All in good time: Datum taps CDMA for timing alternative

Network synchronization or timing is one of those complex-but-crucial issues that typically remains in the background of any discussion about carrier networks. Despite its low profile, however, timing is an important network consideration for any carrier in terms of both capability and cost.

For new carrier entrants, the issue of cost becomes even more critical. New competitors need a synchronization solution that is almost tailor-made for their needs and their financial means. Cesium or Stratum 1 clock methods generally prove cost-prohibitive for carriers with limited means, and even more modern solutions based on the global positioning system (GPS) require expensive installations of antennas and other equipment.

The other timing option available to carriers and corporate network operators is to rely on an incumbent local exchange carrier connection. According to timing solution developer Datum, however, the increasing use of Sonet technology in LEC networks can trip that up because Sonet does not always guarantee the integrity of timing signals.

Datum believes it has the answer to those problems. The vendor, which has a broad embedded base of advanced timing systems in networks of all kinds, decided to pursue development of a synchronization solution that would meet or exceed Stratum 1 timing capabilities without requiring rooftop - or even window-mounted - antennas, thereby eliminating much of the cost of deployment.

"We were getting a lot of inquiries about the cost of GPS installations and about how to put a Stratum 1 clock into a site without an antenna," said Jack Rice, president of Datum's Austin, Texas, operation. Carriers and other organizations in need of timing solutions were seeking an approach that would bypass expensive and challenging rooftop siting and in-building cabling issues but still provide a high level of reliability, he said.

Datum's secret weapon turned out to be code division multiple access (CDMA). The core component of the company's AntennaLess NetSync Plus technology is a timing engine about the size of a standard computer modem. The box captures a CDMA pilot signal from an area wireless carrier using the technology in its network and rides on that signal to link back to the GPS satellite (see figure).

"It turns out the CDMA pilot signal is very strong; it has filtering from the base station and time of day is inherent," Rice said. "It was just a matter of developing an engine to receive the pilot and put it in place of a GPS receiver."

Assuming ample CDMA coverage, carriers and private network operators can synchronize portions of their networks by locating Datum's timing engine within buildings. The Datum device takes the place of a traditional GPS receiver, but because it ultimately links back to the GPS source it still provides GPS synchronization. The lower cost of the gear - Rice estimated that this capability can be put into a network for $1200 or less - means it can be deployed at any point within the network and act as an independent Stratum 1 timing source.

Datum's AntennaLess approach is currently being evaluated by interexchange carriers, incumbent LECs and competitive local exchange carriers, according to Datum. Rice acknowledged that the technology can be a tough sell because it is not a source of revenue generation for network operators - rather, the value is in the problems that it solves.

The company's expectation is that the early adopters will be corporate network operators requiring independent timing mechanisms for premises equipment, as well as corporations and carriers basing their networks on Internet protocol technology. "They're very rapidly discovering that they need this to make a network work," Rice said.