Ameritech has committed to providing broadband access in its region, using a hybrid optical fiber and coaxial cable architecture that can support a wide range of applications, including video services similar to current cable television, expanded digital multicast services, interactive multimedia services, and high-speed data services. By providing a platform for a wide range of applications, a cost-effective solution is achieved (economic data are provided in a later section).
Construction is expected to begin in 1995 in the Chicago, Cleveland, Columbus, Detroit, Indianapolis, and Milwaukee metropolitan areas, ramping up to an installation rate of 1 million lines per year by the end of 1995 and continuing at that rate to deploy 6 million lines throughout the region by the end of the decade. In December 1994, the Federal Communications Commission granted approval for Ameritech to construct the first 1.256 million lines, distributed among the metropolitan areas as follows:
The system architecture employs a hybrid transport network of optical fiber and coaxial cable. Signals are delivered over Ameritech's ATM network to video serving offices, each serving 100,000 to 150,000 customer locations. The signals are then distributed on optical fiber to individual nodes, each serving a total of 500 customer locations, not all of whom may actually subscribe to the service. From each node, the signals are distributed on four parallel coaxial cable systems, each serving 125 customer locations. With this architecture, the coaxial cable network is less than 2,000 feet in length and contains, at most, three amplifiers to any customer location.
The signal on both the optical fiber and the coaxial cable is a broadband analog video signal. The initial deployment will have a bandwidth of 750 megahertz, with capability for upgrade to 1 gigahertz when the reliability of such electronics becomes proven, yielding 110 channels of standard 6 megahertz video bandwidth. The allocation of these 110 channels to various applications is flexible and will be adjusted to satisfy user needs. Based on current estimates, approximately 70 of the channels will carry analog video signals for applications similar to current cable television, including basic and premium channels and pay-per-view. The remaining, approximately 40, of the channels will be digitized using 256 quadrature amplitude modulation, yielding a usable bit rate of over 36 megabits per second on each channel. Approximately 30 of these digitized channels will be used for multicast services, with multiple users viewing each transmitted program. Approximately 10 of the digitized channels will be used for switched interactive services, for which each user requires a dedicated digital circuit for the duration of the session.
On the digitized channels, the video signals will be compressed using the MPEG-2 compression standard. Depending on the particular application, each such signal will require a fraction of the 36-megabit-per-second or greater capacity. The signals will be multiplexed at the video serving offices and demultiplexed by the customer premises equipment, using the MPEG-2 transport layer protocol.
In addition to the downstream capacity, the system will have an upstream capability provided by up to 20 channels, each of 1.5-megabit-per-second capacity. Depending on local conditions of noise and interference, it is expected that at least 15 of these will be usable on each coaxial cable system serving 125 customer locations.
The system is intended to be a platform for a wide range of applications. Accordingly, the customer premises equipment may be a set-top box for use with a television set or an adjunct to a personal computer.