Networking Standards, Protocols & OSI Model

Slide 1 of 14 | CTS1305C | Week 1

Networking Standards,
Protocols & the OSI Model

The universal framework every network professional must know.

A user reports they can ping a server by IP but cannot browse to it by name. Which OSI layer is the problem at? Understanding the model lets you isolate faults layer by layer instead of guessing.

14 Slides Week 1 OSI / TCP-IP / Standards Concepts + Reference

Slide 2 of 14

Why Networking Standards Matter

Without standards, nothing talks to anything else.

IEEE

Institute of Electrical and Electronics Engineers. Defines LAN standards like 802.3 (Ethernet) and 802.11 (Wi-Fi).

IETF

Internet Engineering Task Force. Publishes RFCs that define TCP/IP protocols, HTTP, DNS, and more.

ISO

International Organization for Standardization. Created the OSI reference model (ISO 7498).

Key Concept

Standards ensure interoperability — a Cisco router can talk to a Juniper switch because they both follow the same IEEE/IETF specifications.

Slide 3 of 14

The OSI Reference Model

Seven layers, from physical signals to user applications.

                7
                Application
                Data
                HTTP, DNS, SMTP, FTP — user-facing services
            

                6
                Presentation
                Data
                Encryption (TLS), compression, data formatting (JPEG, ASCII)
            

                5
                Session
                Data
                Establishes, manages, and terminates sessions (NetBIOS, RPC)
            

                4
                Transport
                Segments
                TCP/UDP, port numbers, flow control, error recovery
            

                3
                Network
                Packets
                IP addressing, routing, ICMP, ARP
            

                2
                Data Link
                Frames
                MAC addresses, switches, Ethernet, error detection (CRC)
            

                1
                Physical
                Bits
                Cables, hubs, voltages, frequencies, connectors
            

Mnemonic

Please Do Not Throw Sausage Pizza Away (L1 to L7) — or reversed: All People Seem To Need Data Processing (L7 to L1).

Slide 4 of 14

Upper Layers: Application, Presentation, Session

Layers 7-5 handle user interaction, data formatting, and session management.

Layer 7 — Application

The layer users interact with. Provides network services to applications: web browsers (HTTP/HTTPS), email clients (SMTP/IMAP), file transfers (FTP/SFTP), name resolution (DNS).

Layer 6 — Presentation

Translates data between the application and the network. Handles encryption/decryption (TLS/SSL), compression, and character encoding (ASCII, Unicode, JPEG, MPEG).

Layer 5 — Session

Manages dialog between two hosts. Establishes, maintains, and tears down sessions. Handles checkpointing and recovery. Protocols: NetBIOS, RPC, PPTP.

In Practice

In the TCP/IP model, these three layers are merged into a single Application layer. Most modern protocols handle all three functions within themselves — for example, HTTPS handles session establishment, encryption, and application data.

Slide 5 of 14

Layer 4: The Transport Layer

Reliable or fast — TCP and UDP serve different purposes.

PDU Terminology

At Layer 4, TCP data units are called segments and UDP data units are called datagrams. Port numbers (0-65535) identify the service — source port + destination port + IP = a socket pair.

Slide 6 of 14

Layer 3: The Network Layer

Logical addressing and routing — how packets find their destination.

IP Addressing

IPv4 (32-bit) and IPv6 (128-bit) logical addresses identify hosts across networks. Unlike MAC addresses, IP addresses are assigned and routable.

Routing

Routers use routing tables to forward packets toward destinations. Each hop decrements the TTL (Time to Live) to prevent infinite loops.

PDU

The Layer 3 PDU is a packet. Key protocols: IP, ICMP (ping/traceroute), ARP (resolves IP to MAC at the L2/L3 boundary).

Slide 7 of 14

Layer 2: The Data Link Layer

Physical addressing, framing, and local delivery.

MAC Addresses

48-bit hardware addresses burned into NICs (e.g., AA:BB:CC:DD:EE:FF). First 3 bytes = OUI (manufacturer). Unique per interface.

Switches

Layer 2 devices that use MAC address tables (CAM tables) to forward frames only to the correct port, creating separate collision domains per port.

