NEBS 101

Understanding safety and reliability requirements for telecom equipment is essential in today's fast-paced public network buildout

Dependable power for optimum uptime and reliability is the key to performance for telecommunications networks. Products that are NEBS-compliant assure the customer that the equipment meets industry requirements for personal safety, facilities protection and continuity of operation.

NEBS - which stands for network equipment building system - are guidelines originated by Bell Laboratories in the 1970s to assist equipment manufacturers in designing products that were compatible with the telecom environment. The intention was to reduce product development, installation and maintenance costs.

Since their introduction, the comprehensive NEBS requirements have evolved to include criteria for many physical and electrical aspects of telecom equipment. To assure that equipment is satisfactory for its intended use in various applications, three levels of criteria compliance have been established for telecom equipment. Because the level of compliance has a direct effect on the cost to manufacture the equipment, users can minimize their expenditures by understanding what level of compliance is required for the equipment they plan to install.

Introduction to NEBS

Before the divestiture of the Bell operating companies in 1983, AT&T's Bell Labs/Western Electric established NEBS guidelines for physical configuration and compatibility of telecom equipment used within the Bell System. After divestiture, Bellcore was established to provide the same service to the RBOCs. Bellcore has since been restructured and renamed Telcordia Technologies to serve the current industry, which also includes an ever-growing number of competitive local exchange carriers (CLECs) that provide wireline and wireless voice, data, video and Internet communication services.

Since the original NEBS documents were written, they have periodically been reissued as general requirements. The latest revisions appeared in 1995 as GR-63-Core for physical protection of equipment, and in 1999 as GR-1089-Core for electromagnetic compatibility and electrical safety.

NEBS compliance has become a particularly critical issue to all telecom companies since the Telecom Act of 1996. The act requires all incumbent LECs (ILECs) to provide physical space, power and grounding connections for new CLECs within their existing facilities, better known as co-location facilities. The existing ILEC equipment and the new CLEC equipment must be compatible to operate safely and dependably within the same facility.

To simplify and hasten the compliance process so that new equipment can be deployed rapidly without endangering the integrity and reliability of the base network, the NEBS requirements have been divided into three levels of criteria compliance. A special report titled SR-3580 defines these levels and identifies which of the NEBS criteria apply to each level.

What are NEBS criteria?

The NEBS documents contain criteria for personnel safety, protection of facilities and continuity of operation. Many NEBS criteria are based on national and international standards or FCC requirements. However, NEBS requirements are unique in that they address issues of particular concern to network equipment and the environment of telecom facilities in the U.S.

NEBS requirements are intended to:

- Protect personnel from injury

- Simplify equipment planning and installation

- Protect the network from service outages caused by incompatible equipment

- Prevent interference with licensed radio transmitters and cross-aisle equipment

- Minimize the risk of fires to network facilities and equipment

- Ensure equipment operation under the range of temperature, humidity, vibration and airborne contamination present in network facilities

- Ensure equipment and service survivability in the event of earthquakes

- Ensure equipment compatibility with the network's electrical environment.

The RBOCs require third-party verification that manufacturers' equipment meets NEBS regulations. The NEBS documents include provisions that the various types of equipment "shall be listed for the purpose by a Nationally Recognized Testing Laboratory." An NRTL is an organization that meets standards set by the Occupational Health and Safety Administration and that has received OSHA approval to declare itself as an NRTL. Approved major NRTLs in North American include Underwriters Laboratory and Intertek Testing Services.

The NRTL does the testing or witnesses the testing and issues a report. Each RBOC will individually review the documents and test reports and will individually approve a product on its specific merits.

The GR documents

There are two documents that define NEBS requirements: GR-63-Core, which covers physical requirements, and GR-1089-Core, which covers electromagnetic compatibility and electrical safety. Each document deals with specific parameters, including prescribed test methods and minimum levels of performance.

GR-63-Core. To fully address the physical aspects of equipment, NEBS testing examines different system attributes. The equipment's construction, the physical design of the cabinets and framework is examined to ensure it is consistent with national and international standards. Spatial requirements also are examined, including floor loading, ceiling heights and cable connection allowances. Label readability under normal lighting is verified to determine if there is an adequate level of self-generated illumination. Operational performance measurements also are part of GR-63-Core, including heat dissipation and acoustic noise.

