3Com NBX 100 over 2 T1 lines

Posted on 2005-04-05
Last Modified: 2010-04-12
I am having a problem with a remote site. I have 35 users with 3com VoIP at the location. So they have 35 computers running over the network and 35 phones over the network. I currently have 2 dedicated T1's going to that site. They are having problems with voice cutting out while you are on the phone. The phone conversation is choppy.
Question by:gbauer17
    LVL 15

    Accepted Solution

    Hi gbauer17,
    This is likely to be a problem with packet prioritisation, however it could be down to sheer bandwidth.

    Use the bandwidth calculator at to help you work out how much bandwidth you need between the sites.
    If you had 35 calls happening at once, using G.711 (uncompressed data), then you'd be using 2880 kbps.  I'd imagine that you're using a compressed codec though!

    VoIP gets very fussy about round-trip latency, whereas most data can cope with a few milliseconds delay.

    Do you have routers at each end that are capable of traffic shaping/prioritisation?  You need to configure these to prioritise the VoIP traffic

    It's worth doing some end-to-end ping tests to check what your latency is and make sure that you have no packet loss.
    I suggest taking a look at for more information.

    Does that help?


    Author Comment

    I know that 35 calls at once can produce that problem. But I am pretty sure that not all people are on the phone at once. We are not using any compression though. Any suggestions on what we could use.
    LVL 36

    Expert Comment

    This is a good summary of codecs :-

    I would suggest the Speex codec if supported as you can vary the bandwidth it uses. ILBC and GSM are reasonable. G729 is excelent for the bandwidth it uses but requires a commercial license which might be included in your product.

    Note that if you make data calls over the voice network (faxes for example) they you need to stick with G711 for these as other codecs compress the audio too much and stop them working.

    Write Comment

    Please enter a first name

    Please enter a last name

    We will never share this with anyone.

    Featured Post

    What Is Threat Intelligence?

    Threat intelligence is often discussed, but rarely understood. Starting with a precise definition, along with clear business goals, is essential.

    Suggested Solutions

    In my office we had 10 Cisco 7940G IP phones that were useless as they were showing PROTOCOL APPLICATION INVALID when started. I searched through Google and worked for a week continuously on those phones, and finally got them working. This is a di…
    If your business is like most, chances are you still need to maintain a fax infrastructure for your staff. It’s hard to believe that a communication technology that was thriving in the mid-80s could still be an essential part of your team’s modern I…
    This video is in connection to the article "The case of a missing mobile phone (". It will help one to understand clearly the steps to track a lost android phone.
    Access reports are powerful and flexible. Learn how to create a query and then a grouped report using the wizard. Modify the report design after the wizard is done to make it look better. There will be another video to explain how to put the final p…

    779 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    14 Experts available now in Live!

    Get 1:1 Help Now