osi model ส่วนประกอบ

OSI Model 7 Layers

OSI Model Open Systems Interconnection 7 Layers แต่ละชั้นหน้าที่เฉพาะ ISO มาตรฐานอ้างอิงออกแบบแก้ไขปัญหาเครือข่าย

รายละเอียดแต่ละ Layer

# osi_model.py — OSI Model 7 Layers
from dataclasses import dataclass, field
from typing import List, Dict

@dataclass
class OSILayer:
    number: int
    name: str
    thai_name: str
    function: str
    protocols: List[str]
    devices: List[str]
    pdu: str  # Protocol Data Unit
    examples: List[str]
    security: List[str]

class OSIModel:
    """OSI Reference Model"""

    def __init__(self):
        self.layers: List[OSILayer] = []

    def add_layer(self, layer: OSILayer):
        self.layers.append(layer)

    def show_all(self):
        print(f"\n{'='*60}")
        print(f"OSI Model — 7 Layers")
        print(f"{'='*60}")

        for layer in sorted(self.layers, key=lambda l: l.number, reverse=True):
            print(f"\n  Layer {layer.number}: {layer.name} ({layer.thai_name})")
            print(f"    Function: {layer.function}")
            print(f"    Protocols: {', '.join(layer.protocols)}")
            print(f"    Devices: {', '.join(layer.devices)}")
            print(f"    PDU: {layer.pdu}")
            print(f"    Security: {', '.join(layer.security)}")

    def troubleshoot(self, symptom: str):
        """Troubleshoot ตาม Layer"""
        troubleshoot_map = {
            "no_connection": [1, 2],
            "no_internet": [3],
            "slow_connection": [4],
            "app_error": [7],
            "ssl_error": [5, 6],
        }
        layers = troubleshoot_map.get(symptom, [1, 2, 3])
        print(f"\n  Troubleshooting: {symptom}")
        for num in layers:
            layer = next((l for l in self.layers if l.number == num), None)
            if layer:
                print(f"    Check Layer {num} ({layer.name}): {layer.function}")

model = OSIModel()

layers = [
    OSILayer(7, "Application", "แอปพลิเคชัน",
             "ให้บริการ Network แก่ผู้ใช้และแอปพลิเคชัน",
             ["HTTP", "HTTPS", "FTP", "SMTP", "DNS", "DHCP", "SSH", "Telnet"],
             ["Firewall L7", "Load Balancer", "Proxy"],
             "Data",
             ["เปิดเว็บ HTTP", "ส่งอีเมล SMTP", "ดาวน์โหลด FTP", "แปลชื่อ DNS"],
             ["WAF", "Application Firewall", "DDoS Protection"]),
    OSILayer(6, "Presentation", "การนำเสนอ",
             "แปลงข้อมูล เข้ารหัส บีบอัด",
             ["SSL/TLS", "JPEG", "PNG", "GIF", "ASCII", "EBCDIC", "MPEG"],
             ["ไม่มีอุปกรณ์เฉพาะ"],
             "Data",
             ["HTTPS เข้ารหัส SSL/TLS", "แปลง JPEG PNG", "บีบอัด gzip"],
             ["Encryption TLS 1.3", "Certificate Management"]),
    OSILayer(5, "Session", "เซสชัน",
             "จัดการ Session เปิด ปิด ควบคุม",
             ["NetBIOS", "RPC", "PPTP", "SIP", "L2TP"],
             ["ไม่มีอุปกรณ์เฉพาะ"],
             "Data",
             ["Login Session", "Video Call Session", "VPN Tunnel"],
             ["Session Timeout", "Token Management"]),
    OSILayer(4, "Transport", "ขนส่ง",
             "ส่งข้อมูลถูกต้อง ครบถ้วน ตาม Port",
             ["TCP", "UDP", "SCTP", "QUIC"],
             ["Firewall L4", "Load Balancer L4"],
             "Segment/Datagram",
             ["TCP 3-Way Handshake", "UDP Streaming", "Port 80 443"],
             ["Firewall Port Filtering", "Rate Limiting"]),
    OSILayer(3, "Network", "เครือข่าย",
             "Routing กำหนดเส้นทาง IP Address",
             ["IP", "ICMP", "OSPF", "BGP", "ARP", "IPsec"],
             ["Router", "L3 Switch"],
             "Packet",
             ["ping ICMP", "traceroute", "IP Routing"],
             ["ACL", "IPsec VPN", "Firewall L3"]),
    OSILayer(2, "Data Link", "เชื่อมต่อข้อมูล",
             "MAC Address, Error Detection, Frame",
             ["Ethernet", "Wi-Fi (802.11)", "PPP", "VLAN", "STP"],
             ["Switch", "Bridge", "NIC", "Access Point"],
             "Frame",
             ["Switch ส่ง Frame ตาม MAC", "VLAN แบ่ง Network", "Wi-Fi"],
             ["Port Security", "802.1X", "MAC Filtering"]),
    OSILayer(1, "Physical", "กายภาพ",
             "สัญญาณไฟฟ้า แสง คลื่นวิทยุ",
             ["Ethernet (สาย)", "Wi-Fi (คลื่น)", "Fiber Optic", "Bluetooth"],
             ["Hub", "Repeater", "Modem", "สายเคเบิล"],
             "Bit",
             ["สาย Cat6 Ethernet", "Fiber Optic", "Wi-Fi 6"],
             ["Physical Security", "Signal Jamming Prevention"]),
]

