OSI (Open Systems Interconnection) Model
The OSI model is a conceptual framework used to understand and implement network architecture. It consists of 7 layers, each with specific functions and protocols.
Application Layer
Provides network services directly to end-users and applications.
Protocols: HTTP, HTTPS, FTP, SMTP, DNS, DHCP, SNMP, NTP
Presentation Layer
Translates data between the application layer and the network format. Handles encryption, compression, and data conversion.
Protocols: SSL/TLS, JPEG, MPEG, ASCII, EBCDIC
Session Layer
Establishes, maintains, and terminates connections between applications.
Protocols: NetBIOS, RPC, PPTP, SAP
Transport Layer
Provides reliable data transfer, error recovery, and flow control.
Protocols: TCP, UDP, SCTP
Network Layer
Handles routing and forwarding of data between different networks.
Protocols: IP, ICMP, IGMP, ARP, BGP, OSPF
Data Link Layer
Provides node-to-node data transfer and error detection/correction.
Protocols: Ethernet, PPP, HDLC, STP, IEEE 802.1Q
Physical Layer
Transmits raw bit stream over physical medium.
Protocols: RS-232, USB, Ethernet physical layer, DSL
TCP/IP Model
The TCP/IP model is a more practical implementation-focused model that consists of 4 layers. It is the foundation of the Internet and most modern networks.
Application Layer
Combines the functionality of OSI layers 5-7. Provides network services to end-user applications.
Protocols: HTTP, HTTPS, FTP, SMTP, DNS, DHCP, SNMP, NTP, Telnet, SSH
Transport Layer
Equivalent to the OSI Transport Layer. Provides end-to-end communication and data flow control.
Protocols: TCP, UDP, SCTP
Internet Layer
Equivalent to the OSI Network Layer. Handles routing of packets between networks.
Protocols: IP, ICMP, IGMP, ARP, BGP, OSPF
Link Layer
Combines the functionality of OSI layers 1-2. Interfaces with the network hardware.
Protocols: Ethernet, PPP, HDLC, STP, IEEE 802.1Q, RS-232, USB