Lecture 1 - Introduction

• Instructor: Dr. Apichon Witayangkurn (apichon@siit.tu.ac.th)
• Note: Lecture notes adapted with modification from book material that accompany the book "Computer Networking: a Top-Down Approach"

Course Overview

Objectives of the Class

• Provide principles and concepts of networking and protocols emphasizing application, data link, network, and transport protocols
• Provides insight into practical networks, including various kinds of network architectures, protocols, and routing algorithms
  • For Example: TCP, UDP, HTTP, DNS, FTP, SMTP

Learning Outcomes

• Understand the concept of Computer networks and OSI Layers
• Explain the operation of protocols in the TCP/IP and the requirements of protocols
• Describe the architecture of the Internet and the components involved in the day-to-day running network
• Analyze, capture network traffic and apply the theory of fundamental network performance analysis
• Understand the concept of network security and identify security issues

Class Structure

• Main Lectures: 13 lectures (3 hours with 10-15 mins break)
  • Section 1: Thu 13:00 - 16:00
  • Section 2: Fri 09:00 - 12:00
• Attendance check: random check (5%)
• Homework Assignments: 4 homework (35%)
  • Takes a lot of time to do. (Practical thing)
• Midterm Exam: Onsite-based exams
• Final Exam: Onsite-based exams

Course Schedule

Grading

Remark:

• Check course schedule (date and time)
• Attend lecture
• Work on assignments
• Don't forget exam date!

Textbook

James F. Kurose, Keith Ross
Computer Networking: a Top-Down Approach, 8th Edition
Publisher: Pearson, 2020
ISBN-13: 9780135928738

Lecture notes: adapted with modification from book material that accompany the book "Computer Networking: a Top-Down Approach"

Introduction

Overview/Roadmap

• What is the Internet? What is a protocol?
• Network edge: hosts, access network, physical media
• Network core: packet/circuit switching
• Protocol layers, service models
• Security

What is The Internet?

The Internet is a global network of billions of computers and other electronic devices. With the Internet, it's possible to access almost any information, communicate with anyone else in the world, and do much more.

Think of the Internet like a massive highway system connecting cities (computers) all over the world, allowing vehicles (data) to travel between them.

The Internet: A Basic View

Billions of Connected Computing Devices (Hosts = End Systems)

• hosts = end systems
• Running network apps at Internet's "edge"

Packet Switches

• Forward packets (chunks of data)
• routers, switches

Communication Links

• fiber, copper, radio, satellite
• Transmission rate: bandwidth

Networks

• Collection of devices, routers, links: managed by an organization

Internet: "Network of Networks"

• Interconnected ISPs

Protocols Are Everywhere

• Control sending, receiving of messages
• e.g., HTTP (Web), streaming video, Skype, TCP, IP, WiFi, 4G, Ethernet

Internet Standards

• RFC: Request for Comments
• IETF: Internet Engineering Task Force

A Closer Look at Internet Structure

Network Edge

• hosts: clients and servers
• servers often in data centers

Access Networks, Physical Media

• wired, wireless communication links

Network Core

• interconnected routers
• network of networks

Internet-Connected Devices

Examples of Internet-connected devices:

• Amazon Echo
• Internet refrigerator
• IP picture frame
• Security Camera
• Internet phones
• Slingbox: remote control cable TV
• Gaming devices
• Pacemaker & Monitor
• Web-enabled toaster + weather forecaster
• Tweet-a-watt: monitor energy use
• AR devices
• Fitbit
• sensorized, bed mattress
• bikes
• cars
• scooters
• Others?

Data Center

Colocation Services = put your server in data center

Data Center Components

• 2U BigTwin™
• GPU
• Ultra
• 3U/6U MicroBlade™
• Mainstream Servers
• Storage Systems
• Supermicro RSD

Server Pricing Examples

Server 1U:

• 2,000 2,400 / Month
• IP address (IPv4) 1 IP
• Domestic Bandwidth 1 Gbps
• International Bandwidth
• 3 Mbps (Upload) /10 Mbps (Download)
• Power 1 AMP / 1 Outlet
• NOC Support 24×7

Server 2U:

• 3,000 3,400 / Month
• IP address (IPv4) 1 IP
• Domestic Bandwidth 1 Gbps
• International Bandwidth
• 3 Mbps (Upload) /10 Mbps (Download)
• Power 1.5 AMP / 2 Outlet
• NOC Support 24×7

Access Network Components

Hardware Components

• 2 Port Repeater
• ADSL modem with Wi-Fi
• 8 Port HUB
• Ethernet Card
• 24 Port FE+ 2 Port SFP Combo
• Switch
• Wireless Router Front & Rear View
• Router
• Broadband Router
• Modem with Fiber Optic

