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Linksys SPA9000 Administrator Guide
Document Version 3.01
Chapter 1 Using the Linksys Voice System
Technology Background
Local traffic is not affected by this configuration. When UserA initiates a call to UserB, RTP traffic still
flows directly between the two UAs. The media proxy only affects RTP traffic to a UA connected
through the ITSP.
Using the SPA9000 with a Firewall or Router
When using the SPA9000 behind a firewall or router, make sure that the following ports are not blocked:
• SIP ports—By default, UDP port 5060 and 5061
• RTP ports—16384 to 16482
Also disable SPI if this function exists on your firewall.
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 (see
Figure 1-4).
Figure 1-4 The 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