Courting enterprise customers is increasingly becoming a part of cable operators' game plans, and vendors are responding with technologies to help operators get their foot in the doors of bandwidth-hungry businesses.

Wooing the business market represents an evolution of the traditional hybrid fiber/coax network model, as operators have typically designed their networks to deliver video services to homes, often bypassing or ignoring business parks and office buildings.

The financial rewards of extending existing cable networks to business customers has sparked the development of several enabling technologies–some new, some old–such as passive optical networks (PONs), broadband wireless and gigabit Ethernet, which are designed to make cable networks more business-friendly.

Yet while exciting new technologies are being developed to help cable companies reach out and touch business customers, Comcast Business Communications and Charter Business Networks, two wholly-owned subsidiaries of cable giants Comcast Cable and Charter Communications, have turned to rather traditional, time-tested technologies.

Sonet rings true for Charter

In Charter's north-central region, Charter Business Networks is putting the finishing touches on an OC-48 (2.5 gigabits per second), Sonet (Synchronous Optical Network) fiber ring network in Wisconsin to serve business customers, according to Marshall Frey, director of operations and engineering. In Minnesota, the company has a few lateral networks that it hopes to fashion into a ring architecture as well.

The Wisconsin backbone, says Frey, is a Cisco Systems-powered network, using the Cisco ONS 15454 optical platform, which supports Time Division Multiplexing (TDM), Ethernet and optical interfaces. With Layer 2 cards, Charter can support IP (Internet Protocol) services as well, says Frey. The key attribute of this platform is its ability to support all data services. Eventually, the backbone will have connections to each of Charter's headends in Wisconsin.

Frey says Charter essentially has two flavors of service, one using cable modems to deliver data service, and the other offering direct fiber connections to customers by building optical networks directly to customers' buildings.

With multiple switch locations in each community served by Charter, the company is able to run fiber from the closest switch location to the customer premises. The switch locations, generally in an optical transition node, can be a Charter Business Networks or Charter Communications facility. Connectivity options include Ethernet, including gigabit Ethernet connectivity; private line services such as T-1 connections; IP-based services and even native ATM (Asynchronous Transfer Mode).

This protocol flexibility has allowed Charter to offer services such as transparent LANs (local area networks) running at 100 megabits per second delivering video, voice and data. The largest market segment served by transparent LAN services is medical organizations, one of which has 19 sites served by Charter's network. "This is something they can't get from other providers," says Frey. The service includes both MPEG-2 video as an analog channel over ATM, in addition to IP voice.

Charter also has been offering video distance learning services in Wisconsin for about five years, serving 38 sites with an MPEG-2 Asynchronous Transfer Mode (ATM) network. The company also has outsourced a 24-hour, seven-day-per-week network operations center which uses SNMP (Simple Network Management Protocol)-enabled traps and Hewlett-Packard's OpenView platform to monitor every device and element on the network, from LANcity modems to Cisco and ATM equipment. Charter is in the process of building a regional operations center to bring those monitoring duties in-house before the end of the year.

Future implementations of the network may include PONs, as Charter has reviewed the technology of a number of companies, says Frey.

ATM: The old reliable

While not new to cable TV engineers, passive optical networks (PONs) are becoming one of the tools available to operators to extend their existing HFC networks to businesses' doorstep. PONs are appealing to operators because they require no electronics between the headend and the termination point. Comcast Business Communications is using PONs to augment Comcast's cable network to reach businesses with high-bandwidth optical fiber, says Sherrie Walters, senior manager of corporate communications.

"We actually have a number of different access technologies that we use," including enlisting the cable division to price and (if the numbers jive) build traditional HFC cable network to offices, says Stephen Linskey, vice president of technology development for Comcast Business Communications. At the high end, Comcast will send fiber directly to customers through an integrated access device to deliver OC-3 (155 megabits per second) and higher bandwidth services.

The company is moving quickly to capture business customers as it finishes networks in Baltimore, Philadelphia, and southern New Jersey, and is building networks in northern New Jersey, Delaware, Detroit and in northern Virginia/ Washington D.C., to be completed by the end of the year.

"In a time when many technology companies are downsizing . . . we're doing well finding customers who need these services," says Walters.

For customers seeking more bandwidth than what a cable modem can deliver but less than the punch offered by fiber, "we see PONs as fulfilling the needs of customers with multiple T-1s," and who require several megabits-per-second data rates, says Linskey. He sees "a wide class of customer interest in the 2 to 30 megabit-per-second range," and notes that those customers can be economically served by ATM PONs.

Linskey explains that Comcast Business Communications leases fiber from Comcast's cable division to support the PONs and effectively builds out the passive networks from an existing optical node in the cable HFC plant to a "PON serving area," which is a carefully engineered building within an office or business park.

Before Comcast Business Communications builds out its PONs, Linskey says, it conducts a demographic study to identify buildings and aggregations of buildings that would be suited to its services. Once right-of-way issues are resolved and drop locations negotiated with building and land owners, the PON is built and a sales force blankets the area.