Switch with POE (Power over Ethernet)

POE Switch Configuration

• PoE switch connected to AC power
• Provides both power and data through Ethernet cable
• Distance: up to 100 m

Supported Devices

• IP Phones (PoE supported)
• Wireless Access Points (PoE supported)
• IP Camera (PoE supported)
• PDs (Powered Devices)

Alternative: PoE Injector

• non-PoE Ethernet switch → PoE injector
• AC power → SFP
• Distance: fiber up to 160 m
• Distance: up to 100 m

POE is like having electricity and internet running through the same cable - convenient for devices like cameras and wireless access points that need both.

Access Networks, Physical Media

Network Topology Example

• PC #1 connected to router
• Networked Printer/FAX Copier/Scanner
• Laptop
• New Ethernet Switch with Uplink Port
• PC #2, PC #3
• Router has LAN Ports, WAN Port
• Connection To DSL/Cable Modem

Network Architecture – Office

Office Network Components

• Internet connection
• Firewall for security
• Router for network routing
• WiFi Router for wireless connectivity
• Switch for wired connections
• Multiple Switches for different network segments
• Laptop PC and Smartphone (wireless devices)
• Server for network services
• Desktop PC workstations
• IP Phone systems
• Printer and Scanner devices
• Various Ring topology connections

An office network is like a city's infrastructure - the router is the main highway interchange, switches are local roads, WiFi is public transportation, and the firewall is the city security checkpoint.

Links: Physical Media

Bit Propagation

• Bit: propagates between transmitter/receiver pairs
• Physical link: what lies between transmitter & receiver

Guided Media

• Signals propagate in solid media: copper, fiber, coax

Unguided Media

• Signals propagate freely, e.g., radio

Twisted Pair (TP)

• Two insulated copper wires
  • Category 5: 100 Mbps, 1 Gbps Ethernet
  • Category 6: 10 Gbps Ethernet

Unshielded Twisted Pair (UTP) Categories

CAT7 has additional shielding for better performance.

Links: Physical Media (Continued)

Coaxial Cable

• Two concentric copper conductors
• Bidirectional
• Broadband:
  • Multiple frequency channels on cable
  • 100's Mbps per channel

Fiber Optic Cable

• Glass fiber carrying light pulses, each pulse a bit
• High-speed operation:
  • High-speed point-to-point transmission (10's-100's Gbps)
• Low error rate:
  • Repeaters spaced far apart
  • Immune to electromagnetic noise

Fiber optic cables are like high-speed trains - they carry massive amounts of data very quickly with minimal interference, while coaxial cables are more like regular highways.

Links: Physical Media - Wireless Radio

Wireless Radio Characteristics

• Signal carried in various "bands" in electromagnetic spectrum
• No physical "wire"
• Broadcast, "half-duplex" (sender to receiver)

Propagation Environment Effects

• Reflection
• Obstruction by objects
• Interference/noise

Radio Link Types

1. Wireless LAN (WiFi)

   • 10-600's Mbps; 10's of meters

2. Wide-area (e.g., 4G cellular)

   • 10's Mbps over ~10 Km

3. Bluetooth: cable replacement

   • Short distances, limited rates

4. Terrestrial microwave

   • Point-to-point; 45 Mbps channels

5. Satellite

   • Up to 45 Mbps per channel
   • 270 msec end-end delay

Access Network: Wi-Fi Access

WLAN Frequency Bands Comparison

WiFi Evolution

IEEE Standards:

• 802.11b → 80211g → 802.11n → 802.11ac → 802.11ax → 802.11be
• WiFi → WiFi 4 → WiFi 5 → WiFi 6/6E → WiFi 7 (?)

Access Network: Cell Tower

Images of various cell tower configurations including:

• Traditional cell towers

• Building-mounted antennas

• Directional antennas

• Indoor small cells

• Pico Cell

  • ขยายสัญญาณโทรศัพท์

Access Network: Satellite

Corporate Broadband Services

Star Link system featuring IPSTAR Satellite

Network Configuration

CS LoxInfo Internet Network Operation Center → Internet → Corporate User

Hub/Switch → IP Star Network Box connects to Corporate User

Satellite internet is like having a direct line to space - useful for remote areas where traditional cables can't reach, but with slightly longer delays due to the distance signals must travel.

