The market for enterprise fax servers continues to grow, even as investments in TDM fax-server systems are declining. That’s because IP-based fax servers are more than taking up the slack. Obviously, vendors that continue to “sit this one out” run the risk of being permanently left behind. Fax-server vendors must add support for IP fax. But as IP networking is new technology for many, there are plenty of questions. Chief among them are those concerned with the conversion between TDM and IP transport, the task of the IP-PSTN gateway. Sometimes the prospect has it already handled, presenting an interoperability question; other times your prospect looks to you, the vendor, to provide the gateway function. Then there’s SIP trunking.

There are also questions regarding signaling (SIP is it) and IP carriage: T.38 or G.711 pass-through fax. Although it’s been mostly answered in favor of HMP implementations, there are still lingering questions regarding boards or “boardless ” media servers versus HMP.

HMP or DSPs?

Let’s take one of the easy questions first: boards or HMP (host media processing)? Unless you need to terminate more than 96 simultaneous G.711 pass-through fax sessions or well north of 200 T.38 fax sessions per server, there is no justification for the added expense and lack of configurability of hardware-based fax-termination resources. Keep in mind that T.38 does not benefit from DSPs at all. It’s not a signal-processing task, so an HMP implementation is actually a superior technical solution for T.38 than a DSP-based resource. And, as a distributed client-server architecture, BladeWare can be scaled by simply plugging an additional server blade into the system. Every time you do you get a few-hundred additional channels. Use HMP and save.

SIP or H.323?

Signaling is another easy one: SIP is it. H.323 has very limited investment today, and it’s not going to help you if you ever want to take advantage of SIP trunking (see SIPconnect here). And forget proprietary. Why invest in a disadvantage? Sure, there are still H.323 opportunities, but you need to consider the cost of your development and support for a dying protocol.

T.38 or G.711 Pass Through?

After 10 years of fine-tuning the technology, our industry has figured out how to use packet networks to transport voice. (Have you tried Skype?) We’ve developed a variety of techniques based on the way human hearing works. For example, our ears can’t tell if a 10-millisecond packet has been lost. If it is, we simply duplicate the last packet. Jitter buffer under- or over-run due to lack of PCM clock synchronization? Not a problem, just throw away or synthesize packets.

But what works for the human ear doesn’t work for a modem. To a modem, a dropped packet is the equivalent of a bomb going off to the ear. This is why, unless the IP network is very high performance, G.711 pass-through fax, where a fax call is treated as a special-case voice call, is a source of customer dissatisfaction. So be cautious-do your due diligence when asked to accept responsibility for fax quality when the network’s edge does not deliver T.38-based faxes.

The Gateway Function

This brings us to the consideration of the interconnection of the IP fax server with the wide area network. You may see the following situations:

  • The prospect has a corporate IP network with existing gateways.
  • The prospect has no existing gateway function, and wants you to provide it.
  • The prospect has a production-fax application and is negotiating a service agreement with an IP service provider.
  • The prospect is using SIPconnect for SIP trunking.

It’s possible your customer has installed gateways in each office, and wants you to interconnect with the existing IP network. If that’s the case, you need to find out what gateways are installed. Do they all support T.38, the IP fax-relay protocol? If not, is it a mix of G.711 pass through and T.38? Is it a mix of vendors? Note that the older the gateway, the less chance there is that it will support T.38 and the greater the chance there will be interoperability “issues.”

If there are gateways and terminal adapters without T.38 support, look into the underlying network. If it’s a local LAN (no wide area involved), you’re probably okay, but you’ll need either MMTF or BladeWare with MMTF. It’s pretty easy to find out if you’re going to have problems with G.711 in a site visit with your BladeWare-based system installed on your laptop. It’s best to test by looping back via the PSTN. Send 50 faxes…you’ll know.

If you’re getting fancy and doing IP-based least-cost-routing between offices, be careful about non-T.38 inter-office calls. Does your customer have a service agreement in place for real-time voice service? If not, don’t count on error-free G.711 pass-through faxes (or even if there is one), but T.38 faxes should go through without a problem, even over the public Internet. (We’ve sent a 1000-page fax from Atlanta, Ga. to Melbourne, Australia, without a single error using T.38.) On the other hand, if the customer has, for example, an MPLS VPN with a real-time voice service-level agreement that would apply to all calls to and from your server, you might be able to accommodate non-T.38 fax traffic on your BladeWare-based fax server, handling faxes even from those older non-T.38 endpoints. Again, perform some tests.

Note that the scenarios above expose you to integration and interoperability problems that can eat your profits unless you approach that portion of the sale as a revenue generator. Include a professional-services component.

But there is a way to limit your exposure to the uncertainties of unknown gateway devices. Make the gateway part of your scope of supply. You can do that by qualifying and supplying an off-the-shelf gateway, preferably one with T.38 support. Another approach is to include the gateway as a PCI add-in board. Commetrex offers the MSP-H8 4-8-line analog interface and the MSP-640, with one-to-120 ports (quad E1/T1) on one board as a PSTN-IP gateways.

A Mixed Bag

 

Some of this is shown in the diagram above. The BladeWare -based fax server, in the upper-left corner, serves the entire organization. (After all, IP renders geographic location somewhat irrelevant.) Office A has no legacy fax terminal, but does have client workstations that utilize the enterprise fax server. Office B has a PC with a resident MSP-H8 serving as a T.38 gateway for terminals “behind” the PC using the H8’s FXO interface while also connecting with the PSTN via a station port on the H8. Office C happens to have a Cisco IAD2400 without T.38 support, but the quality and performance of the IP connection to the fax server is such that G.711 does the job. Office D is also equipped with a local-server gateway. In this example, a fax can be sent in real-time directly between the terminals in offices B, C, and D.

BladeWare in the Enterprise

 

You Have Options

As you can see, IP telephony offers the fax-server vendor options and complexities not frequently encountered in the TDM-only world. It is important to choose a vendor that offers the products you need to meet these requirements. And it’s important to recognize the importance of the service component of the sale. Commetrex offers highly experienced support to make sure you’re successful with our products.