ATN Air-Ground Subnetworks

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ATNAir-Ground Subnetworks

• Presentation ATN2.2 by R. Oishi, ARINC
• CAO Regional ATN Seminar
• 6-7 May 2002

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End Systems - Intermediate Systems

• End System (ES)
• Computer system which executes end-user
  application programs
• May implement 7-layer stack as required
• Communicates to Intermediate Systems or possibly
  to other ESs
• Intermediate System (IS)
• Computer system which relays and routes NPDUs to
  other ISs or ESs
• Implements up to Network Layer (Layer 3)
• Implements CMIP and routing protocols

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ATN Functional Components
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Administrative and Routing Domains

• Administrative Domain
• A set of ESs, ISs, and subnetworks operated by a
  single organization or administrative authority
• Routing Domain
• A set of ESs and ISs bound by a common routing
  procedure
• An Administrative Domain may contain one or more
  Routing Domains
• A Routing Domain is always wholly contained
  within one Administrative Domain
• There are smaller and larger area definitions to
  facilitate operation of a worldwide ATN

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Example Administrative Domain
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Routing Protocols

• ISO 9542 ES-IS Host/Router Protocol (Optional)
• Exchanges connectivity information within a local
  subnetwork environment
• ISO/IEC 10589 IS-IS Intra-Domain Protocol
  (Optional)
• Exchanges connectivity and topology information
  among ATN routers (ISs) within a Routing Domain
• Supports dynamic configuration of ATN routing
  tables on a domain-wide basis
• ISO/IEC 10747 IDRP Inter-Domain Routing Protocol
• Exchanges routing information across routing
  domain boundaries
• This is the ATN key element in maintaining
  communication with aircraft

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Protocols in Context
ES
IS
IDRP (ISO/IEC 10747)
BIS
IS-IS (ISO 10589)
ES-IS (ISO 9542)
COTP Class 4 (ISO 8073) CLNP (ISO 8473)
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Mobile Routing - RGS Level
Routing Domain
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Mobile Routing - RD Level
RD 1
RD 2
RD 3
RD 4
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Air/Ground Subnetworks

• VHF Digital Link (VDL)
• Satellite
• Mode S
• HF Data Link

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VHF Digital Link (VDL)General Characteristic

• Very High Frequency radio (118-137 MHz)
• SARPs complete/validated for Modes 2-3
• Line-of-sight from remote ground station (RGS),
  coverage up to 200 NM depending on terrain,
  aircraft altitude, other factors
• Three operational Modes of VDL
• Mode 2 - Data only
• Mode 3 - Data and voice
• Mode 4 - Data only

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VHF Usage
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VDL Technical Characteristics

• Modulation
• Modes 2,3 Differential 8-Phase Shift Keying
  (D8PSK), 31.5 KBPS
• Mode 4 Gaussian Frequency Shift Keying (GFSK),
  19.2 KBPS
• Medium Access
• Mode 2 - Carrier Sense Multiple Access (CSMA)
• Mode 3 - Time Division Multiple Access (TDMA),
  maximum of 4 channels per frequency
• Mode 4 - Self-organizing TDMA (STDMA)

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Satellite Data Link

• Uses Inmarsat geosynchronous satellites which
  provide both telephone and data services,
  operating in L-Band (1550-1630.5 MHz)
• SARPs approved
• Worldwide coverage with 4 satellites, except
  polar areas
• Four channel types
• P-Channel - ground-to-air signaling and user data
• R-Channel - air-to-ground requests or data
• C-Channel - both directions, voice or data
• T-Channel - air-to-ground user data

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Satellite Data LinkTechnical Characteristics

• Modulation
• Binary Phase Shift Keying (BPSK), 1200 or 2400
  BPS
• Quadrature Phase Shift Keying (QPSK), 4.8 or 10.5
  KBPS
• Medium Access
• P-Channel - TDMA
• R-Channel - slotted Aloha
• C-Channel - Single Channel per Carrier (SCPC)
• T-Channel - TDMA

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Satellite Data Link Conventions
Outbound Link
Forward Link
Uplink
Return Link
Downlink
Inbound Link
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Mode S Data Link

• Uses Secondary Surveillance Radar (SSR)
  transponder to transmit data (1090 MHz) and
  receive data (1030 MHz)
• ICAO SARPs approved
• Coverage with data linked SSRs or stationary
  antennas
• Shares transponder with Traffic Alert and
  Collision Avoidance System (TCAS)/Airborne
  Collision Avoidance System (ACAS) and SSR
  functions

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Mode S Data LinkTechnical Characteristics

• Modulation
• Pulse modulation, identifies Mode S from ATCRBS
• DPSK, 4 MBPS for Mode S interrogation
• Pulse Position Modulation (PPM), 1 MBPS for reply
• Medium Access
• Random access, pulse modulation identifies Mode
• Mode S timed to occur within ATCRBS suppression
• Mode S reply by PPM allows reply to get through
  in face of a single ATCRBS interferencing signal
• Other characteristics
• Data transferred in 56 or 112 bits of information
• 24-bit parity error check

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Mode S Data LinkConventions
Interrogation
P1 P2 Data
Reply
Preamble Data
ATC Radar Beacon System (ATCRBS)
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HF Data Link

• Long-range coverage (3000 km) in aeronautical
  high frequency (HF) band (3-22 MHz)
• ICAO SARPs complete
• Multiple data rates (300, 600, 1200, 1800 BPS)
• Frequency Division Multiple Access (FDMA) to
  maximize coverage TDMA to organize data
  transmission

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HF Data LinkTechnical Characteristics

• Modulation M-ary PSK (2PSK, 4PSK, 8PSK)
• Data Rates 300, 600, 1200, 1800 BPS
• Medium Access TDMA, 32 second frame, 13
  slots/frame, 1 MPDU/slot
• Other characteristics
• Aircraft login to ground station
• Ground station squitters transmitted
• GPS synchronized ground stations
• Frequencies coordinated between ground stations

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HF Data Link Frame Structure
HFDL Frame (32 sec, 2700/day)
Slot (13/frame)
MPDU (1/slot)
Message Protocol Data Unit (MPDU)
Prekey Preamble Data
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HF Data Link

• Service for ATC and AOC applications
• 12-16 sites sharing 60 frequencies will
  eventually provide worldwide coverage
• Data link coverage in polar regions
• Multiple frequencies per site, multiple sites per
  aircraft

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Summary

• ATN SARPs include the following air/ground
  subnetworks
• VHF digital link (VDL)
• satellite link (satcom)
• Mode S data link
• HF data link (HFDL)
• VDL Mode 2 will be the first operational ATC link