Lecture 2 - Protocol Architectures

Communication Protocols

Definition

• Communication protocol: A system of rules that allow two or more entities of a communications system to transmit information via any kind of variation of a physical quantity
• Defines:
  • Rules, syntax, semantics and synchronization of communication
  • Possible error recovery methods
• Can be implemented by:
  • Hardware
  • Software
  • Combination of both

The Need for Protocol Architecture

To transfer data, several tasks must be performed:

1. Source activation: Must either activate the direct communications path or inform the network of the identity of the desired destination system
2. Destination readiness: Must ascertain that the destination system is prepared to receive data
3. Application readiness: File transfer application on source must ascertain that the file management program on destination is prepared to accept and store the file for this particular user
4. Format translation: May need to be performed if the file formats used on the two systems are different

Functions of Protocol Architecture

• Modular approach: Instead of implementing communication logic as a single module, the task is broken up into subtasks, each implemented separately
• Vertical stack arrangement: Modules are arranged in a vertical stack
• Layer functions:
  • Each layer performs a subset of functions
  • Relies on next lower layer for primitive functions
  • Lower layers provide services to the next higher layer
  • Layers should be defined so that changes in one layer do not require changes in other layers

Key Features of a Protocol

• Syntax: Format of data blocks
• Semantics: Control information for coordination and error handling
• Timing: Speed matching and sequencing

Simple Protocol Architecture

Agents Involved

• Applications: Examples include file transfer and electronic mail
  • โปรแกรมที่เราใช้จริง เช่น Gmail, LINE, Zoom
• Computers: Execute applications that support multiple simultaneous applications
  • เครื่องที่รันแอปพวกนี้ ซึ่งสามารถเปิดหลายแอปพร้อมกันได้
• Networks: Communication infrastructure
  • โครงสร้างพื้นฐานที่ใช้ส่งข้อมูล (Wi-Fi, 5G, Fiber)

Communication Layers

Three relatively independent layers:

1. Application Layer
   • Contains logic to support applications

   A ส่ง Gmail จาก Port 1, เปิด LINE จาก Port 2
   C อาจจะเปิด Gmail จาก Port 3, LINE จาก Port 4
   ไม่จำเป็นต้องตรงกัน เพราะแค่รู้ว่า port ไหนคุยกับแอปไหนก็พอ

2. Transport Layer
   • Collects mechanisms in a common layer shared by all application

   รับข้อมูลจากหลายแอป แล้วจัดให้ไปส่งถูกแอปที่ปลายทาง
   ใช้ Port number / Service Access Point (SAP) เป็นตัวแยกว่า “ของชิ้นนี้เป็นของ Gmail” หรือ “ของชิ้นนี้เป็นของ LINE”

3. Network Access Layer
   • Concerned with the exchange of data between a computer and the network to which it is attached

   คือการสื่อสารจริง ๆ ระหว่างเครื่องกับเครือข่าย
   ที่นี่เราจะใช้ IP Address → ระบุ “เครื่องปลายทางอยู่ที่ไหน”

Protocol Models

Comparison of Protocol Models

• Upper layers: Handle application-specific functions
• Lower layers: Handle network communication functions

OSI Reference Model

Seven Layers Overview

Example

Layer 7: Application Layer

• Purpose: Provides interface between host's communication software and external applications
• Functions:
  • Synchronization of client/server applications
  • Error control and data integrity between applications
  • System-independent processes to a host
• Example Protocols: HTTP, FTP, SMTP, Telnet, SNMP

Layer 6: Presentation Layer

• Purpose: Acts as data format translator
• Functions:
  • Format translation to ensure data can be read by applications
  • Data structuring and negotiating data transfer syntax
  • Data encryption, decryption, compression, and decompression
• Note: Only layer that can actually change data
• Examples: JPEG, ASCII, EBCDIC, TIFF, GIF, PICT, MPEG, MIDI, QuickTime, RTF

Layer 5: Session Layer

• Purpose: Dialog control among devices
• Functions:
  • Determines beginning, middle, and end of sessions/conversations
  • Acts as intermediary for applications
• Protocols: NFS, SQL, RPC, AppleTalk Session Protocol, X Window, DNA SCP

Layer 4: Transport Layer

• Purpose: End-to-end connections and data delivery between hosts
• Functions:
  • Segmentation and reassembly of data
  • Fault detection and error recovery
  • Establishing, maintaining, and tearing down virtual circuits
  • Reliable networking via acknowledgments, sequencing, and flow control
• Protocols: TCP, UDP, SPX

