Overview; Protocols And Standards - 3Com MSR 50 Series Configuration Manual

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Overview

Voice over frame relay (VoFR) enables a router to transmit voice and voice-band
data (for example, fax data and analog data from a Modem) over a frame relay
network. When voice traffic is sent over frame relay, it is segmented and
encapsulated for transmission across a frame relay network using relay frame
encapsulation.
VoFR supports permanent virtual circuit (PVC) statistical multiplexing to carry
multiple channels of voice, data, and fax over one PVC. In the case of concurrent
transmission of voice and data, voice takes precedence over data. Moreover, VoFR
limits the concurrent session channels according to the voice bandwidth and/or
reserves a bandwidth exclusively for voice to ensure the voice quality.
VoFR satisfies various demands of different user groups. It enables terminal users
to concurrently use different services, like data, voice and faxes, on a leased line,
and thereby improves the bandwidth utilization and lowers the communication
cost.
Fundamental VoFR
Figure 692 Fundamental VoRF architecture
Architecture
RF-supported RF-supported
Frame Relay
voice gateway voice gateway
PSTN
PSTN
Telephone A Telephone B
In Figure 692, the FR-supported voice gateway provides an interface between the
frame relay network and the public switched telephony network (PSTN).
Telephone A and Telephone B are connected to the voice gateway via the PSTN.
When Telephone A originates a call to Telephone B, the originating voice gateway
converts analog signals into digital signals and encapsulates them into voice
packets that can be transmitted over the frame relay network. These voice packets
are then transmitted to the terminating voice gateway, which reduces them to
recognizable analog signals and transmits them to Telephone B across PSTN. Thus,
a phone-to-phone communication process is completed.

Protocols and Standards

VoFR not only complies with audio codecs such as G.711A-law, G.711μ-law,
G.723R53, G.723R63, G.729R8, and G.729A, but also supports the Q.931-like
protocol for call control. In addition, VoFR encapsulates signaling by using T1.617,