打开主菜单

Asterisk权威指南/第二十七章 Asterisk:电话的未来

< Asterisk权威指南


现在不是终点,甚至不是终点的开始。但是可能是,开始阶段的结束。 —丘吉尔

这里是本书的最后一章了。本书讲了很多,但我想补充的是,讲Asterisk仅仅是触及了一种表面现象。接下来,我们花一点时间,从Asterisk和开源电话出发,探讨一下电话的未来

当我写Asterisk第一版《电话的未来》时,我就自信地认为Asterisk等开源电话引擎将改变电信业。现在看来,这个观念多个方面已被证实。虽然电信业进化仍有一段长的路,但Asterisk已经在实质地改变着整个行业。


目录

传统电话的问题编辑

Although Alexander Graham Bell is most famously remembered as the father of the telephone,* the reality is that during the latter half of the 1800s, dozens of minds were working toward the goal of carrying voice over telegraph lines. These people were mostly business-minded folks, looking to create a product through which they might make their fortunes.

We have come to think of traditional telephone companies as monopolies, but this was not true in their early days. The early history of telephone service took place in a very competitive environment, with new companies springing up all over the world, often with little or no respect for the patents they might be violating. Many famous monopolies got their start through the waging (and winning) of patent wars.

It’s interesting to contrast the history of the telephone with the history of Linux and the Internet. While the telephone was created as a commercial exercise, and the telecom industry was forged through lawsuits and corporate takeovers, Linux and the Internet arose out of the academic community, which has always valued the sharing of knowledge over profit.

The cultural differences are obvious. Telecommunications technologies tend to be closed, confusing, and expensive, while networking technologies are comparatively open, well documented, and competitive.

Closed Thinking编辑

If one compares the culture of the telecommunications industry to that of the Internet, it is sometimes difficult to believe the two are related. The technology of the Internet was designed in large part by academics and enthusiasts, whereas contributing to the development of the PSTN is impossible for any individual to contemplate. This is an exclusive club; membership is not open to just anyone.

Although the ITU is the United Nations’s sanctioned body responsible for international telecommunications, many of the VoIP protocols (SIP, MGCP, RTP, STUN) come not from the ITU, but rather from the IETF (which publishes all of its standards free to all, and allows anyone to submit an Internet Draft for consideration).

Open protocols such as SIP may have a tactical advantage over ITU protocols such as H.323 due to the ease with which one can obtain them.‡ Although H.323 is widely deployed by carriers as a VoIP protocol in the backbone, it is much more difficult to find H.323-based endpoints; newer products are far more likely to support SIP.

The success of the IETF’s open approach has not gone unnoticed by the ITU. Since the first edition of this book, the ITU has made all of the ITU-T and ITU-R recommenda- tions available as free downloads in PDF form from its website (http://www.itu.int).

As for Asterisk, it embraces both the past and the future—H.323 support is available, although the community has for the most part shunned H.323 in favor of the IETF protocol SIP and the darling of the Asterisk community, IAX.

Limited Standards Compliancy编辑

One of the oddest things about all the standards that exist in the world of legacy tele- communications is the various manufacturers’ seeming inability to implement them consistently. Each manufacturer desires a total monopoly, so the concept of intero- perability tends to take a back seat to being first to market with a creative new idea.

The ISDN protocols are a classic example of this. Deployment of ISDN was (and in many ways still is) a painful and expensive proposition, as each manufacturer decided to implement it in a slightly different way. ISDN could very well have helped to usher in a massive public data network, 10 years before the Internet. Unfortunately, due to its cost, complexity, and compatibility issues, ISDN never delivered much more than voice, with the occasional video or data connection for those willing to pay. ISDN is quite common (especially in Europe, and in North America in larger PBX implemen- tations), but it is not delivering anywhere near the capabilities that were envisioned for it.

As VoIP becomes more and more ubiquitous, the need for ISDN will disappear.

