the submarine cable-heads to provide rapid restoration to protection strands housed within the same cable.
4.2 Optical Access Networks Access networks provide the "last mile" link between business and residential subscribers and the high capacity core networks. Access networks have always been an important factor controlling the types of services available to subscribers and the rate at which these services can be provided. They provide access to the services commonly used today (e.g., telephony, Internet Service Provider (ISP), ISDN, cable TV (CATV), dedicated private line, and xDSL services). There is a broad array of access service providers within the United States. There are the incumbent local exchange carriers (ILECs) represented primarily by the divested regional Bell operating companies (RBOCs), the new generation of competitive local exchange carriers (CLECs), the franchised CATV companies, and the highly specialized building wiring companies, sometimes called "risers." Access service providers, in part, derive services from the high-capacity core network and deliver these services to their subscribers. They must contend with government regulation, long construction lead times, and large up-front investments as they attempt to reach as many customers as possible.
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