With little fanfare, a relatively obscure subcommittee of the Society of Cable Telecommunications Engineer's Engineering Committee is making big strides toward standardizing a host of network status monitoring specifications. While not as sexy as more high-profile standards efforts, the "blue-collar" work of the Hybrid Management Sub-Layer Subcommittee (HMS) is seen as key to letting operators gain greater visibility into all network elements, both inside and outside plant devices, from power supplies to fiber nodes to, eventually, optical transceivers.

Such a capability will likely facilitate the next wave of advanced services, principally telephony and video-on-demand, but also business services which may or may not be covered by Service Level Agreements–all of which require a greater degree of network uptime and performance than merely delivering video.

"The adoption of standards makes our network more manageable," says an MSO committee member, who asked not to be identified by name. "It reduces our cost of operations, and it is a large advantage for any MSO that delivers or plans to deliver a large variety of services."

"We have a large deployment of legacy (status monitoring) systems," continues the MSO employee. "HMS standards will allow us to choose among multiple vendors. HMS will also lessen the amount of testing required by an MSO, which equates to cost reduction."

Hung Nguyen
Hung Nguyen, chair of the HMS subcommittee and senior staff engineer for Time Warner Cable.
"We've been waiting for this equipment for a long time," agrees Hung Nguyen, chair of the HMS subcommittee and senior staff engineer for Time Warner Cable. "We are tired of dealing with proprietary equipment."

Vendors also have a significant stake in the standardization process. According to Hamid Qayyum, product line manager for Acterna LLC, the company has had to develop 153 different variants of transponders, due in part to the lack of standards. Standards would drop that number tremendously, says Qayyum. "It changes our whole business model," he adds.

"HMS standards should drastically reduce the amount of (transponder/network element) integration time," says William Plant, senior systems engineer for Corp. and vice-chair of the HMS subcommittee.

"The past history of this particular business has been very fractious," explains Jim Ostrosky, principal engineer for Tollgrade Communications Inc. and outgoing secretary of the subcommittee. The development of standards-based interoperable transponders is seen as a way for vendors to expand the market for these devices while giving operators assurance that interoperability will exist.

"There's still a lot of opportunity for transponders to be used out in the network," says Mark Peterson, president and executive vice president of sales for Tollgrade. "I think we're going to see an uptick in demand for this technology now that baseline standards have been set," he adds.


The HMS subcommittee has labored for several years, first under the auspices of Cable Television Laboratories Inc., and later the SCTE, without a lot of progress. But a key milestone was reached last October, when three standards were issued:

  • HMS 005, Hybrid/Fiber Coax Outside Plant Monitoring–Physical Layer Specification;
  • HMS 004, Hybrid/Fiber Coax Outside Plant Monitoring–MAC (Media Access Control) Layer specification; and
  • HMS 022, Hybrid/Fiber Coax Outside Plant Monitoring–Power Supply-to-Transponder Interface Specification.

Also approved were a series of MIB (Management Information Base) definitions that will provide a database of network management information, used by the network management protocol SNMP (Simple Network Management Protocol). These MIBs have been specified for power supply transponders and fiber node transponders, as well as headend controllers, transponder interface buses and alarms. In effect, every piece of equipment to be monitored has (or will have) its own set of MIBs. "The MIB will define what it is we're trying to monitor," says Nguyen (for example, voltage and/or current, optical laser level, etc.).

Figure 1: HMS reference architecture diagram.

The HMS MAC layer spec describes protocols to be used between outside plant transponders and controlling equipment in the headend. Among the features of the MAC protocol include support for message exchange over single forward and single return RF channels on the HFC network, which can be initiated by either the headend controller or the network element.

A so-called "MAC layer domain," then, consists of these single forward and return channels over which a MAC layer bandwidth allocation and management protocol operates, and includes a centralized headend and multiple HMS-compliant transponders interfacing to managed outside plant network elements.

The HMS Physical (PHY) layer spec defines the physical layer portion of the protocol stack used for communicating between transponders interfacing to outside plant network elements and the headend.

The Power Supply-to-Transponder Interface spec outlines a status monitoring scheme to replace existing interfaces for power supplies and power-related equipment. The transponder, under this topology, is simplified by moving all sensors and measurements to the equipment being monitored, in this case the power supplies themselves, through a single multi-conductor cable. Battery parameters, voltages and other data is thereby measured, and status and commands are passed between transponder and monitored equipment through a serial data interface bus. The data is synchronized with associated HMS SNMP MIBs.


With three specs under its belt, the subcommittee embarked on a series of tests at AT&T Broadband's lab facility in Denver, as well as field trials in Time Warner Cable's Lakeland, Fla. system in October and April. The results of the April test led Nguyen to announce that power supply transponders from four vendors are ready for deployment.

"I have recommended that our company should start purchasing this product," says Nguyen.

Power supplies are "the greatest need from the standpoint of the industry as a whole," says the MSO committee member. While operators may choose to monitor other pieces of equipment, power supplies represent the "least common denominator" for element testing, he adds. What made the field trial in Florida a success, says Nguyen, was the fact that "the equipment built to specification works." Plus, the transponders from four vendors can work together, meaning an operator can place transponders from different vendors in the same plant, and they will interoperate.

The power supplies used in the field trials were stand-by power supplies with batteries, and the batteries themselves were monitored.