Slow Release Cycles编辑

It can take months, or sometimes years, for the big guys to admit to a trend, let alone release a product that is compatible with it. It seems that before a new technology can be embraced, it must be analyzed to death, and then it must pass successfully through various layers of bureaucracy before it is even scheduled into the development cycle. Months or even years must pass before any useful product can be expected. When those products are finally released, they are often based on hardware that is obsolete; they also tend to be expensive and to offer no more than a minimal feature set.

These slow release cycles simply don’t work in today’s world of business communica- tions. On the Internet, new ideas can take root in a matter of weeks and become viable in extremely short periods of time. Since every other technology must adapt to these changes, so too must telecommunications.

Open source development is inherently better able to adapt to rapid technological change, which gives it an enormous competitive advantage.

The spectacular crash of the telecom industry may have been caused in large part by an inability to change. Perhaps that continued inability is why recovery has been so slow. Now, there is no choice: change, or cease to be. Community-driven technologies such as Asterisk are seeing to that.

Refusing to Let Go of the Past and Embrace the Future编辑

Traditional telecommunications companies have lost touch with their customers. While the concept of adding functionality beyond the basic telephone is well under- stood, the idea that the user should be the one defining this functionality is not.


Nowadays, people have nearly limitless flexibility in every other form of communica- tion. They simply cannot understand why telecommunications cannot be delivered as flexibly as the industry has been promising for so many years. The concept of flexibility is not familiar to the telecom industry, and very well might not be until open source products such as Asterisk begin to transform the fundamental nature of the industry. This is a revolution similar to the one Linux and the Internet willingly started over 10 years ago (and IBM unwittingly started with the PC, 15 years before that). What is this revolution? The commoditization of telephony hardware and software, enabling a pro- liferation of tailor-made telecommunications systems.

Paradigm Shift编辑

In his article “Paradigm Shift” (http://tim.oreilly.com/articles/paradigmshift_0504.html), Tim O’Reilly talks about a paradigm shift that is occurring in the way technology (both hardware and software) is delivered.§ O’Reilly identifies three trends: the com- moditization of software, network-enabled collaboration, and software customizability (software as a service). These three concepts provide evidence to suggest that open source telephony is an idea whose time has come.

The Promise of Open Source Telephony编辑

 Every good work of software starts by scratching a developer’s personal itch.
 —Eric S. Raymond, The Cathedral and the Bazaar

In his book The Cathedral and the Bazaar (O’Reilly), Eric S. Raymond explains that “Given enough eyeballs, all bugs are shallow.” The reason open source software de- velopment produces such consistent quality is simple: crap can’t hide.

The Itch That Asterisk Scratches编辑

In this era of custom database and website development, people are not only tired of hearing that their telephone system “can’t do that,” but quite frankly just don’t believe it. The creative needs of the customers, coupled with the limitations of the technology, have spawned a type of creativity born of necessity: telecom engineers are like contest- ants in an episode of Junkyard Wars, trying to create functional devices out of a pile of mismatched components.

The development methodology of a proprietary telephone system dictates that it will have a huge number of features, and that the number of features will in large part determine the price. Manufacturers will tell you that their products give you hundreds of features, but if you only need five of them, who cares? Worse, if there’s one missing feature you really can’t do without, the value of that system will be diluted by the fact that it can’t completely address your needs.

The fact that a customer might only need five out of five hundred features is ignored, and that customer’s desire to have five unavailable features that address the needs of his business is dismissed as unreasonable.‖ Until flexibility becomes standard, telecom will remain stuck in the last century—all the VoIP in the world notwithstanding.

Asterisk addresses that problem directly, and solves it in a way that few other telecom systems can. This is extremely disruptive technology, in large part because it is based on concepts that have been proven time and time again: “the closed-source world can- not win an evolutionary arms race with open-source communities that can put orders of magnitude more skilled time into a problem.”

