Bridging VoIP to the PSTN Network by Using a Media Gateway

For voice calls from Office Communications Server to reach the PSTN, a third-party media gateway is required to bridge the IP network and the PSTN network by translating the signaling and media to the protocols used by each network, as shown in Table 4-3.

Table 4-3. Protocol Translation That Media Gateway Performs

TECHNOLOGY

PSTN NETWORK

IP NETWORK

Signaling protocol

SS7 and others

SIP

Media codecs

G.711

RTAudio (Real-Time Audio)

Transport protocol

T-Carrier/E-Carrier

RTP (Real-Time Transport Protocol/SRTP (Secure RTP)

Network type

Circuit switched

Packet-based

Microsoft partners provide such a media gateway. (See the section titled "Additional Resources" at the end of this chapter for the link.) The three ...

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