Yealink Yealink SIP-T48G, Administrator'S Manual, Page: 15 / 319

Product Overview
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preferential to use this method when not using an application layer firewall. Application
layer firewalls like to know what applications are flowing through which ports and it is
possible 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.
This section introduces SIP-T48G and SIP-T22(P) IP phone models with Lync firmware. It is
designed to work with Microsoft
® Lync™ 2013. These IP phones are characterized by a
large number of functions, which simplify business communication with a high standard
of security.
SIP-T48G and SIP-T22(P) IP phones provide a powerful and flexible IP communication
solution for Ethernet TCP/IP networks, delivering excellent voice quality. When these IP
phones are registered with Microsoft
® Lync™ server, you can interact with your Lync
contacts list on your IP phones through Microsoft’s Active Directory.
The following IP phone models are described:

SIP-T48G

SIP-T22(P)
For a list of key features available on Yealink IP phones running the latest firmware, refer
to
Key Features of IP Phones on page 6 .
In order to operate as SIP endpoints in your network successfully, IP phones must meet
the following requirements:

A working IP network is established.

VoIP gateways are configured for SIP.

The latest (or compatible) firmware of IP phones is available.

The Lync server is active and configured to receive and send SIP messages.
This section lists the available physical features of SIP-T48G and SIP-T22(P) IP phones.