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Critical Measurements in Air Traffic Management


Overview

The latest EUROCAE (European Organization for Civil Aviation Equipment) ED-137 inter-operability standards, address migration and implementation of IP technology for voice services for air traffic control. The familiar industry standard SIP protocol is specified to establish, modify, and terminate voice sessions with endpoint equipment within an Air Traffic Services Ground Voice Network (AGVN).  

As shown above, the endpoint equipment can be a SIP based Controller Working Position (CWPs), Next Generation Voice Communication Systems (VCS) and Radios, or VCS/Radio Gateways allowing interworking with older legacy equipment and protocols. The legacy TDM VCS system will initially connect to an IP WAN network backbone using VoIP gateways.

Though migrating to an IP network provides convergence advantages for traffic and interoperable network elements from various vendors, it also poses challenges – of variability of  different implementations  by equipment vendors.  Some of these are: implementation of technologies with varied jitter buffer, packetization, digital signal processing algorithms, VOX operations, and switching from idle to active state. These implementation differences impact end-to-end delay requirements imposed by various industry standard bodies. Characterizing and limiting these impairments is critical to the performance of the system as a whole. Rigorous methods are needed to precisely measure the delay introduced by each network element as events  propagate end-to-end. Recognizing, capturing, timestamping, and correlating events at analog, TDM and IP interfaces are necessary.  Delay measurements should be conducted repeatedly  to ensure  that the device and network under test is performing as expected  consistently over time.

GL has developed MAPS™ TM-ATM (Timing Measurements in Air Traffic Management) test suite to accurately simulate end points in ATM network and provide critical timing measurements for various types of delay occurrences in signalling and voice transmission through the network. It includes all necessary hardware and software to identify, capture, timestamp, and correlate events at Analog, TDM and IP interfaces.

Critical Events and Measurements of Interest

Events of Interest within Network as they propagate within Network:

  • PTT Activation and Deactivation
  • Squelch Enable and Disable
  • Voice to/from CWP
  • Voice to/from Radio
  • Various SIP Signaling
  • Transition in RTP Payload
  • Transition in RTP Headers

Network Delay measurements of interest:

  • Transmitter activation delay
  • Aircraft call indication delay
  • Ground transmission voice delay
  • Transmitter activation and aircraft call indication loopback delay
  • Ground reception voice delay
  • Ground transmission and reception voice loopback delay
  • Frequency key activation response time and more

Some of the standards bodies like the Federal Aviation Administration (FAA) in the USA has published specification for NVS system defining timing requirements in detail. The below TABLE extracted (from the FAA-E-NVS1_NVS-Specification_v1_1_2012-01-10 document: refer Table 3-9) depicts Setup/Teardown Throughput Timing Requirements during Peak Busy Hour (PBH) and Peak Busy Minute (PBM).

Type of Event

Max. Response Time, msec1,2 Percent of 
Event Completions

95%

99.9%

99.99%

A/G Functions within the AVN

 

 

 

System-Generated A/G PTT Transmit (radio cross coupling)

40

 

45

Frequency Select

125

175

 

Frequency Deselect

125

175

 

Frequency cross couple Selection

125

175

 

Frequency cross couple Deselection

125

175

 

Frequency Preemption Activation

25

 

30

PTT Lockout (Preemption) Busy Tone

60

85

 

Frequency Site Selection

125

175

 

Frequency Site Confirmation

125

175

 

Local Receive Mute

50

75

 

Local Receive Mute Indicator

75

100

 

Local Receive Unmute

50

75

 

Local Receive Unmute Indicator

75

100

 

Also shown below, are timing requirements extracted from Eurocae standards document: (ED-136 - VoIP ATM System Operational and Technical Requirements Final Draft 2.0_Oct2008 refer Fig:10 and Fig:11)

To perform these timing measurements, one can setup MAPS™ TM-ATM (Timing Measurements in Air Traffic Management) tools at appropriate strategic interfaces. GL’s MAPS™ TM-ATM is a custom suite of test tools, designed to accurately measure various types of delay occurrence in signalling and voice transmission. It includes all necessary hardware and software to identify, capture, timestamp, and correlate events at Analog, TDM and IP interfaces.

PacketExpert™ SA (PXE104)

The Packet Analyzer, Packetizer and Event Data Logger products are all 1U rack platforms based on the same GL’s PacketExpert™ Ethernet/IP hardware; their functionalities differ through scripts that cater to different needs of test cycle. These tools are equipped with optional TTL I/O ports to trigger events of interest occurrence during tests.


