7 Layers of OSI Model: Functions and Examples

OSI or Open Systems Interconnection model consists of 7 Layers that describes how telecommunication or computing systems use to communicate or operate over a network. It was the first standard model for network communications and still widely used for network isolation and troubleshooting.

Layers Functions / Applications Data Types Examples
(7) Application End User / Desktop
-Mail Services
-Directory Services
-Network Virtual Terminal
-File transfer access/management
Data HTTP,SMTP,FTP,
SSH,DNS,Telnet,
IMAP,POP3,LDAP,
HTTPs,TFTP
(6) Presentation Syntax/ Data Representation
-Translation
-Encryption/Decryption (plain to cipher text)
-Compression
Data ASCII,JPEG,MPEG,
GIF,EBDIC
(5) Session Dialog Coordination
-Session establishment/maintenance/
termination
-Synchronization
-Dialog Controllers
Data RPC, SQL,NFS, PAP,API,Sockets,
Winsock,NetBIOS,
SQL
(4) Transport Transfer of Data
-Segmentation & Reassembly
-Service Point Addressing (port
Segments TCP, UDP
(3) Network -Routing (route from source to destination)
-Logical Addressing (IP address)
Packets/ Datagram Routers, IPv4, IPv6, IPSec,Appletalk,
IGMP,ICMP
(2) Data Link Node to Node Data Transfer
2 sub-layers:
(a) Logical Link Control (LLC)
(b) Media Access Control (MAC)
-Framing (attach special bit patterns to start and end of frame
– Physical Addressing (MAC)
-Error Control
-Flow Control
-Access Control
Frames Switch,Bridge,PPP,
SLIP,IEEE 802.3/802.2
ARP,CDP,FDDI,STP
(1) Physical Physical (Electrical and Optical) Connection
-Bit rate control (bps)
-Bit synchronization
-Transmission mode (simplex,half/full duplex)
-Physical topologies (star,bus,mesh)
Bits Cables,Fiber,Coax,Hubs,
Repeaters,Modems,
Wireless

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