Residential gateway builds a bridge to future fiber-optic networks

April 1, 1996

Residential gateway builds a bridge to future fiber-optic networks

The residential gateway fiber-optic bridge is an architectural concept intended to provide customers with an easy migration from one communications technology to another when market forces such as price, features and services suggest such a move. It hides the complexity of user interfaces and adds functionality to the selected technologies by allowing the customer to easily adapt network services to his needs.

clifford r. holliday

B&C consulting services

The cornerstone principle of the residential gateway focuses on an adaptation of personal computer technology. A bus is used to connect network interface units (NIUs) and customer premises interfaces (CPIs) (see Fig.1). The NIUs are installed on a one-for-one basis to match the desired incoming networks. Therefore, these units are available for asynchronous transfer mode (ATM), direct broadcast satellite, telephony, and cable-TV networks, among others. CPIs are likewise provided to match the devices that deliver the home services. Similarly, television sets, video cassette recorders, telephones and computer CPIs are needed, among others.

All signal transmissions are converted to a digital format to cross the residential gateway bus. On the home side, the transmissions are converted to analog format, if necessary. This gateway aims to provide a standardized connection point for the interface between external networks and the user`s networks and devices. It acts, therefore, like a bridge device that will allow users to move easily from today`s networks and devices to those planned for the future.

Unprecedented demand for services

Passage of the Telecommunications Act of 1996 is expected to create an unprecedented demand for the delivery of voice, video and data communications over fiber-optic cables to businesses and homes. In addition, the existing fiber and copper information-delivery networks and technologies--implemented by both the telephone companies and the cable-TV operators--are expected to be redesigned, upgraded or paralleled so that both types can carry the other`s traditional signal transmissions.

Moreover, many new entrants are expected to invade the information-delivery network business. These new entrants are anticipated to use new network technologies. What`s more, traditional rivals are anticipated to join forces for mutual benefits in a highly competitive communications marketplace. For example, AT&T and MCI--two of the three major long-distance carriers--are talking about partnering to build a new home delivery network.

Such unusual business arrangements are also often associated with unique technology approaches. As a result, competitive communications companies are expected to evaluate and implement all possible voice, video and data service delivery technologies. These technologies include ATM, asynchronous digital subscriber line, synchronous optical network, hybrid fiber/coaxial-cable networks, personal communications services, and fiber-to-the-home, among others.

Some technologies will incorporate digital compression, others will not; some will move to all-analog, others will opt for all-digital; some will contain both analog and digital, and others will start as analog and migrate to digital.

To achieve financial success, the telecommunications marketplace must focus on the customer`s needs. For example, studies reveal that 70% of home subscribers cannot program a video cassette recorder. Consequently, customer interfaces must be user-friendly.

Local network convergence

Cable-TV and telephony networks are converging steadily to meet the customer`s needs (see table). The movement is also encompassing the use of more fiber (that is, fiber-optic cables are being installed deeper into the loop) and digital circuits. At the same time, intelligent control devices are also moving toward the customer.

Results of this migration are indicated in the similarity of network architectures being installed by the telephone companies and cable multiple system operators. If the architectures were modified slightly (that is, if the telephony central office were changed to a cable headend and telephony remote switches to cable neighborhood hubs), the networks would be virtually identical.

The residential gateway fits the migration to fiber in two ways. First, it could be viewed as the ultimate move toward the customer, with fiber terminating on the residential gateway at the customer`s location. Second, it provides the interface element often overlooked in broad views of network architecture--the bridge device.

The residential gateway allows analog and digital, as well as fiber and copper networks (of various types), to coexist. When the final move to fiber and digital is made, it is only necessary to replace the NIU card in the residential gateway and the network is ready for use.

The move of intelligent capabilities to the customer is somewhat subtle, and it has no parallel between the telephony and cable networks. In telephony networks, the intelligence has followed the move of the first switching point out of the central office toward the customer. The first remote switching devices were dumb and depended on the central office to provide the necessary intelligence. As memory and processors vastly improved in price and performance, intelligence was moved into the switching devices.

In cable-TV networks, intelligence has always been emplaced at the customer`s location, as in remote control units for television sets. However, as new broadband services such as video-on-demand and switched digital video have been introduced, cable-TV networks now resemble the telephone networks in operation.

