Integrating Asterisk with Wireless Technologies: Part 1

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Implementing, Administering, and Consulting on Commercial IP Telephony Solutions

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by Colman Carpenter David Duffett Ian Plain Nik Middleton | August 2009 | Linux Servers Networking & Telephony Open Source

The idea of this two-part article by Colman Carpenter, David Duffett, Ian Plain, and Nik Middleton is to give an introduction to the area of wireless technologies by asking, "Why integrate Asterisk with wireless technologies?"

After answering that question, we will look at the wireless device and wireless network options that exist, and consider the advantages and disadvantages for each. We will also look at some configurations for one or two devices and the settings we need to make in Asterisk, before rounding off the article with some example deployment scenarios, for which we will choose the best wireless options.

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.

Advantages

Disadvantages

  • 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!

Advantages

Disadvantages

  • 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.

Advantages

Disadvantages

  • 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.

Asterisk 1.4 – the Professional’s Guide Implementing, Administering, and Consulting on Commercial IP Telephony Solutions
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SIP/DECT phones

A world away from the poor speech quality and short battery life that plagues most Wi-Fi (only) phones are good old DECT cordless phones. They have been around for years and are an optimized technology.

A healthy DECT handset will usually last for days (not hours) on a single charge and the speech quality is excellent, unless you venture to the very edge of its range, which incidentally, is much greater than that of a Wi-Fi (only) phone.

Some clever people thought—Why don't we harness the excellence of the DECT air interface (or radio link) with the ubiquity of SIP for IP telephony, by putting a SIP stack in the DECT base station? So they did, and the results are amazing.

Now, don't expect to take your DECT handset to the airport and make calls from there. This won't work—if you want that kind of functionality, it has to be the Wi-Fi (only) or dual-mode phone for you. But, for in-office mobility, these SIP/DECT phones really are fantastic.

Integration with Asterisk is very easy, it's just a SIP connection. Do note that some of these are consumer offerings, and as such, they have an analog connection on the base station in addition to the LAN connector—the idea being that you connect both and choose which way to route calls by pressing the appropriate buttons on the phone.

Since we are interested in Asterisk installation, we will not use the analog connection and all calls will be routed to Asterisk via SIP.

It is usual to find that multiple handsets can be attached to a base station, and each base station can handle a number of SIP accounts, but beware that each base station will have a restriction on the number of concurrent calls that it can handle, which may be as low as two!

Make sure that you know the limitations of the base stations you are using, and that you deploy the number of base stations you need in order to facilitate the volume of concurrent calls you want. Each handset is linked with a SIP account (or accounts) by checking boxes on the web interface for the base station.

It should also be noted that there are several enterprise-grade SIP/DECT solutions(notably Aastra and Polycom), which offer further facilities including better capacities per base station and much better roaming abilities; some even allow multi-site roaming.

Advantages

Disadvantages

  • Excellent range when compared with Wi-Fi
  • Great battery life
  • Very good speech quality
  • Intuitive use (as in the case of a standard cordless phone)
  • Standard SIP configuration
  • Only mobile within the office
  • Linking handsets with SIP accounts on the base station web interface can be a little confusing the first time you do it

The preceding four sections represent the different types of wireless handsets that can be connected to Asterisk. Any wireless solution you propose is going to be made up of one or more of these options.

To conclude this section of the article, here is a table comparing the four handsets:

Asterisk 1.4 – the Professional’s Guide

Connecting Asterisk to mobile networks

There are times when you will want to connect to Asterisk to a wireless network. This can range from the simplicity of adding a standard wireless access point to the Ethernet network (so that wireless devices can connect to the network, and therefore to Asterisk), to the somewhat more esoteric area of giving Asterisk a direct connection to a mobile network. As the addition of a wireless access point is really standard networking practice, and not specific to VoIP, it will not be covered in this article.

Before we look at the two options for connecting Asterisk directly to mobile networks, let's examine the reason for doing it, which is usually "cost".

In a lot of countries, it is fixed landline to mobile calls which are the most expensive and this is due to the interconnect charges made by the mobile operators to the landline telco, and the profit margin of that telco. The following diagram depicts this situation:

Asterisk 1.4 – the Professional’s Guide

This high-cost situation is in sharp contrast to rates of mobile to mobile calls, which are often included in mobile charging plans (for example, 500 minutes per month), or are sometimes totally free between SIMs on the same mobile network.

This fact has not been left unnoticed by the creative telephony community, and for some time now, devices called GSM gateways have been available. These devices usually have an external aerial and a cut down mobile phone circuit into which you install a SIM for access to a given mobile network. Until recently, the connection to the PBX was an analog line, which would work with Asterisk, but would need the introduction of an analog interface in addition to the GSM gateway.