Time Warner deploys stand-by power supplies for backup power. If line power fails, the network will switch over to battery power. In some cases, the backup power capability is a condition of franchise agreements, says Nguyen. Other operators, such as AT&T Broadband and Cox Communications, have deployed power supplies for telephony services.

Power supply transponder vendors Tollgrade, Acterna, AM Communications Inc., and the German telecommunications gear maker Wilhelm Sihn jr. KG (WISI) demonstrated interoperability of their transponders with headend controllers from, BarcoNet, Scientific-Atlanta Inc., Tollgrade and Acterna. (In the HMS committee's parlance, the headend controller is referred to as the Hybrid Management Termination System, or HMTS.)


Moving forward, the HMS subcommittee is working on details of a fiber node transponder lab trial, tentatively scheduled for September at AT&T Broadband lab facilities in Denver. The tests will focus on interoperability.

At a Denver meeting in June (attended by 43 people from seven countries), the subcommittee laid the foundation to move up the network to address headend optics equipment, referred to as inside plant optics. Accordingly, an inside plant optics working group was formed and scheduled to meet in July in Philadelphia, with proposed inside optics MIBs to be released for review prior to the meeting.

In Denver, it was decided that SNMP version 1 is to be the minimum implementation for inside plant gear, although vendors were encouraged to support higher versions.

The next full meeting of the HMS subcommittee is scheduled for the week of October 7 in Seattle.

Focusing on inside plant elements, says Plant, will eventually drive a look at digital transmission in outside plant gear, for example digital return path transmitters.


Perhaps the biggest driver of HMS-compliant gear has been Callahan Associates International LLC, operator of the ish network in the northwest German state of North Rhine-Westphalia, which is involved in a massive system upgrade to deliver video, data and primary line Internet Protocol-based voice services over its network. According to Mark McGuinness, chief technology officer for Callahan, the operator insisted on HMS-compliant gear when it issued a request for proposal two years ago, long before HMS standards actually existed. "We made sure people would be HMS-compliant," says McGuinness.

"We felt (HMS-compliant gear) was very important so that we could then mix and match (amplifiers and nodes) and get the best economic value in our network," says McGuinness. Specifically, he adds that in a multiple services environment, with voice, video and data running over HFC, it's important to be able to diagnose last-mile active components. Standards-based status monitoring offers the operator the ability to monitor ingress and noise levels and be pro-active, instead of responding to element failures. McGuinness says that visibility into the network is the "key to success" for running multiple services, which translates into multiple revenue streams, over an HFC network.

"We use multiple vendors' hardware in terms of amplifiers and nodes," says McGuinness, adding, "it has been difficult to have the prime vendor, who provides the network management solution, talk to the other vendors' HMS-compliant equipment." While "actual implementation is a bear" says McGuinness, he points out that, "from the network management system for HFC, we are actually monitoring both vendors' (node and amplifier) equipment now."

The primary supplier of amplifier and node vendors is WISI, while the alternative supplier is Motorola Broadband GmbH (aka Fuba Communications Systems). Headend equipment is provided by Scientific-Atlanta, and Callahan uses S-A's Transmission Network Control Systems (TNCS) element management system.


Underlying the fast-moving pace set by the committee are profound concerns about how the standards will be tested– more specifically, how a test plan for the MAC layer specification will be funded and maintained. The goal is vendor self-certification, but the sticking point is the lack of a MAC layer test tool. There's a deep dissatisfaction within the committee about the role of the SCTE in the process.

"We don't feel like we're getting our money's worth," says Nguyen. "We feel that (the development and maintenance of a MAC test plan) is an SCTE responsibility," he stresses. Further, he believes that the issue calls into question "what role does the SCTE play in the industry."

"As chairman," says Nguyen, "we feel that here we are developing standard products for the SCTE, and they're not even acknowledging it." For example, the committee expressed frustration that the SCTE wouldn't publish a press release about the Lakeland interop success.

A few options were discussed during the Denver meeting, including vendor funding for the test plan, although the dollar estimate per vendor for this option was thought to be high. Another idea floated was encouraging the SCTE to refund the committee membership fees, which would then be devoted to developing a test product.

Steve Oksala, vice president of standards for the SCTE, notes that the issue of the MAC test plan has been considered by the organization's board of directors. He says the development of such a tool is an expensive proposition, and points out that becoming involved in product certification, however peripherally, is not something the SCTE wants to touch. "We don't see that as something the SCTE should be getting into," says Oksala, who also notes the possibility of liability issues related to the "correctness" of a test tool.

While noting the lack of a business model for a third party testing entity, Oksala suggested the establishment of a test consortium composed of those willing to spend the money to fund the effort.

Despite the lack of resolution of this issue, however, the subcommittee in Denver formed a working group to define the requirements of a standard MAC test tool.


Responding to the progress of the subcommittee, vendors are rolling out products that are based on the HMS specs. For example, has developed an Integrated Service Management (ISM) platform that has recently been adopted by Time Warner Cable for its Tampa Bay system. The ISM application monitors and manages alarms and service thresholds for both network devices and customer premises equipment. Monitoring information is then integrated into an operator's operational support systems.

It's also expected that power supply and fiber node vendors will begin to ship with integrated transponders, from OEM transponder providers, based on the HMS standards.

Piping in on the HMS theme is S-A, which announced in April an HMS-compliant transponder for its optical nodes and amplifiers, compatible with TNCS and BarcoNet's ROSA system.