OSI Model Flashcards
OSI Model Layers
7 - Application
6 - Presentation
5 - Session
4 - Transport
3 - Network
2 - Data Link
1 - Physical
Please Do Not Throw Sausage Pizza Away
OSI Model Data Layers
Physical - Bits
Data Link - Frames
Network - Packets
Transport - Segments
Session / Presentation / Application - Data
Do Some People Fear Birthdays
Layer 1
Physical; Transmission of bits across the network occurs physically & electrically (1s & 0s)
Layer 1 Transition Modulation
Switching between levels to represent 1 or 0; Copper wire - Voltage (0V for 0, +5V/-5V for 1); Fiber Optic - Light (On for 1, Off for 0)
Layer 1 Wiring Standards
RJ-45 Connector on CAT5/ CAT5E/ CAT6; Crossover Cable - 568A on End A, 568B on End Z; Straight Cable - 568B on both ends
Wiring Standard 568A (L-R)
Green / White
Green
Orange / White
Blue
Blue / White
Orange
Brown / White
Brown
Wiring Standard 568B (L-R)
Orange / White
Orange
Green / White
Blue
Blue / White
Green
Brown / White
Brown
Layer 1 Network Topology
Bus; Ring; Star; Hub-And-Spoke; Full Mesh; Partial Mesh
Layer 1 Processes - Synchronization
Asynchronous Communication - Start & stop bits for out of sync data; Synchronous Communication - real-time communication using a common time source
Layer 1 Processes - Bandwidth Utilization
Broadband - divides bandwidth into separate channels; Baseband - uses all frequency of the cable
Layer 1 Multiplexing
Involves taking some limited amount of a resource and using it more efficiently, example: allowing multiple people to use baseband at the same time
Layer 1 Multiplexing - TDM
Time Division Multiplexing - allocates dedicated time slots
Layer 1 Multiplexing - StatTDM
Statisitical Time Division Multiplexing - dynamically allocates time slots based on when people need it
Layer 1 Multiplexing - FDM
Frequency Division Multiplexing - divides the medium into channels
Layer 1 Devices
Cables (fiber, ethernet, coaxial); Wireless (bluetooth, wi-fi, near field); Infrastructure (hubs, access points, media converters)
Layer 2
Data Link; Responsible for packaging bits from Layer 1 (Physical) into frames and transmitting them; Performs error detection & correction, identifies devices using MAC (Media Access Control) addresses, provides flow control
Layer 2 MAC Address
Media Access Control; for identifying a device physically and allowing it to operate on a logical topology; 48-bit address assigned to every network interface card (NIC), written in hexidecimal numbers (0-9, A-F), First 24 bits is for the manufacturer, last 24 bit for specific device
Layer 2 LLC
Logical Link Control; Provides connection services and acknowledges message receipt ensuring controlled data flow; Limits data sent by a sender and prevents overwhelming receiver; Uses a checksum to detect corrupted data frames
Layer 2 Synchronization Modes - Isochronous
Common reference clock; Time slots for transmissions; Less overhead
Layer 2 Synchronization Modes - Synchronous
Devices use the same clock and control characters for synchronization
Layer 2 Synchronization Modes - Asynchronous
Devices reference own clock cycles; No strict control over communication timing
Layer 2 Devices
NICs (Network Interface Cards); Bridges; Switches
Layer 3
Network; Concerned with routing & forwarding traffic using logical addresses
Layer 3 Logical Addressing Variants - IPv4
4 sets of numbers separated by dots (172.16.254.1)
Layer 3 Logical Addressing Variants - IPv6
8 sets of 4 hexidecimal characters separated by colons (2001:0000:130F:0000:0000:09C0:876A:130B)
Layer 3 Switching / Routing Methods - Packet switching / routing
Data is divided into packets then forwarded
Layer 3 Switching / Routing Methods - Circuit Switching
a dedicated communication link is established between 2 devices
Layer 3 Switching / Routing Methods - Message Switching
data is divided into messages that can be stored then forwarded
Layer 3 Route Discovery & Selection
Routing protocols help decide how data is going to flow across the network & how the routers are going to communicate that information; Routers maintain routing tables for determining the best path; Dynamic protocols enable routers to share and update route info
Layer 3 Connection Services
Augments Layer 2 services; Involves flow control, prevents sender from overwhelming receiver; Packet reordering, ensures data packets arrive & are reassembled in the correct order
Layer 3 ICMP
Internet Control Message Protocol; Used for sending error messages & operational information to an IP destination; Ping - helps troubleshoot network issues by testing connectivity & response times; Traceroute - traces the route of a packet through the network
Layer 3 Devices
Routers; Multi-layer switches (combines Layer 2 switch & Layer 3 router; switch is ALWAYS Layer 2 unless called Multi-layer switch, which makes it Layer 3)
Layer 4
Transport; Divides upper and lower layers; Segments - data type for TCP; Datagram - data type for UDP
Layer 4 Devices
WAN Accelerators; Load balancers & firewalls
