TrixBox Made Easy

By Barrie Dempster , Kerry Garrison
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About this book

TrixBox is a telephone system based on the popular open source Asterisk PBX (Private Branch eXchange) Software. TrixBox allows an individual or organization to setup a telephone system with traditional telephone networks as well as Internet based telephony or VoIP (Voice over Internet Protocol). SugarCRM can be integrated with Asterisk, and is bundled with Trixbox offering real power and  flexibility.

The book begins by introducing telephony concepts before detailing how to plan a telephone system and moving on to the installation, configuration, and management of a feature packed PBX.

This book is rich with practical examples and tools. It provides examples of well laid out telephone systems with accompanying spreadsheets to aid the reader in building stable telephony infrastructure.

Publication date:
October 2006
Publisher
Packt
Pages
168
ISBN
9781904811930

 

Chapter 1. Introduction to VoIP

TrixBox is essentially an easy-to-use system for managing our telephony needs. Before we can understand how to operate the TrixBox telephone system, we need to cover the basic principles that underlie the system. In this chapter, we will talk about the telephone network and the PBX (Private Branch Exchange) that traditional telephone systems run on. Fundamentally, TrixBox is a VoIP (Voice over Internet Protocol) system. So, we will have a look at what VoIP means and why it is useful to us. We will also take a look at any prerequisite knowledge or skills required, with advice on where to get these if necessary. We will define any new terms we come across; however, some of the commonly used terms used in or relating to this book are listed in Appendix A at the end of the book for ease of reference while reading the later chapters.

The PSTN

The acronym PSTN stands for Public Switched Telephone Network. PSTN is the network that traditional phone systems used and was generally controlled by the telecommunication companies. This is the network our calls are travelling over when we pick up our handset and dial a number. This network spans the world and there are many different interfaces to it:

  • POTS: POTS stands for Plain Old Telephone Service. It is commonly used for residential use. POTS is an analogue system and is controlled by electrical loops. It is provided with copper wires run to residences and places of business and is, therefore, the cheapest and easiest telephone service to roll out.

  • ISDN: This is a faster and more feature-filled connection (also more expensive) This gained some popularity within small to medium-sized business as a cost-effective way of connecting to the PSTN and getting some advanced services, like many lines to one office or voice and data lines on one service. ISDN is a digital service and offers a few more features over POTS.

  • T1/E1: This is more expensive and used for high-volume data and voice networks. It is more common in larger companies, although in recent years it has become more affordable. T1/E1 is also a digital service and offers yet more features than ISDN, the most important feature being increased bandwidth that translates, in telephony, to more telephone lines.

The trouble with PSTN is that it's very static and in most countries it is strictly controlled by the telecommunication companies. If a business wants to make a lot of internal calls using the PSTN, it is by no means a cheap way to communicate. ISDN/T1/E1 are most commonly found at the external interface of a company's communication network, with all the internal communications going through internal lines that are controlled by an internal telephone system.

 

The PSTN


The acronym PSTN stands for Public Switched Telephone Network. PSTN is the network that traditional phone systems used and was generally controlled by the telecommunication companies. This is the network our calls are travelling over when we pick up our handset and dial a number. This network spans the world and there are many different interfaces to it:

  • POTS: POTS stands for Plain Old Telephone Service. It is commonly used for residential use. POTS is an analogue system and is controlled by electrical loops. It is provided with copper wires run to residences and places of business and is, therefore, the cheapest and easiest telephone service to roll out.

  • ISDN: This is a faster and more feature-filled connection (also more expensive) This gained some popularity within small to medium-sized business as a cost-effective way of connecting to the PSTN and getting some advanced services, like many lines to one office or voice and data lines on one service. ISDN is a digital service and offers a few more features over POTS.

  • T1/E1: This is more expensive and used for high-volume data and voice networks. It is more common in larger companies, although in recent years it has become more affordable. T1/E1 is also a digital service and offers yet more features than ISDN, the most important feature being increased bandwidth that translates, in telephony, to more telephone lines.

The trouble with PSTN is that it's very static and in most countries it is strictly controlled by the telecommunication companies. If a business wants to make a lot of internal calls using the PSTN, it is by no means a cheap way to communicate. ISDN/T1/E1 are most commonly found at the external interface of a company's communication network, with all the internal communications going through internal lines that are controlled by an internal telephone system.

 

What is a PBX?


A PBX is an acronym for a Private Branch eXchange, which provides for the internal telephone system. Telephone exchanges were initially under the control of the telephone providers, such as AT&T in the US or British Telecom in the UK. These companies handled all line provisioning and call routing between the businesses and the public. Initially, the routing of calls was done by a team of operators (usually female) sitting in the offices of the telephone companies and routing calls by plugging and unplugging cables to connect one caller to another. Eventually, as the reliance and the demands of this service grew, technology evolved to the point where we had automatic systems managing these calls.