Open Architecture编辑

One of the stumbling blocks of the traditional telecommunications industry has been its apparent refusal to cooperate with itself. The big telecommunications giants have all been around for over a hundred years. The concept of closed, proprietary systems is so ingrained in their culture that even their attempts at standards compliancy are tainted by their desire to get the jump on the competition, by adding that one feature that no one else supports. For an example of this thinking, one simply has to look at the VoIP products being offered by the telecom industry today. While they claim standards compliance, the thought that you would actually expect to be able to connect a Cisco phone to a Nortel switch, or that an Avaya voicemail system could be integrated via IP to a Siemens PBX, is not one that bears discussing.

In the computer industry, things are different. Twenty years ago, if you bought an IBM server, you needed an IBM network and IBM terminals to talk to it. Now, that IBM server is likely to interconnect to Dell terminals though a Cisco network (and run Linux, of all things). Anyone can easily think of thousands of variations on this theme. If any one of these companies were to suggest that we could only use their products with whatever they told us, they would be laughed out of business.

The telecommunications industry is facing the same changes, but it’s in no hurry to accept them. Asterisk, on the other hand, is in a big hurry to not only accept change, but embrace it.

In the computer industry, things are different. Twenty years ago, if you bought an IBM server, you needed an IBM network and IBM terminals to talk to it. Now, that IBM server is likely to interconnect to Dell terminals though a Cisco network (and run Linux, of all things). Anyone can easily think of thousands of variations on this theme. If any one of these companies were to suggest that we could only use their products with whatever they told us, they would be laughed out of business.

The telecommunications industry is facing the same changes, but it’s in no hurry to accept them. Asterisk, on the other hand, is in a big hurry to not only accept change, but embrace it.

Standards Compliance编辑

In the past few years, it has become clear that standards evolve at such a rapid pace that to keep up with them requires an ability to quickly respond to emerging technology trends. Asterisk, by virtue of being an open source, community-driven development effort, is uniquely suited to the kind of rapid development that standards compliance demands.

Asterisk does not focus on cost-benefit analysis or market research. It evolves in re- sponse to whatever the community finds exciting—or necessary.

Lightning-Fast Response to New Technologies编辑

After Mark Spencer attended his first SIP Interoperability Test (SIPIT) event, he had a rudimentary but working SIP stack for Asterisk coded within a few days. This was before SIP had emerged as the protocol of choice in the VoIP world, but he saw its value and momentum and ensured that Asterisk would be ready.

This kind of foresight and flexibility is typical in an open-source development com- munity (and very unusual in a large corporation).

Passionate Community编辑

The Asterisk-Users list receives over three hundred email messages per day. Over ten thousand people are subscribed to it. This kind of community support is unheard of in the world of proprietary telecommunications, while in the open source world it is commonplace.

The very first AstriCon event was expected to attract one hundred participants. Nearly five hundred showed up (far more wanted to but couldn’t attend). This kind of com- munity support virtually guarantees the success of an open source effort.

Some Things That Are Now Possible编辑

So what sorts of things can be built using Asterisk? Let’s look at some of the things we’ve come up with.

Legacy PBX migration gateway编辑

Asterisk can be used as a fantastic bridge between an old PBX and the future. You can place it in front of the PBX as a gateway (and migrate users off the PBX as needs dictate), or you can put it behind the PBX as a peripheral application server. You can even do both at the same time, as shown in Figure 27-1.

Figure 27-1. Asterisk as a PBX gateway

Here are some of the options you can implement:

Keep your old PBX, but evolve to IP

Companies that have spent vast sums of money in the past few years buying pro- prietary PBX equipment want a way out of proprietary jail, but they can’t stomach the thought of throwing away all of their otherwise functioning equipment. No problem—Asterisk can solve all kinds of problems, from replacing a voicemail system to providing a way to add IP-based users beyond the nominal capacity of the system.

Find-me-follow-me

Provide the PBX a list of numbers where you can be reached, and it will ring them all whenever a call to your DID (Direct Inward Dialing, a.k.a. phone) number arrives. Figure 27-2 illustrates this technology.

