Layering and architecture

語彙

English	意味
computer networks	computer networks
layering/ˈleɪərɪŋ/	layering
service/ˈsɜːvɪs/	Activities performed to meet people's needs or wants rather than supplying a physical good.
physical/ˈfɪzɪkl/	Describing security measures involving tangible barriers, facilities or protection of people and equipment.
link/lɪŋk/	link
network/ˈnetwɜːk/	A set of connected devices or nodes that can exchange information.
transport/ˈtrænspɔːt/	transport
application	application
encapsulated	encapsulated

English

The stack

Computer networks are built by layering: each layer offers a service to the one above and consumes the one below. The five-course stack: physical, link, network, transport, application.
Data is encapsulated downward — each layer adds its header — and decapsulated upward, each layer seeing only its own promise.

{exercise:uni-cs0901-stack}

実践

A 100-byte payload leaves with how many Ethernet+IP+TCP header bytes?

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English

A change confined to one layer needs no change elsewhere IF the service interface holds. Ethernet went from 10 Mb/s to 100 Gb/s under identical IP because the link service (best-effort frames) never changed.
A leaky interface destroys it: a browser that reads the TTL below is written once and breaks forever.

{exercise:uni-cs0901-interface}

実践

Ethernet could evolve under identical IP because —

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English

A 100-byte payload leaves the application as $14 + 20 + 20 = 54$ bytes of headers around it: the NIC strips 14, IP strips 20, TCP strips its 20.
The internet's hourglass: narrow waist (IP), wide top (applications), wide bottom (links) — one protocol at the waist lets everything above talk to everything below. OSI's 7 layers split our link in two and add presentation and session on top.

{exercise:uni-cs0901-hourglass}

実践

The waist of the internet hourglass is —

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