The Network Core

Key Components

• Mesh of interconnected routers
• Packet-switching: hosts break application-layer messages into packets
  • Network forwards packets from one router to the next, across links on path from source to destination

Two Key Network-Core Functions

1. Routing

• Global action: determine source-destination paths taken by packets
• Routing algorithms

2. Forwarding

• aka "switching"
• Local action: move arriving packets from router's input link to appropriate router output link

Forwarding Table Example

┌─────────────┬──────────────┐
│ Header Value│ Output Link  │
├─────────────┼──────────────┤
│    0100     │      3       │
│    0101     │      2       │
│    0111     │      2       │
│    1001     │      1       │
└─────────────┴──────────────┘

Process:

1. Destination address in arriving packet's header
2. Routing algorithm determines local forwarding table
3. Router uses forwarding table to determine output link

Routing is like planning a road trip across the country (the big picture), while forwarding is like making individual turns at each intersection (local decisions).

Routing vs Forwarding Analogy

Routing

[Map showing route from San Jose to Northampton across United States]

• 45 h driving time
• 3,053 miles total distance
• Plans the overall path from source to destination

Forwarding

[Detailed highway interchange image]

• Makes local decisions at each router
• Determines which exit/road to take based on forwarding table

Routing determines "I need to go from California to Massachusetts" while forwarding decides "at this intersection, I turn right to stay on the correct route."

Public and Private Address Range

Public Address Range

Private Address Range

พูดถึง NAT protocol, convert ip from private to public.

Think of public IPs as street addresses visible on Google Maps (everyone can find you), while private IPs are like apartment numbers within a building (only meaningful within that building's internal system).

The Internet: A "Services" View

Infrastructure that Provides Services to Applications

Applications:

• Web (HTTP protocol)
• Streaming video, multimedia teleconferencing
• Email (SMTP protocol)
• Games
• E-commerce
• Social media
• Inter-connected appliances, …

Provides Programming Interface to Distributed Applications

• Allowing sending/receiving data over network

Examples: HTTP, Skype, Streaming video

The Internet is like a vast postal service infrastructure - it doesn't create the letters (applications), but it provides the reliable delivery system for them to reach their destinations.

What's a Protocol?

Human Protocols

• "what's the time?"
• "I have a question"
• introductions

Network Protocols

• Computers (devices) rather than humans
• All communication activity in Internet governed by protocols

Protocols define the format, order of messages sent and received among network entities, and actions taken on message transmission, receipt

Rules for:

• … specific messages sent
• … specific actions taken when message received, or other events

What's a Protocol? - Examples

A Human Protocol and a Computer Network Protocol

Human Protocol:

Person 1: Hi
Person 2: Hi
Person 1: Got the time?
Person 2: 2:00

Computer Network Protocol:

Client: TCP connection request
Server: TCP connection response
Client: GET http://gaia.cs.umass.edu/kurose_ross
Server: <file>

Protocols are like the rules of conversation - just as humans follow social conventions when talking ("Hello" → "Hello" → conversation), computers follow strict rules for communication (request → acknowledgment → data transfer).

Protocol "Layers" and Reference Models

Networks are Complex, with Many "Pieces"

Components:

• hosts
• routers
• links of various media
• applications
• protocols
• hardware, software

Question: Is there any hope of organizing structure of network?

• and/or our discussion of networks?

Example: Organization of Air Travel

A Series of Steps, Involving Many Services

Departure (Left Side):

• ticket (purchase)
• baggage (check)
• gates (load)
• runway takeoff
• airplane routing

Arrival (Right Side):

• ticket (complain)
• baggage (claim)
• gates (unload)
• runway landing
• airplane routing

Throughout Journey:

• airplane routing

End-to-End Transfer of Person Plus Baggage

How would you define/discuss the system of airline travel?

• A series of steps, involving many services

Example: Organization of Air Travel - Layered Approach

Layers: Each Layer Implements a Service

Service Layers:

1. Ticketing service
2. Baggage service
3. Gate service
4. Runway service
5. Routing service

Characteristics:

• Via its own internal-layer actions
• Relying on services provided by layer below

Each layer of air travel depends on the layer below it - you can't board the plane (gate service) until you've checked your bags (baggage service), which requires having a ticket (ticketing service).

Why Layering?

Approach to Designing/Discussing Complex Systems

Benefits:

1. Explicit structure allows identification, relationship of system's pieces

   • Layered reference model for discussion

2. Modularization eases maintenance, updating of system

   • Change in layer's service implementation: transparent to rest of system
   • e.g., change in gate procedure doesn't affect rest of system

Layering is like building with LEGO blocks - you can change one layer without affecting others, making the system easier to understand, maintain, and upgrade.

