Last month, this column discussed how cable could provide a valuable service to small and medium businesses (SMBs) by offering packages of business communications systems that eliminate the need for an SMB to build its own telephone system. While new systems are a large market, it’s not necessary to replace all existing small business premises communications systems with a cable-provided system to gain share in the SMB voice market. Continuing on last month’s topic, it’s time to explore how the same digital voice product we provide to residential customers can become part of cable’s SMB "hero" package. Two components There are two components to a value-added solution directed toward a business that wants to keep its current premises-based communications system: the communications system and network access. Network access is where our opportunity lies in SMBs with viable communications systems. To penetrate and support this market segment, however, we need to understand how access and communications system work together. Let’s start by reviewing the types of premises-based communications systems that serve SMBs. 50 or fewer The smallest SMBs are those that only require one or two phones to serve less than a handful of employees. This is an easy transition for cable – from a telephony technical perspective, they look just like residential service, and we have a proven technical solution. All that remains is for marketing to create a package of hardware, usage and support that meets both customer and corporate objectives. Support is important and more critical than for residential service. Loss of phone service to a business can become a legal liability, since it is a necessary tool for business operation, and downtime can be equated to lost revenue.

Next up in size is the SMB with more than five, but fewer than 50, employees. These folks will probably have a key telephone system (KTS). KTSs come in two flavors: those with a key service unit (KSU) and KSU-less systems. A KSU is a systems level switch and processor that manages calls between station sets within the business and to or from the outside world. Telephone sets used with a KSU are simple, multiline devices with minimal intelligence. The KSU-less system uses more complex (and expensive) telephone sets that each have the processing capability to store features and handle communications between telephone sets as well as between outside lines. KSU-less systems are easier to set up and are usually found in businesses with fewer than 20 telephone sets. Both types of key systems have one thing in common: The interface to a service provider’s network is a set of standard telephone lines, often only three or four of them, which are accessed directly on station sets via keys. That makes key systems match well technically with the voice solution we already have for residential service, where two- and four-line multimedia terminal adapters (MTAs) are widely available from vendors, and a 12-line version can be obtained from Arris.

This doesn’t mean that we can just walk into an SMB of this size, unplug the telco, connect our lines, and leave. In addition to the downtime issues we noted for the smallest SMB, there are several support issues associated with KTS features that we need to understand. One simple example is the line status light on a KSU-less station set. When the line is disconnected and then reconnected, the status light will often blink until reset. Restoring normal operation may involve only a sequence of feature button depressions, but if an installer leaves without checking and restoring this function, the SMB owner will call to complain about an "incompatibility." The best preparation for this type of problem is to pre-qualify the customer by learning which vendor’s KTS is installed and obtaining an owner’s manual. The next choice is to ask the customer if he has one. Also, the best practice installation is to first check the existing system operation to verify everything is working before beginning the job. 50 to 20,000 The largest business communications system is the private branch exchange (PBX), typically between 50 and 20,000 station set lines. PBXs tend to have more features than key systems. While an attendant position is optional in a key system, a PBX typically includes this feature as standard. More user features are provided, such as grouping of users by organization for conferencing or call coverage and data communications interfaces. The PBX can provide automatic route selection capability, so that calls are always sent through the public switched telephone network (PSTN) using the least costly service provider. Additionally, management features are available to help administrators review system and station traffic, change station features, track costs by station user or group, and keep track of total system configuration.

In addition to handling more station sets on the user side of the PBX, the PBX incorporates trunks instead of lines to connect to the service provider. Trunks are shared by PBX station set lines and have higher usage than a line. A typical ratio of station set lines to service provider trucks in a PBX is 10:1.

Depending on the type of trunk, the physical difference between a line and a trunk can be small. The connection is still one or two pair of wires. One distinction is that the trunks are connected to trunk circuits at the PBX rather than directly to station sets. Depending on the type of trunk, these circuits provide special signaling, ringing, or T-1 multiplexing (another form of concentration).

Cable has been providing T-1 circuits for trunks to business PBXs for some time. Products are available from Vyyo and Phyflex Networks, for example, to implement T-1 over HFC, but both products require new network hardware.

Last year, CableLabs opened the door to a substantially easier way to provide PBX access, with the publication of PKT-SP-ATPBX1.5-I01-060419, the PacketCable specification for Analog Trunking for PBXs. This specification expands the definition of an MTA to include six endpoint trunk interfaces: loop start, ground start, E&M 2 wire, E&M 4 wire, DID PBX, and T-1. Without getting into all the details of signaling and supervision, a summary of the contents is that the customer-facing side of the MTA is defined to recognize requests for service other than a simple loop closure and to behave like a trunk circuit rather than a line while working with the call management server (CMS) to set up and supervise a call.

The benefit of this new interface is that installation of a trunk to a PBX will essentially be the same as installation of a line, requiring only a conforming MTA. The door is thus opened to providing trunk access from any point on an HFC network that passes close to an SMB. Vendor implementation is not yet widespread, nor complete with respect to all the trunking options addressed by the spec. Innomedia, for example, offers its EMTA 3528-4e, but only with ground and loop start signaling.

Support issues for a PBX are the same as for a key system, except greater. With more features in the system, and larger business customers, understanding the PBX as well as the access technology will be critical to avoiding downtime that affects the customer’s balance sheet. Bottom line The bottom line for cable, though, is that opportunity is ours to develop, if we step up to the challenges of new markets. Justin J. Junkus is president of KnowledgeLink and telephony editor for Communications Technology. Reach him at

The Daily


Liberty Broadband’s Charter Stake

Liberty Broadband will sell to Charter , generally on a monthly basis, a number of shares of Charter Class A common stock so that it doesn’t exceed its ownership cap as Charter reduces outstanding shares

Read the Full Issue
The Skinny is delivered on Tuesday and focuses on the cable profession. You'll stay in the know on the headlines, topics and special issues you value most. Sign Up



Hiring? In conjunction with our sister brand, Cynopsis, we are offering hiring managers a deep pool of media-savvy, skilled candidates at a range of experience levels and sectors, The result will be an even more robust industry job board, to help both employers and job seekers.

Contact for more information.