The new Half-Rate vocoder is an extension of the current 7200 bps standard Full-Rate IMBE™ Vocoder that is used throughout P25. Both the new Half-Rate and the older Full-Rate version are based on DVSI’s Multi-Band Excitation (MBE) technology which codes speech using a set of MBE model parameters for each frame of speech. However, the new Half-Rate vocoder includes a number of enhanced features, such as high performance FEC (capable of up to eight bits of soft-decision decoding) built-in Voice/Silence detection (DTx), adaptive comfort noise generation, tone detection and generation of DTMF / Knox tone and North American call-progress tones.

The Net-2000™-P25 VCU goes beyond just implementing DVSI’s patented Half-Rate Voice Compression Software, it also integrates an UDP/IP packet protocol for remote access and control. The 10Base-T Ethernet connection on the Net-2000™-P25 VCU allows full-duplex real-time or half-duplex non-real time voice compression applications over a Local Area Network (LAN). Using the LAN, two Net-2000™-P25 VCUs can communicate to create a Voice Over Internet Protocol (VOIP) Ethernet-based vocoder communication system. Communicating between two Net-2000™-P25 VCUs is as easy as entering the IP address (or host name) of the Net-2000™-P25 VCU units, selecting the desired voice interface and the Full-Rate or Half-Rate Vocoder mode.

When two Net-2000™-P25 VCUs communicate, each converts the input analog speech into digital speech samples, encodes the speech using the selected APCO Full-Rate or Half-Rate mode and then sends the compressed bit stream out as UDP/IP packets over the Ethernet interface. Simultaneously, the compressed bit stream of UDP packets from the other Net-2000™-P25 VCU is read in from the Ethernet interface and decoded back in to digital speech samples. The decoded samples are converted back into analog speech via the AIC-10 codec whose output is sent to both the handset and line-level output connections. Since the channel data is a packet-based UDP Ethernet protocol, users can develop their own customized controls and user interfaces so that the Net-2000™-P25 VCU can fit into an endless array of applications.

Digital Connectivity
The UDP/IP connection can also be used to encode/decode files from a PC, or other UDP/IP device making the Net-2000™-P25 VCU ideal for compressed-voice storage applications or non-real-time testing. Alternatively, the Net-2000™-P25 VCU can loop back the VOIP digital data to itself for voice monitoring and evaluation applications.

The Ethernet connection to a LAN provides the ability for any PC on the network to use a standard web browser to control the Net-2000™-P25 VCU. The user-friendly web server built into the Net-2000™-P25 makes it easy to select analog audio I/O interfaces, select the vocoder mode and to establish communication across the UDP/IP Ethernet connection. In addition to the control, the web pages display information about network settings, operating mode and system status. Since the Net-2000™-P25 uses Ethernet, its web page can even be accessed from notebook or tablet PC via wireless network.

Variety of Inputs
To meet a wide range of communication system requirements, the Net-2000™-P25 Voice Codec Unit hosts a variety of inputs and outputs. For uncompressed analog voice I/O, the Net-2000™-P25 VCU supports 4-wire and handset analog interfaces. For compressed voice-data communication across a channel, digitized speech can be transmitted and received through the UDP/IP packet interface. A unique feature of the Net-2000™-P25 VCU is that the compress voice channel data and the uncompressed voice can be transmitted over Ethernet using the same UDP/IP packet interface.

Fast and Easy Set Up
Initial set up of the Net-2000™-P25 VCU is fast and straightforward thanks to its Ethernet network connection. It is equipped to handle IP address information from a DHCP server when available on the LAN. Alternatively, the Net-2000™-P25 VCU’s RS-232 serial port can be used as a console terminal to allow low-level network set up and selection among the various input and output audio interfaces.

DVSI developed the Net-2000™-P25 VCU to package the latest software into a hardware platform that does not require licensing fees or royalties. With off-the-shelf availability, the Net-2000™-P25 VCU provides cost effective voice compression without the risks and engineering expenses associated with new product development.