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Course Intermediate

Application Layer Protocols

By the end of this course

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01

The HTTP Family

The commitment a method carries, the classes behind status codes, content negotiation through headers, a cookie's scope rules, the framing difference across versions, and cache validation.

  1. 01 HTTP Methods and What They Mean A method is a declaration: the intermediary in between draws the repeatable and storable decisions from it, and nothing verifies the declaration.
  2. 02 Status Codes The status line's first digit is an instruction: the intermediary draws its caching, routing and retry decisions from it without ever opening the body.
  3. 03 Headers and Content Negotiation Adding a field does not buy a decision: three new headers raise the byte count by 82 percent for zero decisions, while declaring the field that enters negotiation fixes nine wrong copies.
  4. 04 Cookies and State Transfer A cookie's scope rule determines which messages it attaches to, its flag rule determines who the stored response goes to; across forty exchanges, three scope rules carry the cookie on 11, 24 and 40 messages in turn, and two exchanges left unflagged cost the intermediary two wrong shareability decisions.
  5. 05 HTTP Versions The same fields are measured across three framing regimes: the text line takes 3724 bytes and 251 blocking units, the binary frame that keeps context gives the same outcome on all 200 decisions for 440 bytes, and in the binary frame with no context 189 decisions move to the endpoints.
  6. 06 HTTP Caching Freshness and validation are separate questions, and the validator has a resolution: it catches 9 of the 12 stale copies across forty exchanges, misses the tag change on 3, and the intermediary calls them fresh — three of the five wrong decisions in the open regime come from here.

02

Secure Transport

The roles of symmetric and asymmetric encryption, verifying the certificate chain, the handshake's round-trip budget, and the certificate's life cycle.

  1. 01 Symmetric and Asymmetric Encryption The roles of the two key models: asymmetric in setup, symmetric in transport. The round-trip cost of setup count per exchange, and the visibility the intermediary loses.
  2. 02 Certificates and the Trust Chain A name binding to a public key, the chain verifying locally all the way to the trust anchor, and this decision never touching the round-trip budget.
  3. 03 The TLS Handshake The handshake's round-trip budget, the round session resumption earns, and the 160 decisions the intermediary loses once the transport envelope closes.
  4. 04 Certificate Life Cycle Revocation as a round debt: how many exchanges not asking costs, the round asking adds per exchange, the knowledge delay of the options in between, and the symptoms of misconfiguration seen at the client.

03

Other Application Protocols

Two-way persistent connections, one-way server streaming, the cost of polling, the channel split in file transfer, the submission/retrieval split in mail, clock synchronization and device management.

  1. 01 WebSocket The upgrade handshake as a regime change: the intermediary falls into a tunnel after 101, all two hundred decisions move to the endpoints, none of the fields the frame carries yields a decision, and masking has a byte cost.
  2. 02 Server-Sent Events What staying HTTP leaves the intermediary: the five decisions the head message carries, the decision point thinning out as event count rises, the wrong readings that a once-taken decision produces when applied to the whole body, and how long a buffering intermediary delays events.
  3. 03 Long and Short Polling Real-time behavior faked by buying rounds: polling adding not a single new field to the protocol, the round cost per decision staying unchanged across four approaches, and the sum of spent rounds and round debt staying fixed.
  4. 04 File Transfer Protocols The split between the control channel and the data channel: which decision the intermediary loses and which it gets wrong when it cannot match the two channels, and how the cost of splitting is separated from the cost of hiding.
  5. 05 Mail Protocols The split between submission and retrieval, and mail's two names: the mail envelope that routes delivery and the header shown to the user are separate fields, they do not verify each other, and the intermediary looks at the envelope.
  6. 06 Time and Management Protocols Time synchronization's one assumption and the round's asymmetry: if the outbound and return delay are not equal, clock offset follows directly from that gap and the protocol has no field in its hands to see it; alongside this, the round and decision balance of the polling and the notifying management model.

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