PacketExpert™ – 1U Rack Unit

Packet Analyzer
Packetizer
Event Data Logger

4-Port PacketExpert™ w/ Embedded Single Board Computer (SBC).
SBC Specs: Intel Atom CPU, 4GB RAM, Windows 7, MSATA SSD, 2 USB Ports.
19" 1U Rackmount Enclosure.

Interface:

4 Total Ethernet ports 
2 10/100/1000 Base-T Electrical only
2 1000 Base-X Optical OR 10/100/1000 Base-T Electrical
Single Mode or Multi Mode Fiber SFP support with LC connector

Dimension:

Length: 16 Inches
Width: 19 Inches

Power Source:

120-230 AC Power Supply

Connectivity:

2 x USB 2.0 (or 10/100 Mbps Management Ethernet)
1 x Serial COM port
1 x Display VGA (Video Graphics Array) port
2 x Ethernet (2 GBit) LAN ports
Optional 4-Port SMA Jack Trigger Board (TTL Input/Output)

 

Audio Analyzer (1U Rack)

GL's Audio Analyzer is a 1U rack platform that uses VQuad™ Dual UTA as the base hardware combined with SBC for PC interfaces. The Dual UTA includes PTT/Audio interface, required for radio interface simulation. With VQuad™, it is capable of automatically keying PTT from the CWP, then transmit and receive audio signals, and generate TTL triggers based on PTT activation.


Audio Analyzer – 1U Rack Unit

Audio Analyzer – Dual UTA

Dual UTA w/ Embedded Single Board Computer (SBC).
SBC Specs: Intel Atom CPU, 4GB RAM, Windows 7, MSATA SSD, 2 USB Ports.
19" 1U Rackmount Enclosure.

Interfaces

  • PTT Power LED
  • Trigger LED
  • Dual UTA LED
  • 3.5mm (Monitor)
  • RJ-45 PTT/Audio Jack
    PTT - Input/ Output Impedance - 600ohms, 1000 ohms and User-Definable

Features

  • 4-Wire Balanced Audio and PTT Contact Closure Interface for connecting to the CWP Dual Jack Module as well as other 4-wire interfaces within the network
  • Provides 4 types of TTL output - PTT Enable, PTT Disable, Audio Trigger - Start of Audio, & Audio Detect
  • Precise One-Way Delay (OWD) measurements as well as event-based TTL or CMOS trigger outputs that can be fed to an oscilloscope
  • Voice Quality Assessment using industry-standard ITU algorithms (PESQ & POLQA)
  • 4-Wire “Bridge” Mode –  To monitor existing TMG’s and provide event-based trigger outputs (for latency testing)
  • Test Automation Capabilities - GUI-based or SDK and CLI versions

Dimension

Length: 16 Inches
Width: 19 Inches

Power Source

120-230 AC Power Supply

Connectivity

2 x USB 2.0 (or 10/100 Mbps Management Ethernet)
1 x Serial COM port
1 x Display VGA (Video Graphics Array) port
2 x Ethernet (2 GBit) LAN ports
Optional 4-Port SMA Jack Trigger Board (TTL Input/Output)

Working Principle

MAPS™ TM-ATM (Timing Measurements in Air Traffic Management) components can be broadly categorized into two sets based on the underlying hardware:

  • Packet Analyzer, Packetizer and Event Data Logger – all these are based on the same GL’s PacketExpert™ Ethernet/IP hardware; their functionalities differ through scripts that cater to different needs of test cycle.
  • Audio Analyzer – this is based on VQuad™ Dual UTA hardware; its main functionality is to simulate radio calls from CWP.

All components of MAPS™ TM-ATM are controlled by a centralised component called MAPS Master Test Controller (MAPS MTC).  MAPS™ TM-ATM support a client server model, with components acting as servers, the MAPS-MTC acts as a client and controls all components acting as servers, from a centralised location.

Some examples of critical timing measurements that can be performed within the Air Traffic Management systems are:

  • Audio Transmittedfrom near-side CWP – to – Audio Receivedat far-side CWP
  • PTT Disabledat near-side CWP – to – Audio Stoppedat far-side CWP
  • Audio Transmittedfrom near-side CWP – to – Audio Received at Radio Station output
  • PTT Enabledat CWP – to – PTT bit set to On within RTP packet exiting CWP
  • PTT Disabledat CWP – to – PTT bit set to Off within RTP packet exiting CWP

The time from which an Air Traffic Controller depresses the PTT until the IP stream indicates that the PTT bit is set is an important testing example. This delay measurement is possible using GL’s Audio Analyzer and GL’s Packet Analyzer. Both are capable of generating TTL triggers based on PTT activation. The Packet Analyzer is capable of generating Packet and TTL triggers based on real time packet detection, filtering, and capture as necessary.

