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InternetVoipPhone Blog

A Blog About Internet VOIP Phones

  • Upgrade 3CX V12.5 to 3CX V14

    Having recently upgraded our 3CX V12.5 to 3CX V14, we'd like to share our experience

    It is important to note that you should fully update your existing 3CX 12.5 edition as there is a service pack that prepares V12.5 for the V14 upgrade

    If you are using IIS and have a third party trusted certificate, it is also important that you export your SSL Certificate to a .pfx file (We'll come back to this later) Continue Reading

  • Important changes to 084, 087, 118 or 080* numbers

    Important changes for customers who own or dial telephone numbers starting 084*, 087*, 118*** or 080*

    In order to simplify call costs for consumers, the telecoms regulator Ofcom is changing the way numbers starting 08, 09 and 118 are charged for. The changes will take effect from 1st July 2015 and are as follows:

    Continue Reading

  • Turn Off SIP ALG On Zyxel P 600 Series Router

    In order to turn off the SIP ALG on Zyxel P 600 Series Routers you will need to telnet on to your router Continue Reading

  • SIP ALG Workaround For Virgin Media Superhub

    The Virigin Media Superhub does not have the ability to turn off SIP ALG, this can cause a number of problems if you are trying to use a VoIP telephone system Continue Reading

  • Hot Desking Using Snom Phones & 3CX

    Hot desking is the concept of logging onto a phone and your extension number following you

    This is very effective when desks are not 'owner occupied'.  Examples of scenarios where you might find hot desking useful might include when staff work from multiple offices/homes or maybe you have shift workers like call centre staff Continue Reading

  • Call delay when making a call from Gigaset DECT handset

    We recently encountered a problem when a caller was explaining that when they made a call, the called handset was picking up the call but there was a 2-3 second delay before the caller heard the pickup and consequently the receiving party was left saying 'hello', 'hello', 'hello'..... before the caller heard any audio

    Continue Reading

  • How to disable SIP ALG on Thompson Technicolor Routers

    By default many Thompson routers have a SIP ALG enabled.  SIP ALG in most scenarios is damaging to voice over IP, often resulting in one way audio Continue Reading

  • Cannot Register Snom Phone On 3CX

    We recently experienced a problem trying to register a Snom 710 phone to a 3CX server.  Whatever we did the phone refused to register.  The phone appeared within the Phones console via PNP but couldn't be automatically or manually provisioned

    We eventually determined that the problem was related to the client using a public ip addressing scheme for their internal network.  In this instance the LAN was 199.x.x.x

    There were two tasks required to resolve this issue:

    1. The IP address of the phone was listed in the IP Blacklist within Security section of the Settings of the 3CX console.  The IP address needed to be removed

    2. Most notably we had to untick the attribute 'Disable use of extension outside the LAN' on the Other tab of the Extension Details

    A bit of a 'gotcha' which won't be missed again!

  • 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

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