Hack4.Use a Softphone with a VoIP TSP

Hack 4. Use a Softphone with a VoIP TSP

Get started with prevalent and freely available SIP softphones.

Depending upon which TSP you choose for your broadband VoIP service, your service agreement might limit you to using only analog phones connected to an ATA. However, if you have a lenient Bring Your Own Device (BYOD) service agreement, your TSP will allow you to use your choice of IP telephony access devices. This might mean you can use an IP phone, a PC softphone, an ATA of your choosing, or even your own telephony server (Chapter 4 is dedicated to this proposition) with the TSP's service. This hack will show you how to use Counterpath's X-Lite softphone with your TSP. But first, a little background on telephone networks, both analog and VoIP.

When you subscribe to broadband VoIP service, what you're really doing is buying a single pathway through the TSP's network. Likewise, when you subscribe to traditional phone service, you're really just leasing a telephone line. With that line, you can use cordless phones, corded analog phones, answering machines, fax machines, modems, and all kinds of other access devices. These different analog devices all use the same electrical access signaling to communicate with the phone company. You could think of this analog protocol as even more primitive than the Morse code. It's simple, but it's what allows analog phone devices to place and receive calls.

If legacy telephony devices are more primitive than the Morse code, Session Initiation Protocol (SIP), the predominant VoIP access signaling protocol, is light-years ahead of both. SIP is a suite of media-signaling software specs that define how streaming media devices (and applications) should interact.

The most significant of modern streaming media apps is IP telephony, of course, which brings me to my point.

Unlike old-fashioned telephone signaling, which is Plug and Play (PnP), using a softphone is a bit more involved. To understand how a softphone works (or an ATA or IP phone, for that matter), you must have a simple grasp of SIP. Although SIP is a sprawling specification with dozens of proposed spinoffs and major revisions, you need to know only a few things to get by with a SIP softphone.

SIP is a lot like Simple Mail Transfer Protocol (SMTP). If you're comfortable with that, SIP will make a lot of sense to you. Like SMTP, SIP clients (the phones) send packet messages to SIP servers (such as proxies and telephone systems) or to other SIP clients (such as other SIP phones). In these packet messages are headers, strings of data that form requests for specific functionality from the device on the receiving end. The requests could be to establish a phone call, or merely to let a SIP server know that the phone making the request is available to receive calls. Another function of these requests is authentication. On many systemslike your broadband TSP's VoIP networkthe calling device must register and pass a username/password authentication to place or receive calls.

1.6.1. Different TSPs, Different Policies

SIP softphones, such as CounterPath's X-Lite, have many, many built-in features. They can signal call transfers, place callers on hold, and even do conference calling so that three or more parties can talk together. But whether these features are enabled by your TSP is another issue. To conference-call, for example, you might need to pay for an extra "line." Bear in mind that from one VoIP service provider to the next, even a feature-heavy softphone product could be impotent (and then there are those TSPs, such as Packet8, that don't support softphones at all).

1.6.2. Install the Softphone

To get X-Lite, download it from http://www.counterpath.com/. X-Lite is, in fact, a scaled-down freeware version of X-PRO, but for the purposes of this hack, the feature disparity between versions makes no difference. Installation is straightforward. On Windows, run the installer package, and on the Mac, drag the X-Lite program icon into your Applications folder. Once installed, launch X-Lite, step through its Audio Tuning Wizard, and look at its user interface. By some strange coincidence, it resembles a nice-looking business phone. Imagine that.

Vonage Users, Beware

If you're a Vonage subscriber, you can download the Vonage-branded version of X-Lite's commercial counterpart, called X-PRO, from your account page on Vonage's web site. If you're using Vonage, you're limited to using Vonage's version of X-PRO, and you won't have nearly the flexibility that the non-Vonage version of the software provides. Indeed, once you have the Vonage version running, the only administrative customization you can do is to change your username and password. You can't really get at the softphone's SIP guts because Vonage's version keeps all that stuff off-limits to the end user. Those seeking a deep hacking experience should probably consider BroadVoice instead. Unlike Vonage, BroadVoice openly supports noncrippled softphones such as X-Lite.

