datasheet explanation

If you're not already familiar with the OSI reference model, take a look here.

(I just did a quick search but there's tonnes of information online) https://www.networkworld.com/article/3239677/lan-wan/the-osi-model-explained-how-to-understand-and-remember-the-7-layer-network-model.html

Essentially a network stack is broken into 7 district layers (for ease of reference - in actuality it's 5 as it's based on the TCP/IP, but don't worry about that for now)

Layer 4 connections refers to the transport layer - TCP/IP think of an IP address and a port number. Traditional firewalls work on Layer 4 as they only block/allow IP addresses and ports. As this is lower down the OSI layer, it requires less compute resource compared to a full Layer 7 request.

A layer 7 request is one that utilises all 7 layers of the reference model such as an HTTP request and you need to process and read information such as headers or cookies. This ultimately uses more processing power as it's more intensive work.