The ETSI standard is the current format for enclosures used in the Telecommunications industry and has been established by the European Telecommunications Standards Institute - hence ETSI. The 19" standard is a general purpose format usable in a wide variety of applications including Telecommunications.
Whereas ETSI enclosures are meant specifically for telecommunications applications and to house telecom equipment built to the ETSI format. However, 19" Rack mountable equipment can also be housed in ETSI cabinets through the use of 19” adapters which convert from ETSI dimensions to 19" mounting dimensions. But the opposite is not possible - i.e. ETSI equipment in 19" Racks.
ETSI cabinets are generally of 2200mm height overall, and either 300mm or 600mm depth, overall. Cable entry provision is provided at top and bottom. Rear panels and front doors are optional. Two versions are on offer the 300mm D "SHALLOW" ETSI Rack which has fixed side panels, and the 600mmD “DEEP” ETSI Rack which has removable side panels.