Fax and Modem Test Solutions

9th, Mar 2018


To successfully deploy fax services requires extensive network design, test and traffic engineering. Test equipment can prove valuable in this process, if it can: Generate and receive fax signals in bulk over wired and wireless networks, monitor and distinguish fax signals in real time for traffic engineering and network design purposes, and analyze fax signals after capture for troubleshooting failed or poorly handled calls.

GL provides comprehensive Fax Testing Solutions over IP, TDM and PSTN networks using its products. A snapshot of Fax and Modem Test Solutions is provided below.

PacketScan™(over Ethernet/IP Networks)

PacketScan™(over Ethernet/IP Networks)

Fax-Over-IP transmission happens in 2 modes.

  • T.38 Decoding and Analysis mode - In T.38 mode, the call is detected as a T.38
  • Transparent mode (pass through) mode - In this mode, the gateway does not distinguish fax calls from voice calls. The T.30 fax traffic is carried over RTP packets using an uncompressed G.711 u-law or A-law inside the RTP packet between the two gateways. For Internet telephony gateways with support for PCM/G.711 audio and no support for T.38 real-time fax, it is recommended to switch the session to fax pass-through mode.

PacketScan™ software supports FaxScanT38™ (PKV104) for capturing and decoding of Fax calls over VoIP in both T.38 mode as well as G.711 pass through mode. The fax call is displayed in the form of call summary, detail call graph, and decoded information for all T.38 messages received on the call. The Extract Fax Image feature enables the user to extract the image in Class F TIFF format from the selected fax call. Optionally, users can also generate verbose log file for monitoring the step-by-step decoding of Fax.

T.38 has been enhanced to reassemble the fragmented data and to identify the T.30 message from it. Identified T.30 message is displayed in the T.38 ladder diagram.

The captured fax calls by PacketScan™ can also be analyzed using GLInsight™ by saving the fax calls directly in (*.PCAP) Ethereal file format.

Call Capture Applications (over TDM and 2-Wire Networks)

Two Wire Voice Capture

GL's Voice Recorder Software with tProbe™ T1E1 FXO FXS or Dual UTA can non-intrusively capture Voice/ Fax / Modem traffic over TDM and 2-Wire Networks. One can non-intrusively 'tap' into the analog 2-wire line via the RJ11 interface and capture the bi-directional voice.  The captured files containing   Voice / Fax traffic can be analyzed near-time using Voice Band Analyzer application with FaxScan™ (VBA038).  The captured fax/ modem files can also be analyzed offline using GLInsight™.

Call Capture Options

T1 E1 Call Capture Application (CCA) software non-intrusively record calls directly from T1/E1 or Analog 2-wire lines (requires Channel Bank). The captured files containing   Voice / Fax traffic can be analyzed near-time using Voice Band Analyzer application with FaxScan™ (VBA038).  The captured fax/ modem files can also be analyzed offline using GLInsight™.

Bulk Fax Call Generation using MAPS™ or VQuad™ Dual UTA (over TDM and 2-Wire)

Bulk Fax Call Generation

GL’ Fax Simulator (XXFT0) is capable of bulk (100's) fax calls over many T1/E1s, over two-wire FXO-FXS lines, and over Ethernet/IP networks. This software is capable of transmitting and receiving fax calls. The software can emulate many "virtual fax machines" – transmitter as well as receiver.

Fax Simulator (XXFT0) has two versions – one, as a stand-alone command-line fax simulator application and other, integrated as a module within GL's MAPS™ IP products, MAPS™ TDM products, and VQuad™ software.

Fax simulator for IP supports both RTP G.711 Pass Through Fax Simulation (PKS200) and T.38 Fax Simulation over UDPTL (PKS211).
Fax simulator for TDM supports T.30, V.17, V.27, V.29, V.33, and V.34, with TX and RX fax rate from 2400 bps to 33,600 bps. Supports all variations of fax, such as page size, resolution, data rates – including high speed fax such as V.34 and codec types.

GL’s Message Automation & Protocol Simulation (MAPS™) and VQuad™ supports real-time emulation of fax calls using Fax Simulator (XXFT0)  over established call over T1 E1/PSTN networks – supported protocols include - CAS, ISDN, SS7, GSM A, and FXO FXS emulators. Typical applications of our Fax Emulation software are load testing of fax servers, qualification testing of T.38 Gateways, testing of ATAs (Analog Terminal Adapters), testing of fax machines, and many more.

GLInsight™(over Ethernet/IP, TDM, and 2-Wire Networks)


GLInsight™ enables offline decoding and analysis of pre-recorded modem and fax transmissions. The transmission signals can be recorded from PSTN or IP media.

GL Insight™ receives the recorded modem or fax transmissions in one of the two ways:

  • As raw signal files (PCM files) - in either mono or stereo format
  • As IP capture files - created by capturing devices or by software

GLInsight™ demodulates the raw transmissions and presents the decoded data in an easy to understand format. It produces extensive log files with all relevant debugging information for easy event tracing which in turn provides insight to potential sources of problems.

Supported Fax and modem standards are –

  • T.38 Stream (IP Packets)
  • T.30 Decoder using G.711
  • Fax traffic - V.34HD, V.17, V.33, V.29, V.27, V.21

Modem traffic - V.92 (Quick Connect and Modem-on-Hold supported, PCM-upstream not supported), V.90, V.34, V.32bis/V.32, V.22bis/V.22, V.21, V.23, Bell 103 / Bell 212

FaxScan™ (over Ethernet/IP, TDM and 2-Wire Networks)


FaxScan™ application is a fax decoder/demodulator application that processes 2-Wire or 4-Wire captures and analyzes voiceband traffic files for fax traffic. The FaxScan™ has two versions – one, as a stand-alone command-line fax analysis application and the other, integrated as a module within GL's Voice Band Analyzer application and PacketScan™, with licenses as FaxScan™ (VBA038 and PKV104) respectively.

FaxScan™ application processes captured files and produce the Fax TIF image and other transmission information.  Some important features -

  • Handles audio streams sampled at 8-Khz.
  • Handles G.711 A-Law and μ-Law streams of 8-bit
  • Handles A-Law and μ-Law streams extracted from RTP sessions within PCAP files
  • Fax traffic - V.17, V.21, V.27, V.29, V.33, V.34

The FaxScan™ module provides statistics for Fax traffic analysis including Fax Status, Standard, Data Rate, Resolution, Encoding, Page Size, Error Lines, Total Lines, Total Bytes, and Total Pages.

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