Compaq W25 - Manual (Page 5)

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2.2 VoIP network
The basic building blocks for Voice and Fax over IP are a SIP server and a
PSTN gateway with T.38 support. Sometimes the PSTN gateway might
consist of two units; Media Controller and Media Gateway. Normally a
Session Border Controller (SBC) is used to handle security.
SIP Server SIP Server
SBC SBC
MGW MGW
MGC-SG MGC-SG
PSTN Networks
TDM
ISUP
W25
SIP
SIP
RTP
SIP/RTP
2.2.1 SIP Server
The SIP server is the heart of VoIP system. It keeps track of the location of
each User Agent (UA). Calls are routed through the server. Each User
Agent has to authenticate to the server.
2.2.2 PSTN Gateway
The PSTN Gateway can be one single unit or divided in a Media Gateway
Controller (MGC), including the Signaling Gateway (for SS7/ISUP
connectivity), and the Media Gateway (MGW). Divided or not the
functionality is the same.
To be able to send fax between FWT and Fax machines on PSTN, each
User Agent in a FWT has an associated E.164 number in the PSTN. The
interworking between PSTN and VoIP is done in the PSTN gateway. Note
that the Fax E.164 number is separate from the E.164 number associated
with the SIM card in the FWT. So there is one E.164 number for fax and
another for voice.
2.2.2.1 Media Gateway Controller (MGC)
The Media Gateway Controller (MGC) provides interworking between the
SIP session control signaling and ISUP call control signaling to/from
external PSTN/PLMN networks. Furthermore, it controls the Media
Gateway resources.
The MGC normally provides the following capabilities:
• Handles multimedia session establishment, modification, and
termination using the SIP protocol in the IP Multimedia domain
and appropriate ISUP protocol in the circuit switched domain.
• Supports addressing and routing of multimedia sessions to and
from SIP server and interconnected PSTN nodes.
• Controls one or more Media Gateways.
• Performs mapping of application level signaling (SIP/ISUP).