Do not confuse the two. While both are NEBS, they are complementary:
GR-63-CORE Issue 5 defines essential physical protection, environmental, and seismic requirements for telecommunications equipment to achieve NEBS compliance. The standard mandates rigorous testing for factors such as thermal cycling, vibration, and fire resistance to ensure equipment reliability in central offices. Access the official standard on Intertek Inform . GR-63 - NEBS Requirements: Physical Protection - Telcordia gr-63-core issue 5 pdf