The TCP/IP Model (Cisco 5-Layer)

Cisco’s TCP/IP model has five layers: the classic model’s Network Access layer is split into Data Link and Physical. Layer Name Function Scope Protocols PDU 5 Application Network services for apps App-to-app HTTP, HTTPS, FTP, SMTP, DNS, DHCP, SNMP, SSH, NTP Messages 4 Transport End-to-end transport, ports, reliability Host-to-host TCP, UDP, SCTP Segments / datagrams […]

The OSI Model — Layers, Scopes, Protocols

Layer Name Main function Scope Typical protocols PDU 7 Application Network services straight to user/system apps App-to-app HTTP, FTP, SMTP, DNS, DHCP, SNMP, NTP, SSH Messages 6 Presentation Formatting: encoding, encryption, compression End-to-end (logical) TLS, SSL, JPEG, ASCII, MPEG Data streams 5 Session Create/maintain/end sessions Session-to-session NetBIOS, RPC, NFS Sessions 4 Transport Reliable/unreliable delivery, flow […]

Encapsulation & Decapsulation

Encapsulation is packing data layer-by-layer with headers (and trailers); decapsulation is the reverse process on the receiver. OSI direction: L7→L1 encapsulates, L1→L7 decapsulates. Protocol data units L7–L5: Data · L4: Segment (TCP) / Datagram (UDP) · L3: Packet · L2: Frame · L1: Bits Headers: L4 TCP/UDP, L3 IP, L2 Ethernet header + FCS trailer […]