s. that the incremental cost of additional frame relay bandwidth for voice traffic may be more cost-effective Echo cancellation on VoFR than standard voice services offered by local or long-distance carriers. Echo cancellation improves the quality of voice trans- VoFR can provide end users with a cost-effective missions. It eliminates the echo that results from the option for voice traffic transport needs between company reflection of the telephony signal back to the caller, locations. For instance, the network manager may in- which can occur in a four-wire to two-wire hybrid con- tegrate some voice channels and serial data over a frame nection between the VFRAD and the telephones or PBX. relay connection between a branch office and corporate The longer it takes the signals to return to the caller, the headquarters (see Figure 3.2-7). By combining the voice more perceptible the echo. and data traffic on a frame relay connection already in place, the user has the potential to obtain cost-effective Voice switching requirements intracompany calling and efficient use of the network bandwidth. Various vendors implement voice switching in their There are potential trade-offs when implementing VFRADs in different ways. Users should consider the VoFR. These include requirements listed following when examining the voice switching capabilities of vendor equipment: loss of the quality commonly associated with toll traf- fic due to VoFR's use of voice compression Flexible numbering plan loss of management and administrative benefits associ- Transparent integration of voice and data ated with carrier voice services (i.e., the loss of con- Easy setup solidated voice billing and invoice itemization, end Network infrastructure CHAPTER 3.2 VoFR service user Primary payloads Signalled payloads VoFR service Frame Relay service Figure 3.2-6 Layered architecture of VoFR. user charge back capabilities, and other advanced IP networks. Traditionally, the voice is transported on features such as ID and accounting codes) a network that us