1.6.2.1. Setting up the basics.

After you've gotten through X-Lite's Audio Tuning Wizard, you're ready to dive into the SIP configuration settings. These define how the softphone will authenticate and interact with your TSP's SIP server. To access X-Lite's configuration settings, click the button to the right of the CLEAR button on X-Lite's main window, as shown in Figure 1-2.

Figure 1-2. X-Lite's main window looks a bit like a cellular phone

When the configuration window appears, double-click System Settings, and then double-click Network This to bring up the network configurations (Figure 1-3). Find the Provider DNS Address setting and change its value to the DNS server provided by your VoIP TSP (not your Internet Service Provider, or ISP). Your VoIP TSP might require the use of its own DNS because its SIP resources might be on a private domain that cannot be resolved through the public DNS system. If your VoIP TSP didn't provide a DNS address, you can leave this setting blank.

Figure 1-3. X-Lite's network configuration window

Click the Back button in the lower-left corner of the screen to get back to the prior window. Here, you'll need to double-click SIP Proxy to open the SIP Proxy Settings window. Double-click Default, and you'll be able to configure the softphone to use a SIP proxy server, which is located at your VoIP TSP and routes your softphone's calls. The X-Lite softphone can use more than one SIP proxy, but in most situations, you'll need to use only one. This list describes the settings you will need to configure:

Display Name

Your name, or as much of it as you can fit.

User Name

The SIP username provided by your TSP. This is likely to be your phone number, including the area code.

Authorization User

This is normally the same as the SIP username provided by your TSP, though some TSPs might issue a distinct authorization username. In circumstances where multiple phones with their own phone numbers are authorized for the same subscriber, the two usernames might vary.

Password

The password you and your TSP established when you set up your VoIP account.

Domain/Realm

This tends to be the domain name associated with your SIP user URI, which is similar to an email address. For [e-mail], your domain/realm would be sip.broadvoice.com. Your TSP will issue you an appropriate realm name if it supports the use of softphones.

SIP Proxy

This is the address of the proxy server that will handle all your VoIP registration activitythings like authentication and notifying the server that you're available to receive calls. Unlike a SIP URI, which always contains sip in the domain, the SIP proxy address can be any valid host-name. Again, your TSP will provide you the address to use when you sign up.

Outbound Proxy

This address is used to handle SIP requests that are bound for other SIP domains. Since most VoIP TSPs don't support calling other realms using SIP, and generally only support calls to and from the public telephone network, an outbound proxy isn't necessary. But BroadVoice, for one, requires that you configure an outbound proxy addressand in its case, it's the same address as that used for the SIP proxy setting.

Use Outbound Proxy

This setting tells X-Lite whether you want to treat all SIP requests as though they are destined for another realm. This effectively circumvents the SIP proxy for any activity other than registration, though if the two proxies have the same address, as in BroadVoice's configuration, it doesn't matter what this setting is set to. The choices are Always and Never, in case you were wondering.

Some TSPs have more than one SIP proxy, and they might allow you to choose among them. To determine which one to use, ping them all. The one with the least amount of variance from one ping packet to the next is the one you want.

Register

This setting tells X-Lite whether you want the SIP client to authenticate and register with the SIP proxy server. It's very uncommon not to register, and you won't get very far with your VoIP service if you don't. So definitely set this one to Always.

For most TSPs, you can leave the rest of the settings unchanged. For a more detailed description of X-Lite's settings, you can download a PDF user manual from CounterPath's web site, http://www.counterpath.com/.

1.6.3. Make the Call

When the X-Lite phone has successfully registered with the TSP's proxy, its main window will display a message like "Logged InEnter a Phone Number." Now, you should be able to type in a valid public telephone network number (try your cell phone for an easy test, if you have one). The service should function at least as well as it would via an ATA and analog phone, with one possible exceptionecho. Echo is common with softphones if you're using your PC speakers to listen to the person on the other end of the call. If you experience echo when you speak, use a pair of headphones to cancel the acoustic feedback loop.