Yealink SIP-T21 E2 Administrator's Guide

Administrator’s Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
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to use content types of other applications other than the one you are trying to let through what
has been denied.
User Agent Server (UAS)
UAS is a server that hosts the application responsible for receiving the SIP requests from a UAC,
and on reception it returns a response to the request back to the UAC. The UAS may issue
multiple responses to the UAC, not necessarily a single response. Communication between UAC
and UAS is client/server and peer-to–peer.
Typically, a SIP endpoint is capable of functioning as both a UAC and a UAS, but it functions
only as one or the other per transaction. Whether the endpoint functions as a UAC or a UAS
depends on the UA that initiates the request.
Summary of Changes
This section describes the changes to this guide for each release and guide version.
Changes for Release 81, Guide Version 81.91
Documentations of the newly released CP920 IP phones have been added.
The following section is new for this version:
 Touch Tone on page 826
 Off Hook Contact Dialing on page 333
 Noise Suppression on page 888
 Smart Noise Block on page 889
Major updates have occurred to the following sections:
 Softkey Layout on page 287
 Bluetooth on page 209
 Local Conference on page 471
Changes for Release 81, Guide Version 81.90
The following section is new for this version:
 Ringer Volume on page 853
Major updates have occurred to the following sections:
 Physical Features of IP Phones on page 1
 Key Features of IP Phones on page 15
 Connecting the Optional USB Flash Drive (Only Applicable to SIP-
T54S/T52S/T48G/T48S/T46G/T46S/T42S/T41S/T29G/T27G/CP860/CP920 IP phones) on
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Yealink SIP-T21 E2 Specifications

General

Brand	Yealink
Model	SIP-T21 E2
Category	IP Phone
Language	English