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NEBS Can Help Guarantee Telecom Reliability

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March 03, 2011

NEBS Can Help Guarantee Telecom Reliability

By Jamie Epstein, TMCnet Web Editor


NEBS is a term that saturates today’s electronics and telecommunications industry. It translates into Network Equipment Building Standards, which are the standardized requirements that regulate the quality and reliability of all prevalent telecom equipment presently in the market. The reason for these standards is to make sure that our communications equipment can function in any situation.


The reliability rate of telecommunications equipment is expected to exceed 99.9 percent, an article by Don Bennet-, of Garwood (News - Alert) Laboratories stated. NEBS, particularly GR-63 CORE and GR-1089 CORE, were specially designed to address the issues of reliability of telecommunications equipment, designed around a central office (CO) installation.

GR-63 CORE pertains to the physical characteristics of the equipment. There are numerous tests involved in the compliance process for GR-63, some more intense than others.

The earthquake simulation is a pretty intense test. It acts like a 32-s time-history shock pulse created by Telcordia (News - Alert), with the shock response spectra (SRS) in the range of 5g at the base of the frame. The low-frequency portion of the time history produces displacements of approximately 10 in. peak-to-peak.

For the simulated earthquake part of the test, the unit under test (UUT) is mounted into a Zone 4 certified test frame, and the frame is configured to best duplicate the mass and stiffness of a fully loaded frame. This is because there is usually a need to fill every available square inch of a rack in a CO. The 32-s time-history shock pulse is exhibited and then the framework is reviewed in two areas- the middle and top of the frame. Displacement at the top of the frame is measured in conjunction to the base in inches, and cannot exceed 3-Inch zero to peak. The UUT must work before and after the test, with a predetermined goal for the unit being the ability to function effectively during the test.

The fire-spread test always falls on the more intensive side. It determines how the UUT will react when a flame is introduced to the system, in hopes that the flames will be able to be completely contained within the UUT. A circuit card is removed from the system, and a blank faceplate is placed over the empty slot. A hole approximately ¾² in diameter is drilled into the blank faceplate, and a six inch burner wand is inserted through that hole. The burner wand forces the circuit card to catch on fire.

The methane gas used for the test is enables a profile to run from 0.5 liters/min to 9.0 liters/min maximum, eventually extinguishing the flame at the 5.5-min mark. Systems with fans are required to power only the fans, preferably off the backplane if that is the normal installation procedure.

It is best to replicate the system’s fan characteristics as closely as possible to find the actual effects of the fans on the fire-spread test, Bennet said. During the testing, many people think that the fans will encourage the flames, however, the fans help disenable heat pockets within the chassis.

Other tests include temperature/humidity and altitude (both functional), handling such as packaged and unpackaged drops, and transportation simulation on a vibration table.

Acoustic noise is measured using sound pressure (dBA) as the measurement factor, to show the amount of noise being caused by the fan system. GR-63 calls for a level of 60 dBA for equipment installed in a CO lineup.

The release of heat is a huge problem with NEBS testing. Because of the increasing amount of hardware within the board, as well as the smaller size of the actual system, the wattage associated with these systems is becoming extremely high—so much so that the heating, ventilation, and air-conditioning systems in many current COs cannot handle the heat release. Many COs try to fix this problem by positioning fans in the aisles to circulate the heat.

GR-1089 CORE Electromagnetic Compatibility and Electrical Safety deals with the electrical characteristics of the telecommunications equipment.  A big issue in the design process of telecommunications equipment is the shielding methods used for emissions. Pre-scans are very useful to try and find where problem areas may lie, as well as halting any system emissions issues.

GR-1089 is divided into four product types. Types 1 and 3 products are directly connected to the outside plant metallic tip and ring conductors. Type 1 is for CO installation, and Type 3 is for customer premises. Types 2 and 4 are not directly connected to the outside plant, with Type 2 being CO and Type 4 being customer premises.

The type represents if a lightning surge will be inter- or intrabuilding. This is a crucial factor because the levels for interbuilding are much higher becausethe unit could be affected by a direct strike to the telecom line as it is exposed to the elements, compared to intrabuilding, which has other equipment involved that would be hit before the outside connection.

The AC power fault test is just like the lightning surge because pertains to a surge in the telecom interface line, like T1. If you quickly can visualize that the telephone lines are too close to the high-voltage power lines, the power lines might have the chance to actually cross over the phone lines. The AC power fault test works like a potential a surge would if the two lines were crossed, and the effect of the lines crossing.

The AC power fault and lightning surge are separated into two important categories­—first-level and second-level. First-level criteria means that the system must function healthily after any of the stresses are applied. According to the second-level criteria, the equipment can stop functioning but must be not cause fire, fragmentation, or an electrical safety hazard.

Some standard issues of testing involve electrostatic discharge (ESD), bonding, and grounding, which show the integrated ground-plane and the isolated ground-plane configurations. Electrical safety keeps the people who work with the equipment safe at all times.

The process for testing to Telcordia NEBS GR-63 CORE and GR-1089 CORE can be an extremely long process. However, NEBS compliance confirms that the equipment being installed will always provide high reliability, no matter how high in the future.


Jamie Epstein is a TMCnet Web Editor. Previously she interned at News 12 Long Island as a reporter's assistant. After working as an administrative assistant for a year, she joined TMC (News - Alert) as a Web editor for TMCnet. Jamie grew up on the North Shore of Long Island and holds a bachelor's degree in mass communication with a concentration in broadcasting from Five Towns College. To read more of her articles, please visit her columnist page.

Edited by Jamie Epstein







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