More recently, not only have these GSM gateways been enhanced to give direct SIP connectivity, but another hardware option has emerged in the form of GSM cards that are installed in the PC. Here is a revised version of that previous diagram, showing the most cost-effective way of calling mobiles from the PBX. Although this diagram shows a GSM gateway box, the principle applies to the GSM card implementation too.

Asterisk 1.4 – the Professional’s Guide

Having looked at the concept, we can now evaluate the two types of implementation.

The GSM gateway (box)

Although the concept of the GSM gateway box has been explained previously, the actual equipment available varies from single SIM to multiple SIMs, connecting via an FXO line, PRI connections, or SIP (there may even be some H.323 models out there).

Asterisk 1.4 – the Professional’s Guide

Because these units are designed to use up the "free" minutes included within the monthly plan for the SIMs, it is common to find more SIMs than radio circuits. The presence of this situation means that there is undoubtedly embedded software somewhere that allows the user to enter the number of included minutes for each SIM, and then, when the unit determines that the 500 minutes, say, from SIM "A" have been used up, it will seamlessly switch over to SIM "B".

Of course, to get a reasonable return on investments for such (multi SIM) systems really requires that your customer currently has quite a heavy fixed-to-mobile call volume.

Even at the single user end of the market, money can be saved, and not only by routing outbound fixed-to-mobile calls straight into the mobile network using one of these (single SIM) devices. Keep an eye out for my "neat money saving tricks" further in this article.

Advantages

Disadvantages

  • Not platform dependent
  • Connect via FXO, SIP, or PRI for large scale deployments
  • Easily scalable-just add more boxes
  • No special drivers required
  • Lots of wires
    • Antenna
    • Power
    • Connection to Asterisk
  • Care needed to ensure inclusive minutes are used effectively

The preceding four sections represent the different types of wireless handsets that can be connected to Asterisk. Any wireless solution you propose is going to be made up of one or more of these options.

To conclude this section of the article, here is a table comparing the four handsets:

Asterisk 1.4 – the Professional’s Guide

Connecting Asterisk to mobile networks

There are times when you will want to connect to Asterisk to a wireless network. This can range from the simplicity of adding a standard wireless access point to the Ethernet network (so that wireless devices can connect to the network, and therefore to Asterisk), to the somewhat more esoteric area of giving Asterisk a direct connection to a mobile network. As the addition of a wireless access point is really standard networking practice, and not specific to VoIP, it will not be covered in this article.

Before we look at the two options for connecting Asterisk directly to mobile networks, let's examine the reason for doing it, which is usually "cost".

In a lot of countries, it is fixed landline to mobile calls which are the most expensive and this is due to the interconnect charges made by the mobile operators to the landline telco, and the profit margin of that telco. The following diagram depicts this situation:

Asterisk 1.4 – the Professional’s Guide

This high-cost situation is in sharp contrast to rates of mobile to mobile calls, which are often included in mobile charging plans (for example, 500 minutes per month), or are sometimes totally free between SIMs on the same mobile network.

This fact has not been left unnoticed by the creative telephony community, and for some time now, devices called GSM gateways have been available. These devices usually have an external aerial and a cut down mobile phone circuit into which you install a SIM for access to a given mobile network. Until recently, the connection to the PBX was an analog line, which would work with Asterisk, but would need the introduction of an analog interface in addition to the GSM gateway.

More recently, not only have these GSM gateways been enhanced to give direct SIP connectivity, but another hardware option has emerged in the form of GSM cards that are installed in the PC. Here is a revised version of that previous diagram, showing the most cost-effective way of calling mobiles from the PBX. Although this diagram shows a GSM gateway box, the principle applies to the GSM card implementation too.

Asterisk 1.4 – the Professional’s Guide

Having looked at the concept, we can now evaluate the two types of implementation.

The GSM gateway (box)

Although the concept of the GSM gateway box has been explained previously, the actual equipment available varies from single SIM to multiple SIMs, connecting via an FXO line, PRI connections, or SIP (there may even be some H.323 models out there).

Asterisk 1.4 – the Professional’s Guide

Because these units are designed to use up the "free" minutes included within the monthly plan for the SIMs, it is common to find more SIMs than radio circuits. The presence of this situation means that there is undoubtedly embedded software somewhere that allows the user to enter the number of included minutes for each SIM, and then, when the unit determines that the 500 minutes, say, from SIM "A" have been used up, it will seamlessly switch over to SIM "B".

Of course, to get a reasonable return on investments for such (multi SIM) systems really requires that your customer currently has quite a heavy fixed-to-mobile call volume.

Even at the single user end of the market, money can be saved, and not only by routing outbound fixed-to-mobile calls straight into the mobile network using one of these (single SIM) devices. Keep an eye out for my "neat money saving tricks" further in this article.

The GSM card

The alternative to a GSM gateway box is a GSM card. PCI cards are still the dominant type available, but there are sure to be PCIe versions around too, which will become dominant as the PCs of today have either one or no PCI slots.

Even when installing a PCI card into a PCI slot in a PC, there can be issues such as minor bus incompatibilities (which can have a major effect on functionality), IRQ issues, and so on. Fortunately, most cards are compatible with both the 5.0V and 3.3V PCI slots found in PCs, so that is one less issue to worry about.

Although a number of cards have the same number of SIM slots as radio circuits (as indicated by the number of antenna sockets on the cards), it is possible to get cards with more SIM slots than radio circuits, for the reasons outlined in the section.

Cards are the "neater" solution, as the only cable involved is the antenna cable, there are no power supplies or Asterisk connections (usually FXO, PRI, or SIP) that you need to deal with, as all of that is looked after by the host PC platform.

Of course, these card solutions do come with the need to install drivers to get working within the Linux environment before you can make use of them within Asterisk. So do make sure that any cards you purchase have a good reputation for ease of installation.

Advantages

Disadvantages

  • Neat solution, card is inside the PBX platform.
  • Less interconnecting cables, just the antenna.
  • Platform compatibility is essential.
  • Expansion may prove difficult, as slots for further cards are required.
  • Setup and configuration can be difficult.
  • Routing coaxial antenna cables (when necessary) could prove problematic.

>> Continue Reading Integrating Asterisk with Wireless Technologies: Part 2

 

[ 1 | 2  ]
Asterisk 1.4 – the Professional’s Guide Implementing, Administering, and Consulting on Commercial IP Telephony Solutions
Published: August 2009
eBook Price: $26.99
Book Price: $44.99
See more
Select your format and quantity:

About the Author :


Colman Carpenter

Colman Carpenter is the MD of Voicespan, a Kent-based company that offers Asterisk-based systems to the SME market across the UK. He is an IT professional of over 20 years standing, with experience in diverse areas such as IBM mid-range software development, Lotus Notes and Domino consultancy, Data Management, E-marketing consultancy, IT Management, Project Management, Wordpress Website Design, and lately, Asterisk consultancy. He is a qualified PRINCE2 practitioner.

Voicespan (http://www.voicespan.co.uk) offers Asterisk-based systems as the cornerstone of a holistic VoIP-telephony service for SMEs. They offer companies a one-stop shop for implementing a VoIP-capable system, encompassing Asterisk-based systems, endpoints, trunks, telephony interfaces and network equipment, and the consultancy necessary to bring it all together into a coherent whole. This is his first book.

David Duffett

David Duffett delivers Asterisk training and consultancy around the world through his own company (TeleSpeak Limited, www.telespeak.co.uk), in addition to designing and delivering training for a number of companies, including Digium, Inc.

A keen Asterisk enthusiast, David also enjoys podcasting, radio presenting, and teaching public-speaking skills. He is a Chartered Engineer with experience in fields including Air Traffic Control communications, Wireless Local Loop, Mobile Networks, VoIP, and Asterisk. David has been in the telecoms sector for nearly 20 years and has had a number of computer telephony, VoIP, and Asterisk articles published through various industry publications and web sites.

Ian Plain

Ian Plain has worked in the telecoms industry since 1981 and has designed some of the largest PBX networks in the UK. Since the late 1990s, he has been involved with VoIP initially for links between systems, and with IP PBX systems since 1999. Since 2003, he has been running a telecoms consultancy based near Bath in the UK, working primarily on high-availability Asterisk-based solutions for corporate customers.

Nik Middleton

Nik Middleton has been in wide-area communications since the mid-eighties. He spent most of the nineties working in the US, where he developed a shareware Microsoft mail to SMTP/POP3 connector that sold some 287,000 copies. He spent six years working for DuPont in VA, developing remote monitoring systems for their global Lycra business. In late 2000, he returned to the UK where he held various senior positions in British Telecom, LogicaCMG, and Computer Science Corp.

In 2005, tired of working in London, he set up his own company (Noble Solutions) providing VoIP solutions in rural Devon, where he now lives with his wife Georgina and three children, Mathew, Vicky, and Isabel. A keen amateur pilot, his favorite place when not in the office is flying over the beautiful Devon countryside.

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