AudioCodes Mediant 4000 SBC, Руководство пользователя

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CHAPTER 28 Advanced SBC Features
Mediant 4000 SBC | User's Manual
Alternative Routing on Detection of Failed SIP
Response
The device can detect failure of a sent SIP response (e.g., TCP timeout, and UDP ICMP). In such
a scenario, the device re-sends the response to an alternative destination. This support is in
addition to alternative routing if the device detects failed SIP requests.
For example, assume the device sends a SIP 200 OK in response to a received INVITE request. If
the device does not receive a SIP ACK in response to this, it sends a new 200 OK to the next
alternative destination. This new destination can be the next given IP address resolved from a DNS
from the Contact or Record-Route header in the request related to the response.
VoIPerfect
The device's VoIPerfect™ feature combines 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 or G.729 (explained later 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%. . However, for VoIPerfect with G.729 (Managed G.729,
discussed later) operating in an MPLS environment, this PESQ score is achieved if bandwidth
overuse is less than or equal to 50%. ISPs can therefore offer service level agreements (SLAs) to
their customers based on the VoIPerfect feature. For more information, contact the sales
representative of your purchased device. 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:
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