Below a remotely located MAPS™ Controller can instruct GL’s Audio Analyzer connected to a CWP to activate PTT and simultaneously generate a TTL trigger.  The Discrete Signal Logger connected to the Audio Analyzer can detect the TTL trigger and post an event to the Event Data Logger. On the IP side, GL’s Packet Analyzer which is monitoring the line non-intrusively can detect the packets of interest (e.g. first RTP packet with PTT bit set) based on the filters set and post an event to Event Data Logger. Centrally located the Event Data Logger time tags these received events and reports these events to the MAPS™ Controller. The MAPS™ Controller will calculate the time difference between different events posted and reports the measured delay.

Test Tools for Delay Measurement

The following outlines the GL Tools used and their functionalities for Timing Measurement:

Audio Analyzer – The Audio Analyzer is a 4-wire audio device that can connect to a CWP and emulate a controller by activating PTT and transmitting audio. It supports PTT interfaces to connect to CWP Dual Jack Module and other 4-wire interfaces. Its can send a PTT signal through 4-Wire interface exactly as though a real user is holding PTT on his/her headset. It can also inject and record analog signals at CWP, Radio and VoIP gateway interfaces. The analyzer  can generate TTL for different actions (PTT ON, PTT OFF, Send Audio, Detect Audio). The Audio Analyzer can also be utilized in other areas of the network where analog audio signals are present.

Packetizer – works in tandem with the Audio Analyzer to convert analog events into packet events. The Packetizer monitors the TTL output from the Audio Analyzer on a regular interval, and for every trigger pulse received, it generates and transmits a timestamped IP packet indicating which pulse it received, to the EDL. The packets generated by the Packetizer are named as Discrete Events. This indicates a certain event has occurred. The Packetizer samples the TTL inputs on a regular interval, for every trigger pulse received, it generates and transmits a timestamped packet indicating which pulse it received.

Packet Analyzer - It functions like a highly precise Ethernet tap. It acts as a transparent Ethernet link in which bidirectional Ethernet traffic flows through at line rate. Additionally, Packet Analyzer can filter certain packets of interest from both directions without disturbing the traffic. The filtered packet's first 12 bytes of the MAC header is modified (overwritten) with useful information such as the filter number, port number, and device ID. These modified packets generated by the Packet Analyzer are named as Timed Events, and are forwarded to the Event Data Logger.

The Packet Analyzer can aggregate filtered and modified packets from both directions and forward over a single output port. 

Packet Analyzer also supports generating output TTL signal pulses for every filter match, so that the TTL signal (representing the Filter match) can be taken out, and processed using an external device like Oscilloscope.

Event Data Logger– The Event Data Logger is located at a central location and receives the event packets forwarded from the various Packetizers and the Packet Analyzer systems throughout the network. It timestamps each received packet, decodes the packet to extract information, and updates both Discrete Events (from the Packetizer) and Timed Events (from Packet Analyzer) to the MAPS™ MTC (Master Test Controller). It utilizes an onboard 2 GB DDR2 memory to temporarily store the received packets before being transferred to the MAPS™ Controller for analysis.

MAPS™ MTC - The MAPS™ MTC is a control/logging application, and it uses TCP/IP to send commands to and receive notifications from all the above-mentioned tools. MAPS™ Controllerwill calculate the time difference between posted events, i.e., Discrete Events (from the Packetizer) and Timed Events (from Packet Analyzer) and reports precise measured delay at different points in the network. MAPS™ TM-ATM is script based and API driven products that can be reused for various purposes during test cycles.

Measurement of TTL Triggers

When Audio Analyzer performs a certain function, it simultaneously sends a discrete TTL pulse to the Packetizer. When the Packetizer receives this pulse, it creates and transmits a timestamped packet indicating which pulse it received. This allows us to get analog and digital events into the same log for delay measurement. Further this packet is filtered out by the Packet Analyzer and forwarded. Up to 16 filters can be operated simultaneously per port. For every packet that successfully passes a filter, the Packet Analyzer can generate TTL Triggers to indicate this event.

The analog signals timing relationship of both Audio Analyzer and Packet Analyzer can be verified by connecting the TTL I/O Ports to Oscilloscope using SMA cables.

