For DOCSIS 3.0, sorting out roadmap from implementation is not a trivial task.
The spec’s feature set provides tools for both future-proofing the network and countering competition. Implementation timing, however, is a separate issue, dependent upon the junction of customer needs, competition, and solutions available across both hardware and software and network readiness.
As a result, while pre-DOCSIS 3.0 deployments of the underlying channel bonding technology have begun, the cable industry remains largely in preparation mode for full-scale, standards-based launches that could begin in the third quarter of 2008. The drivers Apart from channel bonding, the major features of DOCSIS 3.0 are compatibility with Internet protocol version 6 (IPv6), IP multicasting, improved security, and new interfaces to operations systems. Here’s a quick review of that set:
• Channel bonding is the technique that delivers increased downstream and upstream throughput.
• IPv6 compatibility delivers the benefits of a vastly increased number of IP addresses, initially for management purposes, and later for customer applications.
• IP multicasting centralizes the management of the IP multicast protocol at the cable modem termination system (CMTS), making multicast applications more flexible and easier to implement.
• Improved security is achieved through AES encryption, providing further insurance that privacy will be maintained and hacking will be thwarted.
• The interfaces to operations systems were necessary to support the new feature set.
Increased throughput is the benefit of DOCSIS 3.0 that has received the greatest attention, largely because it counters the competitive thrust of Verizon’s FiOS offering.
In a widely publicized demo at the May 2007 NCTA Cable Show involving the ARRIS C4 CMTS and the Touchstone Wideband Modem 650, Comcast CEO Brian Roberts showed how four bonded channels could enable the downloading of a 17 MB commercial in about a second, a 300 MB commercial in 8 seconds, and a 4 GB file containing the 2007 Encyclopedia Brittanica and a Merriam-Webster visual dictionary in less than 4 minutes. Cisco had an eight-channel bonding demo in its NCTA booth, providing a whopping 293 Mbps downstream data rate.
At the same time, the cable industry – again, Comcast in particular – has expressed keen interest in another part of the DOCSIS 3.0 feature set: the vastly expanded universe of addresses enabled by IPv6. "Being the largest provider of data services, we also are the largest consumer of IP addresses," said Steve Craddock, Comcast SVP of new media development at a DOCSIS 3.0 breakfast.
"The need for IPv6 hits us first," Craddock said. "To us, (IPv6) is crucial."
The constraints of IPv4 are widely enough recognized, however. "The IPv4 10.0.0.0/8 space only allows for roughly 16 million IP numbers," said Mourad Veeneman, UPC Broadband VP in an interview with CT late last year. "That’s barely enough for a country like the Netherlands."
By the end of 2007, North America’s largest cable operator continued to underscore its intention to adopt DOCSIS 3.0, with Comcast CTO Tony Werner telling CableNEXT attendees in November that the technology would be rolled out to 20 percent of Comcast’s footprint by the end of 2008. Some may wonder, why only 20 percent?
A closer look at the specification itself may help explain this relatively long windup to deployment. DOCSIS 3.0 specs Channel bonding is the lynchpin for delivery of increased throughput. Bonding associates individual 6 MHz channels into bonding groups, with, for instance, four downstream and four upstream channels, to increase user-available capacity to 160 Mbps downstream and 120 Mbps upstream. Technically DOCSIS 3.0 does not limit the maximum number of bonded channels. (See Figure 1.) Bonding can be implemented in either or both directions. Most vendors are implementing downstream bonding first, in part because most applications are still asymmetrical, but also because upstream bonding is a more difficult implementation. For channel bonding to work properly, sufficient spectrum must be available for for the additional channels that comprise the bonded channel groups, and the 6 MHz bands within the spectrum should be free of impairments that would affect reliable data transmission. Although the 6 MHz channel slots do not have to be contiguous, they must all be within a 60 MHz window. Upper limits to the plant spectrum, intermittent faults on individual legs of the plant, network topology, and traffic demands can all affect user bandwidth availability.
The DOCSIS 3.0 physical layer (PHY) spec provides for a frequency plan with a downstream upper edge that can be as high as 1,002 MHz. There is a considerable consensus that once analog spectrum reclamation is complete, 750 MHz to 860 MHz will remain the typical upper boundary for downstream signals. Should it be necessary to operate above 860 MHz, however, a massive replacement of passive components (splitters, combiners, taps, etc.) may be required to ensure signal quality, depending on the passives in the plant now.
Is there sufficient knowledge of plant health at the taps, amps and nodes to ensure the quality of all channels in a bonded group?
"In the future, it will likely be necessary to dynamically monitor downstream, as well as upstream, plant performance," said Proxilliant Systems CTO Richard Berthold. "We have found that packet loss can be specific to certain frequency ranges and that it varies with the devices connected to the downstream. There is often a correlation with time of day as well. To minimize the implications to service, it is necessary to understand patterns in packet loss and to correlate them with plant location and spectrum."
Traffic planning and network topology become more inter-related with channel bonding. Bonded bandwidth needs to be available for peaks to each subscriber, and usage patterns as well as total number of subscribers determine capacity, which can also include planned oversubscription.
