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A wave of cable modem chips meeting Revision 1.1 of the Data Over Cable Service Interface Spec (Docsis) enables the type of functional integration that CableLabs is pushing in its PacketCable and CableHome programs. In theory, this should mean shunting aside the standalone cable modem in favor of integrated home routers or packet-telephony multimedia terminal adapters. But service providers aren't so sure they like the idea.The integration effort is backed by leading suppliers of single-chip cable modem ICs, such as Broadcom, Conexant, Imedia and Texas Instruments. Specialist processor vendors, such as Sorenson Technologies Inc. with its single-chip video-telephony-over-Internet Protocol solution, see integrated multifunction boxes as key to delivering peripheral functionality in dedicated chip-level hardware.
It's rare to see semiconductor vendors, leading cable modem OEMs and CableLabs (Louisville, Colo.) marching in unison to encourage integration at both the card and bundled-system levels. But cable TV multisystem operators (MSOs) are dragging their heels, for two main reasons.
First, if they lease such systems directly, they are afraid they will take on liability for hackers who get through firewalls, or for VoIP phones that don't operate as well as analog circuit-switched phones. But pity the poor consumer who goes to a retail electronics store to buy a Docsis-certified router off the shelf. Despite working with CableLabs, vendors such as Linksys and D-Link are finding that certification does not mean all MSOs are willing to accept such equipment-or even to supply a MAC address for customers who install routers themselves.
The problem is aggravated as home networking becomes more popular, and thus gives MSOs their second reason to hesitate. Developers in the residential-gateway environment are assuming that a successful home network will be based on an 802.11 wireless LAN link and a network-address translation (NAT) software shim to allow several nodes to share an IP address. Because MSOs have ferreted out a handful of customers who use a wireless LAN access point and NAT program to provide broadband access to their whole neighborhood, a few operators have actually gone so far as to bar customers from using NAT translation with their home modems.
OEMs and representatives from the CableLabs CableHome program are unified in saying that such a policy is untenable in the long run. But Marcello Vieira, business-development manager in Texas Instruments Inc.'s cable modem group, said that it's natural to expect "a continuing battle between the customers and MSOs on how gateways should be used."
IP telephony over cable
Telephony faces a different issue. Because Docsis 1.0 could not support low-latency services, MSOs had to provide telephone access as a circuit-switched function, usually promoted as a direct primary-line alternative to voice service through an incumbent local-exchange carrier. With the Docsis 1.1 specs supporting quality-of-service (QoS) prioritization, MSOs now can support second-line phone service using voice-over-IP. That has spurred new interest in multimedia terminal adapter (MTA) platforms, which combine a Docsis modem with multiple RJ-11 phone jacks for secondary phone service over coaxial cable. At the National Cable TV Association's spring conference in New Orleans, Com21 Inc. showed one of the first such MTAs, the VOXport 2020 (Figure 1).
The change in design strategy by OEMs has been spurred by the completion of two special programs at CableLabs. PacketCable is the culmination of a five-year effort to use the QoS features of Docsis 1.1 to add multimedia and voice support, security features and soft-switch-mediation functions to a core Docsis network (Figure 2). CableHome is a more recent program to marry home networking concepts with interface and aggregation points in the Docsis network.
The CableHome 1.0 spec was released to developers on April 5. The first revision offers managed firewall services, Dynamic Host Configuration Protocol (DHCP) and other LAN software features. Future adjuncts to CableHome will not be numbered in a manner similar to Docsis. Instead, a CableHome-Extended spec will support in-home intercom and paging, while CableHome-Video will add streaming-video support.
At the beginning of the year, CableLabs informally pulled together PacketCable, CableHome and Docsis into a unified program called Broadband Access. A special system-oriented Broadband 1.0 spec will include advanced provisioning and management specs for MSOs that allow for stronger security, end-to-end QoS control, and centralized support of DHCP and Trivial File Transfer Protocol.
David Baran, vice president of Docsis products at Com21, said that the issue of managed services reared its head two to three years ago. As the first full Docsis 1.0 modems came out, MSOs were skittish about adding firewall features, because they worried about becoming liable if a computer user got hacked despite the firewall's presence.
"The flood of manufacturers selling home routers at Fry's Electronics is having an effect on the MSO consciousness, but it's moving slowly," Baran said. "On the first level, the MSOs don't want to assign an address to a retail product that they have no control over. But it's even tougher for those systems manufacturers to sell their products directly to the MSOs."
