Linksys SPA962, SPA942, SPA932, SPA922 manual Ensuring Voice Quality, Supported Codecs

Setting System Features

Ensuring Voice Quality

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	Complexity and Description	MOS Score
Compression
Algorithm)
G.711 (A-law	Very low complexity. Supports uncompressed 64 kbps digitized	4.5
and u-law)	voice transmission at one through ten 5 ms voice frames per	Highest voice
	packet. This codec provides the highest voice quality and uses	quality
	the most bandwidth of any of the available codecs.

Linksys SPA9x2 Phone Administration Guide 37