Dialogic’s Signaling Distributed Architecture (SigDiA)

As any telecom-related application scales up, coordinating the activities of many computing and telecom resources scattered about becomes more and more important, not to mention difficult. Historically, the first major problem was simply coordinating what was happening among the plug-in boards on a backplane and how a PC could talk to a PBX. Just a year after Carl Strathmeyer at DEC concocted the first CTI-PBX link in 1985 (“Computer Integrated Telephony”), Dialogic (www.dialogic.com) introduced the first telephony bus for resource sharing, the Analog Expansion Bus (AEB). The “resources” connected to AEB where in most cases Dialogic boards that fit into a PC AT-expansion slot, such as the DTI/124, D/4x and AMX line.

In 1989 Dialogic introduced the first 12 channel DSP-based voice processing board, the first T-1 interface board for voice processing, and with them the first digital TDM (Time-Division Multiplex) bus for resource sharing, the Pulse-Code Modulation Expansion Bus (PEB). In 1990, Dialogic’s rival, Natural MicroSystems (now called NMS Communications, www.nmss.com) along with seven other vendors, developed their own more powerful inter-board TDM/PCM highway, a bus standard called the Multivendor Integration Protocol, or MVIP-90. Inspired by the old Mitel ST bus reference design, the 2 MHz MVIP-90 bus supported 512 timeslots.

These incompatible ‘mezzanine buses” were based on a ribbon cable that hopped from board to board, attaching to a connector at the top of each board.

Increasing demands for bandwidth, the number of active ports and processing led to Dialogic developing yet another Computer Telephony Bus, SCbus, the core of the Signal Computing System Architecture (SCSA). The led to a major “bus war” between MVIP and SCSA that was resolved with the joint development and approval by the ECTF in 1997 of the H.100 CT Bus hardware standard (and H.110 for CompactPCI form factor boards).

Most of these early systems introduced the idea of a common resource model, wherein there appeared real-time resource management and dynamic resource sharing. A CT Server could handle multiple operations simultaneously and in real time, such as calls to call centers, fax systems and Interactive Voice-Response (IVR) systems. SCbus allowed “hyperchannels” to be set up so that one server could call upon resources residing in another via a particular timeslot.

Today, with the rise of the vast Internet/PSTN hybrid network, telecom applications have a much bigger canvas on which to paint. Signaling between different kinds of components has become a more sophisticated and distributed affair, with a focus on higher-level signaling challenges involving both the traditional SS7-based “Intelligent Network” (IN) and newer “next-gen” packet networks. This has led to more intense interest in middleware and the development by Dialogic of its Signaling Distributed Architecture (SigDiA) for creating and deploying high-performance, distributed, cross-platform, cross-OS signaling applications. SigDiA is an architecture sufficiently flexible so that signaling protocols can run on a board, on a Dialogic signaling server, or on an application server. SigDiA supports automatic failover, load sharing and signaling offload. SigDiA is now integral to Dialogic’s entire range of SIGTRAN/SS7 protocols as well as its SS7 boards and signaling servers.

SigDiA allows those developing large systems the flexibility to mix-and-match the best platforms and form factors for optimum price-performance and time-to-market. It allows for card offload and blade server distribution, shared signaling network access, and supports signal message monitoring on TDM and IP to enable distinctive service delivery and enhanced security.

You can find this technology in products such as Dialogic’s SIGTRAN and AdvancedMC products, particularly their SS7 boards. You can find SigDiA underlying the Dialogic SS7G21 and SS7G22 Signaling Servers, both equipped with Signaling Interface Unit (SIU) software that provides signaling connectivity for distributed, multi-system-based telecom applications. The SS7G21 and SS7G22 offload signal processing from application servers and can run various signaling protocols (including specific local variants), allowing for deployment anywhere in the world. The servers can be ordered with an optional SIGTRAN signaling gateway (SGW) software, making them a modular component in next-gen networks and service platforms, providing the all-important interface between SS7 and IP networks.

Optional Digital Signal Conversion (DSC) software

enables the SS7G21 and SS7G22 to do protocol conversions between SS7 circuit-related protocols and access-signaling protocols, including ISDN and SIGTRAN M2PA for long-haul configurations.

Various sorts of middleware architectures such as Dialogic’s SigDiA and the Service Availability Forum’s (SAF’s) high availability and management software interface specifications add “pseudo layers” to the OSI Reference Model and will move from de facto standards to real ones over time as their utility becomes more recognized. IT

Richard Grigonis is Executive Editor of TMC’s IP Communications Group.

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