Cable Networks: A Primer

From an antenna on a mountain to cable telephony, in 50 yearsPage 3: A Look in the Headend

Topologies change, but the headend is still the focal pointPage 4: Consolidation and Expansion

The big get bigger… and regionalized

System capacity growsPage 5: The Voices of Cable

TDM or VOIP?Page 6: Taking Care of Business

Cable’s three approaches to the commercial marketPage 7: Difficult Choices Ahead

So what are they going to do with these sophisticated platforms?Page 8: More Modems Coming

It’s a Docsis and PacketCable WorldPage 9:New Toys

The unending parade of widgets continues

Next Page: Cable Timeline

About the author: Carl Weinschenk ([email protected]) is a freelance writer specializing in cable, telecommunications, and Internet technology.

The cable television industry is almost as old as the commercial television industry itself, which only thrived after World War II.

Here are some important dates in the technical history of the cable television industry.

1948: Cable television begins in Pennsylvania and Oregon. Coaxial cable and amplifiers bring distant broadcast signals from hilltop antennas to customers.

1982/83: Times Fiber introduces a fiber-optic-based hub designed for use in apartment buildings.

1984: General Electric (NYSE: GE) introduces 2:1 video compression.

1986: Home Box Office scrambles its signals.

1987/88: Oceanic Cable, now part of AOL Time Warner Inc. (NYSE: TWX), deploys an amplitude-modulated system in Honolulu. The approach, which is reliable, cheap, and capacious, is the basis for today’s hybrid fiber/coax (HFC) systems.

1989: General Instrument Corp., now part of Motorola Inc. (NYSE: MOT), compresses a digital signal into the North American Standard 6 MHz channel.

Jones Intercable, now part of Comcast Corp. (Nasdaq: CMCSA, CMCSK), introduces a redundant HFC topology.

1990: In the FCC’s HDTV proceeding, General Instrument’s eleventh-hour submission of a digital concept leapfrogs analog approaches.

1992: Tele-Communications Inc. (now part of AT&T Broadband) Time Warner, and Viacom (NYSE:VIA) (also part of AT&T Broadband, by way of TCI) begin rebuilding to 500-600-home HFC nodes.

1993:The modern direct broadcast satellite (DBS) industry is born, with DirecTV and United States Satellite Broadcasting using high-power K-band satellites to reach 18-inch dishes.

A group of vendors and Time Warner create the Full Service Network (FSN) in Orlando, Florida.

1994: Cox Communications Inc. (NYSE: COX) unveils a topology that passes customers with double self-healing rings.

MPEG 2 (Motion Picture Experts Group) chosen as standard for compressing and transmitting compressed signals.

Concept of regionalization via Sonet and ATM gains ground.

1995: Cable telephony over cable testing begins.

Operators begin aggressive cable modem development.

1996: Six of ten largest operators have modem services. @Home and Road Runner launched.

1997: CableLabs launches Multimedia Cable Networks System/Data Over Cable Service Interface Specifications (MCNS/DOCSIS) and OpenCable projects (see Cable-Modems.Org).

Operators begin deploying DWDM (dense wavelength-division multiplexing).

1999: Various cable telephony trials and projects start.

2000: Trials of open access – through which cable modem subscribers have a choice of broadband ISPs – begin.

2001: Docsis 1.1, PacketCable specs ready, implementation likely in 2002.

AT&T Broadband and Comcast announce merger in a bid valued at about $70 billion. If completed, new company will have more than 22 million customers in 41 states.

Cable commitment to high-definition television remains light, though its commitment to standard-definition digital television and video-on-demand accelerates.

Excite@Home implodes (see 2001 Top Ten: Services ). Customers will be served until early 2002, except for AT&T Broadband, which is cut off in late 2001 and scrambles to serve customers. In the main, it succeeds in replacing the Excite@Home service.

Parallel Docsis 1.1 and PacketCable specs from CableLabs are essentially complete, enabling testing by the R&D lab and subsequent manufacture by vendors. Commercial rollouts expected in 2002.

North American cable operators add more than 1 million cable subscribers during the third quarter – more than double the number of new DSL customers. Operators now serve more than 8 million customers.

Future milestones

2002: With minor demands to sell some systems, the government approves the Comcast/AT&T Broadband merger.

Cable’s interest in the business market continues to grow. The growth is fueled by technical advances and softness in the residential market. These advances focus on using the last-mile cable infrastructure as an underpinning for dedicating large amounts of bandwidth to individual businesses.