Layer 3: Network Layer

• Purpose: Best path determination for packet delivery across networks
• Functions:
  • Routed protocols (IP) for logical addressing
  • Router operations for packet forwarding
• Routing table contains:
  • Network Address
  • Interface (exit interface for forwarding packets)
  • Metric (distance to reach remote network)
• Packet types:
  • Data Packets: Transport data across internetwork (IP, IPX)
  • Route Update Packets: Send updates to neighbor routers (RIP, EIGRP, OSPF)
• Protocols: IP, IPX, AppleTalk DDP

Layer 2: Data Link Layer

• Purpose: Reliable data transfer from Network layer to Physical layer
• Functions:
  • Data formatting into frames for Physical layer transmission
  • Error notification (not correction)
  • Network topology and flow control
• Sublayers:
  • MAC (Media Access Control): Hard-coded address on NIC (48 bits, 12 hexadecimal digits)
  • LLC (Logical Link Control): Framing, error control, flow control, SAP identification

Layer 1: Physical Layer

• Purpose: Moves bits between nodes
• Functions:
  • Electrical, mechanical, procedural, and functional requirements
  • Activation, maintenance, and deactivation of physical connectivity
  • Voltage specifications, wire speed, pin-out cables
  • Interface setup between DTE and DCE

Encapsulation Process

• Encapsulation: Process of adding header or trailer to PDU at each layer
• Protocol Data Unit (PDU): Layer n control information + layer n+1 encapsulated data
• Examples: L7PDU, L6PDU, L2PDU
• Data naming by layer:
  • Application: Data
  • Transport: Segment
  • Network: Packet or Datagram
  • Data Link: Frame
  • Physical: Bits
    

TCP/IP Protocol Architecture

We actually use this one! (Above is like the standards)

Overview

• TCP: Transmission Control Protocol
• IP: Internet Protocol
  • We need to use both of them together!
• Result of protocol research and development conducted in the ARPANET project
• Referred to as TCP/IP protocol suite
• Comprises a large collection of protocols that are Internet standards

TCP/IP Layers

5. Application Layer

• Purpose: Interacts with software application programs on source and destination computers (closest to end-user)
• Functions:
  • Identify communication partners
  • Determine resource availability
  • Synchronize communication
  • Allow users to log on to remote hosts
  • Provide various e-mail services
  • Offer distributed database sources and access for global information

4. Transport Layer (Host-to-Host)

• Purpose: Provides data transport from process on source system to process on destination system
• Functions:
  • Determines how much data should be sent where and at what rate
  • Ensures data units are delivered error-free and in correct sequence
  • Controls reliability through flow control, error control, and segmentation
  • Offers acknowledgment of successful data transmission
• Primary Protocol: TCP (best-known example)

3. Network Layer (Internet Layer)

• Purpose: Send packets from source to destination
• Layer-management protocols:
  • Routing protocols
  • Multicast group management
  • Network-layer address assignment

2. Network Access/Data Link Layer

• Purpose: Defines how data should be sent using the network
• Functions:
  • Responsible for transmission of data between two devices on same network
  • Includes how bits should be optically signaled by hardware devices
  • Interfaces with network medium (coaxial, optical, fiber, twisted-pair cables)

1. Physical Layer

• Purpose: Covers physical interface between data transmission device and transmission medium
• Concerns: Characteristics of transmission medium, nature of signals, data rate, and related matters

TCP/IP Address Requirements

Two levels of addressing needed:

1. Global Internet Address: Each host on subnetwork must have unique global internet address
2. Port Address: Each process must have address (port) that is unique within the host

Protocol Data Units (PDUs) in TCP/IP

• Application byte stream: User data
• TCP segment: User data + TCP header
• IP datagram: TCP segment + IP header
• Network-level packet: IP datagram + Network header

Transport Layer Protocols

Transmission Control Protocol (TCP)

• Purpose: Transport layer protocol for most applications
• Characteristics:
  • Provides reliable connection for transfer of data between applications
  • TCP segment is the basic protocol unit
  • Tracks segments between entities for duration of each connection

TCP Header Fields (20 octets)

• Source Port and Destination Port
• Sequence Number
• Acknowledgment Number
• Header Length, Reserved, Flags, Window
• Checksum and Urgent Pointer
• Options + Padding

User Datagram Protocol (UDP)

