Integrating Asterisk with Wireless Technologies: Part 1

9 min read

Why integrate Asterisk with wireless technologies?

This is a good question, and is worthy of consideration at the outset of the article. As an open-standards (never mind open source) telephony platform, Asterisk is ideally positioned to connect with all manner of devices, and this is excellent news for those that are involved in designing and deploying Asterisk-based solutions, as we are able to choose the best options rather than being restricted by proprietary compatibility issues.

Getting back to the question, or rather the answer to the question, mobility is one of the main reasons people want to hook Asterisk up to the wireless world—both mobility within the office environment and the requirements of a mobile workforce outside the office. Even in this day and age, many international travelers are plagued by heavy roaming costs for their mobile phones. Ironically, a good proportion of them probably carry devices with Wi-Fi and VoIP capabilities, some even staying in hotels with free Wi-Fi, if only they knew!

Other reasons that people and corporations may be looking for wireless solutions include rapid deployments, cost reductions (in implementation costs, running costs,or both), or it may be that they need a portable PBX solution that can be moved around with them without the hassle of running cables and so on, every time they arrive at a new location.

The following table shows business drivers and technology enablers involved:

Business drivers

Technology enablers (and issues)

  • Mobility within the office
    • Work anywhere in or around the building
  • Mobile workforce
    • International travel
    • Field staff
    • Multi-site enterprises
  • Rapid implementations
    • New office installations
    • Fast office installation
  • Cost reductions
    • Reduced “hard” infrastructure (cabling, switches, and so on)
    • Reduced real-estate needed
  • Temporary deployments
  • Hot desking
  • Business continuity*
  • Disaster recovery*
  • Wireless access points are already very common, both within offices and in public locations
  • Wi-Fi and WiMAX technology (may suffer with NAT and firewall issues)
  • Wireless routing means phones (and PCs) can now be rolled out very quickly
  • SIP and IAX2 trunks are usually much more cost effective that traditional trunks
  • IP PBXs can be physically much smaller, meaning less rack/floor space is used
  • The power consumption of an IP PBX can be a lot less than a traditional PBX.

These reasons in particular are a great sell for VoIP, not just wireless.

Wireless technology overview

With this weight of reasons to think about wireless, our next job is to look at the options available so that we can deploy the best technology in each given application. To help us consider the options, I have split the next section into two parts—one that considers wireless handsets and one that considers wireless networks.

There are many types of wireless handsets on the market today, some have been around for quite some time while others are relatively new. Most are aimed at the consumer, a few are definite enterprise plays, and there is even an “industrial strength” offering. Let’s outline each type and home in on their advantages and disadvantages.

Wi-Fi (only) phones

Wi-Fi (only) phones have probably been around the longest, but in most cases, the vendors do not seem to have refined their offerings following the experience of their first products. Rather, Wi-Fi (only) handsets seem to be disappearing in favor of dual-mode cell phones. These devices started out as a piece of Wi-Fi kit that someone attached to a SIP stack and added on a microphone, speaker, and some basic audio-processing apparatus—and it shows.

These phones are usually not excellent. Their issues often include poor battery life and less than perfect audio. Also, something that could be a big issue depending on your specific application, is the ability to roam from one Wi-Fi hotspot to another, which has now been addressed in specification 802.11n. But I have not yet seen many phones which implement this advance.



  • Truly mobile
    • Inside the office or home
    • Other hotspots worldwide
  • Allows PBX extension to travel.
  • Small and portable.
  • Configuration is difficult.
  • Battery life is generally short.
  • Voice quality can be poor.
  • Not a wide choice of phones.
  • If the phone does not have a web browser, you may not be able to connect to hotspots that require a login.

One notable exception to majority of Wi-Fi (only) handsets is the Polycom range. As you would expect, these phones are very well constructed—there is even a rough use version for demanding environments, and they work well too.

For more information, look up UT Starcomm, Hitachi, or Linksys Wi-Fi phone.

SIP desk phones with a wireless link

Imagine all the positive attributes of a good SIP “normal” desk phone—great looks, familiar feel, excellent functionality, high speech quality, and sturdy construction.

Now make it wireless!

This is exactly the idea that Linksys (and others like Mitel) have implemented by bringing out a wireless Ethernet bridge (a device that connects into a standard Ethernet socket on any device and gives it Wi-Fi connectivity), which is specifically designed to fit into the void in the base of their phones.

Asterisk 1.4 – the Professional’s Guide

This brings together the standard-looking office phone (the sort that seems familiar to users and will not scare them) with the convenience of wireless. The intention is not to go wandering around with this phone, as it still needs mains power, but to be able to locate it wherever you want in the office without needing a cabled Ethernet connection, nice!



  • Very user friendly
  • Great for office use
  • Comprehensive features
  • Good for temporary and flexible deployments
  • Additional work of configuring and connecting the wireless Ethernet bridge
  • The devices still need power, and so are not truly wireless
  • Adds significant extra cost per extension

Of course, any wireless Ethernet bridge and any SIP desk phone could be used, as these are standard interfaces that we are talking about. You could just have a wireless Ethernet bridge for a whole room going into a switch and then run cables to a number of phones (if you needed a few), but the elegance and simplicity of the Linksys solution does make it stand out.

Dual-mode (GSM and SIP) phones and PDA/smart phones

Within the last two to three years, these devices have really taken off. There are offerings from UT Starcomm (who also make Wi-Fi [only] handsets) and Pirelli Communications, but it is the Nokia handsets that have set the standard.

Any high end “E” (business) or “N” (multimedia) series Nokia handset will have both Wi-Fi and SIP connectivity, and a SIP client is available for the iPhone, and for Windows mobile phones and PDA devices too. Great news for those wishing to integrate with Asterisk!

These handsets (putting call costs to one side for a moment) provide the ultimate mobility, as they will enable calling through Wi-Fi access points or over the regular mobile network

Often held up as examples of FMC (Fixed Mobile Convergence), GSM/SIP phones are not really that—they are really two phones in one case, a GSM (or 3G) phone and a SIP phone. The only converged thing about them is that they share a microphone, an earpiece, and the contacts list. These devices cannot currently be configured to intelligently route calls over GSM or IP, depending on, say, cost. You have to choose your preferred method of communication, and all calls will go that way unless you choose the alternative (with an inconvenient two key-press method) on a per-call basis.

This is something of an issue in countries like the UK, where it is usually cheapest to call a mobile from a mobile, and most business customers will have their mobile device on a monthly plan that includes minutes—so they will want calls to mobiles routed over the mobile network, and calls to landlines routed over the SIP (Wi-Fi) network.

Having said that, two things have emerged to make things a little more user-friendly.

Firstly, the UT Starcomm phones have two “place call” buttons—one that directs the call over the GSM (or 3G) network and one that directs the call over the SIP (Wi-Fi) network. Secondly, some third-party companies have developed small applications which run on the Nokia handsets (which use the Symbian S60 operating system) to do Least Cost Routing, which to my mind is an excellent development.

Those little gripes aside, can you see the power of a single handset which is both a standard mobile phone AND an extension of your Asterisk PBX, by virtue of its SIP and Wi-Fi capabilities? To give you an idea of the potential benefits, co-author David Duffett describes his experiences:

As someone who travels regularly, I continue to be impressed when my Nokia phone rings while I am in, say, Johannesburg, South Africa because someone back in the UK called my office number! It freaks them out when they find out you are not really in the office, and they are also impressed when you tell them that the call between your telephone system (Asterisk) and your mobile phone is FREE! It is heart-warming to find yourself in a hotel that offers free WiFi, able to make calls back to other extensions in the office at zero cost. And, as the internet (in general) and WiFi access points improve, I am finding that there is no noticeable difference in quality between a regular mobile call and a call placed over the internet.

I have recently been experimenting with placing SIP calls over the 3G network (as opposed to using WiFi internet access) and, where the 3G network is good (mainly town and city centers at present), call quality has been acceptable. This means that if you are on an unlimited data plan as part of your mobile package, you could be calling your office (and any locations peering with it) free.



  • Typically better voice quality than Wi-Fi (only) phones
  • User interface is generally better than Wi-Fi (only) alternatives
  • Great mobility
  • Always on-net, just variable costs
  • VoIP is an “application”
  • Respected vendors
  • Battery life is reduced by having Wi-Fi on, in addition to the regular phone
  • Complex hotspot attachment processes in some environments (not a problem with the phone, just the Wi-Fi hook up)
  • Sometimes frustrating steps to choose call route


For more information, look at Nokia, Pirelli, or UT Starcomm dual-mode VoIP phone, or Windows mobile SIP.


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