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  • 3CX Best Practices
  • 3CX Best Practices

    August 24th, 2021

    MORE BUSINESSES RELY ON VOXTELESYS AND 3CX EVERY DAY! Voxtelesys is your Best-in-Class 3CX Preferred SIP Trunk Carrier. Enjoy huge cost savings With Voxtelesys SIP trunking. Businesses now have more options and better choices for their voice communications. Being able to quickly pivot and adapt in today’s business climate is a tremendous asset. See bullet points at the bottom of this document for more Voxtelesys savings and benefits!

    3CX Smartphone App

    While we do not recommend using the 3CX smartphone app to perform business crucial activities when the web client is available (because there are more features in the web client), there are times when using the app is essential. When you are using the app, you want to have the best call experience possible.

    For starters, you want the smartphone app to have reliable audio. However, certain features may not work as they should from time to time. We have noticed that Android devices occasionally have audio issues.

    If you are having audio issues with your Android device, turn the Earpiece button on and off during a call to regain audio. The iOS app is slightly different as the Earpiece button toggles between two different audio sources: "iPhone" and "Speaker." We have not encountered any audio issues with iOS.

    Crawling up ports

    The local SIP Ports of your phone a.k.a. "Crawling up ports," allow you to define which port the phone will be assigned to in the NAT process. You can have multiple extensions on the same port; most of the time you won't have an issue. However, an issue arises when both extensions are called at the same time. When this happens, you could overhear each others' conversations.

    To prevent this issue in 3CX, common practice is to increase the "Local SIP Port of Phone" by one digit for each extension. You can do this by navigating to the "Extensions" tab in the 3CX Dashboard. In addition to modifying the local SIP port, we recommend advancing the number by 20 on each port on the "Local RTP Audio Ports Start" and "Local RTP Audio Ports End" ports.

    Caller ID (CID) vs. CNAM

    Make sure you are NOT setting the Caller ID as your CNAM in the Management Console. What is commonly referred to as the Caller ID is actually the CNAM. Your Caller ID (CID) displays your phone number to the individual you are calling, while CNAM displays the name associated with your phone number. Under the Caller ID, you should enter the phone number associated with your account.

    You want to be sure that the phone number you use as the Caller ID is registered with Voxtelesys, as your call will fail otherwise. This is set up for network security to prevent spoofing. Spoofing is the deliberate attempt to falsify the identity of someone by changing a single digit in a phone number. This makes a call appear to be from a legitimate source.

    Mobile number format

    Under "Mobile," it is best practice to write your phone number without dashes, as most VoIP service providers do not parse a phone number with dashes. For instance, instead of writing "701-929-9797," you would write "7019299797." Dashes only exist to make it more readable to the user.

    PBX Delivers Audio

    If the audio quality on your physical phone is poor, it is likely that the phone does not have the processor necessary to deliver high-quality audio. In this case, you can turn on "PBX Delivers Audio," as this leaves the audio processing power to your 3CX PBX. We have found that most issues are resolved when "PBX Delivers Audio" is turned on.

    Using Google's DNS

    Make sure you are using (or "Quad 8") as your primary name server on the 3CX. If you do not use Google's DNS, then this will lead to licensing issues. In the Debian version of 3CX, this can be done by putting "nameserver" as the topmost line of your /etc/resolv.conf file. You can optionally add "," Google's secondary DNS server, with the same command.

    The following is a screenshot of the 3CX ISO install:

    The name server addresses are saved in the /etc/resolve.conf file.

    3CX Firewall Checker

    According to 3CX's website, "The 3CX Firewall Checker is a tool that can be used to check that your router or firewall allows network traffic with VoIP Providers, Bridges, External Extensions and 3CX Tunnel connections."

    You will want to ensure that your firewall checker is run and passes with all green. The firewall checker can be found in the middle of the dashboard, under the "Management Console." It is important to note that starting the Firewall Checker will stop all 3CX Services, so you want to run it when there is the least amount of traffic on your network.

    SIP ALG/Firewall configuration

    Excerpt from Michael Jennings, Voxtelesys COO; 3CX install documentation:

    "The most likely part that will cause 3CX to fail is the firewall.

    1. Your firewall must be capable of one-to-one or port NAT. 3CX refers to this as Cone NAT.

    2. You must have the ability to disable SIP ALG/Fixup to enable 3CX behind your firewall.

    3. Persistent port NAT is very important. This is required to ensure that source ports do not get remapped in the firewall.

    As a carrier, we see all kinds of firewall PBX combinations. It is our experience that SonicWALL has been most problematic with voice applications.

    SonicWALL tends to enable SIP ALG after updates. What's more, it has a persistent port NAT issue that complicates VoIP software solutions.

    We have implemented software on our side to help resolve some of these issues, but we recommend that if at all possible to not use a SonicWALL."

    Whitelist known office IP addresses

    You will want to whitelist known office IP addresses, especially if they are static public IP addresses.

    One bad phone configuration in an office can take down all the phones at that site if the public IP address is blacklisted. To prevent this from happening, make sure you whitelist your IP addresses.

    If your desk phones all use the same public IP address as the desktop browser, you run the risk of having all of your phones being blacklisted. If you log into your web client incorrectly three times, this will cause all of your phones to go down. To prevent this, whitelist your public IP address.


    1. Cost Savings: With Voxtelesys SIP trunking, businesses now have more options and better choices for their voice communications. Being able to quickly pivot and adapt to today’s business climate is a tremendous asset.

    2. Security & Fraud Protection: Daily Spend Limit: Hacking into business phone systems has become a huge problem for businesses that have not properly secured their networks. To combat this, Voxtelesys has implemented and deployed a maximum daily spend limit for every customer. This feature minimizes the financial damages caused by fraudsters gaining access to a customer's phone system and making high-cost international calls. We work directly with our customers to set a daily spend limit that matches their daily usage.
      Restricted International Calling: We don't assume everyone wants international calling. We consult with our customers before allowing international calling. We also automatically restrict areas in the highest-cost countries and areas commonly called by hackers until our customers confirm that they are aware of the added risk.

    3. Flexibility: If you want to integrate more than just voice, Voxtelesys supports other real-time telecom resources like texting, images, and video calls. Let us provide a more dynamic range of options to meet the needs of your customers and business operations.

    4. Scalability: Capacity planning becomes a thing of the past with the scalability of SIP trunking. Call capacity can be changed at a moment's notice because there are no limitations or restrictions and it’s easier to accommodate the ebb and flow of call traffic as needed.

    5. Local Presence: For businesses with global offices—or even multiple offices in different area codes—SIP trunking helps you generate a number with a local area code for sending and receiving calls. Establishing a local presence can increase the effectiveness of campaigns because callers are more likely to answer a call from a number with a familiar area code.
  • More Businesses rely on Voxtelesys and 3CX every day!
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    3CX Best Practices