Sip Publish Signaling Improvements - Cisco Small Business SPA509G Administration Manual

Configuring Security, Quality, and Network Features
Ensuring Voice Quality
Cisco Small Business SPA300 Series, SPA500 Series, and WIP310 IP Phone Administration Guide
• Echo—Impedance mismatch between the telephone and the IP Telephony
gateway phone port can lead to near-end echo. Cisco IP phones have a
near-end echo canceller with at least 8 ms tail length to compensate for
impedance match. Cisco IP phones implement an echo suppressor with
comfort noise generator (CNG) so that any residual echo is not noticeable.
• Hardware noise—Certain levels of noise can be coupled into the
conversational audio signals because of the hardware design. The source
can be ambient noise or 60 Hz noise from the power adaptor. The Cisco
hardware design minimizes noise coupling.
• End-to-end delay—End-to-end delay does not affect voice quality directly
but is an important factor in determining whether IP phone subscribers can
interact normally in a conversation. A reasonable delay should be about 50–
100 ms. End-to-end delay larger than 300 ms is unacceptable to most
callers. Cisco IP phones support end-to-end delays well within acceptable
thresholds.
• Adjustable Audio Frames Per Packet—Allows you to set the number of
audio frames contained in one RTP packet. Packets can be adjusted to
contain from 1–10 audio frames. Increasing the number of frames decreases
the bandwidth utilized, but it also increases delay and can affect voice
quality.

SIP Publish Signaling Improvements

The SPA phone resends the SIP PUBLISH message with the voice quality report
once per 5xx response with a valid Retry-After header.
A valid time value in seconds is a positive integer from 0 to 65536. A SIP message
with a Retry-After time value of 0 is treated as a "500 Server Internal Error"
message.
A time value less than 0 is ignored.
The following is a summary of the 5xx messages with Retry-After header that the
phone supports:
5xx SIP Response
500 Server Internal Error
503 Service Unavailable
Description
An unexpected server condition prevents the
fulfillment of request.
The server is unavailable due to a temporary
overload or maintenance.
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