OSI Model Flashcards
OSI
Open Systems Interconnection, 7 layers, 7 to 1 top down, visual model which characterizes and standardizes the communication functions. Each layer serves the layer above it
Layer 7
Application Layer. Highest Layer, where the user interfaces with the computer and that’s when our applications / programs run.
File transfers, email, remote terminal access, DNR, etc.
Layer 6
Presentation Layer, provides translation to/from the application layer. How images or data are presented. Performs data encryption, decryption, compression, decompression.
Layer 6 Protocols
Associated with file formats/protocols such as .jpg, .mpeg, .png, TLS, SSL, Voice Codecs
Layer 7 Protocols
FTP (File transfer protocol) and Telnet (depreciated), HTTP, SSH
Layer 5
Session Layer. Coordinates, establishes, manages, and tears down sessions between applications on either side of the connection.
Responsiblefor coordinating these connections and tears down these connections
Layer 5 Protocols
NetBios, PAP, SIP
Layer 4
Transport Layer. Segments and reassembles data from upper layers and unites them into the same single data stream. Provides flow control for data, loss prevention, as well as reliable and unreliable transport methods
Layer 4 Protocols
TCP (Transmission Control Protocol), UDP (User Datagram Protocol) RTP (Real-time Transport Protocol) ESP (Encapsulating Security Payload)
Layer 4 Protocol Data Unit
TCP: Segment if connection transmission
UDP:Datagram if connection-less tramsission
Layer 7 Protocol Data unit
Data
Layer 6 Protocol Data unit
Data
Layer 5 Protocol Data Unit
Data
Layer 4 Devices
Firewall
Layer 7 Devices
Host Computer/Server
Layer 6 Devices
Host Computer/Server
Layer 5 Devicecs
Host Computer/Server
Layer 3
Network Layer. Routers/Internet Protocols live here. Provides logical network addressing and path determination/routing services. Responsible for packet delivery, fragmentation, and sequencing.
Layer 3 Protocols
IP (Internet Protocol), ICMP (Internet Control Message Protocol), EIGRP (Enhanced Interior Gateway Routing Protocol), OSPF (Open Shortest Path First)
Layer 3 Devices
Routers, Multi-layer switch
Layer 3 Protocol Data Unit
TCP: Packet
UDP: Datagram
Networking Layer
The bottom four layers of the OSI model make up the network layers, (from four to one) Transport layer, Network layer, data link layer, physical layer
Layer 2
Data Link Layer, subdivided into two sub layers LLC (Logical Link Controller) and MAC (Media Access Control).
MAC
Layer 2 sub layer, Media access control, delivers frames using unique hardware addressing
LLC
Layer 2 sub layer, Logical Link Controller, provides error detection and control
Layer 2 Protocol Data Unit
Frame
Layer 2 Protocols
LLC, MAC, 802.3 (Ethernet standards) 802.11 (Wifi standards)
Layer 2 Devices
Switches
Layer 1
Physical Layer. The Wire or Physical Media. Turns raw bits into electrical signaling and defines physical network media.
Layer 1 Protocol Data Unit
Bits (0s and 1s)
Layer 1 Protocols
Voltage, Pinouts, Cable Specs. Half Duplex, Full Duplex
Layer 1 Devices
Hub/Repeater, cables and media
Full Duplex
Data can be transmitted in both directions on a signal carrier at the same time. One workstation can be sending data on the line while another workstation is receiving data
Half Duplex
Between two devices, only one device is capable of transmitting and receiving data on a network or bus at one time. Bi-directional but data can only go in one direction at a time
All people seem to need data processing
Going down the layers of the OSI Model, A, P, S, T, N, D, P
Please do not throw sausage pizza away
Going up the layers of the OSI Model, P, D, N, T, S, P, A
