Layering and architecture

어휘

English	의미
computer networks	Connected devices and communication links that exchange data using agreed protocols.
layering/ˈleɪərɪŋ/	Organising communication functions into levels that use services from lower levels.
service/ˈsɜːvɪs/	The communication capability one protocol layer offers to the layer above it.
physical/ˈfɪzɪkl/	The network layer concerned with transmitting bits as signals over a medium.
link/lɪŋk/	The network layer concerned with transferring frames across a local link.
network/ˈnetwɜːk/	A set of connected devices or nodes that can exchange information.
transport/ˈtrænspɔːt/	The protocol layer providing communication between application processes, such as through TCP or UDP.
application	The layer containing protocols used by applications, such as HTTP and DNS.
encapsulated	Packaged within the protocol information needed by a lower communication layer.

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}

연습

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}

연습

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}

연습

The waist of the internet hourglass is —

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