Voice Compression

Fundamental to the capability of the Vocality range of products is the ability to connect to analogue or digital voice calls and to compress them for transmission over a satellite link. Analogue POTS calls are supported by both subscriber (FXS) and Office (FXO) interfaces, with digital connections being supported by both T1 (National ISDN2, AT&T 5ESS, Nortel DMS-100) and E1 (ETSI DSS1, QSIG) protocols.

Within carrier networks, toll-quality voice traffic is implemented using a full 64Kbps of bandwidth per call as defined by the ITU recommendation G.711. This is acceptable for terrestrial networks where bandwidth is readily available but impractical over satellite networks where cost and capacity dominate. Vocality solves this problem by using a range of standards-based compression algorithms to dramatically reduce the bandwidth requirements, such as G.723.1, G.729A/B and G.726/G.727. The user may select the algorithm most appropriate to operational requirements. This may be purely for low bandwidth using G.723.1, for VoIP network compatibility using G.729 or for the lowest latency using G.726. Vocality technology ensures that the voice transmission path is at all times the most efficient and robust whether supported by a dedicated serial aggregate or an IP-based network.

The objective of a compressed voice network should be to provide a transparent voice network to the user irrespective of the reduced bandwidth. Essential to this is the ability to operate a fully-featured and reliable service, without loss of quality or functionality in comparison to a conventional network. Consequently, the network also has to support the transmission of fax and data modem traffic in the same way as a terrestrial network. Vocality incorporates relay technology in its products to provide this facility, which can automatically discriminate between the different traffic types and adopt the appropriate protocol at the local port to communicate with the attached device, while transmitting its data within the reduced bandwidth. To extend the interoperability into IP-based networks, Vocality also provides gateway support for connection between POTS telephone networks and SIP-based VoIP networks through its scalable SIP User Agent feature.