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Monthly Archives: August 2014

  • Unlimited Horizon - Draytek 2820 Router

    The main issue with the Unlimted Horizon service on the Draytek 2820 Router is UDP fragmentation this can cause issues with DNS resiliency. The following solutions are recommended:

    1. 1. Download the latest firmware from Draytek which should contain a patch to solve the problem with UDP fragmentation
    2. 2. Specify the DNS servers in the Draytek LAN Config to a 3rd party DNS server such as Google (
  • Disable SIP ALG On Your Routers


    Some broadband routers have a SIP ALG enabled. Often this can cause issues with VoIP calls. It is important that you disable SIP ALG where possible

    SIP Application Layer Gateway (ALG) is enabled on the majority of common enterprise, business and home broadband routers. It's purpose is to inspect VoIP traffic packets and prevent problems with the firewall by modifying the packets to permit connections to the protocols and ports required

    VoIP phone systems require SIP ALG to be turned off as it causes a variety of problems as it adjusts and terminates VoIP traffic packets and causes them to become corrupted and this causes issues with VoIP, such as: one way audio, dropped calls, problems transferring calls, handsets losing registration and making or receiving internal calls

    For information on how to turn off the SIP ALG on your router please refer to your routers user guide or you can have a look at some information about known router issues with SIP ALG on some common routers we have tested

    UDP Fragmentation

    In some cases problems with VoIP services can be caused by UDP fragmentation, for example the size of the UDP datagram packets sent between VoIP phone systems and your phones will be greater than the default 1500 bytes, this will cause UDP fragmentation. In order to prevent problems with UDP fragmentation you need to ensure that all network equipment you are using with your VoIP phones support UDP fragmentation. If UDP fragmentation is not supported then a number of problems can occur, such as: issues with BLF (Busy Lamp Field) and Feature Synchronisation

    Known Router Issues

    Known Compatible Routers

    See this spreadsheet

2 Item(s)

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