The Smart ATA Story: Solving Three Big FoIP Problems for the Industry

If you read our newsletters, you may remember that Commetrex has developed a new FoIP technology, Smart FoIP™, which, among other things, improves the success of FoIP session establishment by up to 10% in SIP networks. Now, instead of talking about technology, we’re talking about a product that uses the technology to solve major problems for the industry.

We’ve exhibited at many industry conferences, most notably at the ITEXPOs produced by TMC, and we’ve been frustrated because we’ve not had the Smart FoIP-based products IP service providers have been asking for. These are the guys that tell their business subscribers to keep their POTS lines for fax. Many have tried FoIP, but their customers are frustrated by low connect rates, particularly for outbound calls. Well, now we have what they need — Smart ATA — and and we are formally announcing it at ITEXPO West 2011.

Smart ATA is the industry’s first analog telephone adapter (ATA) to feature Smart FoIP to solve the late T.38 re-Invite problem. But Smart ATA doesn’t just solve one big problem for the industry; it solves three. Smart ATA is also the industry’s first ATA with T.38 V3 with V.34. And it also eliminates PCM clock-sync problems in G.711 mode, as explained in the following stories. So, Smart ATA solves three big problems that have long perplexed the industry:

  • SIP session establishment failures for outbound calls
  • Finally! V.34 in an ATA
  • Elimination of G.711 failures due to lack of G.711 PCM-clock synchronization

We have designed, developed, and are marketing Smart ATA with New Rock Technologies (Shanghai), our long-time partner, which has used Commetrex’ media technologies in their medium-density gateways for the last five years. So, when they told us they were re-purposing their gateway software for an ATA, we suggested that we work together to produce not just another ATA, but the ATA that the industry was demanding … one that finally “makes FoIP work” and adds V.34.

ITEXPO West 2011 will be held in Austin, Texas, September 13-15. So be sure to visit booth 722 to get the full Smart ATA story. Not going to the show? Then email us at for more info now.

The Late T.38 re-Invite Secret

If you have a high-performance implementation of T.38 and you use it over the open Internet, you are probably aware that T.38 works, and works well. But if you try it over IP-carrier networks to reach PSTN-connected fax terminals, you might be disappointed in the connect rates of FoIP compared with PSTN fax.

There are many reasons for this: There’s always the possibility of interop problems. But most of the time the problems are caused by less-than-optimum routing of FoIP calls by service providers and IP carriers. Their selected routes all too often result in the SIP signaling being slowed to the point where the T.38 re-Invite arrives so late that the fax session is actually killed by the gateways switching to T.38 after the endpoint terminals have gotten far enough into the T.30 protocol that they can no longer be interrupted.

Smart ATA solves this problem by attaching V.21 modems to the two G.711 RTP streams in order to monitor the T.30 protocol state of the endpoint terminals. Once the caller has sent its command signal (DCS), it’s too late to accept a T.38 re-Invite, and Smart ATA doesn’t while all other ATAs do since they don’t use our patent-pending technology.

This converts failed sessions to G.711 pass-through sessions, which are less robust than T.38, but Smart FoIP’s unique clock-sync solution is there to bring the V.17 G.711 sessions to near-T.38 reliability on many networks.

Email us at for more details on Smart ATA and Smart FoIP.

PMC Clock Sync?

Most industry vets are unaware that the reason longer faxes fail in G.711 pass-through mode is not because of lost packets, but because the clocks used to drive the gateway’s PCM jitter buffer and the clocks in the endpoint terminals that drive their modems are never the same speed. A 100-part-per-million difference in the two clocks means one extra (or less) packet every 100 seconds, which is why it usually takes a fax longer than one page to see the problem.

The jitter buffers in a gateway are fixed for modem calls. Adaptive jitter buffers for voice calls have the same problem, but the fix is simple. If the buffers become full because the endpoint-terminal clock is too fast, just toss some buffers. Your ears will usually not notice. If a buffer is about to run dry because the sender’s clock is slow, no problem, just repeat the last buffer. But don’t try this for a modem call since it will probably fail because modems have no tolerance for fake data.

So, how does Smart ATA eliminate that problem? With more patent-pending technology that monitors the state of the T.30 state machines in the endpoint terminals by attaching V.21 modems to the media streams. Smart FoIP knows when it is safe for the gateway to reset its jitter buffers without aggravating the modems. Presto! Say goodbye to G.711 clock-sync failures.

Huge problem solved.

For more info on Smart ATA, email us at

Finally, an ATA with V.34

As we’ve explained in earlier newsletters, it’s hard enough negotiating a T.38 V0-with-V.17 FoIP session, and without Smart FoIP it’s nearly impossible to negotiate a T.38 V3 session with V.34 because V.34 changes all the rules. With V.17 fax, the called/receiving/off-ramp gateway is responsible for determining whether a call is fax and issuing the re-Invite, but with V.34 endpoints and V.34-capable gateways, the calling/sending/on-ramp gateway is responsible for the re-Invite due to the way the V.8 protocol negotiates a session’s capabilities.

The V.8 protocol, which is used by both V.34 fax and data modems, is required if the gateway is to properly handle both call types, even if it does not offer T.38 with V.34. Smart ATA (analog telephone adapter) handles all this for you.

Smart ATA operates in four different modes, depending on whether it is the calling or called gateway and whether it is to support V.34 fax:

  • Called GW, V34 fax supported
  • Called GW, V34 fax not supported
  • Calling GW, V34 fax supported
  • Calling GW, V34 fax not supported

For example, to support the called-gateway no-V.34 mode, Smart ATA detects whether the called terminal emits CED (G3 fax), ANSam (high-speed modem), or voice. The appropriate state machine is started and then responds to 24 different events. For example, if ANSam is detected, as configured by the user, the gateway can either force a fallback to T.38 V0, resulting in a 14,400-bps image transfer or leave the session in G.711 pass-through mode for a V.34 session between the two endpoints. If V.34 were configured, Smart FoIP would handle the spoofing required to establish a T.38 V3 V.34 session, assuming the on-ramp gateway supported it as well.

Now, it could be reasonably asked, if Smart ATA is the first to market with V.34 support, what good is it since no other ATAs and gateways support V.34? Well (and you already know the answer) someone has to assume the leadership role. Moreover, we are actively working with tandem-gateway vendors to add V.34 support, so we’re doing everything we can to bring V.34 to FoIP.