• OSI 7-layer model
• TCP/IP 4-5 layer model
• Mapping OSI ⇄ TCP/IP
• Encapsulation and PDU names
• Key protocols by layer
• Troubleshooting by layers
• Exercises

1. Physical: bits, signaling, media.
2. Data Link: frames, MAC, switches, VLANs (Ethernet, 802.1Q).
3. Network: packets, routing, IP addressing (IPv4/IPv6).
4. Transport: segments/datagrams, reliability (TCP, UDP).
5. Session: dialogs, checkpoints (rarely distinct in practice).
6. Presentation: encoding, TLS, compression.
7. Application: HTTP, DNS, SMTP, etc.

• Link (Network Access): Ethernet, Wi‑Fi.
• Internet: IP, ICMP, ARP/ND, routing.
• Transport: TCP, UDP, QUIC (at app layer but transport semantics).
• Application: HTTP(S), DNS, TLS, SSH, SMTP, etc.

• OSI 1–2 → TCP/IP Link
• OSI 3 → Internet
• OSI 4 → Transport
• OSI 5–7 → Application

• Application: data
• Transport: segments (TCP) / datagrams (UDP)
• Internet: packets (IP)
• Link: frames (Ethernet)
• Physical: bits

[App Data] → TCP hdr → IP hdr → Ethernet hdr/trailer → bits on wire

• Link: Ethernet, 802.11, PPPoE, VLANs, STP.
• Internet: IPv4/IPv6, ICMPv4/v6, ARP, ND, NDP.
• Transport: TCP (handshake, congestion control), UDP, QUIC.
• Application: HTTP/1.1, HTTP/2, HTTP/3, TLS, DNS, SMTP.

• L1/2: link up, duplex/speed, errors (CRC), VLAN tagging.
• L3: addressing, routes, TTL, fragmentation; ping/traceroute.
• L4: ports, state, retransmits; netstat, ss, tcpdump.
• L7: app headers, certs, HTTP status; curl, browser devtools.

1. Draw the encapsulation stack for an HTTPS request over Wi‑Fi and label PDUs.
2. Capture a TCP handshake with a packet analyzer and annotate each flag/field.
3. Map OSI layers to TCP/IP for three protocols (DNS, TLS, QUIC).