for layer in layers:
    model.add_layer(layer)

model.show_all()
model.troubleshoot("no_connection")

Python Network Programming

# network_layers.py — Network Programming ตาม OSI Layer
import socket
import struct

# Layer 4: TCP Socket (Transport)
def tcp_client_example():
    """TCP Client — Layer 4 Transport"""
    # sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    # sock.connect(("example.com", 80))
    # sock.send(b"GET / HTTP/1.1\r\nHost: example.com\r\n\r\n")
    # response = sock.recv(4096)
    # sock.close()
    print("  TCP Client: socket.SOCK_STREAM (Layer 4)")
    print("    Connect -> Send -> Receive -> Close")

# Layer 4: UDP Socket (Transport)
def udp_client_example():
    """UDP Client — Layer 4 Transport"""
    # sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    # sock.sendto(b"Hello", ("example.com", 53))
    # data, addr = sock.recvfrom(4096)
    # sock.close()
    print("  UDP Client: socket.SOCK_DGRAM (Layer 4)")
    print("    SendTo -> ReceiveFrom (No Connection)")

# Layer 3: ICMP Ping (Network)
def ping_example():
    """ICMP Ping — Layer 3 Network"""
    # icmp = socket.getprotobyname("icmp")
    # sock = socket.socket(socket.AF_INET, socket.SOCK_RAW, icmp)
    # # Build ICMP Echo Request
    # header = struct.pack("bbHHh", 8, 0, 0, 1, 1)
    # sock.sendto(header, ("8.8.8.8", 0))
    print("  ICMP Ping: socket.SOCK_RAW (Layer 3)")
    print("    Send ICMP Echo Request -> Receive Echo Reply")

# Layer 7: HTTP Request (Application)
def http_example():
    """HTTP Request — Layer 7 Application"""
    # import urllib.request
    # response = urllib.request.urlopen("https://example.com")
    # html = response.read()
    print("  HTTP Request: urllib/requests (Layer 7)")
    print("    GET/POST -> Response (HTML/JSON)")

# Layer 2: MAC Address (Data Link)
def mac_address_example():
    """MAC Address — Layer 2 Data Link"""
    import uuid
    mac = ':'.join(['{:02x}'.format((uuid.getnode() >> i) & 0xff)
                    for i in range(0, 48, 8)][::-1])
    print(f"  MAC Address: {mac} (Layer 2)")

print("Network Programming by OSI Layer:")
tcp_client_example()
udp_client_example()
ping_example()
http_example()
mac_address_example()

