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) - multimedia, multichannel, fully blended cloud contact center solutions.

Available by subscription as CCaaS, fully managed and supported by Sytel, or for quick and easy deployment by partners and 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 Software

Softdial Contact Center™ - rich functionality, all-in-one, designed to deliver at scale
  • Contact Center as a Service (CCaaS)

    CCaaS for subscribers - global service​, with no upfront costs

  • Contact Center Platform – CCaaS Partners

    Build your own CCaaS business using the power and flexibility of Sytel software

  • Contact Center Platform – Enterprise

    High performance platform to drive contact center productivity – cloud, on-premise or hybrid

Blended Media Desktop

Fully customisable, multi-channel, multi-session workspace

Work Anywhere

Browser-based tools, no software installation required

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 Channels

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

Agent Multi-Tasking

Work with multiple live contact sessions of any media channel

Dynamic Workforce Management

Automated, ‘best available’ decisions to manage agents and balance work load, across all media channels

Predictive Dialing

Best-of-breed performance under compliance

Optimised Inbound 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


Drive operational efficiency, increase customer satisfaction & improve agent performance

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™

Maximum predictive dialing performance, 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™

Automation to optimise any outreach strategy

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

By Business Type


A full featured contact center software solution, designed for optimum performance at scale

Small/ Medium Business

Options for SMBs to subscribe to our full-featured cloud service managed and hosted by either one of our partners or by Sytel themselves

By Industry

Customer Service

Connect quickly to well equipped agents

Market Research

Best-of-breed predictive dialing with CATI integration

Debt Collection

Automated inbound/ outbound blending integrated with any debt management app

Sales & Telemarketing

Maximise agent productivity with best-of-breed predictive dialing


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