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Layering and protocol stacks

The OSI and TCP/IP models, what a service, an interface and a protocol are, how each layer wraps the data from above in its own header (encapsulation), the name of the unit at each layer (message, segment, datagram, frame, bit), and which device works up to which layer (hub, switch or bridge, router, host).

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CN-02Cheat sheet1 pageIn a paid pack

Layering and Encapsulation

The principles of layering for GATE CS: the OSI seven-layer reference model next to the five-layer TCP/IP model, the difference between a service, an interface and a protocol, encapsulation and the protocol data unit at each layer (message, segment, datagram, frame, bit), the address each layer uses, which jobs belong to which layer, and which device (hub, bridge or switch, router, host) works up to which layer. Includes a header-overhead example checked by script and the past question on matching layers to jobs.

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Diagrams from CN-02

Encapsulation down the TCP/IP stack: application data; the transport layer adds a TCP header; the network layer adds an IP header; the link layer adds an Ethernet header and an FCS trailer; the physical layer sends bits.
New header at each layer (shaded); the link layer also adds the trailer. Source: sheet CN-02.