OSI Model Flashcards
Layer 1
Physical
Layer 2
Data Link
Layer 3
Network
Layer 4
Transportation
Layer 5
Session
Layer 6
Presentation
Layer 7
Application
Layer 1 devices
Ethernet/fiberoptic, Bluetooth, Wifi, Repeaters, Hubs etc. Dumb devices that just repeat the data sent into them
Layer 2 devices
Simple switches, Network Interface Cards, Bridges
Layer 3 devices
Routers, Multi-layer switches, IPv4 Protocol, IPv6 Protocol, ICMP
Layer 4 Devices
TCP, UDP, Firewalls, Load Balancers
Layer 5 devices
H.323 - H.264, NetBIOS
Layer 6 devices
How is the data requested displayed. E.G:
HTML, XML, Scripting languages
ASCII, EBCDIC, UNICODE
Gif, Mov, JPG
TLS, SSL
Layer 7 Devices
Not applications, from a wider persepective eg. the services that allow applications to function.
Email (SMTP, IMAP, POPv3)
Internet Browsing (HTTP, HTTPS)
Domain Name Service
File transfer protocol (FTP, FTPS)
Remote Access (SSH, Telnet, RDP)
SNMP
Layer 1 functions
Transmission of bits across the network
Wiring standards
Physical topology
Synchronising bits
Multiplexing strategy
Bandwith Usage
What are the common topology types?
Bus - Single line of failure
Ring
Ring FDDI - Dual ring operating in different directions
Star - Centered communication from server
Hub - Some level of failover - hubs connect close devices and communicate with each other
Mesh - Every devices is linked with every device - fully redundant, however impratical for larger networks
Partial Mesh - Combination between mesh and hub, not fully redundant
How is communication synchronised?
Asynchronous - Communication is modulated by transmitting a start and stop bits to initiate communication
Synchronous - communication occurs based on the agreed reference clock
Bandwidth utilisation?
Broadband - Multiple data streams through the same transmission infrastructure
Baseband - entire stream is dedicated to one purpose eg ethernet, phone calls
What is the purpose of multiplexing?
To allow communication between multiple devices on the network to communicate without having data clashes.
Multiplexing strategies?
Time-division multiplexing - Communication occurs within dedicated timeslots that have been assigned to different devices
Statistical division multiplexing (StatTDM) - Dynamically assigns timeslots to devices based on an as-needed basis instead of statistically assigning
Frequency division multiplexing (FDM) - Transmission medium is divided into different channels based on frequency - eg broadband
Layer 2 functions
Packaging bits into frames for transmitting those frames on the network. Performing error correction/detection, and identifying devices through MAC addresses
MAC
Physical Addressing
Logical Topology
Method of transmission
Logical Link control - connection services and syncronising transmissions
What is a MAC address and how is it identified?
Media Access Control - an address that uniquely identifies Network Interface cards
48 bit address - First 24 are manufacturer code, last 24 are device identifier
What is LLC?
Logical Link Control - provides connections services, acknowleges receipt of a message and provides flow control. Identifies the amount of data that a receiver can handle.
How is communication syncronised at this layer?
Isochronous - Communications are coordinated by a common reference clock and have dedicated timeslots - similar to TDM
Synchronous - Network devices agree on clocking method to indicate beginning and middle of frames. Uses control characters or separate timing channel
Asynchronous - devices use a start and stop bit to indicate transmission, and reference their own start/stop bits.