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Digital Telephony

Digital telephony is used in the provision of digital telephone services and systems. The upper end of this software can provide a V.110, V.120, V.14, HDLC, or a direct binary framing layer. V.110 is a rate adaptation standard which defines how data terminal equipment (DTE) with asynchronous or synchronous serial interfaces can be supported on an ISDN network through a bit-by-bit alignment between the DTE and the ISDN B channel. V.120 is used to synchronize data streams in North America between a telephony network and asynchronous devices, such as a serial UART.

VOCAL’s embedded software libraries include a complete range of ETSI / ITU / IEEE compliant algorithms, in addition to many other standard and proprietary algorithms. Our software is optimized for execution on ANSI C and leading DSP architectures (TI, ADI, AMD, ARM, MIPS, CEVA, LSI Logic ZSP, etc.). These libraries are modular and can be executed as a single task under a variety of operating systems or standalone with its own microkernel.

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Telephony Signaling

  • MF Generation/Detection
  • MF R2 Compelled/Semi-Compelled Signaling
  • MF R1 Signaling
  • TIA 468A DTMF Signaling
  • Bellcore Interoffice Signaling
  • Q.921 LAPD Protocol
  • Q.922 LAPF Protocol
  • Q.931 ISDN Call Signaling
  • Q.932 Frame Relay Call Signaling

Framing Layers

  • ISDN Interface
  • V.110 Rate Adaptation
  • V.120 Rate Adaptation
  • HDLC B Channel (7 or 8 bit)


  • IO/M-2/GCI/ST Frame Assembly/Disassembly
  • IO/M-2/GCI/ST 2B + D Multiplexing
  • V.110 Rate Adaptation
  • Bonding implementation of 2 or 6 B channels for 128 to 384 kbps aggregate throughput
  • Q.921 LAPD Data Protocol Optional
  • Q.931 Call Control Optional
  • Q.922/Q.932 Switch Circuit Frame Relay Optional
  • U.S. National ISDN Call Control Optional
  • Modular software suite available with controller code
  • Optimized for high performance on leading edge DSP architectures
  • Multi-tasking environment compatible


  • V.110, V.120, V.14, HDLC and direct binary framing layer
  • Can be combined with analog data modulations (V.90, V.34, V.32bis et al.)
  • Can be combined with analog facsimile modulations (V.34fax, V.17 et al.) and protocols (T.30)
  • Can be combined with analog telephony functions including speakerphone
  • Compatible with Siemens, Motorola and National U interface chips
  • Frame Relay/PPP Terminal adapter

ITU Recommendation V.110

ITU Recommendation V.120

VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Amherst New York 14228
Phone: +1-716-688-4675
Fax: +1-716-639-0713