Computer Networks · TEE · mocks

Q1B · Reference models

TEE mock C · full paper

TEE · 100 attempted marks · solutions for every choice · current syllabus 702AI0C023

TEE practice mock · Q1B. Draw the OSI reference model and explain the function of each layer. [5 mock marks]

Answer

The Open Systems Interconnection (OSI) model separates network functions into seven layers. A layer offers services upward and uses services below. Peer layers communicate logically through protocol rules; actual data moves down the sender’s stack, across links and up the receiver’s stack.

Swipe across the diagram to read its labels ↔
OSI layers mapped to the four-layer TCP/IP model
Diagram: OSI layers mapped to the four-layer TCP/IP model. Labels: OSI layers mapped to the four-layer TCP/IP model | OSI layers mapped to the four-layer TCP/IP model | 7 Application | 6 Presentation | 5 Session | 4 Transport | 3 Network | 2 Data link | 1 Physical | Application | HTTP, DNS, FTP, SMTP | Transport | Internet | Link / network access | Includes physical access | Some textbooks split link into data link + physical: five layers.
OSI seven-layer model mapped to the four-layer TCP/IP model.
LayerTaskExample
7 ApplicationServices used by network applicationsHTTP, DNS, FTP, SMTP
6 PresentationRepresentation, encoding and application data transformationsCharacter encoding, serialization; encryption as a conceptual function
5 SessionManage dialogue and synchronization/checkpointsSession establishment and resumption concepts
4 TransportProcess delivery; reliability/flow control where suppliedTCP, UDP, SCTP; ports
3 NetworkLogical addressing and routing across networksIP; routers
2 Data linkFraming, local link addressing, medium access and error detectionEthernet/Wi-Fi; MAC addresses
1 PhysicalTransmit signal symbols/bits through a mediumElectrical, optical or radio signals

Encapsulation and delivery

  1. Application creates data. Transport adds a transport header: TCP segment or UDP datagram.
  2. IP adds its header to form a packet. The link adds a header and usually a trailer to form a frame.
  3. The physical layer carries signals. The destination reverses the process and sends the data to the receiving process.
  4. At a router, local framing changes for the next link. A transit router primarily forwards at Layer 3; it need not run the end application.