Network Answering Machine Detection – Myth Or Reality?

April, 2012

Sytel's contribution to the latest controversy over Network AMD, and some background on how we got here.

It has become traditional around this time of year for Sytel to comment on the ongoing debate over answering machine detection. Does AMD deliver real benefits to the call center? What about ‘false positives’? For some background, read our previous posts from May 2010 and May 2011.

The latest controversy is over Network Answer Machine Detection (i.e. AMD based on ISDN signaling, rather than sound patterns). Before we give our view on this, let’s review the context.

The standard method used by most vendors for many years is the cadence method. This is the analysis of bursts of volume (speech) interspersed with silence. One sample could be identified as the “Hello?” of a live person; another, the “Hello, we are not in right now…” of an answering machine/ voicemail service.

This method produces reliability of around 85%-90%. (Any claims from vendors to go above this are either based on wrong measurement, or biased sampling.) You may think that sounds quite good, but this means that 10% of answer machines will get put through to agents as live calls, and also crucially that 10% of the calls classified as machines are in fact live respondents, and hung up on. These are known as ‘false positives’, and here’s the problem. Ofcom regulation in the UK stipulates that a ‘reasoned estimate’ of these must be included in the calculation for abandoned calls. Under normal conditions, a ‘best case’ estimate of 90% reliability already pushes the abandoned call rate beyond Ofcom’s regulatory limit of 3% of all live calls. If you run AMD in the UK, you can say goodbye to any benefit from your predictive dialer.

As a result of this dilemma, many vendors have sought alternative methods of doing AMD in order to keep the practice alive. Two themes are recurrent; Network Answer Machine Detection and byte pattern recognition.

  1. Network Answering Machine Detection
    In our (informed) view, any claims to use AMD based on ISDN signaling are fatuous. It does not exist. If it did there would be no debate, everyone would be using it, detection rates would be 100% accurate and Ofcom’s job would be made a lot easier.
  2. Byte pattern recognition
    This works by picking up encoded audio which follows defined sequences of bytes. This technique works but has very limited application. There is no such thing as a standard network voicemail message. Networks must offer consumer choice. Some consumers customise, some simply switch voicemail off and some networks have equipment that does not encode voicemail speech consistently. The result of this is that network voicemail can be reliably detected using byte pattern recognition in around 15% of cases in the UK.

The inescapable conclusion is (still) that AMD in the UK using the methods described above simply cannot deliver the low levels of nuisance calls that Ofcom rightly mandates. If anyone knows of other methods that are more accurate we’d love to hear about it.

If you are outside the UK and still convinced that you need AMD, then Sytel’s is a good as any. But our advice remains that use of AMD is bad practice, leading to bad customer relations and lower call center profits. As Sytel has always said: just switch it off.

For a more in-depth analysis, ask for a copy of our white paper on The Science Behind Answering Machine Detection.

What We Offer

Sytel Limited develops and supplies Softdial Contact Center® (SCC), offering multimedia, multichannel, fully blended cloud contact center solutions, for quick and easy deployment by partners offering CCaaS or enterprise users. All Sytel cloud components are secure, resilient and scale seamlessly from 10 agents to 10,000+, whether local, mobile or remote.

  • Flexible Contact Center Platform

    Softdial Contact Center™ – tightly integrated modules, designed to deliver at scale

  • Blended Media Desktop

    Fully customisable, multi-channel, multi-session workspace

  • Work Anywhere

    Browser-based tools, no software installation required

  • Cloud Or On-Premise, Multi-Tenant

    Scalable, resilient, secure, proven

  • Customise, Localise, White Label

    Design all user interfaces to individual requirements

  • Integration Via APIs

    ‘Swap out’ components and integrate with 3rd party apps

  • World Class Development

    Continuous evolution pushing technical boundaries


Softdial Contact Center™ (SCC) is designed to be flexible, extensible and scalable, integrating with any legacy equipment, and meeting the most complex of requirements.

  • All Media Types

    Voice, chat, email, social, etc – fully integrated and blended

  • Agent Multi-Tasking

    Work with multiple live contact sessions of any media type

  • Dynamic Media Blending

    Automated, ‘best available’ decisions to blend and balance work load across all media types

  • Predictive Dialing

    Best-of-breed performance under compliance

  • Intelligent Routing

    Smart rules and ‘best-available’ decisions to drive great customer service

  • Agent Scripts

    Help agents achieve and maintain excellence

  • Voice and Screen Recording

    See and hear exactly how agents are interacting

  • Analytics and Data Feeds

    Measure and evaluate performance at every level

  • IVR, Bots & Conversational AI

    Design effective automated flows or integrate with 3rd party providers

  • Customer Journey Tracking

    Stored customer contact history, to aid routing and add context to conversations


A complete suite of tools, with unique flexibility to extend and swap out modules to deliver a tailored contact center solution for any environment

  • Softdial One™

    Highly flexible unified web UI for agents, supervisors and administrators

  • Softdial Scripter™

    Create complex process flow scripts for agents, IVR, chatbots and other applications

  • Sytel AI Dialer™

    Best-of-breed predictive dialing under any compliance rules

  • Softdial Pathfinder™

    Precise routing rules for ‘best available’ connection

  • Softdial Media Server™

    Core telephony functions to manage all inbound/ outbound SIP calls

  • Softdial Reporter™ 5

    Fully customisable performance stats, charts and reports, across all channels

  • Softdial Publisher™

    Comprehensive data output to build your own reports

  • Softdial Recording Monitor™

    Audio and screen recording of agent activity to ensure the highest standards

  • Softdial Campaign Manager™

    Comprehensive configuration and control for outbound campaigns

  • Softdial Repository™

    Central storage and configuration of common resources

  • Sytel Global Compliance™

    Flexible ‘no contact’ rules to protect contact center and consumer


Performance and efficiency for a wide range of business applications

  • Customer Service

    Connect quickly to well equipped agents

  • Sales & Telemarketing

    Maximise agent productivity with best-of-breed predictive dialing

  • Healthcare

    Secure, highly-configurable multichannel communications for excellence in patient care

  • Market Research

    Best-of-breed predictive dialing with CATI integration

  • Collections

    Automated inbound/ outbound blending integrated with any debt management app