VoIP calling

If a legacy telephony connection from an Asterisk PBX to an old PBX can be es- tablished, Asterisk can provide access to VoIP services, while the old PBX continues to connect to the outside world as it always has. As a gateway, Asterisk simply needs to emulate the functions of the PSTN, and the old PBX won’t know that anything has changed. Figure 27-3 shows how you can use Asterisk to VoIP-enable a legacy PBX.

Low-barrier IVR编辑

Many people confuse Interactive Voice Response (IVR) systems with automated at- tendants (AAs). Since the automated attendant was the very first thing IVR was used for, this is understandable. Nevertheless, to the telecom industry, the term IVR repre- sents far more than an AA. An AA generally does little more than present a way for callers to be transferred to extensions, and it is built into most proprietary voicemail systems—but IVR can be so much more.

IVR systems are generally very expensive, not only to purchase, but also to configure. A custom IVR system will usually require connectivity to an external database or ap- plication. Asterisk is arguably the perfect IVR, as it embraces the concepts of connec- tivity to databases and applications at its deepest level.

Here are a few examples of relatively simple IVRs an Asterisk system could be used to create:

Weather reporting

Using the Internet, you can obtain text-based weather reports from around the world in a myriad of ways. Capturing these reports and running them through a purpose-built parser (Perl would probably eat this up) would allow the information to be available to the dialplan. Asterisk’s sound library already contains all the required prompts, so it would not be an onerous task to produce an interactive menu to play current forecasts for anywhere in the world.

Math programs

Ed Guy (the architect of Pulver’s FWD network) did a presentation at AstriCon 2004 in which he talked about a little math program he’d cooked up for his daugh- ter to use. The program took him no more than an hour to write. What it did was present her with a number of math questions, the answers to which she keyed into the telephone. When all the questions were tabulated, the system presented her with her score. This extremely simple Asterisk application would cost tens of thousands of dollars to implement on any closed PBX platform, assuming it could be done at all. As is so often the case, things that are simple for Asterisk would be either impossible or massively expensive with any other IVR system.

Distributed IVR

The cost of a proprietary IVR system is such that when a company with many small retail locations wants to provide IVR, it is forced to transfer callers to a central server to process the transactions. With Asterisk, it becomes possible to distribute the application to each node, and thus handle the requests locally. Literally thou- sands of little Asterisk systems deployed at retail locations across the world could serve up IVR functionality in a way that would be impossible to achieve with any other system. No more long-distance transfers to a central IVR server, no more huge trunking facility dedicated to the task—more power with less expense.

These are three rather simple examples of the potential of Asterisk.

Conference rooms

This little gem is going to end up being one of the killer functions of Asterisk. In the Asterisk community, people find themselves using conference rooms more and more, for purposes such as these:

• Smallcompaniesneedaneasywayforbusinesspartnerstogettogetherforachat. • Salesteamswanttohaveweeklymeetingswhererepscandialinfromwherever they are. • Developmentteamsneedtodesignateacommonplaceandtimetoupdateeach other on progress.

Home automation

Asterisk is still too much of an über-geek’s tool to be able to serve in the average home, but with no more than average Linux and Asterisk skills, the following things become plausible:

Monitoring the kids

Parents who want to check up on the babysitter (or the kids home alone) could dial an extension context protected by a password. Once authenticated, a two-way audio connection would be created to all the IP phones in the house, allowing Mom and Dad to listen for trouble. Creepy? Yes. But an interesting concept nonetheless.

Locking down your phones

Going out for the night? Don’t want the babysitter tying up the phone? No problem! A simple tweak to the dialplan, and the only calls that can be made are to 911, your cell phone, and the pizza parlor. Any other call attempt will get the recording “We are paying you to babysit our kids, not make personal calls.” Pretty evil, huh?

Controlling the alarm system

You get a call while on vacation from your mom who wants to borrow some cook- ing utensils. She forgot her key, and is standing in front of the house shivering. Piece of cake: a call to your Asterisk system, a quick digit string into the context you created for the purpose, and your alarm system is instructed to disable the alarm for 15 minutes. Mom better get her stuff and get out quick, though, or the cops’ll be showing up!

