VoIP Hacks: Tips & Tools for Internet Telephony

Hack 10. Pick a Desktop VoIP Client

There's no shortage of fantastic VoIP software for Windows, Mac, and Linux. But which one (or two) do you need?

VoIP applications tend, like email, to have a few servers facilitating interaction on behalf of many clients. In the case of email, those clients are applications like Microsoft Outlook, Eudora, and Apple Mail. But in Voice over IP, clients can be standalone devices, like IP phones and interface boxes (ATAs like those described in Chapter 1), or desktop applications like softphones or instant-messaging apps. The information in this hack will help you decide which VoIP client is right for you.

Some VoIP clients use well-known standards such as the Session Initiation Protocol (SIP) and are designed for use with your choice of VoIP service providers. Others are designed specifically to attach only to a certain service such as AOL Instant Messenger (AIM). Still others are built using open standards but are hard-wired to work with only certain services; Yahoo! Messenger uses SIP but works only with the Yahoo! service. That is, you can't use the VoIP features of Yahoo! Messenger with your own choice of VoIP service providers.

Some VoIP clients are quite functional "out of the box," such as Skype, which provides a user-friendly wizard to sign you up for Skype service and get you logged in. With others, such as X-Lite and GnoPhonewhich are designed for use with your choice of service providers, or even with your own VoIP serveryou really need to know what you're doing to get much use out of them. Since X-Lite and GnoPhone aren't officially sanctioned for use with a particular provider, you've got to know how to configure them yourself.

2.4.1. Meet H.323, SIP, and IAX

VoIP clients and servers use three common standards for signaling call events. (These events might be the beginning and end of a call, an attempt to join a voice conference, or looking up a phone number to discover the best way to reach a particular user on a VoIP network.) These three communication protocols are H.323, SIP, and IAX. Very rarely does a single client support more than one of these protocols (Firefly is an exception, and provides support for both SIP and IAX). Having a basic grasp of the different protocols will help you choose a VoIP client.

2.4.1.1. H.323: the earliest VoIP standard.

An H.323 client, such as Microsoft's Net-Meeting, really is good only in a corporate telephone system environment. It was once fashionable to use H.323 to have voice conversations with buddies over the Internet, but the rise of broadband firewall routerswhich break the H.323 signaling protocoland the growth of better protocols such as SIP led to a backslide in NetMeeting's popularity as a personal VoIP tool. Microsoft has since replaced much of the functionality of NetMeeting in its Windows Messenger IM software. So unless you need a softphone that works with your H.323-based PBX system (like an early-model Nortel PBX or Cisco media gateway), you're probably best served by foregoing H.323-based software.

2.4.1.2. SIP: the dominant VoIP standard.

SIP has become the dominant multimedia communication protocol, used by an overwhelming majority of VoIP service providers and professional phone system vendors. Aside from voice, you can use SIP components to signal video and instant-messaging conversations, too. I'll concentrate on SIP as it applies to voice, though.

There are two kinds of SIP VoIP clients: those that allow you to connect to a VoIP system of your choice and those that are programmed for use only with a certain provider. SIP-supporting VoIP client software includes products such as Yahoo! Messenger, Apple iChat, sipXphone, Firefly, GnoPhone, Gizmo Project, and lots of others.

2.4.1.3. IAX: a really cool VoIP protocol.

Inter-Asterisk Exchange protocol (or IAX, pronounced eex) is used by a growing number of VoIP client programs and service providers. The coolest thing about IAX is that it's firewall-proof. In situations where SIP and H.323 are rendered inoperable by NAT firewalls like your home broadband router, IAX shines. The only problem is finding a service provider with which to use IAX (visit http://www.teliax.com/ to learn about one that offers an IAX-based VoIP telephone service). IAXPhone and Firefly use IAX.

2.4.2. Understand VoIP Client Features

You ultimately will decide on a VoIP client based on features and compatibility. While one VoIP client might support the protocol you needsay, SIPit might not support the features you need. iChat and X-Lite are both SIP software, but you can't use iChat with your own VoIP server; you need X-Lite for that. (If you're reading this book from front to back, you might be wondering if I'm planning to show you how to build a VoIP server. For the record, I am, but not until Chapter 4.)

Then again, the protocol or innards of the software might make absolutely no difference to you (plenty of folks use Skype, which doesn't use a standard protocol at all). Table 2-1 is a matrix of VoIP client software and their features and compatibility.

As you work through the hacks in this and the following chapters, you'll become very comfortable with the differences and similarities of these programsand you'll have an even better feel for their strengths and weaknesses. A quick Google on any of these program names will get you to a place where you can download and install the program. And, speaking of Google, to get the most out of Google when using telephony, read "Google for Telephony Info" [Hack #21].