The document discusses how to voice-enable apps using Nexmo's Voice API. It provides an overview of Nexmo's cloud communications platform and voice features such as call control, conferencing, call recording, text-to-speech, and inbound call processing. Example use cases for voice APIs include building contact centers, call tracking systems, and voice proxies. The basics of how voice APIs work for inbound and outbound calls is also explained.

1. How to Voice-Enable Your App
with Nexmo Voice API
Roland Selmer, Product Lead
Phil Leggetter, Head of Developer Relations

2. About Nexmo
Reinventing communication
Nexmo’s Cloud Communications Platform enables you to develop faster and easier than ever before.
Our Platform
A set of cloud-based communication APIs designed to remove the pain of integrating with multiple
carriers – and take you global in the blink of an eye.
7 Billion
Phones reached globally
130,000
Developers
5 Billion
API calls annually
99.997%
Platform uptime
1235+
Networks connected
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3. Nexmo’s Cloud Communication Platform
Messaging API
High deliverability &
low latency globally
Verify API & SDK
Turnkey solution
for phone verification
IoT API (alpha)
Next generation solutions
for connecting IOT devices
and M2M
Voice API
Text-to-Speech,
VoiceXML and SIP
Number Insight API
Know your customers,
communicate with context
Phone Number API
Largest global reach,
instant provisioning for
SMS & Voice
Chat App API
Access to all chat apps
with one API
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4. Leaders have chosen Nexmo in key verticals
Chat Apps Transport Social Communication FinanceTravel
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5. Voice
Call From The Cloud

6. What is a voice API & why?
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An API used to make, receive and control a telephone call through a REST interface
Voice is still the most natural interface across varying form factors
7.22 billion mobile phones in a world of 7.19 billion people

7. ▪ Disruptive: Build a contact centre in software $10k Vs $10m
▪ Agile: Compete with Telcos and create things they can’t e.g AI, IOT etc.
▪ Use cases: Unlock new use cases with advanced features like split call recording for transcription,
sentiment analysis etc.
▪ Zero Install: No proprietary software to install, upgrade or maintain
Benefits of Voice in the Cloud
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Faster Time to Market & Simplicity High Quality Global Reach Easy to scale/lower TCO

8. Voice Features
Built for the modern web
With our powerful Voice API you can build
apps that scale easily with the web
technologies that you are already using.
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Build high-quality voice applications in the cloud
88
Low Latency, High-Quality Voice
Latency can make or break voice
services. So we use only the highest
quality routes and tier 1 carriers with
most major codecs supported.
More Numbers in More Countries
We have more SMS, Voice and Toll-Free
numbers in more destinations than any
other provider – and that includes
traditionally difficult to access countries.

9. Buy vs Build Vs API
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Buy: H/W & S/W
▪ Quick solution to a business problem
▪ No technical skills required
▪ Expensive legacy per seat pricing
▪ Can also be inflexible
Build: DIY
▪ Maximum flexibility: custom solution
per use case
▪ Very expensive and difficult to scale
▪ Specialised skills required to maintain
complicated software
Build: API
▪ Every digital business is an API run
business
▪ Flexibility: custom solution per use case
▪ Elastic: Scale on demand
▪ Pay as you go model
9

10. Feature Overview: Voice API
Call Control
Call transfer, hold and playback audio to a live call
Conferencing
Simple and moderated conferences, muting,
earmuffing, notifications
Call Recording
Record inbound and live calls, store recordings
Phone Numbers
Largest global reach, instant provisioning
Only pay for what you use with “per second” billing
Text-to-Speech
Send text-to-speech messages, prompt for response
Inbound Call Processing
Nexmo Call Control Object manages inbound calls
using developer-friendly JSON
SIP Trunking
Basic SIP trunk for PBX type application
Programmability
Nexmo Call Control Object manages Inbound calls
using developer-friendly JSON
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11. Voice
Use Cases

12. Use Case: Proxy
Value - Enables buyers and sellers to connect anonymously
▪ Improved privacy
▪ Keep transactions on platform and prevents revenue leakage
▪ Enables transaction audit for customer service
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Guest Host
Masked communication via
virtual numbers
Nexmo
Voice API
1313

13. Use Case: Call Tracking
Value - Setup call system for dentists and patients
▪ Call tracking can be used to track communication with assigned numbers
▪ Can be used for various phone-based processes
▪ Data-driven: Track response rates and analytics
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Inquiries
1414
Nexmo
Voice API

