The need for high reliability, along with always required cost efficiency, has established a widly accepted cabling concept in recent years which today is well defined in international standards like EN50173-5 or TIA942. Data centres are split into four levels that help allocate the typical services and appli­cations. The Client level contains devices like a server - let it be desk top or rack format or even the modern blades - and all kind of storage devices and systems like SAN or NAS, including tape recording devices for backup purposes.

Access switches are situated at the next level, made to couple and connect all devices from client level. The Distribution level is where routers and layer3 switches operate to make dynamic links between the access level with its aggregated data traffic and the customer application driven from remote place.

The Core level in data centres forms the gate­ way with firewall functionality to the group of network service providers connecting the data centre to the outside world.