Slide 8 of 14

Layer 1: The Physical Layer

Raw bits on the wire — cables, signals, and connectors.

Key Concept

Layer 1 defines the physical medium and signaling method. The PDU is a bit (0 or 1). Devices: hubs, repeaters, cables, connectors. Problems here show up as no connectivity, intermittent drops, or speed mismatches.

Slide 9 of 14

Encapsulation & De-Encapsulation

Data is wrapped in headers (and trailers) as it moves down the stack.

Remember

Sending = encapsulation (add headers going down). Receiving = de-encapsulation (strip headers going up). Each layer only reads its own header.

Slide 10 of 14

Protocol Data Units at Each Layer

Know the name of the data at every layer.

Exam Tip

The PDU naming is one of the most tested concepts. Remember: Data → Segments → Packets → Frames → Bits (top to bottom). UDP calls its L4 PDU a datagram.

Slide 11 of 14

OSI vs TCP/IP Model

The OSI model is the reference; TCP/IP is what actually runs on the internet.

OSI Model (7 Layers)

7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical

Theoretical reference framework (ISO 7498)

TCP/IP Model (4 Layers)

4. Application (= OSI 7+6+5)
3. Transport (= OSI 4)
2. Internet (= OSI 3)
1. Network Access (= OSI 2+1)

Practical model used by the real internet

Why Both?

The OSI model is better for troubleshooting — its granularity helps isolate problems layer by layer. The TCP/IP model reflects how protocols actually work in production networks. Know both.

Slide 12 of 14

IEEE Standards & the RFC Process

The documents that define how networks work.

IEEE 802.3 — Ethernet

Defines wired LAN standards: frame format, CSMA/CD, speeds (10 Mbps to 400 Gbps), cable specifications. The backbone of every LAN.

IEEE 802.11 — Wi-Fi

Wireless LAN standards: 802.11a/b/g/n/ac/ax (Wi-Fi 6). Defines frequencies, modulation, CSMA/CA, channel widths, and MIMO.

IEEE 802.1Q — VLANs

Adds a 4-byte VLAN tag to Ethernet frames, enabling virtual LANs. Trunk ports carry multiple VLANs between switches.

RFCs (Request for Comments)

Published by the IETF. Define internet protocols: RFC 791 (IP), RFC 793 (TCP), RFC 2616 (HTTP/1.1), RFC 8200 (IPv6). Open, peer-reviewed, permanent.

How Standards Are Made

IEEE and IETF follow public, consensus-driven processes. A proposal becomes a draft, undergoes review, and is ratified as a standard. RFCs are numbered sequentially and never deleted — they are obsoleted by newer RFCs.

Slide 13 of 14

Protocols Mapped to OSI Layers

Where each protocol operates in the model.

Protocol Placement

Some protocols span multiple layers. ARP operates at the L2/L3 boundary. DNS is an application-layer protocol that uses UDP (usually port 53) at L4. Knowing where protocols operate is critical for troubleshooting.

Slide 14 of 14

Summary & Key Takeaways

Everything you need to remember from this presentation.

1 Standards bodies (IEEE, IETF, ISO) ensure interoperability between vendors through published specifications.

2 The OSI model has 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, Application.

3 PDUs change names at each layer: Data → Segments → Packets → Frames → Bits.

4 Encapsulation adds headers going down the stack; de-encapsulation strips them going up.

5 The TCP/IP model has 4 layers and maps to the real internet. OSI is the reference; TCP/IP is the implementation.

6 IEEE 802.3 = Ethernet, 802.11 = Wi-Fi, 802.1Q = VLANs. RFCs define TCP/IP protocols.

7 Troubleshoot bottom-up (L1 first) or top-down (L7 first) — the OSI model gives you a systematic approach.

The user from our opening scenario can ping by IP (L3 works) but not browse by name (L7/DNS is broken). The OSI model told us exactly where to look: DNS resolution at the Application layer. Check the DNS server, verify the A record, and the problem is solved.

Networking Standards, Protocols & OSI Model — Cable Run CTS1305C