As the modern telephone networks began to take shape, private companies saw a greater reliance on telephone communication. Many decided to implement their own services so that they could handle calls internal to the organization. Usually, the equipment was leased or bought from the telephone companies mentioned previously, so they were quite happy to help with these services. These companies also got to charge for the lines and calls connecting the company externally, and so they could profit from this too. As we saw in the previous section, the more expensive digital lines were now being used only as a means of communicating outside the building, rather than using externally provided lines for all communication.

At this point, it became obvious that there was a need for these companies to install their own telephone equipment to route internal calls and, in some cases, to make sure calls going out or coming into the company went via the correct routes. For example, you don't want Alice in accounting calling Bob in HR through a line that leaves the company and crosses continents if they sit within the same building. Therefore, there is a requirement for a PBX to effectively manage calls and ensure that they go via the most cost effective and reliable routes in order to keep the company communicating internally between departments and employees, and externally with customers and suppliers.

In its basic form, a PBX is the interface between the public telephone network and the private network within the company. Since most companies need fewer phones lines than the number of employees they have, they can get away by having a few outgoing lines but many internal extensions so that employees can converse internally. This costs little more than the maintenance of the PBX and internal cabling, and there are no line rentals or other call charges being paid to the telecommunications provider. The PBX then handles all of the routing in and out of the company using the lines effectively. The PBX also handles calls within the company so that a call from one internal phone to another does not have to go out onto the phone circuits and back in.

As PBXs became more common, businesses and their employees required more features and functionality such as voicemail, call parking, call transfers, music on-hold, IVR menus, least-cost routing, and an Automatic Call Distributor (ACD) in order to provide for calling groups. With the increase in demand for communications in all aspects of a business, the features required in a phone system become more complex and more expensive. If modern companies had to rely on the telecommunications provider for all these features, the cost of communication could become prohibitively high.

The Traditional PBX System

It is not hard to spot a traditional PBX system. It is usually a large box full of mechanical switches and relays mounted on a wall in 'the phone room'. When a company's requirement changes, they generally contact their PBX provider who will charge varying rates to make hardware and configuration changes to fit the new requirements. With PBXs being very complicated and each differing from the others greatly, it can take a considerable level of training and experience to provide the support for a busy PBX system. This leads to most PBX customers relying on their PBX suppliers for, often expensive, support. So while by bringing the communications internally businesses could benefit from savings on line rentals, they still often had a reliance on their providers for support. Often, the companies selling and supporting the PBXs were the same telecommunication companies providing the external lines.

With a traditional PBX system we would also almost always purchase our phone system from the same manufacturer as the PBX system, usually with very few options to choose from when it comes to contract options and hardware such as telephone handsets or headsets. Adding features like voicemail can usually be an expensive add-on to the base system, sometimes requiring an entirely new piece of equipment! A traditional PBX system has the following structure:

Although some legacy PBX systems now have options for network access and VoIP functionality, these options are often very expensive upgrades and they generally lack the features and configuration options in the newer VoIP systems.

Hybrid PBX System

A hybrid PBX system combines the features of a traditional PBX system with VoIP functionality. In some cases, the VoIP functionality may just be the way the PBX communicates with the phones. Some other VoIP functionalities may include the ability to have remote extensions or Soft Phones, and the ability to use Internet Telephone Service Providers (ITSPs) and not just the traditional public telephone network. The main added benefit is the combined functionality, as we can keep all our existing lines and numbers and add in VoIP for substantial savings where possible.

The Asterisk PBX system is a full hybrid system combining numerous types of connections to the public telephone network as well as VoIP functionality including:

  • Use of industry-standard SIP-compliant phones

  • Remote extensions using either SIP-compliant phones, or Soft Phones

  • Support for IAX (Inter-Asterisk eXchange)

  • Bridging remote Asterisk systems together to act as a single system

Following is an example of a hybrid PBX system:

 

VoIP


We have covered, in brief, how a traditional PBX system could lack some of the features of a Voice over Internet Protocol system and discovered some of the basics of the PSTN. We can now take a look at VoIP in a little bit more detail to get an idea of what the benefits are.

Firstly, it's important to realize that VoIP doesn't entirely replace the PSTN (although it could). VoIP is yet another, cheaper, and easier way to connect to the PSTN. You can make and receive calls that are initiated and terminated entirely across VoIP and you can call a standard PSTN number from VoIP and vice-versa, as long as your ITSP (Internet Telephony Service Provider) supports it or if you link your VoIP system to the PSTN yourself. Both of these are options to consider with TrixBox.