14. Use Cases: Contact Center
Customer
15
How it works - Building a contextual, automated customer experience
Callback
Enables customer to enter
their number to receive a
local callback
Distributed
Remote agents, remote offices
on one system
Measurable
Track response rates, call
duration, ROI
Cloud IVR
Contextual and simple, to
optimize customer experience
Recording
Enable instant call recording
Integrated with CRM
Add Voice support to your CRM
for outbound sales
Contextual
Connects customers to the right
people with the right data
100% Cloud
No hardware required, easy to
setup and adapt
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Nexmo
Voice API

15. Voice
The Basics: How a Voice API Works

16. Caller A
Answer URL Event URL
Calls & Conversations
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Conversation
C
Caller B
17

17. How it Works: Inbound
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Inbound call is made to a Nexmo LVN
Long virtual number
1
2
1818
Answer URL
Event URL
Nexmo
Platform
Customer
Server
[LVN]
The Nexmo platform requests an NCCO
(Nexmo Call Control Object) from the
Answer URL on the application server
to execute some instructions
e.g. play a file, play TTS, collect DTMF
for an IVR etc.
3 Call events are sent to the Event URL

18. How it Works: Outbound
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Nexmo
Platform
1
Customer
Server
2
End user
3
1919
Call events such as (‘started’,
‘ringing’, answered, ’busy’,
‘failed’, ‘timeout’, ‘cancelled’,
‘machine’, ‘completed’ ) are
sent to the Event URL
Initial HTTP request made
by customer’s server to
the Nexmo platform &
applicable HTTP response
is received
1. HTTP API
3. Answer URL
4. Event URL
2. Outbound Call
Nexmo platform
initiates outbound
call to number
specified in the HTTP
request
Once call is answered, the
Nexmo platform requests NCCO
from the Answer URL to execute
instructions e.g. play a file, play
TTS, collect DTMF for an IVR etc.
4

19. ▪ Introduced to support more complicated use cases
▪ Applications are a container that allow developers to store use case specific settings
▪ Applications also generate and hold authentication information, used to generate
tokens that authorise the use of the API
▪ Applications are created through an API call or through the Nexmo Command Line
Interface (CLI) tool
> Developer implication: Customer use cases become more modular, more
manageable
Nexmo Applications
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20. ▪ We are moving to a token based authentication method
▪ JSON Web Tokens are an open, industry standard (RFC 7519) method for authenticating API’s
▪ Private Key generated from Application used to sign JWT
▪ Slight increase in complexity as developers will mint their own tokens
> Developer implication: Important for customers requiring more security e.g Fintech
verticals
Authentication: JSON Web Tokens
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21. Beginning of stack [
{
"action": "conversation",
"name": "nexmo-company-call"
}
]
Action
Options
> Developer implication: Easier to build complex use cases
Nexmo Call Control Object
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22. Connect - Used to to connect an inbound call to another number
E.g. use case: Voice proxy for call
Transfer - Used to move a call leg from one conversation to another
E.g. use case: Call transfer for contact centre
Talk - Used to generate TTS
E.g Use case: Voice broadcast, critical voice alert, 2FA
Stream - Used to stream a file to a call leg or conversation
E.g. use case: Play music on hold for contact centre; voice files for 2FA
Record - Used to record a either a call leg or a conversation
E.g. use case: Recorded voice proxy; recorded contact centre
NCCO Actions: Building Blocks
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23. ▪ Input - Collects DTMF digits that have been pressed by a caller
E.g. use case: Collect input to navigate an IVR; Get confirmation from a TTS call
▪ Conversation - Used to create a conference call
Eg. use case: a conference call with two or more participants; warm transfer in a call centre
▪ Delay - Pauses the execution of the NCCO call stack
E.g. use case: Time to complete a network action like real time translation
▪ Reject - Rejects an incoming call without answering it
E.g. use case: Hosted voicemail
NCCO Actions: Building Blocks
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24. How to Build a Voice Application
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Create a
Voice App
1
Retrieve Keys
Perform REST request
to Nexmo API
Assign LVN to
Application
(for inbound)
2
3
4 5
Use JWT to authenticate
REST calls to the voice API
Use private key to
mint new JWT
Retrieve application ID &
public/private key pairs
Create an application,
setting answer &
event URL’s
For inbound calls, configure an LVN to
point to to the new application
Mint a JSON
Web Token