Next-generation, standards-based gear continues to emerge. Trends include miniaturization and collapsing of multiple functionality – for instance, high speed data and cable telephony – into a single unit.

Cable telephony adoption picks up. A majority of operators opt for hybrid approaches in which the cable portion is in the IP format and the wide-area network uses traditional TDM (time-division multiplexing) techniques.Sources: The Cable Center, Cable Datacom NewsFurther reading:

Next Page: A Look in the Headend

Conceptually, the headend remains the heart and soul of a cable system. The advent of fiber and the regionalization of the industry have drastically changed precisely what a headend is, however.

In the past, the industry comprised thousands of small islands of self-contained cable systems. Indeed, that is still the model in many rural and exurban areas that don’t produce enough revenue to interest corporate types in modernizing.

In the suburban and metropolitan areas, however, the definition of a headend has changed in several key ways. First, many have disappeared, as companies use Sonet, DWDM, and Asynchronous Transfer Mode (ATM) to link their systems. Some headends have been demoted from fully featured affairs to partial facilities that provide redundancy and a small number of functions.

These scaled-down headends are sometimes called hubs. Headends and hubs, in turn, are connected to nodes that serve pockets of residences. Today, nodes generally serve 500 or more homes. Designers, aware that penetration increases could eventually require reduction in node sizes, have made the subdivision of 500-node homes to two 250- , four 125-, and eight 75-home affairs a matter of simply moving and changing electronic devices already in the field.

Other elements of a cable headend are more stable. Here’s a look at what can be found in most of them:

Video

Operators get their programming from many sources. These include dedicated point-to-point connections (from local broadcasters, for instance), satellites (for national feeds of cable and broadcast programming), the operator’s own studios (local origination and local access – cable-sponsored community programming and carriage of local events – are requirements of virtually all franchise agreements), and gear that inserts local advertising into commercial programming feeds.

HDTV (high-definition TV), SDTV (standard-definition digital) programming, and VOD (video-on-demand) each requires its own specialized equipment. The digital element of a headend is often supplemented by statistical multiplexing gear that can delegate capacity on a real-time, as-needed basis. For instance, more capacity can be dedicated to broadcasting an HDTV basketball game than to a standard-definition digital talk show, but those deployments can be automatically reversed when demand proportion changes (during commercials, for instance).

All these signals arrive in a variety of formats. Equipment at the headend does several things. The main tasks are to impress the signals into the proper modulation schemes – amplitude modulated vestigial sideband (AM-VSB) for analog channels and, most often, quadrature amplitude modulation (QAM) for digital signals. All these signals must then be sent through an upconverter, which places them on the desired frequency (channel position). They are put through a combiner, which melds them together, and then transmitted.

Data

High-speed data requires several pieces of equipment. The linchpin is the cable modem termination system (CMTS). This device has two main functions: It trades packets with, and manages, modems in the field and connects to networks – such as the Internet or private IP networks – outside the cable system.

Other key data gear includes Dynamic Host Configuration Protocol (DHCP) servers (which assign IP addresses to modems), Domain Name System (DNS) servers (which translate domain names into IP address), email servers, content caches, and time-of-day servers.

As operators get into either voice over Internet protocol (VOIP), circuit-switched telephony, or hybrids, various other pieces of equipment – such as GR-303 interfaces and the as-yet vaguely-defined softswitch category – may be necessary. The GR-303 is a gateway between a traditional TDM system and the public switched telephone network (PSTN), while a softswitch translates between the IP network and the TDM-based network and helps import service features. Operators employing TDM systems also need access to a class 5 switch.

Common Elements

There are common elements in addition to the amplifiers, modulators, and combiners. Fully-featured headends usually have two types of laser transmitters. 1310nm lasers are used for local distribution, while 1550nm lasers handle long-haul ring transmission tasks. Other pieces of gear include status monitoring, billing, operational support system/business support system, air conditioning, and backup powering equipment.

Nodes

In many systems, the node is the collection point closest to the end user. The main task of a node is to translate light impulses to electrical signals for delivery to premises or, conversely, converting from electrical to optical for the trek back to the headend. In some cases, CMTS functionality will find its way to the node.

Further reading:

Next Page: Consolidation and Expansion

During the past ten years, the cable industry has undergone two interrelated transformations: It has consolidated and rebuilt its plant.

