The terms layer4 and layer7 refer to the protocol layers at which a load balancer operates within the OSI networking model. Layer4 load balancers operate at the transport layer, whilst layer7 load balancers operate at the application protocol level, affording them greater visibility and understanding of the application it is processing itself. This enables advanced functionality and optimisation features including intelligent traffic management, content caching, security and compression. Acceleration Features Layer4 load balancers are still available although their market share has been reducing significantly as layer7 advanced load balancers and ADC’s become more powerful and cost effective.