1. Data Communications

Definition

• Telecommunication: Communication at a distance (between two parties ประมาณนั้น)
• Data: Information presented in whatever form agreed upon by parties creating and using it
• Data Communications: Exchange of data between two devices via transmission medium (e.g., wire cable or wireless)

Effective Characteristics of Data Communication

• Delivery: System must deliver data to correct destination (intended receiver)
• Accuracy: System must deliver data accurately (unchanged data)
• Timeliness: System must deliver data in timely manner
• Jitter: Variation in time delay between signal transmission and reception
  • Causes uneven delay in audio/video streaming
  • Results from network congestion, configuration errors, improper queuing

Five Components of Data Communication

1. Sender: Generates data
2. Transmitter (Message?): Transforms & encodes data
3. Transmission Medium: Carries the signal
4. Receiver: Decodes & converts data into acceptable format (e.g., convert analog signal into bit stream)
5. Protocol: Set of rules governing communication (all agree to some kind of rule)

Data Flow Types

• Simplex: One-way communication (e.g., server to client device)
• Half-duplex: Two-way communication, but not simultaneous (e.g., walkie-talkie)
• Full-duplex: Two-way communication simultaneously (e.g., telephone)

Data Communications Trends

Current Trends

• Traffic Growth: High & steady rate
• New Services Development: Continuous innovation
• Technology Advances: Rapid improvements
• Internet of Things (IoT): Growing connectivity (many devices exchange data together in a network)
  • e.g. Smart Home

Significant Changes in Requirements

• High-speed LANs: Emergence and widespread adoption
• Corporate WAN needs: Increasing demands
• Digital electronics: Widespread implementation
  

Notable Trends in Technology

• Faster and Cheaper: Both computing and communication improving
  • More powerful computers supporting demanding applications
  • Optical fiber and high-speed wireless reducing costs, increasing capacity
• Intelligent Networks: More sophisticated capabilities
  • Differing levels of Quality of Service (QoS)
  • Customizable services in network management and security
• Internet Dominance: Web and associated applications
  • "Everything over IP" approach
  • Intranets and extranets for proprietary information
  • Internet of Things (IoT) expansion
• Mobility Revolution: Mobile device impact
  • iPhone, Android, iPad driving business network evolution
  • Enterprise applications on mobile devices
  • Cloud computing adoption
  • Automated vehicles

Changes in Networking Technology

• Emergence of High-Speed Networks: Meeting increased bandwidth demands
• Corporate WAN Needs: Growing requirements for wide area connectivity
• Digital Electronics: Transition from analog to digital systems

Emergence of High-Speed LANs

• Driver: Personal computers and workstations becoming essential office tools
• Two Significant Trends:
  1. Explosive growth in speed/computing power of personal computers and mobile devices
  2. LANs recognized as viable and essential computing platform
• Requirements for Higher-Speed LANs:
  • Centralized server farms
  • Power workgroups
  • High-speed local backbone

Corporate Wide Area Networking Needs

• Driving Factors:
  • Growing use of telecommuting
  • Changed application structure nature
  • Intranet computing
  • More reliance on personal computers, workstations, and servers
  • More data-intensive applications
  • Every organization requires Internet access
  • More unpredictable traffic patterns
  • Rising average traffic load
  • More data transported off premises into wide area

Digital Electronics Impact

• Consumer Electronics Conversion: Rapid shift to digital technology
• Network Impact: Dramatic increase in image and video traffic
• Applications: Video live streaming, online meetings, online learning

Key Communications Tasks

Tasks เหล่านี้จะ happen ตอนเรา data communicate

• Transmission system utilization
• Interfacing
• Signal generation
• Synchronization
• Exchange management
• Error detection and correction
• Flow control
• Addressing
• Routing
• Recovery (in case of lost data)
• Message formatting
• Security
• Network management

Communications Model

• Source System: Generates and transmits data
• Transmission System: Carries data between source and destination
• Destination System: Receives and processes data

Process Flow

1. Input Information (m) → Source generates data — เขียน Email
2. Input Data g(t) → Transmitter transforms & encodes (digital bit stream)
3. Transmitted Signal s(t) → Analog signal through transmission system
4. Received Signal r(t) → Signal received at destination
5. Output Data g’(t) → Receiver decodes & converts to acceptable format
6. Output Information (m') → Destination processes data

Transmission Medium

• Selection Considerations:
  • Internal use: Business choice
  • Long-distance: Carrier decisions
• Technology Advances: Fiber optic, wireless
• Cost Factor: Transmission costs still high
• Efficiency Focus: Interest in improvement methods

2. Networks

Network Definition

• Network: Set of devices (nodes) connected by communication links (medium)
• Node: Computer, printer, or any device capable of sending/receiving data

Network Criteria

• Performance Measures: (based on its performances)
  • Transit time (device to device)
  • Response time (inquiry to response)
  • Throughput (number of communications happen in a period of time)
  • Delay
• Reliability:
  • Duration of functional operation without interruption
  • Measure of network robustness against failures
• Security:
  • Protection of networking infrastructure from unauthorized access, misuse, or theft

