SLR04 – Network typologies, protocols and layers AQA GCSE SLR4 Star and bus network topologies AQA GCSE SLR4 Common network protocols AQA GCSE SLR4 The 4 layer TCP IP protocol model Also in this topic... SLR01 – Systems architecture SLR05 – System security SLR06 – Hardware and software SLR07 – Ethical, legal and environmental issues SLR12 – Classification of programming languages