Earlier today, whilst on a client site, waiting for a PC to rebuild (5 times – and I thought my desktop support days were over… maybe that’s why they should be…), I saw a diagram of the open systems interconnection (OSI) reference model pinned up above a desk. I’ve seen many OSI model representations over the years, but this one was probably the clearest example I’ve seen in a while (especially for TCP/IP), so I’ve reproduced it here: