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28 msdn magazine

Machine-to-machine (M2M) computing is fast becoming a

technology that all developers and architects need to embrace.

Numerous studies suggest a coming world of tens of billions of

devices (a half-dozen for every human on earth) by 2020 (bit.ly/M2qBII).

One reason this is happening is because it has never been easier for

garage tinkerers and hobbyists to prototype a consumer or com-

mercial device for later manufacture and sale. Getting started with

both the hardware and soft ware is incredibly inexpensive. For less

than $100, you can order an Arduino or a Raspberry PI.

But you do get what you pay for and these devices—especially

the Arduino—represent the low end of the device-capability spec-

trum. With 32KB of Flash storage and 4KB of RAM, they lack the

power to run anything but the simplest aspects of a Web stack.

Th e Arduino is an open source microcontroller fi tted with a small

chip, memory and storage. The software consists of a standard

programming-language compiler and a boot loader that executes

on the microcontroller. You can add expansion boards that plug

into the device, hooking up motor controls, GPS, Ethernet, an LCD

display, sensors, actuators and more. Pay a little more money and

you can get the more powerful Raspberry PI, which comes with a

version of the GNU/Linux OS and 256KB of RAM.

These devices rarely have value unless they’re connected to

something else, perhaps a cloud back end that receives data and

sends commands. But connecting to, communicating with and

managing these devices from an application running in the cloud

presents some special challenges. The sheer number of devices,

as well as their limited battery life and bandwidth, forces a cloud

developer to carefully consider all options.

In this article, we’ll take a look at how developers are trying to

overcome the key challenges of addressability, bandwidth and

security. We will debunk the myth that IPv6 and virtual private

networks (VPNs) are simple, effi cient, and secure, and will pro-

pose that the Windows Azure Service Bus is the perfect product to

elegantly overcome these challenges. To drive home some of the

concepts, we’ll present four patterns you can use on your client

device when communicating with the cloud back end. Finally,

we’ll present a brief introduction to Service Bus support for the

Advanced Message Queuing Protocol (AMQP) 1.0—an interop-

erable and effi cient protocol for device-to-cloud communication.

For many years, secure connectivity meant using TCP/IP with

IPv4, combined with VPNs. Th is worked reasonably well, but is

now showing signs of age. For starters, it’s diffi cult to get a unique

IP address out on the public Internet to use with a device—we’ve

pretty much run out of IP addresses. Diehard fans of this approach

promise that IPv6 will come to the rescue. The conventional

wisdom is that if you give the device a unique IP address, all your

diffi cult problems are solved. Unfortunately, this solves only a small

part of the overall problem. Giving each device its own unique IP

address is defi nitely not the silver bullet many had hoped.

Just to be clear, IPv6 and VPNs are fraught with problems in a

crowded, connected-device world. Bandwidth, in particular, is a

challenge. Chatty connectivity between device and network can

lead to excessive traffi c. Moreover, using typical HTTP request/

response approaches for all messaging drains battery life on many

devices. Perhaps most important is that security can’t be guaranteed.

VPNs are defi nitely insecure in some scenarios. Before presenting

a solution, let’s dive a little deeper and explore these problems.

Devices that create excessive network traffi c communicating with the

cloud back end are problematic. Bandwidth costs money, potentially a

The Windows Azure Service Bus

and the Internet of Things

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Figure 1 Arduino Sprinkler System Reference Architecture

Sprinkler Valve

National

Weather

Service

Home Network

Windows

Azure

HTTP

Mobile

Services

Data/State

Blob

NoSQL

Database

Worker

Role

Linux Virtual

Machine Python

Admin

Web Role

Service

Bus

Arduino

Sprinkler

Controller