Managing teenagers’ calls

How about allocating a specific phone-time limit to your teenagers? To use the phone, they have to enter their access codes. They can earn extra minutes by doing chores, scoring all As, dumping that annoying bum with the bad haircut—you get the idea. Once they’ve used up their minutes...click...you get your phone back. Incoming calls can be managed as well, via caller ID. “Donny, this is Suzy’s father. She is no longer interested in seeing you, as she has decided to raise her standards a bit. Also, you should consider getting a haircut.”

The Future of Asterisk编辑

We’ve come to love the Internet, both because it is so rich in content and inexpensive and, perhaps more importantly, because it allows us to define how we communicate. As its ability to carry richer forms of media advances, we’ll find ourselves using it more and more. Once Internet voice delivers quality that rivals (or betters) the capabilities of the PSTN, the phone company had better look for another line of business. The PSTN will cease to exist; all its complexity will be absorbed into the Internet, as just one more technology. As with most of the rest of the Internet, open source technologies will lead this transformation.

Speech Processing编辑

The dream of having our technical inventions talk to us is older than the telephone itself. Each new advance in technology spurs a new wave of eager experimentation. Generally, results never quite meet expectations, possibly because as soon as a machine says something that sounds intelligent, most people assume that it is intelligent.

People who program and maintain computers realize their limitations, and thus tend to allow for their weaknesses. Everybody else just expects their computers and software to work. The amount of thinking a user must do to interact with a computer is often inversely proportional to the amount of thinking the design team did. Simple interfaces belie complex design decisions.

The challenge, therefore, is to design a system that has anticipated the most common desires of its users, and can also adroitly handle unexpected challenges.

Festival编辑

The Festival text-to-speech server can transform text into spoken words. While this is a whole lot of fun to play with, there are many challenges to overcome (for more on integrating Festival with Asterisk, refer back to “Text-to-Speech Utilities” on page 440).

For Asterisk, an obvious value of text-to-speech might be the ability to have your tel- ephone system read your emails back to you. If you’ve noticed the somewhat poor grammar, punctuation, and spelling typically found in email messages these days, you can perhaps appreciate the challenges this poses.

One cannot help but wonder if the emergence of text-to-speech will inspire a new generation of people dedicated to proper writing. Seeing spelling and punctuation er- rors on the screen is frustrating enough—having to hear a computer speak such things will require a level of Zazen that few possess.

Speech recognition编辑

If text-to-speech is rocket science, speech recognition is science fiction.

Speech recognition can actually work very well, but unfortunately this is generally true only if you provide it with the right conditions—and the right conditions are not those found on a telephone network. Even a perfect PSTN connection is considered to be at the lowest acceptable limit for accurate speech recognition. Add in compressed and lossy VoIP connections, or a cell phone, and you will discover far more limitations than uses.

Asterisk now has an entire speech API, so that outside companies (or even open source projects) can tie their speech recognition engines into Asterisk. One company that has done this is LumenVox. By using LumenVox’s speech recognition engine along with Asterisk, you can make voice-driven menus and IVR systems in record time! For more information, see http://www.lumenvox.com.

High-Fidelity Voice编辑

As we gain access to more and more bandwidth, it becomes less and less easy to un- derstand why we still use low-fidelity codecs. Many people do not realize that Skype provides higher fidelity than a telephone; it’s a large part of the reason why Skype has a reputation for sounding so good.

If you were ever to phone CNN, wouldn’t you love to hear James Earl Jones’s mellif- luous voice saying “This is CNN,” instead of some tinny electronic recording? And if you think Allison Smith* sounds good through the phone, you should hear her in person!

In the future, we will expect, and get, high-fidelity voice through our communications equipment.

As more and more hardware vendors start building support for high-fidelity voice into their VoIP hardware, you’ll see more support in Asterisk for making better-than-PSTN- quality calls.

