Linksys SPA9000 Administration Guide

Linksys Voice System Administration Guide 133
Technology Background
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 ports 5060 through 5063
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 A-3).
Figure A-3 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

Linksys SPA9000 Specifications

Physical Interfaces

Ethernet ports	2 10/100BaseT RJ-45
Phone ports	2 RJ-11 FXS
Ring voltage	40-55 VRMS
Ring frequency	10 Hz - 40 Hz
Maximum ringer load	3 REN

Power

On-hook voltage	-50 V NOMINAL
Off-hook current	25 mA min
Terminating impedance	Configurable, including 600 ohms