Networking Overview

• Current Scale: Over 20 billion fixed and mobile networked devices
• Growth Drivers:
  • Increasing number and power of computers
  • Need for interconnection
  • Integration of voice, data, image, and video technologies

Network Categories

Wide Area Networks (WAN)

• Coverage: Spans large geographical area (large size)
• Infrastructure: Requires crossing public rights-of-way, relies on common carrier circuits
• Technologies Used:
  • Circuit Switching
  • Packet Switching
  • Frame Relay
  • Asynchronous Transfer Mode (ATM)

Circuit Switching

• Method: Uses dedicated communications path for conversation duration
• Characteristics:
  • Sequence of physical links with dedicated logical channel
  • Example: Telephone network
• Process: Establishes path, maintains connection, releases path

A จะส่งข้อมูลให้ C ต้องจอง Line นั้นก่อนให้มัน Available ถึงจะส่งข้อมูลได้
จะคล้าย ๆ กับเวลาโทรศัพท์ พอรับสายแล้วนั่นคือ Line นั้นถูก established ละ

• Drawback: ถ้า Hacker รู้ channel (once established แล้ว) ก็สามารถขโมยข้อมูลได้เลย

Packet Switching

• Method: Data sent in sequence of small chunks (packets)
• Process: Packets passed from node to node between source and destination
• Usage: Terminal-to-computer and computer-to-computer communications

A → C, B → D ไม่ต้องรอให้ ฝ่ายไหนฝ่ายนึงเสร็จก่อนเลย

• More difficult to steal data, because data will go everywhere
  • Even if someone grabs one packet, it’s just a fragment, they can’t read the whole message easily.

Circuit Switching vs Packet Switching Comparison

Frame Relay

• Evolution: Advanced packet switching system
• Advantage: Large overheads removed for error compensation
• Rationale: Modern systems more reliable, errors caught at end system
• Benefit: Higher speeds with reduced error control overhead
• Method: Packet switching methodology on virtual circuit (virtual circuit packet switching implementation)

• Overhead เหมือนเป็นการจั่วซองจดหมายอะ (route, destination) อย่างของ Circuit switching, มัน establish เส้นนั้นแล้วก็ไม่ต้องบอกละว่าส่งให้ใคร

• Circuit Switching = ขบวนเสด็จ

  ปิดถนนทั้งเส้นให้ A → B ใช้คนเดียว ต้องรอจนกว่าจะเสร็จก่อนคนอื่นถึงจะได้ใช้

• Packet Switching = รถหลายคันวิ่งบนถนน

  รถของใครมาก่อนก็ใช้ได้ก่อน วิ่งคนละเลน คนละเส้นทาง ไม่ต้องรอกัน ขอแค่ถนนว่าง

• Frame Relay = จองเลนไว้ล่วงหน้า

  เหมือน A ↔ B ขอจองเลนหนึ่งไว้เฉพาะตัวเอง รถยังวิ่งแยกกันเป็นคัน ๆ
  แต่มีการจองทรัพยากรบางส่วน

Asynchronous Transfer Mode (ATM)

• เป็นแค่สิธีก่รในการส่ง days
  
• Evolution: Development of frame relay
• Packet Type: Fixed-length packets called "cells"
• Error Control: Even less overhead than Frame Relay
• Speed Range: 10s and 100s of Mbps to Gbps range
• Method: Constant data rate using packet switching with multiple virtual circuits
• Goal: Combine best of both worlds - guaranteed delivery of circuit-switched networks and robustness/efficiency of packet-switching networks

Local Area Networks (LAN)

• Scope: Smaller area (building or small campus)
• Ownership: Usually owned by same organization as attached devices
• Performance: Much higher data rates
• Types:
  • Switched LANs (e.g., Ethernet)
  • Wireless LANs

Metropolitan Area Networks (MAN)

• Position: Middle ground between LAN and WAN
• Ownership: Private or public network
• Characteristics: High speed, large area coverage

The Internet

Historical Background

• Origin: Evolved from ARPANET (1969)
• Developer: Advanced Research Projects Agency (ARPA), U.S. Department of Defense
• Significance: First operational packet network
• Extensions: Applied to tactical radio & satellite networks
• Standardization: Need for interoperability led to TCP/IP protocols

Internet Elements

• Components:
  • Standalone mainframes
  • Local Area Networks
  • Wide Area Networks (e.g., ATM)
  • Routers
  • Ethernet switches
  • Information servers
  • LAN PCs and workstations

Internet Architecture

• Structure: Hierarchical system of Internet Service Providers (ISPs)
• Components:
  • Residential subscribers
  • Regional ISPs
  • Backbone ISPs
  • Corporate LANs
  • Private peering connections
  • Network Access Points (NAP)
  • Points of Presence (POP)

Example Configuration Elements

• Access Methods:
  • Residential user connections
  • High-speed links (e.g., SONET)
  • Internet Service Providers (ISPs)
• Network Infrastructure:
  • Routers
  • ATM networks
  • Ethernet switches
  • Firewall hosts
  • Private WANs
  • Information servers
  • LAN PCs and workstations

Summary

• Key Topics Covered:
  • Data communications needs and model
  • Data communications definition and characteristics
  • Network overview and types
  • Internet introduction and architecture
  • Communication technologies and trends