Compaq W25 manual SIP Server, PSTN Gateway, VoIP network

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	ISUP
	SIP Server		MGC-SG
	SIP
	W25
	SIP/RTP		TDM
	RTP			PSTN Networks
	SBC

MGW

2.2.1SIP 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.

2.2.2PSTN 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.

2.2.2.1Media 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).

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