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Post Mortem Analysis of T.30 and T.38 Traffic

Home » Blogs/Events » Post Mortem Analysis of T.30 and T.38 Traffic

Fax traffic has followed voice traffic in its migration to the Internet. Historically, the T.30 protocol has been used to transmit facsimile messages over the traditional PSTN network. Because T.30 contained a variety of timing constraints that could not be guaranteed with packet traffic routing over the Internet, another standard, T.38, was created to relay traffic in a method consistent with the Internet’s constraints. The new enabling hardware is a gateway that converts the T.30 protocol into a T.38 data stream, as shown in the diagram below.

Anytime you transform one protocol into another, errors can be introduced. Until the release of QualityLogic’s DataProbe T30-T38 Analyzer, there has been no efficient way to find these kinds of errors in T.38 gateway firmware. DataProbe monitors both the IP and PSTN traffic on both sides of a gateway, then provides a complete cross analysis as shown in the screen shot below.

DataProbe and its monitoring hardware are typically used in a test lab environment. The test configuration can be somewhat involved and there is typically the need to automatically monitor hundreds or thousands of calls.

An intriguing aspect of QualityLogic’s DataProbe T30-T38 Analyzer software is that it can be used to do post mortem analysis of traffic captured with simple open source tools. All that needs to be done is for a telecom engineer in the field, who has access to both the PSTN and digital sides of the gateway, to capture the IP traffic using Wireshark and to record a simple wave audio file of the concurrent T.30 traffic. These two files can then be imported into DataProbe to see a full cross analysis of the T.30 and T.38 traffic. Pretty cool!

This capability allows engineers in the field to forward the captured files to a telecom engineer for post mortem analysis using a copy of the DataProbe software. I think this really expands the potential usefulness of this product. Let me know what you think.

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