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Asterisk Manager Socket API Syntax

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Appendix C

APPENDIX C

Asterisk Manager Socket API Syntax

AbsoluteTimeout Channel Timeout

Sets an absolute timeout in seconds for the specified channel. The call will be ended after the time has elapsed. The following example limits the call on the current channel to 10 minutes:

Action: AbsoluteTimeout

Channel: SIP/201

Timeout: 600

ChangeMonitor Channel File

Equivalent of ChangeMonitor( ).

Action: ChangeMonitor

Channel: Zap/1-1

File: Zap1-1-incsound

Command command

Execute the specified dial-plan command. The command must include all arguments necessary for it to work.

GetVar Channel Variable

Gets a variable from the specified channel.

Hangup Channel

Hangs up specified channel. Equivalent to SoftHangup( ).

IAXpeers

Lists IAX peers. Equivalent of IAX2 show peers CLI command.

ListCommands

Lists available Manager API commands.

Logoff

Closes the connection to the Manager.

MailboxCount Mailbox

Gets the message count for the specified mailbox.

MailboxStatus Mailbox

Gets the message-waiting indication for the specified mailbox.

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PSTN Trunks

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Chapter 12

CHAPTER 12

PSTN Trunks

While private trunks connect voice switches on your private network, PSTN trunks serve another purpose: connecting your PBX or your VoIP network to the outside world. They can be analog phone lines, digital phone lines like T1s, ATM connections, or VoIP based, depending on what kinds of service are available from your

PSTN carrier.

Legacy telephony purists will balk at the use of the word trunk to describe a T1 or an

ATM connection, arguing that a trunk is nothing more than a phone line connecting two switches. In fact, the definition has grown to mean any connection between two voice networks. A 5-mile-long T1 between two old-school PBXs is a trunk, and so is a UDP pathway between two VoIP servers. Even in non-voice scenarios, the word trunk is used to describe a pathway between two switches—take VLAN trunks as an example.

The way you think about trunk connections is different when they’re PSTN trunks.

While privately owned trunks are relatively cheap or free, PSTN trunks incur service fees. Careful design, utilization, and monitoring of PSTN trunks is important to your bottom line. PSTN trunks can also offer calling features that let you do things that may be less easy to do with private trunks: features like distinctive ring and threeway calling can be integrated into your voice network to simplify your PBX design or to enable functions that you otherwise couldn’t provide.

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VoIP Vendors and Services

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CHAPTER

VoIP Vendors and Services

Telephony software is everywhere, and a majority of it is free. Much of it is open source. It’s a good idea to experiment with as much of this stuff as you can, because the VoIP family of technologies is evolving continuously. The capabilities and efficiency of these tools rise daily.

Whether you use Linux, Solaris, Windows, or Macintosh, plenty of fully developed softphones, servers, troubleshooting tools, APIs, and sample code are available.

What follows is a partial list of some excellent VoIP software and service providers.

Many of them have been used in projects throughout this book.

We’ll also briefly cover the growing list of vendors that manufacture modular and turnkey telephony hardware.

Softphones and Instant Messaging Software

OhPhone

OhPhone and OhPhoneX are H.323 softphones that support Windows, Linux, and

Macintosh. Unlike NetMeeting, OhPhone is open source, but it is not as polished.

OhPhone is a part of the Open H.323 distribution (http://www.openh323.org).

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Linux as a PBX

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Linux as a PBX

Evaluating VoIP for enterprise or for your home phone setup means a lot of experimentation, and you’ll need to build a test server with which to hone your VoIP skills.

That test server should be something you can get a lot out of without spending a bundle or committing to a specific vendor’s commercial VoIP platform before you’ve done your homework. Free telephony software lets you do that homework.

Free Telephony Software

If you were learning engine repair instead of VoIP, you probably wouldn’t use a Ferrari for your experiments. You would want something more forgiving and easier to work on, like a nice Dodge Omni. Luckily, there’s Asterisk PBX software—the very open, roomy-under-the-hood telephony server. Like a Dodge Omni, Asterisk is easy to work on, support is a snap to find, and experimenting is cheap. In fact, Asterisk is free

(although its development is supported by Digium, Inc., http.//www.digium.com). So is its source code.

But like a Ferrari, Asterisk is very powerful. Asterisk supports several Voice over IP communication protocols: H.323, SIP, IAX, and others (see Chapter 7 for more on these). Using these protocols, it can support just about any IP telephone, as well as traditional analog and digital telephones. Asterisk has some industrial-strength features like call-queuing, conference calling, voice mail, and caller ID.

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Traditional Apps on the Converged Network

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Traditional Apps on the Converged

Network

When first designed, landline phone service was intended to carry sound signals, and its uses as a carrier of data were years away from realization. It’s ironic that the technology that predated the telephone was itself a data transport technology: the telegraph. This device carried encoded messages from terminal to terminal across the

19th-century equivalent of a peer-to-peer network.

A lifetime later, in the 1960s, sound-encoding devices emerged, and, very soon, computers were able to send data, represented as sound, across the telephone network.

Those devices were modems, and later fax machines—the descendants of the telegraph. Modems, fax machines, voice mail systems, emergency 911 service, and a slew of other messaging tools evolved around the international telephone network.

Today voice and data networks converge and VoIP begins to replace Bell’s brainchild. IP telephony has the same fundamental goal as legacy telephony: facilitate human interaction at a distance. But, since IP telephony goes about this goal differently, not all of the specialized devices that evolved around the old system work with the new one. Fax machines, modems, and voice mail systems aren’t necessarily compatible with VoIP, because they grew into a mold that was shaped by the old network.

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