Layer 7: Application Layer
Provides network services to end-users; deals with application-specific functionalities.
HTTP - HyperText Transfer Protocol
Stateless; Client-server model
HTTPS - HyperText Transfer Protocol Secure
Encrypted communication; TLS/SSL based
FTP - File Transfer Protocol
File transfer; Control & Data connections
TFTP - Trivial File Transfer Protocol
Lightweight file transfer; No authentication
SFTP - SSH File Transfer Protocol
Secure file transfer; Runs over SSH
SMTP - Simple Mail Transfer Protocol
Email sending; Store-and-forward
IMAP - Internet Message Access Protocol
Email retrieval; Synchronization supported
POP3 - Post Office Protocol v3
Simple email retrieval; Downloads & deletes from server
DNS - Domain Name System
Hostname-to-IP mapping; Hierarchical & distributed
SNMP - Simple Network Management Protocol
Network device monitoring; Uses UDP; MIB-based
NTP - Network Time Protocol
Clock synchronization; Precision in milliseconds
DHCP - Dynamic Host Configuration Protocol
Automatic IP allocation; Lease concept
Telnet
Remote login; Plaintext, insecure
SSH - Secure Shell
Remote login; Encrypted & secure
Layer 6: Presentation Layer
Responsible for translation, encryption, and compression of data.
TLS - Transport Layer Security
End-to-end encryption; Session security
SSL - Secure Sockets Layer
Older version of TLS; Less secure
XDR - External Data Representation
Platform-independent data format
ASN.1 - Abstract Syntax Notation One
Telecom encoding rules; Used in SNMP/LDAP
MIME - Multipurpose Internet Mail Extensions
Defines data types for email attachments
Layer 5: Session Layer
Maintains sessions between applications; dialog control and synchronization.
NetBIOS - Network Basic Input/Output System
Session communication; Legacy Windows networking
PPTP - Point-to-Point Tunneling Protocol
VPN tunneling; Insecure/legacy
SIP - Session Initiation Protocol
VoIP signaling; Establish, modify, terminate calls
RPC - Remote Procedure Call
Distributed computing; Abstracts function calls
SMB - Server Message Block
File/printer sharing; Windows environments
Layer 4: Transport Layer
Ensures end-to-end communication, reliability, error correction, and multiplexing.
TCP - Transmission Control Protocol
Reliable; Flow control (sliding window); Congestion control
UDP - User Datagram Protocol
Unreliable; Low latency; Used in DNS, VoIP
SCTP - Stream Control Transmission Protocol
Supports multi-streaming; Used in telecom signaling
DCCP - Datagram Congestion Control Protocol
Provides congestion control without reliability
QUIC - Quick UDP Internet Connections
Google protocol; Runs over UDP; Built-in encryption & multiplexing
Layer 3: Network Layer
Provides logical addressing, routing, and path determination.
IP - Internet Protocol
IPv4 (32-bit addressing); IPv6 (128-bit addressing)
ICMP - Internet Control Message Protocol
Diagnostics & error messages; Used by ping/traceroute
IGMP - Internet Group Management Protocol
Manages multicast groups; IPv4 only
RIP - Routing Information Protocol
Distance-vector; Max hop count = 15
OSPF - Open Shortest Path First
Link-state; Uses Dijkstra’s algorithm; Fast convergence
BGP - Border Gateway Protocol
Path-vector; Internet backbone protocol; Policy-based routing
IS-IS - Intermediate System to Intermediate System
Link-state; Used in ISP backbones
MPLS - Multiprotocol Label Switching
Label-based forwarding; Traffic engineering
Layer 2: Data Link Layer
Handles framing, error detection, and MAC addressing; ensures node-to-node reliability.
Ethernet (IEEE 802.3)
Dominant LAN technology; Frame-based
PPP - Point-to-Point Protocol
Encapsulation over serial links; Authentication supported
ARP - Address Resolution Protocol
IP-to-MAC mapping; Local networks
VLAN (IEEE 802.1Q)
Network segmentation; Logical LANs
STP - Spanning Tree Protocol
Prevents switching loops; Builds tree topology
LACP - Link Aggregation Control Protocol
Combines multiple links; Load balancing & redundancy
FDDI - Fiber Distributed Data Interface
Legacy; Fiber-based LAN rings
HDLC - High-Level Data Link Control
Bit-oriented; Encapsulation over WAN
Layer 1: Physical Layer
Concerned with raw bit transmission over physical media.
Wi-Fi (IEEE 802.11)
Wireless LAN; Uses CSMA/CA; Multiple standards (a/b/g/n/ac/ax)
Bluetooth
Short-range; Low power; IoT, peripherals
DSL - Digital Subscriber Line
Broadband over telephone lines
Ethernet Physical
Defines cables, connectors, electrical signaling
SONET/SDH - Synchronous Optical Networking
High-speed fiber transport; Carrier-grade
ISDN - Integrated Services Digital Network
Digital transmission; Voice & data over telephone lines
NFC - Near Field Communication
Short-range wireless; Contactless payments
Zigbee
Low-power mesh networking; IoT devices