When your handset send a message to our Hosted VoIP platform your DrayTek router will translate the internal IP address to an external IP address and maintain this translation for a predetermined length of time. If this expiry time occurs before your handset sends another message (such as a keep-alive) then the translation will be removed and you will experience incoming call failures and BLF will no longer function.

Very often security appliances will set a NAT session timeout to a very low value, which will interfere with VoIP. We recommend the UDP timeout is set to 300 seconds (5 minutes) at the least.

This guide explains how to check and adjust the NAT session timeout value on the following DrayTek models:

• Vigor 2760
• Vigor 2800
• Vigor 2820
• Vigor 2830
• Vigor 2832
• Vigor 2860
• Vigor 2862
• Vigor 2920
• Vigor 2925
• Vigor 2926
• Vigor 2952
• Vigor 2960

Even if your particular DrayTek model is not listed, these instructions should still apply if your model is in the same series.

1. Press the Windows Start button and in the search box type in cmd and hit Enter
2. Type in
   

   telnet 192.168.1.1

   and hit Enter
   Note Recent versions of Microsoft Windows may not have Telnet installed by default.
   To install Telnet, click on Start → Control Panel → Programs → Programs and Features → Turn Windows Features on or off → Ensure TELNET CLIENT is checked and click OK.

3. When prompted, enter your router username and password.
   The default username is admin and the default password is admin

1. Type in
   

   portmaptime -l 

   and hit Enter

2. Note the UDP Timeout

If you need to change the timeout value…

1. To set the new timeout value type in
   

   portmaptime -u 300

   and hit Enter
   We recommend a value of at least 5 minutes (300 seconds)

2. To confirm the setting type in
   

   portmaptime -l 

   and hit Enter

3. To save the change type in
   

   sys commit

   and hit Enter

Do not adjust your IP phone keep-alive interval to a value below 30 seconds. Our network may block SIP traffic that is too frequent which will affect phone calls and BLF.

• How to Disable SIP ALG on a DrayTek Vigor Router

NAT on DrayTek Routers at www.draytek.co.uk (registration required to see article).