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RAG, retrieval-augmented generation, is text our code adds to a prompt before the model sees it. The agent searches the user's notes on every prompt, and puts the closest passages in front of it. The model answers from what the request holds. It still makes every decision: call a tool, or answer. The agent, the loop …

An AI agent is a program that runs a loop around a model. The user types a prompt. The model makes every decision: call a tool, or answer. The agent carries out the decisions, and keeps the conversation. A program around a model is also called its harness. The top bar picks the API: Anthropic Messages or OpenAI Chat …

HTTP keeps nothing between requests, so a server that wants to know who is asking must be told on every request. Basic authentication, defined in RFC 7617 , does it the simplest way: every request carries the username and password in a header. The tool shows each message whole, so the password can be read crossing the …

A session moves the password off the wire. The browser sends the password once, in a login form. The server creates a record, "this random id belongs to alice", and hands the id back in a cookie. The browser returns the cookie on every request, and the server looks the id up to learn who is asking. It follows Basic …

A home or café router has one public address and gives its clients private ones, so it rewrites every packet that crosses it. On the way out, it rewrites the source. On the way back, it rewrites the destination. The NAT table, in the pane on the right, is what drives both. Step runs the clock to the next event, through …

TCP numbers every byte it sends, and every ACK names the next byte it expects, so each acknowledgment can be traced back to the segments it covers. Host A sends from left to right, Host B from right to left. Step plays six scenes, one after another: the handshake, data and close; a lost segment and its retransmission; …

TLS protects a password on its way to a server, and that raises one question: how does a browser know it is talking to shop.example, and not to someone standing in its place? Only the server has to answer it, because the browser is the one about to hand over a secret. Six parties play out the answer: a root CA, an …

TLS is what turns the password of Basic HTTP Authentication from readable text into ciphertext. Before any HTTP is sent, the client and the server agree on a secret that nobody on the path can compute. The server proves that it holds the private key of a certificate issued for the name the client typed. Every record of …

When a link fails, the routers at its two ends describe the network afresh and flood the news to everyone in the area; every router then reruns SPF on the new database. The demo cuts the R1B–R1D link in area 1 of the network from the earlier demos, while a host on R1A's LAN sends a steady stream of packets to ABR-1B, …

Inside an area every router holds the whole map, but no router LSA ever leaves its area. Routes between areas are carried by the ABRs as summary LSAs: a prefix and a cost, with nothing of the links behind them. This demo follows one such route from area 2 to area 1 across the network from the Hello , Database Exchange …