Table 1: Cable Consolidation

In addition to the relative growth of the top companies, three of 1995's top five have themselves been acquired:

Now AT&T Broadband itself is in play. The top suitors are Cox Communications Inc. (NYSE: COX) and Comcast Corp. (Nasdaq: CMCSA, CMCSK).

Thus, the cable industry superficially resembles the Baby Bells of a decade ago: Much of the territory – including virtually all of the highest revenue-producing metro areas – are controlled by a small group whose decisions essentially dictate matters for everybody else. The less desirable areas are left to smaller companies to serve. The consolidation has led to uniformity in overall design characteristics.

Even if these big companies don’t do everything precisely the same way, they typically use a mix of DWDM, Sonet, and ATM to ring their metro areas. The rings carry both digital and analog data, which is a mix of some or all of the following: traditional cable programming, digital programming, HDTV, video-on-demand, VOIP, TDM (traditional) phone, Internet content for cable modem subscribers, streamed media, and internal communications.



Ten years ago, each pocket of cable subscribers would be served by a unique headend. Many of these headends have been eliminated or their functions curtailed, and the subscribers they served are now serviced off the ring.



In the local area, the prehistoric tree-and-branch systems have evolved into topologies in which fiber is delivered to nodes or hubs, where the signal conversion from optical to electrical (in the downstream path toward customers) or electrical to optical (upsteam to the headend) takes place. From that point, the radio frequency (RF) signals travel coaxial cables to premises. These paths traverse no more than three or four amplifiers. The local area is two-way, with bandwidths of 550 MHz, 750 MHz, or 860 MHz. Many systems are 1-GHz-capable.

The industry’s rebuilding of its last mile is entering the home stretch. The National Cable & Telecommunications Association estimates that 92 percent of its plant is at least 550 MHz (about 83 downstream channels) and 81 percent at 750 MHz (about 116 channels) or more. Many operators are above these figures, and compression techniques can drastically multiply the number of actual programs being transmitted on each channel.

Interactive capabilities are also growing. Today, about 75 percent of subscribers are passed by activated two-way plant capable of supporting interactive services.

Next Page: The Voices of Cable

Cable executives generally agree that there is a tremendous amount of money in voice. But that’s about where the agreement ends and the debate begins.

On one side is the group that feels that to get into the game in a meaningful way operators have to jump right in with traditional circuit-switched operations and worry about emerging technologies later. The rationale goes like this: Voice over IP is too far off and too speculative, especially if the goal is to provide an alternative to small and medium-sized businesses that will deliver mission-critical performance. The opportunities are now, and it could be a half-decade before the development and implementation cycle is truly complete.

Then there are those that feel VOIP is worth the wait. Getting into traditional TDM services, they say, is not prudent, simply because it will demand the replication of the infrastructure underlying the incumbent local exchange carriers (ILECs) with which they would compete, including massively expensive class 5 switches. It’s one thing to be born a dinosaur, they say, but why opt to become one?

A third option is to somehow combine circuit switched and VOIP in a hybrid manner that can eventually migrate to IP. This, of course, looks like the winner. But all these choices – and the fact that operators have a bountiful choice of other services to offer – has led to a less-than-enthusiastic entrance into the voice business by cable operators. In general, VOIP testing is ongoing and new TDM rollouts are on hold, though operators are trying to deepen offerings in areas in which they do offer TDM service.

However, for a few years now, cable has been saying that its goal is to be a voice player – and it’s getting close to put-up or shut-up time. The 18 months ahead will likely see a concerted push, based on Docsis 1.1 and PacketCable, on the cable plant (see Page 8 for details) and TDM techniques outside the system.

Further reading:

Next Page: Taking Care of Business

The cable industry is has its sights squarely set on the small and medium-sized business (SMB) market.

The cable industry has always been infatuated with this market, but today the goal seems more realistic. Operators now have the infrastructure and multichannel acumen to make a more realistic play for business customers. It doesn’t hurt that the traditional CLECs, after introducing the concept of competition for local telephony services, are struggling.

Companies such as Time Warner Telecom and Adelphia Communications have long offered CLEC services. These companies, however, depend more on their parent companies’ name recognition and pocketbooks than their infrastructure.

Another group, featuring Cox Business Services, Comcast Business Communications, and Charter Business Networks, is more tightly integrated with their parents’ ring topologies, high-speed backbones, and last-mile coaxial cable.

