Troubleshooting VoIP

Terry Slattery
Principal Architect

I’ve done a few seminars on troubleshooting VoIP at VoiceCon (Fall 07 and Spring 08).  Somewhere along the way, someone mentioned a relatively new web site to me:

I finally took time today to look at it.  The content is potentially useful, depending on your level of expertise.  If you’re a long-time VoIP troubleshooter, then you’ll already know much of what’s there (or should).  If you’re getting started, it has some useful background knowledge and procedures.  The main menu has items about VoIP basics, online diagnosis, tools and resources, and links for additional reading.  It is not a lot of information, which is sometimes helpful when starting out in a new technology.

One of the things that I didn’t see there were procedures for diagnosing problems specific to voice gateways or to DSP (digital signal processor) pools used for transcoding.  In the Network Symptoms page, they have a nice matrix of the types of problems that generate unacceptable jitter, packet loss, or out of order packets (interesting, nothing there about unacceptable delay).  In the matrix, I would have put Duplex Mismatch under Intermittently, not Continuously, because it is most often a factor when the link with the duplex mismatch is running at high enough loads that the duplex mismatch causes packets to get damaged.  But still, it is a good start – more than I’ve seen in other places.

Under the Online Diagnosis link, there’s a neat calculator in which you select the codec, frame size, and packet loss rate and it shows you the MOS score, R Factor, and required bandwidth.

This site may be a reasonable resource if you’re starting to work with VoIP.



Re-posted with Permission 

NetCraftsmen would like to acknowledge Infoblox for their permission to re-post this article which originally appeared in the Applied Infrastructure blog under


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Nick Kelly

Cybersecurity Engineer, Cisco

Nick has over 20 years of experience in Security Operations and Security Sales. He is an avid student of cybersecurity and regularly engages with the Infosec community at events like BSides, RVASec, Derbycon and more. The son of an FBI forensics director, Nick holds a B.S. in Criminal Justice and is one of Cisco’s Fire Jumper Elite members. When he’s not working, he writes cyberpunk and punches aliens on his Playstation.


Virgilio “BONG” dela Cruz Jr.

CCDP, CCNA V, CCNP, Cisco IPS Express Security for AM/EE
Field Solutions Architect, Tech Data

Virgilio “Bong” has sixteen years of professional experience in IT industry from academe, technical and customer support, pre-sales, post sales, project management, training and enablement. He has worked in Cisco Technical Assistance Center (TAC) as a member of the WAN and LAN Switching team. Bong now works for Tech Data as the Field Solutions Architect with a focus on Cisco Security and holds a few Cisco certifications including Fire Jumper Elite.


John Cavanaugh

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Chief Technology Officer, Practice Lead Security Services, NetCraftsmen

John is our CTO and the practice lead for a talented team of consultants focused on designing and delivering scalable and secure infrastructure solutions to customers across multiple industry verticals and technologies. Previously he has held several positions including Executive Director/Chief Architect for Global Network Services at JPMorgan Chase. In that capacity, he led a team managing network architecture and services.  Prior to his role at JPMorgan Chase, John was a Distinguished Engineer at Cisco working across a number of verticals including Higher Education, Finance, Retail, Government, and Health Care.

He is an expert in working with groups to identify business needs, and align technology strategies to enable business strategies, building in agility and scalability to allow for future changes. John is experienced in the architecture and design of highly available, secure, network infrastructure and data centers, and has worked on projects worldwide. He has worked in both the business and regulatory environments for the design and deployment of complex IT infrastructures.