Polycom SIP 3.1 - Manual (Page 29)

Overview
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— Multiple Call Appearances —The phone supports multiple concurrent
calls. The hold feature can be used to pause activity on one call and
switch to another call.
— Multiple Line Keys per Registration —More than one line key can be
allocated to a single.
— Multiple Registrations —SoundPoint IP desktop phones support
multiple registrations per phone. However, SoundStation IP
conference phones support a single registration.
— Network Address Translation —The phones can work with certain
types of network address translation (NAT).
— Presence —Allows the phone to monitor the status of other
users/devices and allows other users to monitor it. Requires call
server support.
— Real-Time Transport Protocol Ports —The phone treats all real- time
transport protocol (RTP) streams as bi-directional from a control
perspective and expects that both RTP end points will negotiate the
respective destination IP addresses and ports.
— Recording and Playback of Audio Calls — Recording and playback
allows the user to record any active conversation using the phone on
a USB device. The files are date and time stamped for easy archiving
and can be played back on the phone or on any computer with a media
playback program what supports the .wav format. This feature is part
of the Productivity Suite.
— Server Redundancy —Server redundancy is often required in VoIP
deployments to ensure continuity of phone service for events where
the call server needs to be taken offline for maintenance, the server
fails, or the connection from the phone to the server fails.
— Shared Call Appearances —Calls and lines on multiple phones can be
logically related to each other. Requires call server support.
— Static DNS Cache —Set up a static DNS cache and provide for negative
caching.
— Synthesized Call Progress Tones —In order to emulate the familiar
and efficient audible call progress feedback generated by the PSTN
and traditional PBX equipment, call progress tones are synthesized
during the life cycle of a call. Customizable for certain regions, for
example, Europe has different tones from North America.
— Voice Mail Integration —Compatible with voice mail servers.
• Audio Features
— Acoustic Echo Cancellation —Employs advanced acoustic echo
cancellation for hands-free operation.
— Audio Codecs —Supports the standard audio codecs.