Voiperfect - AudioCodes Mediant 4000 SBC User Manual

29.10 VoIPerfect

AudioCodes VoIPerfect™ feature combines the device's Access and Enterprise SBC
technology to ensure high speech (call) quality (MOS) between the Enterprise SBC and the
Access SBC (located at the Internet service provider / ISP) during periods of adverse WAN
network conditions (such as packet loss and bandwidth reduction). VoIPerfect adapts itself
to current network conditions. Before adverse WAN network conditions can affect the
quality of the call, VoIPerfect employs sophisticated technology using the Opus coder (as
later explained in this section) to ensure that high call quality is maintained.
VoIPerfect guarantees that 95% of your calls will achieve a Perceptual Evaluation of
Speech Quality (PESQ) score greater than or equal to 3.6 if the summation of bandwidth
overuse and packet loss is less than or equal to 25%. ISPs can therefore offer service level
agreements (SLAs) to their customers based on the VoIPerfect feature. For more
information, contact your AudioCodes sales representative. In addition, by ensuring high
call quality even in adverse network conditions, VoIPerfect may reduce costs for ISPs such
as SIP trunk providers and Unified Communications as a Service (UCaaS) by eliminating
the need for dedicated WAN links (such as MPLS and leased links) and instead, allow the
use of standard broadband Internet connections. However, it can also be used in tandem
with existing infrastructure.
VoIPerfect uses Temporary Maximal Media Stream Bit Rate (TMMBR) negotiation
capabilities for Opus coders. Through TMMBR, VoIPerfect can receive indications of
network quality and dynamically change the coder's payload bit rate accordingly during the
call to improve voice quality. TMMBR is an RTCP feedback message (per RFC 4585)
which enables SIP users to exchange information regarding the current bit rate of the
media stream. The information can be used by the receiving side to change the media
stream parameters (e.g., coder rate or coder) to enhance voice quality. TMMBR is
negotiated in the SDP Offer/Answer model using the 'tmbr' attribute and following syntax:
a=rtcp-fb:<payload type> ccm tmmbr smaxpr=<sent TMMBR packets)
VoIPerfect also supports the SDP attribute 'a=rtcp-rsize', which reduces the RTCP
message size (RFC 5506). As feedback messages are frequent and take a lot of
bandwidth, the attribute attempts to reduce the RTCP size. The attribute can only be used
in media sessions defined with the AVPF profile and must also be included in sessions
supporting TMMBR; otherwise, the call is rejected.
VoIPerfect supports two modes of operation, where the Access SBC can be configured to
support both modes and each Enterprise SBC serviced by the Access SBC can be
configured to support one of the modes:

Managed Opus: If the SBC detects WAN network impairments during a call using the
Opus coder between the Enterprise SBC and Access SBC, it can adjust the Opus
coder's attributes (e.g., bit rate) for that specific call to ensure high voice quality is
maintained. The advantage of the Opus coder is that its' bit rate can change
dynamically according to bandwidth availability. This mode is useful for unstable
networks, allowing Opus to dynamically adapt to adverse network conditions.
Configuration of the Enterprise SBC:
•
Coders Group with Opus
•
Allowed Audio Coders Group with Opus
•
IP Profile:
User's Manual 586
Mediant 4000 SBC
Document #: LTRT-40203