Linksys BUSINESS SPA922 - Manual (Page 44)

Linksys SPA9x2 Phone Administration Guide 37
Ensuring Voice Quality
Setting System Features
The phone can be configured for secure provisioning using the factory-installed security
certificate. To determine if the Client Certificate is installed on the phone, press 6 from the
Product Info menu, or scroll down to the highlight Client Cert, and press the select soft button.
Secure Call Indication Tone
This tone is played when a call has been successfully switched to secure mode. It should be
played only for a short while (less than 30 seconds) and at a reduced level (less than -19 dBm),
so it does not interfere with the conversation. You can configure it on the Regional web page
under Call Progress Tones.
Defaults to 397@-19,507@-19;15(0/2/0,.2/.1/1,.1/2.1/2)
Ensuring Voice Quality
Voice quality perceived by the subscribers of the IP Telephony service should be
indistinguishable from that of the PSTN. Linksys SPA9x2 phones support several codecs. See:
• ”Supported Codecs” section on page 37
• ”Bandwidth Requirements” section on page 38
• ”Factors Affecting Voice Quality” section on page 39
Supported Codecs
Negotiation of the optimal voice codec sometimes depends on the ability of SPA9x2 phone to
“match” a codec name with the far-end device/gateway codec name. SPA9x2 phones allow the
network administrator to individually name the various codecs that are supported such that
the correct codec successfully negotiates with the far-end equipment.
Note that SPA9x2 phones support voice codec priority. You can select up to three preferred
codecs.
The administrator can select the low-bit-rate codec used for each line. G.711a and G.711u are
always enabled. The following table shows the codecs supported by SPA9x2 phones. The third
column shows the voice quality Mean Opinion Score (MOS), with a scale of 1–5, in which higher
is better.
Codec (Voice
Compression
Algorithm) Complexity and Description MOS Score
G.711 (A-law
and u-law) Very low complexity. Supports uncompressed 64 kbps digitized
voice transmission at one through ten 5 ms voice frames per
packet. This codec provides the highest voice quality and uses
the most bandwidth of any of the available codecs. 4.5
Highest voice
quality