How to Successfully Tap Your (SIP) VOIP Phone Line for Free

I’d like to present a free solution for Windows XP that reliably records incoming and outgoing SIP phone calls. I’m currently using it to record traditional conference calls for a team of software developers.

What you need

  • Either Windows XP or Debian/Ubuntu (or work-alike)
  • A SIP account (either public – e.g. sipgate – or private one)
  • Either a soft phone or a SIP telephone and an Ethernet Hub
  • Oreka: Audio streams recording and retrieval

What you’ll get

  • A .wav file for each outgoing or incoming VOIP call.
  • There are additional components available from OrecX (some of which are being sold and thus are not for free), e.g. for saving phone calls within a database for later retrieval. I neither used nor needed those, as my primary concern was just to record daily stand-up telephone meetings.

How to Install

  • From Oreka: Download the files for your system environment
  • Install the Oreka audio capture server

Fine Tuning Capture Formats

By default, Oreka will produce .WAV-files using GSM compression. GSM is widely used for mobile phones, thus files are very small (about 100kBytes/minute), but sound quality is a little bit on the dull side and older applications might fail to understand GSM encoding. If space is of lesser concern, I’d recommend the plain old uncompressed pcmwav format (about 1MByte/minute) that can be read by virtually any program, or the ulaw (best in USA + Japan) or alaw (best in Europe and for international calls) encodings (about 500kBytes/minute) that are commonly used for SIP voice data and can be read by most programs.

With Oreka, audio file storage format can be set up within Oreka’s config.xml (Caution: do not choose native):
   <!– Audio file storage format: choose from: native, gsm, ulaw, alaw, pcmwav –>
   <StorageAudioFormat>pcmwav</StorageAudioFormat>

Converting to MP3

When publishing recordings, I’d suggest to produce .mp3-files. Oreka can’t do this on its own (at least the free version). I’m using WavePad to do the job: Drag your .wav file to WavePad, then click Effects, Dynamic Wave Compressor…, Threshold -24dB, Ratio 5:1, Limit 4dB, OK, then Save File As…, MP3, Constant Bitrate, 16kbps, Mono. You’ll end up with tiny files whose quality is superior to the one produced by commercial conference recording systems. 

Using an External Hardware SIP Phone

When using an external SIP phone (my favorite is the Thomson Speedtouch ST2030), for Oreka to successfully record your phone calls, it is required that Oreka “hears” all the data being sent from and to your SIP phone. That’s quite easy when using a soft phone on the very same PC that Oreka is running on, but will be more complicated when using an external hardware SIP phone. Current computer network equipment uses network switches to interconnect devices. Switches are smart. They know how to direct network data packets, so that reach their intended receivers – and only those. Let’s assume you’ve connected three devices to your switch (the switch itself possibly having been integrated within your DSL router):

  1. Your DSL router
  2. Your SIP phone
  3. Your PC (with Oreka installed and trying to eavesdrop your phone calls) 

Now, when you place a phone call, your switch will forward voice data from the internet to your phone (and vice versa). Your PC however will not receive any data sent from or received by your phone, effectively deafening Oreka. Although Oreka has instructed the network card within your PC to listen for any traffic (including the traffic that’s not destined for your PC), you won’t be able to record any phone call at all.

So are we stuck yet? Depends. If you are using a VOIP-DSL router where you have plugged your analog phone(s) into, the answer is yes. Read no further. Either look for conferencing services (e.g. Basement Ventures Free Conference Call Services) or analog taps that go in between the cable from your phone and to its handset (e.g. the Radio Shack Mini Recorder Model 43-1237 or the JK Audio THAT-1). However, if you are using a VOIP phone (one that uses Ethernet and does the SIP itself), you’ll get away by replacing your switch with a hub.

Provided you are using a SIP VOIP phone, you’ll either need a switch that features port mirroring (quite expensive) or a network hub, which forwards any data received on one of its ports to all other ports. As far as I know, hubs are no longer being manufactured at all, so you’ll either have to snatch one from a museum or get a used one from eBay. I’ve successfully tested the Netgear FE 10x and DS 10x hubs, both readily available and very inexpensive.

Credits

Tom Keating’s article VoIP Call Recording within his VoIP & Gadgets Blog has provided a plethora of invaluable information and thus served as an ideal starting point – a must have!

About Reiner

Born 1954 in Ratisbon (Bavaria, Germany), in 1976 punched cards at Berlin Technical University, caught hacking one of its mainframes by Horst Zuse (son of Konrad Zuse), started studying computer science and soon was offered a job whithin their computer department doing systems programming for IBM VM/370. While studying, jobbed around Germany at various places doing all sorts of things, then returned to Berlin to work at SRZ (computer aided typesetting). Never finished my master degree, but chose to take up self-employed work (which didn't turn me rich nor famous). Now working for a mid-sized software company within a very promising department as head of server software development.
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2 Responses to How to Successfully Tap Your (SIP) VOIP Phone Line for Free

  1. Bruce Kaskey says:

    Reiner – thanks for using oreka, if you have any specific questions concerning oreka or orecx, please send us an e-mail Also do you have Tom Keatings e-mail?

    Like

  2. Reiner says:

    Hi Bruce,

    first I have to confess my admiration for Oreka/Orecx: I’ve only just scratched Oreka’s surface and I’m very much impressed by its ease of use: It’s working like a charm – exactly as advertised (and even on Windows XP Embedded with just a little bit of tweaking, as in my case). I still have to explore more complex use cases – involving web gui and the like.

    Regarding Tom’s email – no I don’t have it (I’m not a buddy of his). If I were up to contact him, I’d have a look at http://www.tmcnet.com/tmclabs/. Tom’s phone number is right there – waiting for customers and contracts 🙂

    Take care,
    Reiner

    Like

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