Video编辑

While most of this book focuses on audio, video is also supported in many ways within Asterisk. Video support is not complete, however. The problem is not so much one of functionality as one of bandwidth and processing power. Asterisk 1.10 is expected to contain better support for handling media, including video.

The challenge of videoconferencing编辑

The concept of videoconferencing has been around since the invention of the cathode ray tube. The telecom industry has been promising a videoconferencing device in every home for decades.

As with so many other communications technologies, if you have videoconferencing in your house, you are probably running it over the Internet, with a simple, inexpensive webcam. Still, it seems that people see videoconferencing as a bit gimmicky. Yes, you can see the person you’re talking to, but there’s something missing.

Why we love videoconferencing

Videoconferencing promises a richer communications experience than the telephone. Rather than simply hearing a disembodied voice, you have access to all the nuances of speech that come from face-to-face communication.

Why videoconferencing may never totally replace voice

There are some challenges to overcome, though, and not all of them are technical.

Consider this: using a plain telephone, people working from their home offices can have business conversations, unshowered, in their underwear, feet on the desk, coffee in hand—if they use a telephone. A similar video conversation would require half an hour of grooming to prepare for, and couldn’t happen in the kitchen, on the patio, or... well, you get the idea.

Also, the promise of eye-to-eye communication over video will never happen as long as the focal points of the participants are not in line with the cameras. If you look at the camera, your audience will see you looking at them, but you won’t see them. If you look at your screen to see whom you are talking to, the camera will show you looking down at something—not at your audience. That looks impersonal. Perhaps if a video- phone could be designed like a Tele-Prompt-R, where the camera was behind the screen, it wouldn’t feel so unnatural. As it stands, there’s something psychological that’s missing. Video ends up being a gimmick.

Wireless编辑

Since Asterisk is fully VoIP-enabled, wireless is all part of the package.

WiFi

WiFi is going to be the office mobility solution for VoIP phones. This technology is already quite mature. The biggest hurdle is the cost of handsets, which can be expected to improve as competitive pressure from around the world drives down prices.

WiMAX

Since we are so bravely predicting so many things, it’s not hard to predict that WiMAX spells the beginning of the end for traditional cellular telephone networks.

With wireless Internet access within the reach of most communities, what value will there be in expensive cellular service?

Unified Messaging编辑

This is a term that has been hyped by the telecom industry for years, but adoption has been far slower than predicted. Unified messaging refers to the concept of tying voice and text-messaging systems into one. With Asterisk, the two don’t need to be artificially combined, as Asterisk already treats them the same way.

Just by examining the terms, unified and messaging, we can see that the integration of email and voicemail must be merely the beginning—unified messaging needs to do a lot more than just that if it is to deserve its name.

Perhaps we need to define “messaging” as communication that does not occur in real time. In other words, when you send a message, you expect that the reply may take moments, minutes, hours, or even days to arrive. You compose what you wish to say, and your audience is expected to compose a reply.

Contrast this with conversing, which happens in real time. When you talk to someone on a telephone connection, you expect no more than a few seconds’ delay before the response arrives.

Several years ago, Tim O’Reilly delivered a speech entitled “Watching the Alpha Geeks: OS X and the Next Big Thing” (http://www.macdevcenter.com/pub/a/mac/2002/05/14/ oreilly_wwdc_keynote.html), in which he talked about someone piping IRC through a text-to-speech engine. One could imagine doing the reverse as well, allowing us to join an IRC or instant messaging chat over a WiFi phone, with our Asterisk PBX providing the speech-to-text-to-speech translations.

Peering编辑

As monopoly networks such as the PSTN give way to community-based networks like the Internet, there will be a period of time where it is necessary to interconnect the two. While the traditional providers would prefer that the existing model be carried into the new paradigm, it is increasingly likely that telephone calls will become little more than another application the Internet happily carries.

But a challenge remains: how to manage the telephone numbering plan with which we are all familiar and comfortable?