The residential gateway puts the last network intelligence point at the customer`s location (see Fig. 2). The placement of this intelligence at the customer site offers the opportunity to literally customize each customer`s telecommunications services based on individual desires, tastes, and home equipment. It also allows rapid change by the customer in network-delivered services, home devices or both. In addition, it creates functionality by allowing the customer more flexibility in using combinations of devices and network-delivered services.

The Gilder Microcosm

In his book Microcosm, George Gilder outlined his Law of the Microcosm. This stated that the economics of technology developments were driving many industries toward a decentralization of capital investment. This book correctly predicted the outcome of many of what were then just-developing technology trends, such as widespread use of the Internet and the cheap, dumb PC.

In the telecommunications arena, Gilder`s `law` has been interpreted to be a network that provides high bandwidth, all the intelligent devices at the ends--the nodes--of the network, all fiber-optic cables and all digital equipment. This network represents the residential gateway migration path, at least from the viewpoint of the customer. By incorporating the customercentric concept, the residential gateway focuses on the customer`s control capabilities rather than on the network. The intention is to remove barriers that keep the customer from making full use of fiber-optic digital network technology.

Further developments

The residential gateway is not a finished entity; it is still in the concept stage. Work has begun on many fronts (in standards bodies, at interested manufacturers, and in the laboratories and test beds of interested carriers) to extend the concept to prototype products. Some important next steps in terms of technology evaluations and decisions are as follows:

Bus selection. The first requirement for bus selection is to provide sufficient data-transfer capability (from NIUs to CPIs) to allow the coexistence of envisioned broadband services. The highest bandwidth requirements for the backplane will thus be determined by video services, which require more data transfer than other services. In addition to a bandwidth requirement that can handle at least 200 mega bytes (four slightly compressed video signals), the backplane must be robust and capable of long-term support. It must also provide expansion slots for home use.

Some industry-standard interface buses used for PC, both current and emerging, should fit the requirements. Specifically, the peripheral component interface (PCI) and IEEE 1394 (also known as Firewire) are two buses that have been assessed as meeting the envisioned requirements. An issue with these buses, however, might be the number of expansion slots that can be used. Consequently, the final gateway design might need multiple buses. For example, the bus combination might be the PCI bus for high-speed requirements and a low-speed bus (for example, the Universal Serial Bus) for telephony and low- to medium-speed data requirements.

Processor and memory selection. The selected microprocessor should be one that is (or will be) in high-quantity production to keep costs down and to allow the use of off-the-shelf auxiliary support chip sets. These requirements dictate a mass-produced PC processor and 8 megabits of RAM. To minimize maintenance, no hard disk is planned at this time.

Operating system selection. Candidate operating systems include OS/2, OS/9 David, Unix, Windows NT and Windows 95. An off-the-shelf operating system is suggested for the same reasons as the off-the-shelf processor: It should be as decoupled as possible from the selection of the processor and the backplane to prevent the risk of standards going in different directions.

Operations-support considerations. The residential gateway concept attempts to place most of the hardware at the outer limits of the network. To avoid network service disasters, it is mandatory that analysis be concentrated on the issues relating to network operations, administration, maintenance and provisioning. The deployment of the residential gateway is expected to place millions of intelligence points in the network rather than thousands, as is currently the case in telephone central offices and cable-TV headends, or tens of thousands, as would be the case with many of the developing networks (HFC, fiber-to-the-curb, etc.). It demands a methodology for the two-way transmission of operations data between the residential gateway and the network operator`s center. It will also require a means at that center to access the individual data streams in order to take appropriate action for individual residential gateways.

Ultimately, the residential gateway NIUs should be compliant with the Telecommunications Management Network interface specifications. A new specification (GR-2833) is currently being developed by Bell Communications Research and other standards groups. This specification allows the transfer of operations, administration, maintenance and provisioning information between network devices and central systems.

Legislation is now in place to allow full development of a highly competitive communications marketplace. The last step needs to be taken to bring the customer into the network design process. Action is needed on the part of the industry and the standards bodies to bring the residential gateway to the same stage of development as the transmission hardware and software proposed for many of the new networks. u

Clifford R. Holliday heads B&C Consulting Services, a technology planning consultancy in Colleyville, TX.