Following signals can be monitored at Audio Analyzer TTL Output ports –

  • When a PTT signal sent through 4-Wire interface of Audio Analyzer, exactly as though a real user is holding PTT on his/her headset, a TTL Pulse is sent out TTL Port 1 to Packetizer for packetization
  • When PTT signal on 4-Wire interface stops TTL Pulse sent out TTL Port 2 to Packetizer for packetization
  • TTL Pulse is sent out TTL Port 3 at start of transmission of Pre-recorded voice file
  • TTL Pulse is generated out TTL Port 4 when audio is detected (i. e. not when the command is executed, like the other triggers)

Following signals can be monitored at Packet Analyzer TTL Output ports –

Packet Analyzer can define 2 filters per port, each of which is mapped to the TTL I/Os as shown in the table below:

Ports Filters I/O
Port2 Filter1 I/O 1
Filter2 I/O 2
Port3 Filter1 I/O 3
Filter2 I/O 4
  • When Port 2 filters (Filter1 and Filter2) each have one matched packet, corresponding mapped TTL Port1 and Port2 generate a single TTL pulse, which can be viewed on a connected oscilloscope
  • When Port 3 filters (Filter1 and Filter2) each have one matched packet, corresponding mapped TTL Port3 and Por4 generate a single TTL pulse, which can be viewed on a connected oscilloscope
  • The number of trigger pulses generated on TTL Ports exactly matches the filter match count

Simulation Test Tools in ATM

MAPS™ ED137 Radio and Telephone Emulators - GL's MAPS™ ED137 Radio and MAPS™ ED137 Telephone emulators can simulate Radio and Telephone calls as per EUROCAE's ED137-1B and ED137-2B specifications. Using Bulk Call capability of these tools user can generate hundreds of calls as background traffic while making delay measurements. Good sample applications can be to simulate real time scenarios like PBH and PBM by generating required bulk calls in the background.

IPNetSim™ – GL's IPNetSim™ an IP Network Emulator connects to the 2 end points of a WAN link, allowing it to be configured to act either as a transparent bidirectional Ethernet link or a simple Ethernet bridge between 2 end points. It emulates a 10 Gbps or a 10/100/1000 Mbps full duplex link. . The incoming traffic can be identified into separate user defined stream for each direction, which can then be modified to simulate network malfunctions. Each direction supports up to 16 streams, allowing up to a total of 32 streams in both directions.

IPNetSim™ supports various impairments like:

  • Bandwidth emulation from 100 Kbps up to 10 Gbps in increments of 1 Kbps emulating various WAN technologies like Modem, DSL, T1/E1/T3/E3/OC3/OC12 etc
  • Latency/Delay emulation from 0 milliseconds to 8 seconds, with single, uniform and random distributed delay emulation capabilities
  • Packet Loss emulation, from 0 to 100%
  • Packet Reordering emulation, from 0 to 100% with random reinsertion delay
  • Packet Duplication emulation, as a percentage of total packets, from 0 to 100%
  • Logic Error Insertion - inserts error anywhere within the frame, from 10-1 to 10-9 rate

Buyer's Guide

Please Note: The XX in the Item No. refers to the hardware platform, listed at the bottom of the Buyer's Guide, which the software will be running on. Therefore, XX can either be ETA or EEA (Octal/Quad Boards), PTA or PEA (tProbe Units), UTA or UEA (USB Units), HUT or HUE (Universal Cards), and HDT or HDE (HD cards) depending upon the hardware.

Item No. Item Description

PKS118

MAPS™ ED137 Radio

PKS119

MAPS™ ED137 Telephone

PKS107

RTP EUROCAE ED137

PKS109 MAPS™ High Density RTP Generator

PKS111

MAPS™ Remote Controller

PKS170 CLI Support for MAPS™
PKS121 MAPS™ SIP Conformance Test Suite (Test Scripts), requires PKS120
PKS102 RTP Soft Core for RTP Traffic Generation
PKS200 RTP Pass Through Fax Emulation
  Related Software
PKS122 MAPS™ MEGACO Emulator
PKS123 MAPS™ MEGACO Conformance Test Suite (Test Scripts)
PKS124
MAPS™ – MGCP Protocol Emulation with Conformance Test Suite
PKS130 MAPS™ SIGTRAN Emulator
PKS100 PacketGen™ with PacketScan™
PKV100 PacketScan™ (Online and Offline)
PKV120 PacketScan™ HD w/4 x 1GigE
PKV120p PacketScan HD™ w/4 x 1GigE - Portable
PKV123 PacketRecorder HD™ & PacketRePlay HD™
PKV121 PacketScan™ FB
PKB100 RTP Toolbox™
PKB105 G.168 Echo Canceller Test Compliance Suite
PKB070 Audio Processing Utility
  Related Hardware
IPN502 IPNetSim™ - 1G – MultiStream – Rack System
IPN504 IPNetSim™ - 10G – MultiStream – Rack System
IPN505 IPNetSim™ - 1G Tablet

 

 
 
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