OSI Model vs TCP/IP Model (Internet Protocol Stack)

Model Comparison

OSI Model (7 Layers):

1. Application Layer
2. Presentation Layer (compression, encryption)
3. Session Layer (Manage session, Socket)
4. Transport Layer
5. Network Layer
6. Data Link Layer
7. Physical Layer

TCP/IP Model (4 Layers):

1. Application Layer
2. Transport Layer
3. Internet Layer
4. Network Access Layer

Updated TCP/IP Model (5 Layers):

1. Application Layer
2. Transport Layer
3. Network Layer
4. Data Link Layer
5. Physical Layer

TCP/IP Protocol Suite

Application Layer Protocols:

• HTTP
• SMTP
• Telnet
• FTP
• DNS
• RIP
• SNMP

Transport Layer Protocols:

• TCP
• UDP

Network Layer Protocols:

• ARP
• IP
• IGMP
• ICMP

Data Link Layer Protocols:

• Ethernet
• Token Ring
• ATM
• Frame Relay

Physical Layer:

• Copper Cable, Coax, Fiber, Wireless, Radio

Layered Internet Protocol Stack

Five-Layer Model

┌────────────────┐
│  application   │
├────────────────┤
│   transport    │
├────────────────┤
│    network     │
├────────────────┤
│      link      │
├────────────────┤
│   physical     │
└────────────────┘

Layer Descriptions:

1. Application: Supporting network applications

   • HTTP, IMAP, SMTP, DNS

2. Transport: Process-process data transfer

   • TCP, UDP

3. Network: Routing of datagrams from source to destination

   • IP, routing protocols

4. Link: Data transfer between neighboring network elements

   • Ethernet, 802.11 (WiFi), PPP

5. Physical: Bits "on the wire"

Services, Layering and Encapsulation

Application Layer

Source → Destination

M (message)

Application exchanges messages to implement some application service using services of transport layer

Transport Layer

Ht | M (segment)

Transport-layer protocol transfers M (e.g., reliably) from one process to another, using services of network layer

Transport-layer protocol encapsulates application-layer message, M, with transport layer-layer header $H_t$ to create a transport-layer segment

• $H_t$ used by transport layer protocol to implement its service

Network Layer

Hn | Ht | M (datagram)

Network-layer protocol transfers transport-layer segment $[H_t | M]$ from one host to another, using link layer services

Network-layer protocol encapsulates transport-layer segment $[H_t | M]$ with network layer-layer header $H_n$ to create a network-layer datagram

• $H_n$ used by network layer protocol to implement its service

Link Layer

Hl | Hn | Ht | M (frame)

Link-layer protocol transfers datagram $[H_n | [H_t | M]]$ from host to neighboring host, using network-layer services

Link-layer protocol encapsulates network datagram $[H_n | [H_t | M]]$, with link-layer header $H_l$ to create a link-layer frame

Services, Layering and Encapsulation - Complete View

Source to Destination Flow

Source:

┌────────────────┐
│  application   │ → M (message)
├────────────────┤
│   transport    │ → Ht | M (segment)
├────────────────┤
│    network     │ → Hn | Ht | M (datagram)
├────────────────┤
│      link      │ → Hl | Hn | Ht | M (frame)
├────────────────┤
│   physical     │
└────────────────┘

Destination:

┌────────────────┐
│  application   │ ← M
├────────────────┤
│   transport    │ ← Ht | M
├────────────────┤
│    network     │ ← Hn | Ht | M
├────────────────┤
│      link      │ ← Hl | Hn | Ht | M
├────────────────┤
│   physical     │
└────────────────┘

Encapsulation is like sending a letter: you write the message (application), put it in an envelope with recipient info (transport), the post office adds routing labels (network), and it's placed in a delivery truck (link/physical). Each layer adds its own wrapper with information needed for that layer's job.

Encapsulation: An End-End View

Complete Network Path

Source:

┌────────────────┐
│  application   │
├────────────────┤    message: M
│   transport    │    segment: Ht | M
├────────────────┤    datagram: Hn | Ht | M
│    network     │    frame: Hl | Hn | Ht | M
├────────────────┤
│      link      │
├────────────────┤
│   physical     │
└────────────────┘

Switch (Link/Physical only):

┌────────────────┐
│      link      │ → Hl | Hn | Ht | M
├────────────────┤
│   physical     │
└────────────────┘

Router (Network/Link/Physical):

┌────────────────┐
│    network     │ → Hn | Ht | M
├────────────────┤    Hl | Hn | Ht | M
│      link      │
├────────────────┤
│   physical     │
└────────────────┘

Destination:

┌────────────────┐
│  application   │ ← M
├────────────────┤    Ht | M
│   transport    │    Hn | Ht | M
├────────────────┤    Hl | Hn | Ht | M
│    network     │
├────────────────┤
│      link      │
├────────────────┤
│   physical     │
└────────────────┘

Key Points:

• Switches operate at Link/Physical layers
• Routers operate at Network/Link/Physical layers
• Only end systems use all 5 layers

Network Security

Original Design Limitations

• Internet not originally designed with (much) security in mind
  • Original vision: "a group of mutually trusting users attached to a transparent network" ☺
  • Internet protocol designers playing "catch-up"
  • Security considerations in all layers!

