OSI Model

Question 1

OSI Layers

Answer 1

Physical
Data Link
Network
Transport
Session
Presentation
Application

Question 2

Physical

Answer 2

Media Layer
Data Unit - Bit
—–
Concerned with the transmission and reception of the unstructured raw bit stream over the physical medium.
—–
Application: Physical Structure. Cables, Hubs, etc.
Example: Data Encoding - Physical medium attachment - Transmission technique - Baseband or Broadband - Physical medium transmission Bits & Volts
—–
Central device - Hub

Question 3

Data Link

Answer 3

Media Layer
Data Unit - Bit/Frame
—–
Provides error-free transfer of data frames from one node to another over the Physical Layer
—-
Application: Frames (“envelopes”, contains MAC address)(NIC card - Switch - NIC Card)(end to end)
Example: Establishes & terminates the logical link between nodes - Frame traffic control - Frame sequencing - Frame acknowledgment - Frame delimiting - Frame error checking - Media access control
—–
Central device - Switch, Bridge, Wap
Protocol - PPP/SLIP

Question 4

Network

Answer 4

Media Layer
Data Unit - Packet/Datagram
-----
Application: Packets ("letter", contains IP address)
Example: Routing - Subnet traffic control - Frame fragmentation - Logical-physical address mapping - Subnet usage accounting
* Packet Filtering
-----
Central Device - Routers
Protocol - IP/IPX/ICMP

Question 5

Transport

Answer 5

Host Layer
Data Unit - Segments
—–
Ensures that messages are delivered error-free, in sequence, and with no losses or duplications
—–
Application: TCP. Host to Host, Flow Control
Example: Message segmentation - Message Acknowledgement - Message traffic control - Session multiplexing
* Packet Filtering
—–
Protocol - TCP/SPX/UDP

Question 6

Session

Answer 6

Host Layer
Data Unit - Data
—–
Allows session establishment between processes running on different stations
—–
Application: Synch & send to ports. Logical Ports
Example: Session establishment, maintenance and termination - Session support - perform security, name recognition, logging, etc
—–
Central Device - Logical Ports
Protocols - RPC/SQL/NFS/NetBIOS names

Question 7

Presentation

Answer 7

Host Layer
Data Unit - Data
—–
Formats the data to be presented to the Application layer. It can be viewed as the “Translator” for the network.
—–
Application: Syntax layer. Encrypt & decrypt (if needed)
Example: Character code translation - Data conversion - Data compression - Data encryption - Character Set Translation
—–
Protocols - JPEG/ASCII/EBDIC/TIFF/GIF/PICT

Question 8

Application

Answer 8

Host Layer
Data Unit - Data
—–
Serves as the window for users and application processes to access the network services.
—–
Application: End User Layer. Program that opens what was sent or creates what is to be sent
Example: Character code translation - Data conversion - Data compression - Data encryption - Character Set Translation
—–
Central Device - User Applications
Protocols - SMTP