OSI Layers - Paiet/Tech-Journal-for-Everything GitHub Wiki
OSI Layers
Layer 1 -- Physical
Works at the actual physical layer
Data at the physical layer are called BITS
Cable media
UTP
Fiber
Coax
Connectors
RJ45
SC/ST/LC
BNC
Wireless antennae
Electrical signal transmission/reception
NIC
Network Hub
Signal repeater
Data is sent as electricity, light, or RF
Electrical signal
Changes in voltage up and/or down
Light
Light frequencies and change in pattern
RF
Radio frequencies for wireless TX/RX
Layer 2 -- Data link
Provides the transmission of the data as well as error notification and flow control
Data at this layer is divided into small chunks called FRAMES
Devices that operate at this layer are
Network bridges/switches
Access points
Individual hosts are identified by their layer 2 Media Access Control (MAC) address
The data-link layer delivers data using the MAC address of the host NIC
Defines how data is to access the physical media
Defines the logical topology
Error notification
Cyclic Redundancy Check (CRC)
Ordered frame delivery
Flow control
Logical Link Control
LLC is responsible for flow control and error detection and provides service to layer 3 by forwarding layer 3 protocols to the necessary network interface
Protocols that operate at layer 2
Ethernet
Frame Relay
Wifi
L2TP
Layer 3 - Network
Responsible for defining and connecting networks through logical addressing
IP version 4
IP version 6
Data encapsulated at this level are called PACKETS
Encapsulates data with layer 3 header for transmission by layer 3 devices
Fragmentation is the process of breaking down data into packets small enough for transmission using layer
2 protocols
Data packets are then reassembled after being received
Internet Protocol addressing
Defines networks and hosts on the network
Routing/Routers
Use layer 3 protocols for delivering data
OSPF
BGP
MPLS
Layer 4 - Transport
Responsible for end-to-end communications over a network
Data at this layer is referred to as SEGMENTS
Transport Control Protocol (TCP)
Connection oriented protocol
Implements 3-way handshake to verify properly established connection before sending data
SYN: Synchronization bit is set and sent to the destination host
SYN/ACK: Both Synchronization and Acknowledgement bits are set and sent back to the source host
ACK: Acknowledgement is sent to the destination host and the connection is established
DIAGRAM
Flow Control
Insures data integrity
Receiving host sets limit on how much data the sending host can transmit at one time as to avoid congestion and data loss
Uses sequencing numbers and acknowledgments to check for errors in delivery and then correct them
Windowing
The amount of data that can be sent to the receiving host's buffer while processing already received data
User Datagram Protocol
Connectionless protocol
Fast delivery
Basically none of the features of TCP
Layer 5 - Session
Responsible for setting up, managing, and tearing down
sessions between Presentation Layer entities
Protocols at layer 5
NetBIOS
Network File System (NFS)
Server Message Block (SMB)
Layer 6 - Presentation
Presents data to the Application layer and is Responsible for data translation and code formatting
Translation ensures that both sending and receiving nodes are able to read and understand the data being transferred
Formatting
Responsible for formatting the data in a way that is usable by the Application layer
Compression/decompression
JPEG
MP3
MPEG
HTML*
HTML works on both layer 6 and 7
It recognizes the formatting at layer 6 and presents it using layer 7
Encryption/decryption
TLS/SSL
Layer 7 - Application
Creates a way for computer applications to access and interface with a network (send and receive data)