Light ramp 2000 fiber optic local access architecture

Details Light ramp 2000 fiber optic local access architecture Light ramp 2000 fiber optic local access architecture

1997-11-24

2003-04-01

Pascal, Leslie (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200, C359S199200

Reexamination Certificate

active

06542267

ABSTRACT:

CROSS REFERENCES
This section is omitted as there are no other related applications at present.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of this application is multimedia digital optical communications, including telephony, data and video, both switched and non-switched.
2. Background Art
Search of Patent Depository
A search was conducted at the Boston Public Library, a U.S. Patent Depository. A total of 25 listings are on file for patents issued under subject heading: Telephone, Class-LightPhone, subclass—Optical Communications (359/149). No issued patent covers the design and application contemplated by LightRamp 2000. All extant patents predated 1986.
Other Background Art
Attempts to date to employ fiber optics in local access networks have focused on two architectures: (1) corporately fed passive fiber to the subscriber, using Tree and Branch architecture, featuring optical splitting of the main feed signal for distribution to separate destinations, and (2) fiber to the premise, in which individual fibers carry trunk signaling to an interface box, the signals then being converted to conventional telephone or cable drops. The first class of fiber to the residence employs a single main optical feed in which signals for multiple users are multiplexed. The corporately fed optical signal is then split into individual tributaries to each subscriber. In the British Telecom's TPON corporately fed fiber to the home scheme, long wavelength laser driven optics carry time division multiplexed traffic to multiple homes via optical splitter and propagated over a tree and branch structure. At the residence/premise the arriving traffic is then demultiplexed from the incoming high speed stream. Coding in the form of scrambling is utilized to prevent one subscriber from receiving another's messages.
A second type of Fiber to the Home (FTTH) employs a dedicated fiber pair to the premises, using digital trunk signaling. The fibers terminate at an interface unit at the entry to the premise. The remaining connections to telephones or other terminals are made over metallic wire, using conventional DC loop signaling. This type of design is exemplified by the experimental system tested by Bell South/Bell Northern Research at Heathrow, Fla., (Refs. 1 and 2). The Heathrow trial system successfully carried ISDN over a dedicated fiber pair to the premise, using trunk type digital signaling to the residence. The final drop to the telephone instrument from a side wall mounted demarcation interface box reused existing household wire pairs. These pairs carried out DC loop supervision and BORSHT functions generated by a SLIC located in the demarcation box. In effect, this arrangement was a single channel optical digital loop carrier to the residence.
The Heathrow scheme was characterized and limited by the following attributes:
(1) In using conventional tip and ring line supervision over the wire pair(s) extending from the demark unit to the telephone instrument, no new protocols were devised to achieve line supervision.
(2) fibers were employed for the Basic Rate ISDN(BRI) 2B+D service only, with one fiber in each direction. No other service was offered over the fiber pair.
(3) Laser technology was used at Heathrow, resulting in costs that are higher than permissible to satisfy the BellCo's deployment criteria; i.e., that first costs for the fiber must be comparable to a conventional metallic pair in order to justify an installation decision. More economical ELED technology was not then available. This dedication of transmission capacity to specific service, rather than combining multiple services one single medium, characteristic of traditional telephone practice, is not compliant with ITU ISDN goals.
(4) no video or wide band data was carried on the fiber, nor was ATM traffic attempted or feasible. Video (NTSC) was carried over separate coaxial cable in channelized analog form.
The Heathrow experiment, although technically successful, did not, in the opinion of the lead investigators from Bell South and BNR, lead to a design that was ready for introduction to the market. This was due to the a priori constraints imposed by the testers, as well as by the state of the electro-optical art prevailing in the late 1980 time frame. A number of major shortcomings to the overall design, admitted by the researchers, included the basic flaw of substituting fiber for wire on a per service one for one basis. This assumption failed to take advantage of the economics to scale and scope possible with fiber, which allows additional services to be added at minimal marginal cost. No such economies were sought or realized at Heathrow.
Limitations of Hybrid Fiber-Wire Connections to Premise
Almost all previous and current attempts to convey multi-media services traffic (voice, data, video) via fiber to a premise all use fiber to an intermediate nodal concentrator located in the neighborhood. The individual services are then separated and each delivered over separate media to the user. Typically, voice is conveyed over a twisted metallic pair, video is conveyed over coaxial cable, and data over two wire pairs. In every instance field tested to date, telephone service used conventional two wire metallic loops to provide both line supervision signaling and signal conveyance.
The three most frequently mentioned hybrid fiber/metallic designs are Fiber to the Curb(FTTC), Hybrid Fiber/Coax (HFC) and Asymmetrical Digital Subscriber Link(ADSL). In FTTC a node is located in the neighborhood within 800 feet of the premise/residence. This distance, fixed by the signaling capability of the wire pair, means that a local node can reach 16 residences in rural areas and 32 residences in cities. Alternative HFC designs planned by cable MSOs and some LECs utilize fiber to the service area (FSA), with the coaxial distribution reaching out to about 500 homes. In HFC/FSA the required cable run exceeds 1400 feet, requiring line extension amplifiers. A single coaxial cable serves many subscribers with one way video service. In some cases two way data service is also offered. In that event two way amplifiers are needed beyond 1000 feet. ADSL has a different feeder structure, but is nearly identical to FTTC over the last ‘mile’.
The use of a fiber feeder and metallic distribution/drop combination in FTTC and ADSL carries with it the following burdens which are eliminated in the all passive structure of Light Ramp 2000: (a) an active intermediate node is required to convert and distribute the signals and thirty two or more such nodes are required per square mile; (b) the active intermediate node, also called an Optical Network Unit (ONU), delivers dial tone, ringing, and on hook/off hook status, among other line supervisory functions in order to support telephone service. They are known as the BORSHT functions and are implemented by a subscriber line interface circuit (SLIC). The BORSHT functions require a current carrying DC metallic loop and are not portable over fiber, which is electrically non-conductive; (c) to perform its functions the ONU requires an electrical power source, typically provided via a separate power feed from the Telco Central Office or local remote terminal(RT); finally, (d) the two wire metallic drop is severely limited in bandwidth and distance, restricting true broadband services to one direction only over an 800 foot drop. In effect this capability includes only entertainment and highly asymmetrical data retrieval services. Thus, the introduction of true symmetrical two way wide band digital services, requiring greater than 1-2 Mbps in each direction, is severely restricted and is generally precluded over conventional telephone wire over distances exceeding 1000 feet.
In view of their wire limitations, Hybrid Fiber-Coax or Hybrid Fiber-Metallic systems are considered as interim configurations, in anticipation of eventual extension of fiber directly to the home(FTTH) or business premise(FTTB). The Regional Bell Operating Companies have stated that FTTH is the eventual goal. Knowledg

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