Complete Communications Engineering

By law, banks, brokerage houses, and financial institutions and many other businesses are required to monitor all facsimile (fax) transactions between themselves and other entities. Typically this is done to capture all transactions all the time and satisfy requirements for corporate compliance (e.g. Sarbanes Oxley) but it may also be performed for other reasons, such as to periodically assess the quality and performance of fax communications over various networks. Analysis of fax transmissions over different networks or connections is performed to compare performance and quality of service (QoS) or to identify issues with error and retransmission rates, throughput, bottlenecks, etc.

Fax monitoring and recording activities must capture incoming and outgoing transmissions over both PSTN and IP network connections. Passive fax interception methods work best because they do not interfere with network throughput or impose additional recording requirements on personnel. Although there are many places in modern communication networks to intercept transmissions, a cost-effective approach is to capture the actual data packets used to transfer a fax on IP networks and on digital portions of the PSTN.

For PSTN, the audio signals (PCM) are captured and recorded. On IP networks, both Fax over IP (FoIP) and Modem over IP (MoIP) packets must be intercepted. FoIP protocol data packets are sent as either the T.38 protocol or as G.711 audio packets using Fax Relay, while MoIP protocol are similarly transmitted as G. 711 audio packets using a Voice over IP (VoIP) pass through mechanism. Depending on the amount of fax traffic and the number of network connections, systems can be designed to not only monitor and record audio over PSTN as well as FoIP and MoIP but also to extract and record the underlying images in real-time.

VOCAL’s fax demodulation software can be used to extract and recover fax images from PSTN audio signals and FoIP data packets. It allows effective monitoring, recording and analysis of fax communications either in real-time or from previously recorded files. VOCAL data and fax modem libraries are used in many applications such as Lawful Interception, QoS network analysis, and corporate security and compliance.

For more information about fax demodulation software and image extraction libraries:

Passive Fax Recording

Passive Fax Recording uses an Analog Telephone Adapter to record fax images sent or received by an analog fax machine without manual intervention. The fax machine line connection is tapped and fed to the Foreign Exchange Port (FXS) port of the gateway. There modem audio signals are input to fax extraction algorithms as they are received. Fax images are recorded to an NAS or, if desired, a local mass storage device.

Alternatively, the fax machine line connects to the Foreign Exchange Port (FXS) port of the gateway. There modem audio signals are input to fax demodulation software image extraction algorithms as they are received from the unit or prior to transmission to the unit and after they have been converted from Fax Pass Through or T.38 Fax over IP data packets received over the network from another fax device. Fax images are recorded to an NAS or, if desired, a local mass storage device.

Both approaches will capture and record fax images. The first approach is a much simpler and lower cost implementation. Whereas the second approach would require more costly processing resources to convert modem audio input to/from data packets as well as simultaneously extract and record fax images.