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Routers Adjustments Guidelines for Better VoIP/SIP Performance

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You may own a router that is not listed in our buying guide as recommended or adjustable to work with Telebroad’s telephony services. While we can only guarantee optimal performance with the routers we mentioned, you may still want to try and use your existing equipment. 

You can try the following general adjustments guidelines to facilitate compatibility with our services and achieve better VoIP/SIP performance. 

You are advised to seek additional specific information for your situation and consult with your Internet Service Provider, network administrator, and network security expert where applicable. 

Automatic VoIP features

Routers will sometimes come with features designed for VoIP performance or sometimes sense existing network and apply suitable customization via a wizard or in the installation process. But such VoIP specific customizations usually achieves the opposite, resulting in interference to optimal VoIP data flow . The Telebroad system does not require any specific VoIP features. You should turn off any such feature you can see or decline installing or activating it from software wizards.


This is an extension of the above advice. SIP stands for Session Initiation Protocol. It is a communications protocol for controlling multimedia communication, specifically in our case VoIP traffic. ALG stands for Application Level Gateway. It is a  a security component found in many commercial routers that augments firewall security and is aimed at preventing some of the problems caused by them. It is also sometimes referred to as SIP Inspection. 


When it comes to VoIP the ALG may modify VoIP data to allow it to pass through the firewall,resulting in reduced quality and performance or even even complete loss of audio signal or connection. You should therefore turn off this feature. 


SPI and DoS Protection

SPI stands for Stateful Packet Inspection. It is another firewall security feature often included in a business networks. It only allows data matching known active connection to pass through. DoS stands for Denial or Service and is a kind of network attack aimed at overwhelming a computer network and making it dysfunctional. Both protections help the router to identify and approve or reject data for security reasons. 

However, because of the nature of telephony data these protections usually misdiagnose valid VoIP traffic as a security risk and therefore should be turned off. The problem is more likely to appear on a larger office where many phones are involved leading to a blockage of traffic. 

Before turning off DoS protection see if there is an option to increase the number of connections acceptable by it. This will basically raise the threshold for the amount of traffic allowed to pass through before triggering a block. 


Double NAT Conflicts

NAT stands for Network Address Translation. It is an essential network technology that allows multiple devices to share a single IP address.

Double NATing is a situation where more than one router is performing the address network translation on a network. The most common example is a Wi-Fi router that is connected to a Cable or DSL modem where both devices have NAT enabled (generally Cable modems present less problems in this regard). Double-NATing is known to cause problems for VoIP phones.

To solve this problem you can try to put the modem in “bridge” mode by accessing its settings with a web browser. This will  essentially disable NATing for the specific router and ensure network public IP addressing and NAT functions are only performed by the other router. 

If this doesn't work can try putting the second router IP Address in your first router’s DMZ Demilitarized Zone. The DMZ allows all traffic to pass through without any address translation and in theory will counteract the effect of double NATing.  Since sending traffic through the DMZ can expose you to security risks, this configuration should be consulted with a network security expert to make sure it does not introduce vulnerabilities into your network!


Router Custom Firmware or Firmware Upgrade

If your router doesn't support the above mentioned adjustments you can try to upgrade its firmware from the manufacturer website or install a custom router firmware on it that does support them.

You should do so if you actually own the router, otherwise you would need to talk with your ISP to see if upgrading or installing a custom firmware is permissible. With some ISPs it might be that their service will only work with the router's current firmware and configuration! 

If you need to install a custom firmware, there are two options available – DD-WRT and OpenWRT. Make sure to download the exact firmware version for your router, otherwise you may risk making it permanently unusable. 

Pay attention to the following points:

  • Never power off the router at any time during a firmware upgrade or installation.

  • If upgrading the firmware, you should export a backup of your current router configuration and settings. You can then import the backup after the installation is done to restore the configuration.

    It is a good idea to take note of the major settings, just in case configuration restoration fails.

  • You would not be able to import and restore the settings with a custom firmware installation. You would need to make notes of the all relevant settings and reconfigure the router manually after the installation.

  • While it is possible to run an upgrade over Wi-Fi,  you should actually try not to do so and upgrade your router over a more stable wired connection.

  • You would need to factory reset before installing a custom firmware or before upgrading some router brands.  

If the installation/upgrade fails you can try to perform a factory reset and start over.

Firewall and IP Telephony Protocols

UDP User Datagram Protocol, SIP Session Initiation Protocol, and RTP   Real-time Transport Protocol are all technologies that needed for the proper functioning of IP Telephony. Make sure you are not blocking any of them. Restrictions on any of these protocols in your firewall settings may cause one way or no audio during calls or completely block calls. Outbound restrictions are particularly crucial in this regard. Any modifications to your firewalls should, again, be handled with the advice of a network security expert.

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