The Open Systems Interconnection (OSI) Reference Model
Developed by the International Organization for Standardization in 1984, updated in 1994
ISO/IEC 7498-1:1994(E)
ITU-T Rec. X.200 (1994 E)
Upper
Protocol Data Sample Associated TCP/IP Stack or
Layer Name What Happens Unit (PDU) Protocols Devices Comparison Lower
The user (host) connects HTTP
to the Internet via an SMTP
application, such as a SSH Host
7 Application browser or mail client. Data DNS devices
Data is formatted, JPEG
compressed, encrypted or MP3 Upper
otherwise manipulated to GIF Application
Layers
establish a common SSL
6 Presentation syntax. Data TLS n/a
Connection between SOCKS
devices is negotiated and L2TP
managed. Logical port PPTP
5 Session numbers are assigned. Data NETBIOS n/a
Delivery of data, either
"connection-less" or
"connection-oriented".
Transport
Functions include flow TCP
control, error checking, UDP
4 Transport and segmentation. Segment n/a
Routing of data between
networks. Functions IP
include fragmentation, ICMP Internet
quality of service, and error OSPF
3 Network notification. Packet RIP Routers
Delivery of data to devices Lower
in the same network. Layers
Matches IP address to ARP
MAC addresses. Often Ethernet
split into two parts, media 802.11
access control and logical Bluetooth
link control. Functions PPP Network
include traffic Access
synchronization and flow
2 Data Link control. Frame Switches
Transmission of raw data
between devices. Often Cables
refererred to as "bits on NICs
1 Physical the wire". Bits Modems
References:
https://blogs.cisco.com/cloud/an-osi-model-for-cloud
https://www.iso.org/standard/20269.html
http://www.itu.int/rec/T-REC-X.200-199407-I
http://www.ieee802.org/
https://www.lifewire.com/layers-of-the-osi-model-illustrated-818017
Marcelle Lee, March 2018, marcellelee.github.io
