Aeronautical Ground Earth Station (GES) Emulator

The Square Peg Communications Inc. (SPCI) Ground Earth Station (GES) emulator provides a simple and flexible means of testing the operation of Aeronautical Earth Stations (AESs) and end-to-end applications for the Inmarsat Classic Aero service, without the expense of airtime charges. It can be used to test basic AES functionality, including Aero I/H+ and Aero H voice calls, and data transfer applications such as ACARS.

The emulator implements a simplified GES. It transmits P channels to the AES and receives R channels from the AES, both for system management and for data traffic. It also receives T channel data traffic from the AES and supports the T channel reservation protocols. The emulator supports circuit switched services over both 8,400 and 21,000 bps C channels.

The emulator maintains a list of valid AESs, and handles logons by and calls to or from any AES on the list. Multiple simultaneous calls can be supported, depending upon the hardware configuration.

Aero-I/H+ calls are supported by external SPCI Voice Codec Units (VCUs) connected to the emulator. The VCU provides a standard 2wire or 4wire analog phone connection, enabling an end-to-end voice conversation to take place between the emulator and the AES handset. The encoded voice stream from an AES can also be looped back to the AES handset.

The emulator supports Data-2 services over the P, R and T channels at all SDM-defined data rates. Data traffic can be exchanged with an external application (e.g., an ACARS server) over a UDP-based link service user interface. Communication of ACARS data over an X.25 WAN interface (e.g., to the SITA or ARINC network) is also supported. A basic ACARS messaging exerciser is included, which can provide automated acknowledgements of downlink messages and responses to ACARS UTC time requests. Free-text messages can also be generated.

The GES emulator is based on the SPCI Aeronautical Ground Data Unit (GDU), which can also be used for detailed physical layer and protocol testing of AESs and GESs. The same hardware platform supports similar physical layer and protocol test applications for other Inmarsat services such as Swift64 and SwiftBroadband.

  • GES Emulator Configuration

  • Emulator Components

    PLT Channel Unit (CU)
    with Sync I/O interface(s)

    Sync I/O interface required for operation with VCU
    Optional X.25 interface

    PLT RFU Unit and high
    power attenuator

    High power attenuator required if interfacing after HPA

    GDU software

    Ground Data Unit application
    GES emulator application

    Voice Codec Unit (VCU)

    Aero-I/H+ codec with 2W or 4W interface, or customer-furnished Aero-H codec

    Supported Scenarios

    Terminal types


    AES class

    1, 2, 3 or 4

    Number of simultaneous
    AES logged on


    Circuit-mode services

    Aero-I/H+ voice calls
    (4.8 kbps AMBE)
    Aero-H voice calls
    (9.6 kbps LPC)

    Maximum number of calls

    Shared Rd/Rsmc: 2
    Independent Rd/Rsmc: 1

    Packet-mode services


    P/R/T-channel bit rates

    600, 1200, 2400, 4800, 10500

    Voice Call Routing


    Initiated by AES; dialed number determines terminating interface


    Initiated via GUI; dialed number determines AES and terminal ID


    Initiated by AES; dialed number determines terminating AES and terminal ID (audio loopback if same)

    Data Interfaces


    UDP interface with external link service user
    X.25 WAN to packet network


    Simple ACARS link service user application is included

    • Response to UTC time requests
    • Acknowledgement of other downlink messages
    • Transmission of free text uplink messages

    Example Configurable Parameters

    Ocean region

    System Table
    Spot Beam Map
    Operating frequencies/power

    Satellite ID and GES
    Psmc/Rsmc frequencies

    Obtained from currently selected System Table

    Authorized AESs

    List of authorized AES IDs

    Dialing strings

    Map dialed numbers to VCU port or AES loopback

  • GES Emulator Data Sheet

  • Contact Us
  • © 2020   Square Peg Communications Inc.