Telecom equipment is required to withstand different conditions. Many tests are conducted to evaluate its durability in different environments and its ability to withstand environmental changes.

For example, thermal operation tests determine how the equipment performs in a range of thermal environments and humidity levels. Also, altitude tests determine its ability to operate in high altitude locations, up to 4000 meters. Office vibrations testing analyzes the ability to operate while being subjected to low amplitude vibrations in the 5 to 100 Hz range.

GR-63-Core also provisions for airborne contaminant testing, which measures how equipment operates under indoor levels of dust and pollutants found in the outdoor atmosphere. Flammability tests examine fire spread, heat flux, rate of heat release and fire resistance. Zone 1 to 4 seismic testing simulates an earthquake to see how equipment operates after very low frequency vibrations at high amplitudes, as experienced in different earthquake zones.

Because much of this equipment will be shipped to different locations, GR-63-Core compliant equipment also must be tested to determine its ability to withstand temperature and humidity variations while in storage and to withstand possible vibration or mishandling while in transit.

GR-1089-Core. While GR-63-Core addresses the physical attributes of the equipment, GR-1089-Core address its electromagnetic compatibility and electrical safety.

Electrical safety is of great importance to ensure protection of personnel by limiting voltages and leakage currents. Listing requirements are reviewed to ensure that registration and listing by a recognized safety agency is complete. Bonding and grounding testing looks at multipoint grounding, types of connections and short-circuit fault currents.

EMI emissions and EMI immunity also are examined for GR-1089-Core compliance. Emissions are measured for radiated electric and magnetic fields, and equipment is tested with or without doors and with panels open or removed. Conducted emissions levels for power, voiceband and signal leads also are measured. In addition, immunity testing is performed to determine if the equipment will operate properly when subjected to radiated fields and conducted RF signals on AC and DC power and signal leads.

Complete operational tests are performed to ensure maximum safety and operability. Tests include, but are not limited to, output short-circuit, lighting and power fault immunity and electrostatic discharge.

Levels of compliance

Special Report SR-3580 groups the generic NEBS criteria (from GR-63-Core and GR-1089-Core) into three levels of compliance. This grouping is intended to "clarify the impact of non-conformance" and "allow the broad range of NEBS requirements to be judiciously applied to equipment based on the equipment's application and impact to operation of the network." The table above summarizes the criteria for each level.

Level 1 criteria. Level 1 is the minimum acceptable level of environmental compatibility needed to protect the network facility (equipment and structure) and operating personnel. Possible applications where Level 1 compliance is acceptable include trials of prototype equipment, limited installations of equipment used for non-vital services and the minimum requirement established by RBOCs and other incumbent carriers for co-located equipment installed by CLECs. It is important to know that there is no assessment of equipment operability associated with Level 1 conformance. Operability criteria only are assessed at Levels 2 and 3.

Level 2 criteria. Level 2 is the minimum level of compatibility needed to provide limited assurance that the equipment will operate within the network facility environment. It also incorporates all the protection requirements of Level 1. The assurance of operability is limited to controlled environments, such as data centers, or "normal" environments as defined by the criteria. Other possible applications that require Level 2 compliance include widespread or long-term installations of equipment performing non-critical network service where loss of equipment operation under environmental extremes can be tolerated.

Level 3 criteria. Level 3 is the minimum level of compatibility needed to provide maximum assurance that the equipment will operate within the network facility environment. It incorporates the protection and requirements of Level 1, the performance requirements of Level 2 (at a greater degree of severity) and additional criteria intended to ensure that the equipment will not experience excessive service interruptions over the equipment's anticipated life. Possible applications requiring Level 3 compliance include critical network equipment such as digital switches, transport products and power systems.

Application of the NEBS criteria can enhance network integrity and protect the equipment and the safety of the personnel who operate it. On the other hand, failure to understand them can jeopardize network integrity and safety or dramatically increase the cost of the equipment by specifying compliance levels beyond what the application requires.