Richard Nelson, director of marketing for broadband products at Broadcom Corp., said there are similar problems in trying to get MSOs interested in complex hardware products like routers, and in promoting MSOs' turn to managed services based on Broadband 1.0 specs.
"The operators want to trial the business model before getting into routers," Nelson said. "If users won't pay extra for an advanced service, forget about it. If an advanced service increases truck rolls or support calls, forget about it."
AT&T Broadband is one operator that has proved to be an exception. The company has begun trials with Linksys for direct distribution of routers to customer premises, and developers are hoping that this represents the start of MSOs' learning to live with routers today-and with true residential gateways tomorrow.
Matthew McRae, broadband strategist in Linksys' broadband services group, said that most MSOs are looking at AT&T and realizing they will have to accept Docsis-certified equipment that customers buy independently. A few holdouts worry about aspects like combining NAT and 802.11, but "at the end of the day, there's nothing MSOs can do about it," he said.
"We have to recognize that each MSO will have its own trend in working with home routers," McRae said. "Some will work with a 75 percent retail mix, while some will follow AT&T in pursuing a 95 percent leasing model."
McRae said there is still a problem with updated modems that are not officially certified for Docsis 1.1 but that are being used in MSO networks. "But the CableLabs backlog is a minor matter, when you look at how CableLabs has made deployment so much better than the DSL model," he said. "We're aggressively working in DSL, but the interoperability problems among carriers are just so much more of an issue without the equivalent of a CableLabs for the incumbent phone industry."
Wireless home vs. MSOs
It helps matters that home networking's physical layer has become less diverse than in years past, although that doesn't always mean that a particular media-access control (MAC) chip should be integrated directly into a cable modem chip set. Conexant Systems Inc. has been critical of Broadcom's aggressive efforts to put 802.11 MACs into its core design, particularly given Intersil Inc.'s dominance in 802.11. But the decision to lead with wireless LANs finds general support in the design community.
"We are 100 percent believers in 802.11 as the primary home network," said Dennis Rauschmayer, director of marketing of cable modem products at TI. "There is no RFP [request for proposal] support for HomePNA, so the phone line networking aspect is not very active. We see some limited support for HomePlug, but it's not too active. The baseline for the home gateway will be a wireless LAN as the distribution point."
McRae of Linksys said he sees some residual interest at Time-Warner Cable and a few regional MSOs in supporting HomePNA, but that all other cable providers are putting their primary efforts into developing wireless LAN connectivity.
All of the debates center on separate systems, existing outside the PC, that perform gateway or MTA functions. There is a further level of integration, favored by semiconductor manufacturers, that CableLabs has tried to promote as the customer premises equipment-controlled cable modem. This single-card implementation features low power dissipation and primary system memory centralized in the cable modem termination system (CMTS) headend. But the concept has been greeted somewhat coolly by both PC OEMs and MSOs. Many no doubt were burned by the Universal ADSL Working Group experience from the DSL world, where Intel Corp. and Microsoft Corp. joined with PC vendors to promote embedded DSL, an effort that got little support at the end of three years' effort.
However, there is hope of renewed PC OEM interest in embedded Docsis modems, thanks in part to the Microsoft Freestyle PC model advocated for Windows XP. Al Servati, director of marketing in Conexant's cable modem group, said that it will take the combined clout of Microsoft, Intel, PC manufacturers and IC makers to get the MSOs to go for an add-in card that supports Docsis access from the PC.
Chip-level integration of standard data, QoS and security in the CCCM form factor is not a problem, Servati said. The real issue is having the MSOs support an Ethernet interface in the PC as their primary point of visibility into the local broadband connection. That's often as scary for the provider as a gateway that a customer buys retail, he said.
"The MSOs need to change their business model to emulate the electrical utility companies," Servati said. "The electric company just puts a meter on the outside of your house. It doesn't care how many electrical ports I might have, provided my ports are approved. Of course, the interfaces to the cable system have to be certified by someone like CableLabs, but beyond that, it should not be an MSO's concern. Whether a customer has a NAT, uses a router, shares bandwidth with others-none of that should matter to the MSO. But we're still a way from the cable industry adopting that model."
VoIP revenue potential
It would be an exaggeration to say that MSOs were uninterested in providing telephone service until the advent of voice-over-IP and Docsis 1.1. Broadcom's Nelson pointed out that there have been some regional successes with the circuit telephony service offered by Cox and AT&T Comcast. But a packet service that does not have to offer battery backup for lifeline service, and that does not have to represent a total replacement of the primary phone company service, can often be an easier sell for the MSOs.
