Open Telecommunications Framework®,
A New Architecture for Fax Telephony
A Commetrex White Paper
August 2004

Commetrex has developed an architecture for high-density telephony that smoothes the transition from TDM to IP transports for applications such as IVR, unified messaging, audio conferencing, and especially fax. Commetrex’ Open Telecommunications Framework (OTF) takes advantage of the MSP Media Gateway PCI cards configured as “fax boards” to offer analog and digital interfaces to the PSTN. But it goes further by leveraging the economies made possible by blade servers combined with the OTF Kernel telephony middleware to extend the OEM’s coverage to IP networks on the same system platform. This architecture gives the telephony system developer unprecedented options in networks and media that support new high-value applications such as IP-based fax servers.

The enterprise and carrier-equipment vendors must be able to cost-effectively develop applications where the underlying platform renders the network—IP or PSTN—or the transport—G.711 pass-through, T.38 fax relay, or traditional fax modems—transparent to the application. Developers of enterprise systems must be able to take advantage of the power of today’s host processors, which double in power every 18 months while the MIPS required to process a fax media stream have remained relatively constant, and, in the case of T.38, have actually gone down. In today’s market, business as usual with traditional “fax boards” just doesn’t fill the bill.

But why is Commetrex the company to come forward with a new architecture for the industry? It’s the natural result of Commetrex’ position as a leading developer and licensor of fax technologies and framework software, and the Company’s unmatched record of innovation in fax and related technologies.

• In 1994 Commetrex shipped MultiFax, the industry’s first fax software-add-in product. It turned the NMS voice boards into voice-fax boards, and later became the basis of NMS’s NaturalFax. Today, AudioCodes, BICOM, NMS, and Pika, in addition to countless telecom equipment manufacturers (TEMs), base their fax products on Commetrex technology.
• In 1997 Commetrex founded the MSP Consortium (http://www.msp.org/) to bring the benefits of open architectures to the media-technology level of digital-media telephony. In 1998 the M.100 Media Streams Processing environment specification was published; Commetrex shipped OpenMedia, its M.100 implementation, in 2000.
• In 2000 Commetrex shipped PowerRelay for T.38 and I.366.2 ( http://www.commetrex.com/products/algorithms/fax_relay/PowerRelay/ PowerRelayProductBulletin.html) as licensed technology.
• In 2001 shipped TerminatingT38 (http://www.commetrex.com/products/algorithms/TT38PB.html), the industry’s first and only product to support sending and receiving T.38 real-time IP fax transactions, just as multi-line “fax boards” send and receive PSTN faxes.
• In 2002 opened the hugely successful T.38 Interoperability Lab (http://www.commetrex.com/TT38Forum/T38_portal.html), significantly improving the interoperability of T.38 products from a dozen TEMs.
• In 2003 shipped Multi-Modal Terminating Fax (MMTF) (http://www.commetrex.com/products/algorithms/Multi-Modal.html), which allows media servers to send and receive IP faxes whether they are sent through T.38-capable gateways or those that only support G.711 pass-through fax.
• In 2004 shipped BladeWare (http://www.commetrex.com/products/CTMiddleware/BladeWarePB.html), the industry’s only SIP-based host-media-processing framework for telecom equipment manufacturers.
• In 2004 shipped the MSP series ( http://www.commetrex.com/products/hardware/MSP-H8/MSPH8.html) of open-architecture PCI telephony boards.

Now, Commetrex is rolling up this portfolio of innovative technologies and products into a new architecture, Open Telecommunications Framework (OTF), which allows the industry’s OEMs and system developers to support, easily and cost-effectively, both PSTN and IP voice and fax applications on the same platform.

The OTF architecture (http://www.commetrex.com/OTF_Portal.html), shown in Figure 1, is comprised of OTF Kernel, which includes client APIs to access system, call, and media services, and the system services, such as authentication, media storage, and call routing. Call control commands are passed on to resource service managers; media services are passed on to media resource controllers. As OTF Kernel is completely open, OEMs can replace or extend any of these services.

Dual-Network Support

Within OTF, the critical components for the fax system developer are Multi-Modal Terminating Fax and the MSP series of PSTN network-interface boards. MMTF is Commetrex’ unique host-based product that terminates hundreds of simultaneous IP faxes on one server blade. The MSP boards extend the system’s reach into the PSTN.

