Yealink SIP-T4X Administrator's Manual page 19

preferential to use this method when not using an application layer firewall. Application
layer firewalls like to know what applications are flowing though 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 the SIP-T4X IP phone family. SIP-T4X IP phones are endpoints in
the overall network topology, which are designed to interoperate with other compatible
equipments including application servers, media servers, internet-working gateways,
voice bridges, and other endpoints. SIP-T4X IP phones are characterized by a large
number of functions, which simplify business communication with a high standard of
security and can work seamlessly with a large number of SIP PBXs.
SIP-T4X IP phones provide a powerful and flexible IP communication solution for Ethernet
TCP/IP networks, delivering excellent voice quality. The high-resolution graphic display
provides content in multiple languages for system status, call log and directory access.
SIP-T4X IP phones also support advanced functionalities, including LDAP , Busy Lamp
Field, Sever Redundancy and Network Conference.
The following IP phone models are described:
SIP-T48G

SIP-T46G

SIP-T42G

SIP-T41P

SIP-T4X IP phones comply with the SIP standard (RFC 3261), and they can only be used
within a network that supports this type of phone.
In order to operate as SIP endpoints in your network successfully, SIP-T4X IP phones must
meet the following requirements:
A working IP network is established.

Routers are configured for VoIP .

VoIP gateways are configured for SIP .

Product Overview
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