A PON-type architecture was selected because Comcast is providing both voice and data services, and in Linskey's view, the most economical way to provide high-quality voice is with a circuit-switched ATM infrastructure. If there is a shortage of fiber from the headend to a node in a given targeted area, Comcast will use dense wavelength division multiplexing.

In an ATM PON configuration, an ATM switch is located at the cable network headend, while an integrated optical terminal at the customer premises receives the signal. There are a few distance constraints with an ATM PON, says Linskey, most of which are power-driven and depend on how many couplers–devices that split and multiplex optical signals–are used in a given distance. "Twenty kilometers seems to be a natural upper bound," says Linskey.

In building its PON networks, Comcast Business Communications is using gear from Quantum Bridge Communications, which makes an optical access switch and optical terminal unit.

Despite its reliance on ATM PONs, Linskey points out that, "we are constantly looking at a wide range of technologies," including gigabit Ethernet, which it is testing, along with other technologies, in its laboratories. Whether or not Comcast Business Communications deploys gig-E is up to the company's product developers, but once customer demand is demonstrated and they give the OK, "we'll be ready," Linskey notes.

Not your typical PON

While acknowledging that PONs are the least expensive way to get fiber to businesses, Burnie Atterbury, senior director of product marketing for Alloptic, believes that Ethernet provides a more flexible protocol than ATM and delivers more than twice the bandwidth for PON applications. Earlier this year, Alloptic introduced its second-generation IP gigabit Ethernet PON equipment, including a central office or headend chassis and an optical network unit (ONU). The chassis is designed to be the hub point between the local loop and the wide area network and is capable of serving up to 1,024 ONUs with 1.25 gigabits per second of symmetrical bandwidth.

According to Atterbury, the platform can deliver up to three wavelengths, and services such as T-1, 64 kilobit pulse-code-modulated telephone service, video and, of course, Ethernet.

Alloptic has trial agreements with (unnamed) MSOs that should commence this year, Atterbury says. Last year, Scientific-Atlanta announced it would invest up to $8 million in Alloptic and co-develop access services.

Also moving forward with PON trials is Terawave Communications, which said in a release that Shaw Communications, among other telecom providers, would be testing its optical access PON gear.

Gig E vs. PON

Arguing against the utility of PONs is Chris Bonang, senior director of market development for Harmonic Inc. Bonang advocates the installation of Ethernet switches in optical nodes and Ethernet switches at the customer premise and crafting an Ethernet overlay network on top of the RF HFC network using a separate fiber.

Bonang cites the proprietary nature of PON architectures and questions whether a point-to-multipoint Ethernet PON actually is standardized Ethernet, because technically, Ethernet only supports point-to-point links over fiber. In addition, Ethernet node switches include two upstream ports for redundancy, and although PONs typically deliver split fiber to end-users, Ethernet switch architectures can bring dedicated 100BaseT Ethernet connectivity directly to businesses, using less fiber than PONs in the process.

Wireless bridges

Another company working with Scientific-Atlanta is BridgeWave Communications, which has developed a broadband wireless technology designed to let cable operators extend the reach of HFC networks to businesses. BridgeWave, according to Gregg Levin, senior vice president of marketing and business development, chose to work in the millimeter wireless range–between 20 gigahertz and 42 GHz–because of the higher bandwidth capacity of that range. The technology is targeted to HFC systems that come close, but don't actually reach business parks or office buildings. If an operator, positioned at a network node, can see an office or business park, then he or she can send a millimeter signal to that customer.

To best integrate millimeter wireless systems into a DOCSIS-based network, BridgeWave developed a modulation technology called Signal Code Modulation (SCM). Levin says SCM is a mixed, analog/digital technique designed to seamlessly send higher-order quadrature amplitude modulation (QAM) over lower-order QAM wireless links.

By combining the transparency of analog modulation with digital modulation's robustness (and ability to use forward error correction), SCM converts the original signal into digital and analog components. An SCM modulator uses the digital component to create a low-order QAM symbol, with the analog value representing the fine detail of the original signal and also representing the difference between the original signal and the digital approximation. After transmission over the wireless link, the SCM demodulator reconstructs the original signal from the interleaved analog and digital symbols, which contain the approximate digital and detailed fine analog values of the waveform. The reconstructed signal can then be fed directly into a cable modem.

Levin notes that video can also be sent over this wireless bridge in addition to as many as four upstream DOCSIS channels. With digital video delivery possible, an operator may choose to offer enterprises a package of business-oriented video programming, such as CNBC and C-SPAN. Levin points out that BridgeWave will be conducting field trials this quarter and will demonstrate integration with Scientific-Atlanta transmission gear. The technology will also be installed at S-A headquarters.

With several vendors developing both new and mature technologies, cable operators looking to serve businesses have an ever-growing list of tools to make high-speed connections.