This architecture is shown in Figure 2, which depicts the major elements of a system that supports the termination (send and receive) of PSTN faxes and IP-based G.711 pass- through and T.38 faxes.

The figure is simplified by not showing the MSP PSTN-interface boards required to interface with the PSTN. For the MSP-H8, call control means hook control and in-band call-progress analysis. The analog modems are implemented on the host for both the MSP-H8 and BladeWare. The same modems are used for each, but in the case of IP connections, the PCM streams are packaged into RTP packets while they are sent directly to the analog MSP-H8 for PSTN calls. All of this is transparent to the application.

For IP-based calls, call control is managed by an IP call-control facility, such as SIP, H.323, or H.248, labeled “IP Call Control” in the diagram. (SIP is currently supported in BladeWare.) In all cases, the same T.30 protocol engine is used (“Fax Service Manager”) to control the fax session. For those gateways that support T.38, the call stream is routed through the T.38 protocol engine. Gateways that do not support T.38 resort to what is known as “G.711 pass-through”. In G.711 pass-through the analog stream is packetized into an RTP stream, so it must be modulated/demodulated by analog modems. (This means 10 times as much IP bandwidth as T.38 and no spoofing, so the faxes are error-prone due to lost packets and mismatches between PCM clocks.) Therefore, a dual-transport-capable OTF system can send-receive faxes from any PSTN-connected G3 fax terminal or any gateway via IP.

When configured as an IP-based software-only system, the platform is called BladeWare. BladeWare Fax Media Server (FMS) adds the SIP-based Media Server Command Mark-up Language application ( http://www.commetrex.com/products/CTMiddleware/BladeWareFMS.html). Of course, if IP-network functionality is not required, the MSP line of network-interface boards can be configured as traditional “fax boards”, both analog and digital.

Enterprise Fax

The diagram below (Figure 3) depicts an application of OTF in a multi-location enterprise that integrates all locations through an IP network. The MSP-H8 analog interface serves as an end-point media gateway in two of the offices. The other offices are handled by pre-existing equipment: one an IAD without T.38 capability, the other an access router with T.38. The requirement is to seamlessly handle faxes from all offices, which are interconnected via the enterprise IP network, the Internet, or VPN. Client workstations in all offices access the corporate fax server via their LAN without requiring any hardware resources.

The office with the IAD is a home office, which uses the IAD supplied by the employee’s DSL provider.

The two offices equipped with an MSP-H8 have a mix of FXS and FXO interfaces to support both voice and fax stations, as well as PSTN connectivity. Since the MSP-H8 supports both interfaces, and OTF Kernel supports both PSTN and IP routing, the remote office can hairpin-turn faxes to the PSTN or route them to another office via the Internet using T.38 fax relay. The correspondent office can then terminate the fax or route it via T.38 to another office or out to the local PSTN. This can result in significant toll savings, especially if the offices are in different countries.

To accomplish this, the application determines the cost of the available routes for a fax to reach its destination. It then executes OTF Kernel commands that will cause the fax to be routed either directly to the PSTN or to the MSP-based gateway in another enterprise location. This is possible because the OTF system has the media technologies needed to support PSTN fax with multi-line fax modems (the MSP Media Gateways serving as fax boards), T.38 IP real-time faxes, and G.711 pass-through faxes.

OTF makes the multiple transports transparent to the application. It isolates the application from any specific signaling system by the OTF System Call Router (SCR) API, which exposes generic call-control functions such as “place call” to the application. The system takes care of the routing using routing rules, which are maintained independently of the application.

Fax Boards

But if all you need is a traditional “fax board”, Commetrex’ MSP Media Gateway boards are configured for fax support, and for voice if required. This means Commetrex’ fax modems and T.30 protocol engine, each with 10 years of field experience, are applied to your application. Your customers benefit from this experience by unrivaled interoperability.

Both of these boards are sold without software. Then, you only need to license the number of ports required by your application. In the case of the MSP-H8, each port also requires a field-pluggable trunk interface as well as an incremental software runtime license. The board, as shown above, supports one-to-8 lines. The MSP-320 configured with its Quad E1/T1 Daughterboard, supports one-to-120 fax ports over four T or E spans.