ตอนเขาสร้าง Internet ก็ไม่ได้คิดหรอกว่าจะ Popular มาฮิตฮอดกันขนาดนี้อะ ตอนนั้นก็เลยไม่ได้คิดเรื่อง Security ขนาดนั้น

We Now Need to Think About

1. How bad guys can attack computer networks
2. How we can defend networks against attacks
   • Multiple tools: firewall, IDS
   • ไปหามาว่า IDS ทำงานยังไง?
3. How to design architectures that are immune to attacks
   • Load balance,

Confidentiality, Integrity, Availability

CIA Triad

• (Redundancy) Uplink: คืออะไร
• Backup: เราก็สามารถใช้ NAS ได้ backup every day, week.

The CIA triad is like protecting a valuable painting: Confidentiality means only authorized people can see it, Integrity ensures it hasn't been altered or damaged, and Availability means it's accessible when the museum is open.

Bad Guys: Packet Interception

Packet "Sniffing"

Interception: Attack on Confidentiality

• Broadcast media (shared Ethernet, wireless)
• Promiscuous network interface reads/records all packets (e.g., including passwords!) passing by

Wireshark, TCP dump software used for our end-of-chapter labs is a (free) packet-sniffer

• Wireshark uses the libpcap (Packet Capture library) to capture live network data on most systems.

Packet sniffing is like eavesdropping on a party line telephone - if the network is shared (like WiFi), someone can listen in on all conversations unless they're encrypted.

Bad Guys: Fake Identity

IP Spoofing

Injection of packet with false source address

IP spoofing is like sending a letter with a fake return address - the recipient thinks it came from someone else. This can be used for malicious purposes or to hide the attacker's identity.

Bad Guys: Denial of Service

Denial of Service (DoS)

Attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic

Attack Process:

1. Select target
2. Break into hosts around the network (see botnet)
3. Send packets to target from compromised hosts

• ที่ต้องมีหลาย ๆ อันเพราะว่า Firewall / IDS จะตรวจจับได้ยากไง ถ้าเป็นแค่ DoS เครื่องเดียว มันก็ตรวจได้เลยสิ เออ!
  • แต่ละเครื่องก็อาจจะเป็นของคนทั่วไปที่โดน Malware infected นี่แหละ

         ┌─── attacker ───┐
         │                │
    ┌────┴────┐      ┌────┴────┐
    │ zombie  │      │ zombie  │
    └────┬────┘      └────┬────┘
         │                │
         └────→ target ←──┘
                  ↑
         ┌────────┼────────┐
    ┌────┴────┐   │   ┌────┴────┐
    │ zombie  │───┘   │ zombie  │
    └─────────┘       └─────────┘
    
    Multiple compromised hosts
    (zombies/bots) all attack target

• Target (Connection → Port → 16 bits → 65k ports ถ้า botnet มาเชื่อมหมดแล้ว คนอื่นก็เข้ามาไม่ได้สิ) (CHECK?)

A DDoS attack is like a flash mob intentionally blocking a store's entrance - so many fake customers crowd the doorway that real customers can't get in to shop.

Lines of Defense

Security Measures

1. Authentication: Proving you are who you say you are
   • Cellular networks provides hardware identity via SIM card; no such hardware assist in traditional Internet
2. Confidentiality: Via encryption
   • Protocol like HTTP, FTP, Telnet, Plain SMTP should NOT be used! (Sent in plain text)
   • HTTPS, SSH, TLS, SSL
3. Integrity checks: Digital signatures prevent/detect tampering
4. Access restrictions: Password-protected VPNs
5. Firewalls: Specialized "middleboxes" in access and core networks:
   • Off-by-default: filter incoming packets to restrict senders, receivers, applications
   • Detecting/reacting to DOS attacks

Network security is like securing a building: authentication is checking ID at the door, encryption is speaking in code, integrity checks are tamper-evident seals, access restrictions are locked doors, and firewalls are security guards filtering who gets in.

Summary

Key Topics Covered

• Internet overview
• What's a protocol?
• Network edge, access network, core
• Layering, service models
• Security