• Purpose: Alternative to TCP
• Characteristics:
  • Does not guarantee delivery, preservation of sequence, or protection against duplication
  • Enables procedure to send messages with minimum protocol mechanism
  • Adds port addressing capability to IP
  • Used with Simple Network Management Protocol (SNMP)
  • Includes checksum to verify no error occurs in data

UDP Header Fields (8 octets)

• Source Port and Destination Port
• Segment Length and Checksum

Internet Protocol (IP)

IPv4 Header (20 octets)

• Version, IHL, DS, ECN, Total Length
• Identification, Flags, Fragment Offset
• Time to Live, Protocol, Header Checksum
• Source Address, Destination Address
• Options + Padding

IPv6 Header (40 octets)

• Version, DS, ECN, Flow Label
• Payload Length, Next Header, Hop Limit
• Source Address (128 bits)
• Destination Address (128 bits)

Protocol Architecture Standardization

Service Primitives and Parameters

Services between adjacent layers expressed as:

• Primitives: Specify the function to be performed
• Parameters: Used to pass data and control information

Service Primitive Types

1. REQUEST: Primitive issued by service user to invoke service and pass parameters
2. INDICATION: Primitive issued by service provider to:
   • Indicate procedure has been invoked by peer service user
   • Notify service user of provider-initiated action
3. RESPONSE: Primitive issued by service user to acknowledge or complete procedure previously invoked by indication
4. CONFIRM: Primitive issued by service provider to acknowledge or complete procedure previously invoked by request

Service Types

• Confirmed Service: Uses Request → Indication → Response → Confirm sequence
• Nonconfirmed Service: Uses only Request → Indication sequence

• ฝั่งขวาพวก UDP Only

Traditional Internet-Based Applications

Three common applications standardized to operate on top of TCP:

Simple Mail Transfer Protocol (SMTP)

• Provides mechanism for transferring messages among separate hosts

File Transfer Protocol (FTP)

• Used to send files from one system to another under user command
• Accommodates both text and binary files

Secure Shell (SSH)

• Provides secure remote logon capability

Multimedia Applications

Multimedia Terminology

• Media: Form of information including text, still images, audio, and video
• Multimedia: Human-computer interaction involving text, graphics, voice and video; also refers to storage devices for multimedia content
• Streaming media: Multimedia files that begin playing immediately or within seconds after received by computer from Internet/Web

Media Types

• Text: Information entered via keyboard, directly readable and printable
• Audio: Sounds produced by human speech mechanism
• Image: Communication of individual pictures, charts, or drawings
• Video: Sequences of pictures in time

Multimedia Application Domains

Sockets Programming (เพิ่มเติม)

If we need to create network ourselves

Overview

• Concept developed in 1980s in UNIX environment as Berkeley Sockets Interface
• De facto standard Application Programming Interface (API)
• Basis for Windows Sockets (WinSock)
• Enables communication between client and server process
• May be connection-oriented or connectionless

The Socket

• Definition: Formed by concatenation of port value and IP address
• Characteristics:
  • Unique throughout the Internet
  • Used to define an API
  • Generic communication interface for writing programs using TCP or UDP

Socket Types

1. Stream sockets: All data blocks guaranteed for delivery and arrive in order sent
2. Datagram sockets: Delivery not guaranteed, order not necessarily preserved
3. Raw sockets: Allow direct access to lower-layer protocols

Core Socket Functions

Connection-Oriented Socket Flow

Server Side:

1. socket() - Open communication endpoint
2. bind() - Register well-known address with system
3. listen() - Establish client's connection; request queue size
4. accept() - Accept first client connection request on queue
5. send()/recv() - Send/receive data
6. close() - Shutdown
   Client Side:
7. socket() - Open communication endpoint
8. connect() - Set up connection to server
9. send()/recv() - Send/receive data
10. close() - Shutdown

Summary

Key Concepts Covered

• Protocol Architecture Need: Modular approach to communication tasks
• Simple Protocol Architecture: Three-layer model (Application, Transport, Network Access)
• TCP/IP Protocol Architecture: Internet standard protocol suite
• TCP/IP Layers: Application, Transport, Network, Data Link, Physical
• TCP and UDP: Reliable vs. unreliable transport protocols
• IP and IPv6: Network layer protocols for packet delivery
• Protocol Interfaces: Service primitives and parameters for layer communication
• Standardization: Framework for protocol development within architecture
• Internet Applications: SMTP, FTP, SSH as traditional applications
• Multimedia: Media types and application domains
• Sockets Programming: API for network application development