E.164编辑

The ITU defined a numbering plan in its E.164 specification. If you’ve used a telephone to make a call across the PSTN, you can confidently state that you are familiar with the concept of E.164 numbering. Prior to the advent of publicly available VoIP, nobody cared about E.164 except the telephone companies—nobody needed to.

Now that calls are hopping from PSTN to Internet to who-knows-what, some consid- eration must be given to E.164.

ENUM

In response to this challenge, the IETF has sponsored the Electronic NUmber Mapping (ENUM) working group, the purpose of which is to map E.164 numbers into the Do- main Name System (DNS).

While the concept of ENUM is sound, it requires cooperation from the telecom industry to achieve success. However, cooperation is not what the telecom industry is famous for, and thus far ENUM has foundered.

e164.org

The folks at http://e164.org are trying to contribute to the success of ENUM. You can log onto this site, register your phone number, and inform the system of alternative methods of communicating with you. This means that someone who knows your phone number can connect a VoIP call to you, as the http://e164.org DNS zone will provide the IP addressing and protocol information needed to connect to your location.

As more and more people publish VoIP connectivity information, fewer and fewer calls will be connected through the PSTN.

Challenges编辑

As is true with any worthwhile thing, Asterisk will face challenges. Let’s take a glance at what some of them may be. Too much change, too few standards

These days, the Internet is changing so fast, and offers so much diverse content, that it is impossible for even the most attentive geek to keep on top of it all. While this is as it should be, it also means that an enormous amount of technology churn is an inevi- table part of keeping any communications system current.

Toll fraud

As long as long-distance calls cost money, there will be criminals who will wish to steal. Toll fraud is nothing new, but with many unsecured Asterisk systems now on the In- ternet, the popularity of scripts to find these systems and compromise them has ex- ploded. Administrators of Internet-connected telephone systems will need to carefully design their security to ensure that any calls made from their systems are made only by authorized users.

VoIP spam

Yes, it’s coming. There will always be people who believe they have the right to incon- venience and harass others in their pursuit of money. Efforts are under way to try to address this, but only time will tell how efficacious they will be.

Fear, uncertainty, and doubt

The industry is making the transition from ignorance to laughter. If Gandhi is correct, we can expect the fight to begin soon. As their revenue streams become increasingly threatened by open source telephony, the traditional industry players are certain to mount a fear campaign, in hopes of un- dermining the revolution.

Bottleneck engineering

There is a rumor that the major network providers will artificially cripple VoIP traffic by tagging and prioritizing the traffic of their premium VoIP services and, worse, de- tecting and bumping any VoIP traffic generated by services not approved by them.

Some of this is already taking place, with service providers blocking traffic of certain types through their networks, ostensibly as some public service (such as blocking pop- ular file-sharing services to protect us from piracy). In the United States, the FCC has taken a clear stand on the matter and fined companies that engage in such practices. In the rest of the world, regulatory bodies are not always as accepting of VoIP.

What seems clear is that the community and the network will find ways around block- ages, just as they always have.

Regulatory wars

A former chairman of the United States Federal Communications Commission, Michael Powell delivered a gift that may well have altered the path of the VoIP revo- lution. Rather than attempting to regulate VoIP as a telecom service, he championed the concept that VoIP represents an entirely new way of communicating and requires its own regulatory space in which to evolve.

VoIP will become regulated, but not everywhere as a telephony service. Some of the regulations that may be created include:

Presence information for emergency services

One of the characteristics of a traditional PSTN circuit is that it is always in the same location. This is very helpful to emergency services, as they can pinpoint the location of a caller by identifying the address of the circuit from which the call was placed. The proliferation of cell phones has made this much more difficult to achieve, since a cell phone does not have a known address. A cell phone can be plugged into any network and can register to any server. If the phone does not identify its physical location, an emergency call from it will provide no clue as to where the caller is. VoIP creates similar challenges.

Call monitoring for law enforcement agencies

Law enforcement agencies have always been able to obtain wiretaps on traditional circuit-switched telephone lines. While regulations are being enacted that are de- signed to achieve the same end on the network, the technical challenges of deliv- ering this functionality will probably never be completely solved. People value their privacy, and the more governments want to stifle it, the more effort will be put toward maintaining it.