# TCP vs UDP
comparison = {
    "Connection": {"TCP": "Connection-oriented (3-Way Handshake)", "UDP": "Connectionless"},
    "Reliability": {"TCP": "Reliable (Retransmission)", "UDP": "Unreliable (No Guarantee)"},
    "Ordering": {"TCP": "Ordered (Sequence Numbers)", "UDP": "Unordered"},
    "Speed": {"TCP": "ช้ากว่า (Overhead)", "UDP": "เร็วกว่า (Lightweight)"},
    "Use Case": {"TCP": "Web, Email, File Transfer", "UDP": "DNS, Streaming, Gaming, VoIP"},
    "Header": {"TCP": "20-60 bytes", "UDP": "8 bytes"},
}

print(f"\n\nTCP vs UDP:")
for feature, values in comparison.items():
    print(f"  {feature:<12} TCP: {values['TCP']:<35} UDP: {values['UDP']}")

OSI vs TCP/IP

# osi_vs_tcpip.py — OSI Model vs TCP/IP Model
osi_layers = [
    {"osi": "7 Application", "tcpip": "Application", "protocols": "HTTP DNS SMTP"},
    {"osi": "6 Presentation", "tcpip": "Application", "protocols": "SSL/TLS JPEG"},
    {"osi": "5 Session", "tcpip": "Application", "protocols": "NetBIOS RPC"},
    {"osi": "4 Transport", "tcpip": "Transport", "protocols": "TCP UDP"},
    {"osi": "3 Network", "tcpip": "Internet", "protocols": "IP ICMP"},
    {"osi": "2 Data Link", "tcpip": "Network Access", "protocols": "Ethernet Wi-Fi"},
    {"osi": "1 Physical", "tcpip": "Network Access", "protocols": "Cable Fiber"},
]

print("OSI Model vs TCP/IP Model:")
print(f"  {'OSI Layer':<20} {'TCP/IP Layer':<18} {'Protocols'}")
print(f"  {'-'*60}")
for layer in osi_layers:
    print(f"  {layer['osi']:<20} {layer['tcpip']:<18} {layer['protocols']}")

# Common Ports
ports = {
    20: "FTP Data",
    21: "FTP Control",
    22: "SSH",
    23: "Telnet",
    25: "SMTP",
    53: "DNS",
    67: "DHCP Server",
    80: "HTTP",
    110: "POP3",
    143: "IMAP",
    443: "HTTPS",
    993: "IMAPS",
    3306: "MySQL",
    3389: "RDP",
    5432: "PostgreSQL",
    6379: "Redis",
    8080: "HTTP Alt",
    27017: "MongoDB",
}

print(f"\n\nCommon Ports:")
for port, service in sorted(ports.items()):
    print(f"  Port {port:<6} {service}")

เคล็ดลับ

• จำ 7 Layers: Please Do Not Throw Sausage Pizza Away (Physical Data Network Transport Session Presentation Application)
• Troubleshoot: เริ่มจาก Layer 1 ขึ้นไป สายหลุดีไหม IP ถูกไหม Port เปิดีไหม
• TCP vs UDP: TCP เชื่อถือได้ แต่ช้า UDP เร็ว แต่ไม่รับประกัน
• Security: แต่ละ Layer มี Security เฉพาะ Layer 3 IPsec Layer 4 Firewall Layer 7 WAF
• สอบ: CCNA CompTIA Network+ ออกเรื่อง OSI Model ทุกครั้ง

OSI Model คืออะไร

Open Systems Interconnection โมเดลอ้างอิงสื่อสารเครือข่าย 7 Layers ISO มาตรฐานออกแบบแก้ไขปัญหาเครือข่าย

สรุป

OSI Model 7 Layers Physical Data Link Network Transport Session Presentation Application แต่ละชั้นหน้าที่เฉพาะ Protocol อุปกรณ์ Security TCP/IP 4 Layers ใช้จริง Troubleshoot เริ่ม Layer 1 ขึ้นไป CCNA CompTIA