Demystifying Lawful Intercept and CALEA TMC

Do Probes Provide Complete Solutions for VoIP?

February 28, 2007
In my last entry I talked about Active vs. Passive intercept and the use of probes from a high level perspective. In this entry I want to identify a couple of cautions with regard to the use of probes to intercept VoIP calls.

Probes can be useful in VoIP LI solutions when positioned appropriately in the network. Typically they will need to be deployed to capture both the content (near the edge of the network) and the signaling (near the core). However, even with the appropriate positioning of probes they most likely won't be able to capture all call scenarios.

One of those scenarios includes calls that are forwarded or redirected off of the carrier's VoIP network to the PSTN (or any other network for that matter). In this scenario, the target has forwarded his phone to a number off of the VoIP carrier's network. An associate then calls the target's phone, the target's network determines that this call is forwarded to a number off of its' network and immediately redirects the call back out to the PSTN for proper termination. In this scenario the call content only reaches the gateway at the edge of the network and a probe solution wouldn't be able to access it.

Another area of caution includes the carrier's responsibility to provide Dialed Digit Extraction (DDE). DDE was one of the Punchlist requirements established with J-STD-025A. This requires that any DTMF digits entered during a call be identified, isolated and sent to the LEA as Call Data. Preferably these digits are extracted from the in-band content so that they can't be spoofed. Most probes don't have any DSP resources and therefore can not extract these digits and send them to the LEA as required by J-STD.

Just a few more reasons to make sure any investment in an LI implementation is comprehensive in nature and covers all scenarios, not just most.

Till next time ...



Related Tags: , , , , ,

Listed below are links to sites that reference Do Probes Provide Complete Solutions for VoIP?:

Trackback Pings

TrackBack URL for Do Probes Provide Complete Solutions for VoIP?:
http://blog.tmcnet.com/mt3/t.fcgi/31959

Comments to Do Probes Provide Complete Solutions for VoIP?


(If you haven't left a comment here before, you may need to be approved by the site owner before your comment will appear. Until then, it won't appear on the entry. Thanks for waiting.)