It was precisely this factor that caused Com21 to wait for the arrival of Docsis 1.1 before leaping into MTA development, said Baran. Com21's expertise in continuous-bit-rate ATM algorithms helped the company in jump-starting its packet telephony efforts, he said. But Com21 anticipates having to educate the market and to seed MSOs with some VOXport trials in order to prod the slower service providers into effective telephony services.
VoIP could represent a significant leap in the MSOs' business, perhaps more so than digital TV or video-on-demand, although they understand the latter markets better. At the recent International Conference on Communications, FCC program manager J. Scott Marcus cited a Morgan Stanley Dean Witter study that predicted MSOs could provide approximately 35 percent better "net present value" in networks by adding VoIP telephony.
A mid-May report from Allied Business Intelligence predicts that cable telephony subscribers will reach 5.21 million worldwide at the end of the year, compared with 2.93 million in 2001. Currently the market is virtually all circuit-switched. ABI predicts that significant packet telephony ramps will not happen until 2004 but that IP will quickly overtake circuit switching, hitting 20 million subscribers at the end of 2006. In 2007, the research firm expects the total number of subscribers to approach 53 million, with 30 million packet customers and 23 million circuit customers.
Conexant and TI claim they are in a good position to offer VoIP support with a minimum of chips, by using programmable DSP engines for compression and packetization and by customizing the hardware with middleware for a particular application. Rauschmayer said that TI already has moved to a software-reuse model, utilizing the same home-gateway software for chip sets used in DSL, cable modems and home networking.
It is of particular importance that CableLabs has put some urgency into setting up certification programs for PacketCable and CableHome, placing those programs on a faster track than the completion of the Docsis 2.0 program, a new MAC effort that improves upstream speeds of cable modems. Many of the same OEMs that have had standard modems certified for Docsis 1.1 are now getting enhanced MTA or gateway products certified for PacketCable or CableHome. Once the availability of standard voice products is sufficient, Rauschmayer said, the MSOs' interest will pick up.
Depending on how vendors such as 2Wire and Linksys define the multipurpose residential gateway, some platforms may include both router and packet-voice support. But Greg Gum, director of marketing at DSL chip set supplier Ishoni Networks Inc., warned that there may be some hidden problems in such integration for both DSL and Docsis systems.
"If you use a firewall, how does voice traverse through that firewall? Will it add latency to a VoIP flow? These are issues that could impact the design of home-networking gateways," Gum said.
Because the silicon in cable modem markets has jumped ahead of the market itself, one might expect semiconductor suppliers to be sitting on their hands as the work on Docsis 2.0 commences. Not quite. TI demonstrated some advanced TDMA features for Docsis 1.1 modems at NCTA in May that allowed the modems to offer some upstream speedups beyond the 1.1 spec. And Broadcom has been rolling out Propane, a physical-layer compression scheme that preserves Docsis 1.1 compatibility but offers more upstream compression and aggregation support.
Terayon subsidiary Imedia Semiconductor recently debuted its IM6030 chip, with support for both advanced TDMA and Terayon's synchronous code-division multiple access (Figure 3). The release was timed to coincide with the introduction of the company's TJ 715 cable modem based on the chip. Imedia is calling the chip Docsis 2.0-ready, since the physical and MAC layers meet all draft functions proposed to date for the next major Docsis release.
Mark Rooney, who left Terayon recently to head up Finland-based VDSL Systems Oy, said that incumbent phone carriers had better understand that Docsis 2.0 could represent the "end game." Since 2.0 will allow symmetric transmission of a variety of video, packet-voice and data streams, VDSL will represent the only digital subscriber line technology derivative with any hope of catching up with Docsis capability.
"The MSOs already understand bundled services by offering digital video and cable modem service together," Rooney said at the recent DSLcon conference. "Cable telephony may represent a bit of a learning curve, but the MSOs understand bundles. We've heard a lot about the necessity of bundled services here [at DSLcon], but the phone companies must move much further in this direction to be competitive."
The next round of Docsis 2.0 cable modem chips is expected to provide 30-Mbit/second upstream speeds for true bidirectional broadband support. The advantage in demonstrating advanced features now, TI's Rauschmayer said, is to give MSOs a preview of the services they can offer as new applications such as multiuser gaming and music file uploading emerge. By that time, chip set vendors agree, the MSOs might figure out how to offer end-to-end integrated services and make money while doing so.
Loring Wirbel is editorial director of Communication Systems Design and the editorial director for CMP Media's Communications Initiative. He can be reached at lwirbel@cmp.com.
