• Decimal (Base 10): 0–9
• Binary (Base 2): 0, 1 → used in computing
• Hexadecimal (Base 16): 0–9, A–F → readable format for binary
• Conversions: Binary ↔ Decimal ↔ Hex (4 binary bits = 1 hex digit)

• Bit (b): Smallest unit
• Byte (B): 8 bits
• Prefixes:
• Decimal: kilo (10³), mega (10⁶), giga (10⁹)
• Binary: kibi (2¹⁰), mebi (2²⁰), gibi (2³⁰)
• Speed/Throughput: e.g. 90.4 Mbit/s, 125.8 MB/s

• LAN (Local Area Network): Small, local (e.g. office)
• WAN (Wide Area Network): Large-scale, connects LANs (e.g. Internet)

1. Physical: Cables, signals
2. Data Link: MAC, Ethernet, VLAN
3. Network: IP, routing
4. Transport: TCP, UDP, QUIC
5. Session
6. Presentation
7. Application

• Copper: Twisted pair, coaxial
• Optical Fiber:
• Multi-mode: Shorter range, cheaper
• Single-mode: Long range, high bandwidth
• Wireless:
• WLAN / Wi-Fi (802.11)
• Point-to-point radio links
• Mobile telecom (3G/4G/5G)

• Amplifier: Boosts signal + noise (not used)
• Repeater: Regenerates clean signal
• Media Converter: Converts between mediums
• Hub: Multi-port repeater (collision domain)

• TDM (Time Division Multiplexing): Legacy, time slots
• WDM (Wavelength Division Multiplexing):
• CWDM: Coarse, passive
• DWDM: Dense, active, high capacity

• MAC Address: 48-bit, unique per device
• Ethernet (802.3): Frame-based, error checking
• Switch: Directs frames, reduces collisions
• VLAN (802.1Q): Logical separation, VLAN tags

• IPv4: 32-bit, 4 decimal blocks
• IPv6: 128-bit, 8 hex blocks
• Netmask: Defines network size (e.g. /22)
• Network Address: Lowest IP in subnet
• Broadcast Address: Highest IP in subnet
• Router: Connects networks, uses routing table
• Layer 3 Switch: Combines switch + routing

• TCP: Reliable, connection-oriented
• UDP: Fast, connectionless
• QUIC: Reliable over UDP, encrypted
• Firewall: Filters traffic based on IP, port, protocol

• DNS: Resolves domain names (UDP/TCP port 53)
• DHCP: Assigns IP addresses (UDP ports 67/68)
• SNMP: Manages network devices (UDP ports 161/162)
• NTP: Synchronizes time (UDP port 123, Stratum 0–16)

• Confidentiality: Low priority
• Integrity: High priority (error checks)
• Availability: High priority (redundancy)
• Redundancy: Dual-attached equipment in Skyguide

• AFTN: Legacy message network
• PENS / NewPENS: Pan-European IP network
• AMHS: Modern replacement for AFTN/CIDIN

• HFDL: HF data link (global coverage)
• VDL Mode 2: VHF data link (CPDLC)

• ASTERIX: Surveillance data format (EUROCONTROL)
• FMTP: Flight message transfer (TCP)
• ACARS: Aircraft ↔ Ground messaging
• AIDC: Inter-centre coordination
• OLDI: Flight data exchange between ATC units

• Framework for ATM data exchange
• Covers aeronautical, meteorological, trajectory, airport info
• Uses interoperable services and PENS for delivery

DNS (Domain Name System)

It resolves human-readable domain names (e.g. www.skyguide.ch) into IP addresses.

• TCP is connection-oriented, reliable, and ensures data delivery with acknowledgments.
• UDP is connectionless, faster, but does not guarantee delivery or order.

• Confidentiality – Protect data from unauthorized access
• Integrity – Ensure data is accurate and unaltered
• Availability – Ensure systems and data are accessible when needed

• PENS (Pan-European Network Services): Secure IP network for European ATM data exchange
• NewPENS: Upgraded version of PENS
• ATN (Aeronautical Telecommunication Network): ICAO-defined global network for air-ground and ground-ground communication
• AFTN: Legacy message network
• AMHS: Modern replacement for AFTN
• VDL Mode 2: VHF data link for CPDLC
• HFDL: HF data link for global coverage

• Air-Ground:
• ACARS
• VDL Mode 2
• HFDL
• Ground-Ground:
• AFTN
• AMHS
• OLDI
• FMTP
• AIDC

• Layer 1 (Physical): Repeater, Media Converter, Hub
• Layer 2 (Data Link): Switch, Network Interface Card (NIC)
• Layer 3 (Network): Router, Layer 3 Switch
• Layer 4 (Transport): Firewall (filters based on TCP/UDP ports)

A switch connects devices within the same network (LAN), using MAC addresses.

A router connects different logical networks, using IP addresses and routing table

• LAN (Local Area Network): Covers a small area like an office or building
• WAN (Wide Area Network): Covers large distances, connects multiple LANs (e.g. Internet)

• Layer 2 (Data Link): MAC address (hardware address)
• Layer 3 (Network): IP address (logical address)
• Layer 4 (Transport): Port number (e.g. TCP/UDP port 80, 443)