Topology becomes important because channels must be configured at the CMTS to the node that serves a subscriber. Things get complicated because bonded channels can be shared among multiple fiber nodes, and in addition, a channel can be primary for one node and secondary for another. Primary channels carry configuration information, while secondary channels are only associated with getting content across the network. Moving forward Despite an apparent urgency to have channel bonding in place before the competition arrives, the number of tasks needed to prepare a system for DOCSIS 3.0 makes it unlikely that widespread implementation will occur in the United States before the third quarter of this year. Among the tasks that have to be completed are hardware certification and operator tests, spectrum re-allocation, support system transitioning, headend re-cabling and re-combining, and back office support.
The key hardware components are the CMTS and the cable modem. To speed up the process of getting hardware certified, CableLabs has created three levels of DOCSIS 3.0 CMTS certification. The intention behind the levels is to provide incentives for vendors to submit partial implementations as development continues, rather than waiting for full compliance.
Full certification indicates that all the DOCSIS 3.0 specifications have been met. While the exact meaning of the lower two levels is proprietary to CableLabs vendors and member companies, CableLabs press releases indicate that bronze certification ensures that downstream channel bonding has been met, and silver certification includes a working upstream and downstream bonding, compatibility with IPv6, and AES encryption.
At the completion of certification wave 56 in December 2007, no CMTSs or cable modems had received full certification. Casa Systems’ C2200 CMTS was silver qualified, and both the ARRIS C4 CMTS and the Cisco uBR10012 were bronze qualified. Certification wave 57 results will be published after April 15, when the Certification Board next meets.
Because cable modems do not have a tiered certification, it is unlikely any will carry certification until they can be tested with a fully qualified CMTS. Although a few products are being marketed as DOCSIS 3.0 compliant, most operators will only risk early commitment to these solutions in critical markets with heavy competitive pressure for high throughput offerings.
The analog-to-digital transition is helping free downstream spectrum, but it will not be complete until analog broadcasting ceases in February 2009. In the interim, DOCSIS bonded channels are contending with digital services, such as high definition television (HDTV), for available spectrum. Expansion above 860 MHz is possible, but only if the plant is capable.
Operations support system (OSS) upgrades may be a sleeper issue that could become urgent quickly. DOCSIS 3.0 defines 2,130 MIBS vs. 1,385 for DOCSIS 2.0. The OSSI spec requires that provisioning be backward compatible, but does not place the same constraint on monitoring, leaving monitoring compatibility open to vendor implementation. Since most operators have mixed OSS suppliers, systems integration will be needed to ensure information continues to be available. In an attempt to head off problems, CableLabs briefed OSS vendors at an OSS summit last year and holds monthly engineering discussions on the impact of DOCSIS 3.0 on OSSs. Getting ready Prior to certification, several "DOCSIS 3.0-compliant" products have become available from different vendors. Motorola, for example, announced its line of SurfBoard DOCSIS 3.0 cable modems in late February to complement an already available BSR 64000 CMTS. The ARRIS and Cisco CMTS bronze-qualified products are also available, as are "2.0B" modems, which provide for downstream channel bonding.
Except for limited trials and lab tests, however, U.S. operators have not chosen to begin offering higher throughput solutions with these options.
Traction for channel bonding has been gained, however, in non-U.S. markets. For example, Starhub of Singapore has been offering early deployment of pre-DOCSIS 3.0 channel bonding at 100 Mbps downstream since 2007 using Motorola CMTS and cable modem equipment. In Canada, Videotron has launched a three-channel bonded service.
Even though DOCSIS 3.0 features will probably not be implemented commercially in the United States before August, DOCSIS 3.0-capable hardware is being installed in headends today to take advantage of increased CMTS capacity stemming in part from hardware and processing efficiencies added to support higher throughput applications.
"Right now, capacity rather than channel bonding is driving upgrades," said Steve Krapp, ARRIS product management director. "Most operators are looking at two or three for one swaps," he continued, "and when they are ready to turn on DOCSIS 3.0, it’s a relatively simple upgrade. Even if the changeouts don’t realize more capacity per home passed, more homes can be served per CMTS."
Also, CableLabs is advising operators through the changeout process. Regular monthly engineering and operations telephone meetings are chaired by Lakshmi Raman and are open to all member companies.
Justin J. Junkus is president of KnowledgeLink and telephony editor for Communications Technology. Reach him at email@example.com. Sidebar: 3.0 Features DOCSIS 3.0 features are detailed in four specification documents and one technical report:
• The MULPI spec provides for channel bonding on upstream and downstream channels, IPv6 compatibility and dual existence with IPv4, moving the responsibility for multicast protocol awareness from cable modems to the CMTS, and a standard mechanism for configuring the quality of service (QoS) for IP multicast sessions.
• The PHY spec provides a reference architecture and the framework for signal processing and modulation.
• The SEC spec defines encryption and key management based upon the AES standard.
• The OSSI spec, addition to supporting channel bonding, IPv6, multicast, and improved security, details provisioning multiple upstream receivers per port, updating plant topology for DOCSIS 3.0 features, enhanced diagnostics, performance data collection, and signal quality monitoring, and usage based billing.
• Technical report MGMT-3 DIFF summarizes the differences in DOCSIS management interfaces between DOCSIS 2.0 and DOCSIS 3.0.