Fiber to the Curb
The term Fiber to the Curb (FTTC) has been used to describe a variety of network architectures in which optical fiber is brought close to the residence, where an optical network unit (ONU) couples the fiber to some form of metallic wiring that in turn leads to the residence (see Figure 5-1). Elsewhere you will see references to technologies such as Fiber to the Building (FTTB) and Fiber to the Cabinet (FTTCab). FTTB refers to the placement of the ONU in a multiple-dwelling unit (MDU), such as condominiums, apartments, and office buildings, where the ONU is placed on the MDU premises and where metallic wiring is distributed to the various tenant dwellings.
FTTCab refers to the placement of the ONU in a cabinet in the neighborhood, such as a street pedestal, from which metallic wiring can connect to individual residences. However, FTTB, FTTC, and FTTCab refer to the same basic architecture—that of an ONU within roughly 200 meters of the residence, with metallic wiring going the final leg to the customer application.
Figure 5-1. FTTC Architecture
The Digital Audio Visual Council (DAVIC) has specified four variations of FTTC, called, creatively enough, Profiles A, B, C, and D. Profile A specifies the use of coaxial cable as the drop wire to the residence and has the highest speed. Relatively little product development has occurred for this form of FTTC. The companies with the coaxial cable, namely the MSOs, are currently preoccupied with their fiber buildouts, and telephone companies have shown little interest in overbuilding their twisted-pair networks with cable. Competitive carriers are more inclined to use VDSL as well because there is simply more twisted-pair in the world to leverage.
Profiles B, C, and D use twisted-pair copper as the drop wire. When configured with phone wire, Profiles B, C, and D are basically VDSL, with minor variations. Those variations are: 1. the standardization work for VDSL is being carried out in the ADSL Forum, ETSI, and the ITU, (G.993.1), whereas FTTC Profiles B, C, and D have been discussed in DAVIC; and 2. VDSL will have a specification for POTS splitting, which is not specified in FTTC.
The valid bit rates and drop wiring (wire between the ONU and the residence) for the various DAVIC profiles are shown in Table 5-1.
| DAVIC Profile | Downstream | Upstream | Drop Wire |
|---|---|---|---|
| A | 51.84 Mbps | 19.44 Mbps | Coaxial cable |
| B | 51.84 Mbps | 1.62 Mbps | Coax or phone wire |
| C | 25.92 Mbps | 1.62 Mbps | Coax or phone wire |
| D | 12.96 Mbps | 1.62 Mbps | Coax or phone wire |
Important vendors of FTTC are Next Level Communications, Marconi (formerly Reltec, now a unit of General Electric [UK], www.marconi.com ), Broadband Technologies ( www.bbt.com , Nasdaq: BBTK), and Alcatel ( www.alcatel.com , NYSE: ALA).
While some standardization work in DAVIC has defined physical-layer and MAC-layer specifications over coaxial cable, most of the work of DAVIC has been superceded by DOCSIS, DVB, and OpenCable when specifying higher-level protocols.
Therefore, the term FTTC is largely a generic or marketing term referring to any access network that brings fiber to within a few hundred meters of the residence. The majority of current standardization is happening under the guise of VDSL or HFC.
Fiber to the Building
Due to the short distances separating the residences within a single multiple-dwelling unit, the initial use of FTTC is MDUs, where the cost of a single ONU can be amortized over multiple paying customers. With Fiber to the Building (FTTB or, perhaps as it should be known, Fiber to the MDU), fiber is brought to the premises of the MDU, and metallic wiring is distributed to the tenants using coaxial cable, phone wire, or possibly Category 5 twisted-pair wiring, commonly used for Fast Ethernet. Depending on coaxial cable or phone wire implementation, the ONU is connected to either a CMTS/DVB CMTS or a DSLAM. The property owner will also likely house application servers to deliver video on demand (VoD) or e-mail services to tenants.
From the property owner's point of view, FTTB provides a new role: that of telecommunications operator. It thereby provides a potential new revenue opportunity. Some apartment owners are considering active deployment of FTTB services, requiring all tenants to subscribe to the service. The theory is that tenants would pay a rental premium in an MDU with high-speed network access. The property owner could even be certified as a competitive local exchange carrier, entitling the owner to interconnection with major carriers and collecting settlements. The rental premium could be split between the property owner and the carrier. Because of the high density of MDUs, there is considerable FTTB interest in Asia.
FTTB can be a major transition factor in moving from today's services to FTTH. It is a relatively smooth transition from ADSL to VDSL/FTTC to FTTH. The carrier can start with lower-speed technologies and proceed to higher speeds by pushing the ONU farther into the neighborhood, from the curbside to the MDU to the home. This can be a measured process that can be funded in part by the maintenance budget of the telephone companies, who enjoy regulatory relief for maintenance costs.
Bell South (NYSE: BLS, www.bell-south.com ) offers a tariffed service for FTTC called Personal Computer/Data Network Access (PC/DNA). The customer premises connect to the carrier via a pair of twisted-pair phone wires, which in turn attach to an ATM-based fiber optic trunk called Integrated Fiber in the Loop (IFITL).
BellSouth has been testing FTTC since 1995. As of this writing, Bell South has deployed FTTC to more than 100,000 homes and plans to add approximately 80,000 homes annually in areas of new developments.
FTTC Issues
FTTC has many of the costs of FTTH without the benefits. For starters, it is costly to deploy, at least for single-family residences. Furthermore, at least in the United States, MDU tenants may not have the interest or the income to justify high-speed Internet access; they may be served just as well by V.90 modem capability.
Standardization issues also are at work. Competing work is occurring in the ADSL Forum, ETSI, and ATM Forum, and there are proprietary schemes as well. Therefore, it is difficult for manufacturers to get the critical mass of customers needed to drive down costs. Meanwhile, cable and ADSL are revving up quickly, garnering the interest of the popular press and the investment community. As of this date, similar momentum has not been achieved with FTTC.
The result is that specialists in FTTC, such as Broadband Technologies, have fared poorly and need to change their business models.