issues with a Nortel i2004 IP phones over a Contivity VPN solution

Hi, all. I was wondering if anyone could help me

Recently, we deployed an IP telephony solution where Nortel i2004 telephones are connected to Nortel Contivity 221 VPN switches. The Contivity 221 is then connected to an ADSL modem which provides Internet Connectivity. Through an IPSEC tunnel in Aggressive mode (since the IP addresses for the Contivity 221s are dynamically assigned), we then connect to a Contivity 600 which uses a 5 megabit LAN extension circuit as its Internet connection. The Contivity 600 has a static IP address

The tunnels seem to stay up constantly, however, and I never drop any pings.

We're experiencing frequently disconnected calls on all the IP telephones at random intervals. There doesn't seem to be any pattern. I'm also not seeing the VPN tunnels themselves drop more than every 24 hours (which is the timeout we set on the VPN tunnels).

The keep alive timer is set to 1 minute on the Contivity 600, and on the 221s, we have the VPN sessions set to "Nailed Up". The ADSL lines are completely error free.

Does anyone have any idea what might be causing the periodic drops?

Thanks very much!

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Ken Gallagher
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I forgot to mention. The Telephones are using a BCM 400 as the telephony solution, which is connected to a Cisco Catalyst 3560 switch in the same VLAN and IP subnet as the Contivity 600.

Ken Gallagher wrote:

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