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Advanced Topics in SPA9000 Administration
Technology Background
SPA9000 Voice System Administration Guide 169
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SPA400 SIP-PSTN Gateway
When a local user on the SPA9000 network initiates a call to a PSTN subscriber, the
SPA400 acts as the SIP-PSTN gateway, which converts the SIP and RTP media
packets into the appropriate signal for transmission to the PSTN switch. For
example, if UserA calls UserD, the SIP request is routed by the SIP proxy in the
SPA9000 to the SPA400.
Figure 3 SPA400 as a SIP-PSTN Gateway
The SPA400 then converts the SIP and RTP packets it receives from UserA and
the signals it receives from the PSTN switch.
SIP Proxy
Switch
SPA9000
UserA
UserB
SPA400
1 to 4 DID lines
SIP-PSTN
Gateway
UserD
Internet (WAN) Interface
PSTN