R2511-HP MSR Router Series Voice Configuration Guide(V5)

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Configuring VoFR

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.

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. This improves the bandwidth use and

lowers the communication cost.

Fundamental VoFR architecture

Figure 99 Fundamental VoFR architecture

In Figure 99, the FR-supported voice gateway provides an interface between the frame relay network and

the public switched telephone network (PSTN). Telephone A and Telephone B are connected to the voice

gateway through 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 converts them back to recognizable analog signals and transmits them to

Telephone B across PSTN. This completes a phone-to-phone communication process.

Protocols and standards

VoFR not only complies with audio codecs such as G.711A-law, G.711-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 and voice by using FRF.11. Figure 100 sh

ows the protocols and

standards that VoFR complies with.

Frame Relay

PSTN

Originating

voice gateway

Terminating

voice gateway

Telephone A

Telephone B