Installing the UC520 behind an SRP521W

Unanswered Question
Dec 7th, 2009

We are planning on deploying the SRP521W to existing UC520 customers, and also plan on selling SRP521W units in new UC500 deployments.

I would like to have the SRP521W configured to do the following:

  • Fail over to 3G backup
  • Have the VPN ports forwarded to the UC520. We need VPN tunnels terminated on the UC520 to support the following:
    • Cisco IP Communicator softphone
    • Remote UC520 administration
    • Remote CUE administration
    • Multisite deployments
    • Remote administration of devices behind UC520 - such as computers, network printers, network surveillance cameras, ESW switches, AP500 access points, IP phones, etc.
  • Have SIP signaling passed through from the SRP521W to the UC520, and have RTP packets passed through from the SRP521W to the UC520. We do not need to worry about transcoding on the SRP521W, as the UC520, UC540, and UC560 can transcode calls if necessary. We also do not need to worry about failover to the FXO port on the SRP521W as the UC520 units we deploy normally have FXO ports. We have not yet deployed a version of the UC500 that does not have FXO ports, and probably will only sell versions that have FXO ports.
  • Have the SRP521W perform network address translation

I would like to have the UC520 configured to do the following:

  • Have calls go out to our IP to IP gateway. We do not want calls transcoded by the SRP521W, but we want the SIP signaling updated by the SRP521W (except for calls traversing over the site-to-site VPN tunnels, which do not require any changes to SIP signaling).
  • Have inbound calls sent to the UC520 unit. We want the UC520 to do the codec negotiation that it does when it is not behind the SRP521W, and we do not want the SRP521W to transcode calls or alter the UC520 codec negotiation behavior.
  • Have its NAT feature disabled. We want the SRP521W to do NAT. In SR520 in front of UC520 or SA520/SA540 in front of UC520 scenarios, NAT is normally disabled on the UC520 unit.
  • Terminate the IPsec VPN tunnels
I have this problem too.
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Maulik Shah Mon, 12/07/2009 - 12:27

Thanks for the interest in the SRP 521W. We are primarily focused on the Service Providers for the SRP but can see how this can be used as you outine below. Currently the SRP is not supported within CCA but on our radar (cannot divulge further roadmap details). Hence the deployment will not be similar to the SR500 + UC500 where CCA is the only tool but you will need to use CCA + SRP GUI.

The SRP 521 does have a GUI that you can do the below:

- setup 3G backup to its primary WAN interface.  Note running voice over 3G is not something we recommend so maybe something to consider if using SIP trunks on the UC500. ALso if using 3G the WAN IP address will be different so VPN may not work from the client side unless you re key the IP address - DDNS may help some in this but not

- SRP 521 does have NAT enabled with an option to enable SIP ALG. Also the SRP does allow you to setup port forwarding for various TCP / UDP ports.

We will post an SRP admin guide soon at to help setup but you can logon to the GUI if its at factory default by putting a PC on the SRP LAN ports and pointing your browser to - login as admin / admin.

For the UC500 side - you would use CCA to setup the VPN server and SIP trunk pieces as you do today.


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