Anti-monopolistic practices

These practices are already being seen in the US, with fines being levied against network providers who attempt to filter traffic based on content.

When it comes to regulation, Asterisk is both a saint and a devil: a saint because it feeds the poor, and a devil because it empowers the phrackers and spammers like nothing ever has. The regulation of open source telephony may in part be determined by how well the community regulates itself. Concepts such as DUNDi, which incorporate anti- spam processes, are an excellent start. On the other hand, concepts such as caller ID– spoofing are ripe with opportunities for abuse.

Quality of service

Due to the best-effort reality of the TCP/IP-based Internet, it is not yet known how increasing real-time VoIP traffic will affect overall network performance. Currently, there is so much excess bandwidth in the backbone that best-effort delivery is generally quite good indeed. Still, it has been proven time and time again that whenever we are provided with more bandwidth, we figure out a way to use it up. The 1-MB DSL con- nection undreamt of five years ago is now barely adequate.

Perhaps a corollary of Moore’s Law† will apply to network bandwidth. QoS may be- come moot, due to the network’s ability to deliver adequate performance without any special processing. Organizations that require higher levels of reliability may elect to pay a premium for a higher grade of service. Perhaps the era of paying by the minute for long-distance connections will give way to paying by the millisecond for guaranteed low latency, or by the percentage point for reduced packet loss. Premium services will offer the five-nines‡ reliability the traditional telecom companies have always touted as their advantage over VoIP.

Complexity

Open systems require new approaches to solution design. Just because the hardware and software are cheap doesn’t mean the solution will be. Asterisk does not come out of the box ready to run; an Asterisk system has to be designed and built, and then maintained. While the base software is free, and the hardware costs will be based on commodity pricing, it is fair to say that the configuration costs for a highly customized system will be a sizable part of the overall solution cost. In fact, in many cases, because of Asterisk’s high degree of complexity and configurability, the cost will be more than would be expected with a traditional PBX.

The rule of thumb is generally considered to be something like this: if it can be done in the dialplan, the system design will be roughly the same as for any similarly featured traditional PBX. Beyond that, only experience will allow one to accurately estimate the time required to build a system. There is much to learn.

Opportunities编辑

Open source telephony creates limitless opportunities. Here are some of the more compelling ones.

Tailor-made private telecommunications networks

Some people will tell you that price is the key, but we believe that the real reason Asterisk will succeed is because it is now possible to build a telephone system as one would a website: with complete, total customization of each and every facet of the system. Cus- tomers have wanted this for years. Only Asterisk can deliver.

Low barrier to entry

Anyone can contribute to the future of communicating. It is now possible for someone with an old $200 PC to develop a communications system that has the intelligence to rival the most expensive proprietary systems. Granted, the hardware would not be production-ready, but there is no reason the software couldn’t be. This is one of the reasons why closed systems will have a hard time competing. The sheer number of people who have access to the required equipment is impossible to equal in a closed shop.

Hosted solutions of similar complexity to corporate websites

The design of a PBX was always a kind of art form, but before Asterisk, the art lay in finding creative ways to overcome the limitations of the technology. With limitless technology, those same creative skills can now be properly applied to the task of com- pletely answering the needs of the customer. Open source telephony engines such as Asterisk will enable this. Telecom designers will dance for joy, as their considerable creative skills will now actually serve the needs of their customers, rather than being focused on managing kludge.

Proper integration of communications technologies

Ultimately, the promise of open source comes to nothing if it cannot fulfill the need people have to solve problems. The closed industries lost sight of the customer, and tried to fit the customer to the product.

Open source telephony brings voice communications in line with other information technologies. It is finally possible to properly begin the task of integrating email, voice, video, and anything else we might conceive of over flexible transport networks (whether wired or wireless), in response to the needs of the user, not the whims of monopolies.

Welcome to the future of telecom!