A more amorphous third group – which includes members of the first two – are going after the low-hanging fruit of small businesses and SOHOs by offering commercial services through their residential units. Road Runner, Time Warner Cable’s house broadband ISP, is putting increased emphasis on offering business services.

Not only is the topology more sophisticated, but operators, sensing the opportunities, have regionalized. This makes cable telecom services more attractive to healthcare, education, government, and other sectors that tend to have more than one facility in a particular geographic area.

The SMB market will be a big target for cable operators during the next few years. Cox and Comcast recently created separate divisions to address this market, and other operators – such as Charter, which is owned by Microsoft co-founder Paul Allen – are headed in the same direction.

Here is a selection of players in the nascent cable SMB sector:

Table 2: In Business

Next Page: Difficult Choices Ahead

Cable’s platform unquestionably has the flexibility to deliver a wide variety of new services. This ubiquity itself brings challenges, however.

When cable operators only delivered analog video, the revenue stream was essentially guaranteed. The massive rebuilding and upgrading of the past ten years – which was financed against expectations of increased revenues – hikes the risks.

Cable is suddenly in the big leagues, and a misreading of subscribers’ and potential subscribers’ desires will have dire consequences.

There is commonality among the basic components of many of the potential new services. However, there comes a time when operators must decide precisely what services they want to offer. Here is an overview of some of those choices:

Table 3: Service Pros and Cons

Next Page: More Modems Coming

Among cable’s most important ongoing issues is the rollout of products incorporating standards created by the industry operator consortium, Cable Television Laboratories Inc. (CableLabs).

In the 1995-1996 time frame, cable operators realized that they were in the enviable position of using their plant to offer a high-speed alternative to dialup Internet access. Instead of dickering over standards at that point, they rushed out a generation of pre-standard modems. In this way, they were able to quickly tap into the general dissatisfaction with dialup service and establish themselves as the team to beat in broadband connectivity. It is an advantage they have yet to relinquish.

Simultaneously, they began working on standards-based modems. This led to the first standard, Docsis 1.0, which is the basis for most of the cable modems in homes and businesses today. It is a no-frills, low-security, best-effort affair. It does one thing really well, however: It gets customers to fork over about $40 per month.

The second iteration of the Data Over Cable Service Interface Specifications – Docsis 1.1 – is coming to market this year (2002). The main advance of Docsis 1.1 is the addition of quality of service (QOS) and class of service (COS) capabilities. This will enable operators to offer differentiated services such as standards-based VOIP and streaming.

In Docsis 1.0, modems are identified to the headend gear – called a cable modem termination system (CMTS) – by service identifiers (SIDs). This one-size-fits-all designation doesn’t enable different types of service. Docsis 1.1 solves this problem by replacing SIDs with service flows. Service flows, as the name suggests, enable the system to distinguish among packets given different priorities and, if need be, interrupt processing of low-priority packets in favor of those designated as more urgent. Thus, operators now can differentiate between residential surfing and latency- and jitter-sensitive VOIP calls and charge for those sessions accordingly.

PacketCable is, in essence, the effort to add actual services to the QOS and COS framework that Docsis 1.1 creates. PacketCable 1.0’s first service will be VOIP. In later PacketCable 1.x and 2.x versions, such applications as streaming, realtime gaming, and voice/video conferencing will be available.

CableLabs certifies vendors’ gear as standards-compliant in cycles it calls “waves.” Here’s how the future looks for PacketCable and Docsis 1.1 rollout. So far, two Docsis 1.1 modems and two Docsis 1.1 CMTSes have been given the CableLabs seal of approval. Testing of PacketCable gear is expected this year.

CableLabs will also finalize the core design of Docsis 2.0 next year. This spec will enable transmission capacity of 30 Mbit/s in the usually constrained upstream (end user to headend) path. This compares with about 5 Mbit/s for Docsis 1.0 units and 10 Mbit/s for Docsis 1.1 gear. Docsis 2.0 will achieve the higher data rates by employing two advanced modulation techniques: advanced frequency agile time division multiple access (A-TDMA) and synchronous code division multiple access (S-CDMA).

Next Page: New Toys

Here is a non-exhaustive list of some of the interesting young companies that cable insiders are watching.

Advent Networks

Alopa Networks Inc.

CedarPoint Communications Inc.

Channelogics

ClearBand

Emperative Inc.

Jedai Broadband Networks Inc.

Narad Networks Inc.

Navic Networks

Stargus Inc.

Wave7 Optics, Inc.

Xtend Networks Ltd.