A VoIP system can use a variety of protocols and we will cover each of those protocols relevant to TrixBox as we come across them. VoIP is a catch-all term for these protocols and refers to transferring voice data over the Internet.

As the Internet grew and became a more flexible system than the PSTN, it became apparent that it was possible and, in many cases, preferable to use the Internet for carrying voice as well as data. There were a few limitations that had to be overcome before this could be feasible. For example, data connections can tolerate some latency in communication but latency in voice can be very annoying as it leads to gaps in conversation and constant repetition. Watching a news broadcast from a reporter using a satellite phone is a very good example of how frustrating and error prone this form of communication can be. As Internet connection latency decreased and speeds increased, voice communication has become more viable.

There is a tendency to think of VoIP as a new technology. However, it is almost two decades old and has only recently become so popular because there are now a few good pieces of software that use this technology. There are also many companies investing in VoIP, since the data lines that provide Internet services are now at a level where they are usually reliable enough to be used for voice communication. Customers and employees expect these data lines to be low-latency, clear, and always available. While many Internet services still have problems, the situation is certainly much better than it was in the late 80s and early 90s when VoIP was first touted as the killer technology. It wasn't quite there then, but is certainly getting there now.

Why Choose VoIP?

The most important facet of VoIP is that it is "over Internet Protocol". This means that it benefits from the layered design of Internet communication and can be a very flexible communication mechanism. A VoIP implementation can generally be shifted from one service provider to another with little or no effect on the systems in use. Anyone that has gone through the nightmare of moving just a single telephone number between providers will realize the benefit VoIP brings in this area. Flexibility in communication is an important aspect for businesses as it helps to control the business process.

VoIP is also many times cheaper than traditional telephone services as it can be routed over a variety of cheap lines. The most important aspect here is usually the long distance rates. Calls can traverse the Internet until they get to the same country, state, or city as the recipient before touching the PSTN and in some cases bypass the PSTN entirely, meaning that we are no longer shackled to our telecommunications provider. We can pick and choose from the many Internet Providers and/or Internet Telephone Service Providers. The one downside to VoIP is that Internet connections are often less stable than the PSTN and therefore we can have occasional downtime in our telephony service. This can be mitigated by having multiple providers with failover, something which is near to impossible or prohibitively expensive with a PSTN service!

Before choosing VoIP, we should carefully examine the available service plans and options of the available PSTN providers as well as the ISP/ITSPs in our area. It's important to determine our current costs, our current needs, and the features we require in our telephone system as well as what we expect these needs to grow to in the foreseeable future. Armed with this information, we can make a valid choice as to which communication medium is the most appropriate and cost effective for our business.

 

Summary


In this chapter, we have covered the basic background to the traditional telephone network and have introduced VoIP as a cost-saving and flexible system for managing our telephone system. We've introduced some of the terminology we will be using throughout the book. There is, however, a more detailed list in Appendix A. We should have an understanding of why VoIP is growing in popularity and why it may be a sensible choice for our needs. The chapter also provided us with a good understanding of what a PBX is and what makes a VoIP PBX different from a traditional PBX system.

About the Authors

  • Barrie Dempster

    Barrie Dempster is currently employed as a Senior Security Consultant for NGS Software Ltd a world-renowned security consultancy well known for their focus in enterprise-level application vulnerability research and database security. He has a background in Infrastructure and Information Security in a number of specialised environments such as financial services institutions, telecommunications companies, call centres, and other organisations across multiple continents. Barrie has experience in the integration of network infrastructure and telecommunications systems requiring high calibre secure design, testing and management. He has been involved in a variety of projects from the design and implementation of Internet banking systems to large-scale conferencing and telephony infrastructure, as well as penetration testing and other security assessments of business critical infrastructure.

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  • Kerry Garrison

    Kerry Garrison has been in the IT industry for over 20 years with positions ranging from IT Director of a large multi-site distribution company to developing a large hosted web server platform for a major ISP, to finally running his own IT consulting business in Southern California. Kerry was introduced to the world of Asterisk by a friend and began running his own business on it. After about a year of working with it and writing some articles that became extremely popular on the net, he felt it was time to start putting clients onto Asterisk-based systems. Today, Asterisk PBX systems represent a significant portion of his business revenue. Kerry has spoken at Astricon and does a regular seminar series in California. He is also the publisher of both http://www.voipspeak.net and http://www.asterisktutorials.com. He is very active with the Asterisk and FreePBX community and has even contributed modules to the FreePBX project.

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