nate8108 wrote:
I've tried looking into the NAT settings but the only info I can find is in regards to port forwarding wich according to the document you suggested to read is not recommended.
Port forwarding is a security risk and should be avoided. It makes you more susceptible to being hacked.
1. Ensure that whatever modem/router combo that was issued to you by your ISP is in bridge mode. Contact your ISP if need be.
2. Ensure that these options are enabled in your ATA:
Enable SIP Options Keep Alive: Yes
SIP OPTIONS Keep Alive Interval: 20
SIP Registration Failure Retry Wait Time: 120
Register Expiration: 60 minutes
Reregister before Expiration: 0
Use Random SIP Port: Yes
3. If the issue coincides with a new IP being leased with your cable modem or internet connectivity being lost and regained, there's probably not much more you can do other than use third party firmware, Tomato, to more easily adjust both Assured and Unreplied UDP timeouts. Unfortunately, I have no experience with Tomato and would be unable to help you with it. However, I'm sure you could ask here:
https://www.reddit.com/r/TomatoFTW/.
You want to satisfy these conditions:
UDP Unreplied Timeout (in your router) < NAT Keep-alive Interval (in your ATA) < UDP Assured Timeout (in your router) < SIP Registration Failure Retry Wait Time (in your ATA)
"<" means less than
NAT Keep-alive interval is 20 in your ATA, and SIP Registration Failure Retry Wait Time should be 120.
Beyond that I have no further suggestions, except, perhaps, checking whether there's a newer firmware version available to you for your router:
http://support.dlink.ca/ProductInfo.aspx?m=DIR-868L.