Convergence /

IP-based soft phones

Users gain control of many telephony features, but overall voice-quality still lags.

By Betsy Yocom, Cheryl Molle, Marc Frigo and Michael Hommer
Network World, 02/25/02

Soft phones - client-side software that turns a desktop PC into an IP-based phone - are easy to install and use; offer effective integration with popular applications, such as Microsoft Outlook and Lotus Notes; and give users latitude in how and when they receive and answer their calls. But according to our tests, the downside of these products is that overall voice quality doesn't match that of regular telephones.

We tested seven soft phone products: five PBX-based soft phones from Alcatel, Avaya (two products), Mitel and Siemens, and two server-based IP PBXs from Cisco and Swyx Communications. PBX-based systems are traditional time division multiplexed/digital PBXs that have been retrofitted to support IP telephony, while server-based systems support IP end to end.

This review assessed soft phones from the user's perspective. That is, how does the end user interact with the phone; what benefits does it offer the user; and how does the user perceive voice quality. For this reason, we did not assess management, which is a function of the underlying PBX. Also, our installation and ease-of-use ratings pertain only to the soft phone, not the underlying platform on which it operates.

Alcatel e-ND's 4980 Soft Phone was clearly a cut above the others, earning our World Class Award. In the features realm, this product supported 37 of the 41 features we deemed necessary for use in a corporate setting. Alcatel's product also topped the ticket in terms of installation, ease of use and configuration.

How we did it
NetResults (chart)
List of test-bed equipment used in the tests
View the IP phone interfaces

Both of Avaya's products - the Definity G3 SI Soft Phone and the IP600 Soft Phone - had strong showings in the features category, offering the largest set of basic telephony features including call hold, call forwarding and call waiting. The Definity is targeted to a high-end customer, the IP600 to smaller networks or branch offices. Otherwise, they offer identical features and functionality.

Swyx, a German company, came in with its SwyxIt soft phone, which offered an innovative features set including many options for customizing the user interface, setting ring tones and integrating with applications such as Microsoft Outlook.

Focus on features

All the products were rich with features including tight integration with popular applications; many adjustable options for the screen; and options that let "road warriors" adapt their soft phones to achieve better services.

We asked the vendors to prove support of 41 telephony features, including call forwarding, automatic callback, call conferencing, instant messaging and directory support, that our research shows are critical in corporate environments.

Assessing features on soft phones presented some challenges because some - such as call retrieval and a call-duration (timer) feature - were supported on the PBX with which a soft phone worked, but not readily accessible through the soft phone itself. Other features, such as voice mail and intercom capabilities, were supported only on external phone calls or on separate servers that weren't available for testing.

Avaya's IP600 and Definity Soft Phones and Swyx's SwyxIt offered an array of telephony features, but Alcatel's 4980 soft phone offered the most. Among the least-supported telephony features were intercom (only Alcatel and Mitel supported it); instant messaging; the ability to create multiple user profiles; time-of-day routing (supported only by Cisco and Swyx); the ability to record announcements, and unified messaging; or an equivalent service.

PBX-based soft phone vendors realize that to obtain widespread customer acceptance in the workplace, the full complement of available PBX features must be accessible on the soft phone. For example, Avaya lets IP600 and Definity Soft Phone users access its 450-plus telephony features via access codes. Alcatel's 4980 soft phone supports 16 programmable feature keys. We programmed some features and found the process to be straightforward.

In terms of other distinguishing features, Alcatel's Nomadic Mode lets a user toggle between a soft phone and regular telephone. Users experiencing poor voice quality via dial-up links on their laptops can switch over to any phone and still maintain the functionality of the soft phone, including placing calls, conferencing and transfers.

Avaya's telecommuter configuration lets a user be on a soft phone connection and a public switched telephone network connection to a circuit-switched phone simultaneously. The IP600 or Definity establishes the voice connection to a circuit-switched telephone, while a TCP/IP connection is maintained for signaling control.

While Cisco's CallManager supported the fewest telephony features, it supported some noteworthy add-on options. Most impressive was the Cisco Personal Assistant - an additional server that lets users access personal call-routing features, such as time-of-day and location routing, via a Web page. This is a big deal because an end user can set a personalized way to handle calls without administrative help. That's central to what soft phones offer in a corporate network: more options for user customization without an administrator's assistance.

Swyx's Call Routing Manager lets a user record additional greetings and ring tones and choose how calls should be answered. Another option, Swyx's Graphical Script Editor, is a Visio-type application that lets users set up hunt groups - predefined groups of extensions to which calls are automatically diverted if the original destination is busy - or specialized features on the screen.

Siemens' optiClient 360, Mitel's 5822, SwyxIt and the Alcatel 4980 soft phones supported tight integration with Outlook, letting users answer and place calls directly through the Outlook directory. Alcatel's 4980 and the SwyxIt soft phones also supported excellent integration with Microsoft NetMeeting.

Performance issues

Voice-quality ratings were acceptable on all products under all conditions tested with none of the ratings falling below 3.5 (out of five with a 3.0 being the lowest rate acceptable on Miercom's interactive rating scale). Our testing did point out some latency deficiencies that affected overall voice quality, including voice clipping and echoes.

Latency measurements ranged from a low of 60 msec on the Avaya IP600 phone (tested with a G.711 voice coder [vocoder]) to a high of 317 msec also on the IP600, when tested using G.729 vocoding. Only Alcatel, Avaya and Cisco supported G.729 vocoders; only Alcatel and Siemens supported G.723 vocoder.

A vocoder converts an analog speech signal into a binary, digital stream for transmission over the IP link, and vice versa. A G.711 vocoder uses 64K bit/sec of bandwidth per direction (not including IP or packet overhead). G.729 and G.723 vocoders use less bandwidth (8K and 5.3K or 6.3K bit/sec, respectively.) Lower bandwidth vocoders tend to have higher latencies so there's a trade-off to using them. Latency measurements using both were higher than G.711 latencies overall.

In our experience, voice quality begins to degrade noticeably at a latency of 100 msec and beyond. At about 150-msec latency, we heard "gaps" in the voice stream and clipping of words. As the latency increased, gaps got much worse, rendering the speech unintelligible.

Although the Avaya IP600 and Definity are identical products, they did not achieve identical scores for performance. While the IP600 rated a 3.5 (based on G.711 vocoding) and 3.7 (based on G.729 vocoding), the Definity scored 4.0 on both tests.The Definity was tested with a new software release, which Avaya believes accounts for the differences in voice quality.

We tested two soft phones from each vendor - one loaded on a laptop PC, the other on a desktop machine (see "How we did it"). Latency measurements on laptop-to-desktop links were considerably lower - almost half - than on the desktop-to-laptop link. For example, latency on the Alcatel 4980 soft phone was 92.67 msec when tested on the laptop-to- desktop PC link (using G.711 vocoding), but 244 msec when tested on the reverse-from desktop to laptop (with G.711 vocoding). Changing vocoders (to G.723 and then to G.729) didn't improve the situation.

The desktop PCs decoded information more quickly than the laptop machines even though both supported 1-GHz processors and 256K of RAM and were running the same Windows 2000 release. Differences in laptop circuitry played some role in the latency differences.

Stability was also an issue on some products. The Siemens optiClient 360 sometimes lost IP connectivity, and also experienced some lockups that required closing the program and rebooting.

The SwyxIt soft phone also was unstable at times. While we installed a Universal Serial Bus headset or handset and then returned to the soft phone that was already opened, the phone locked up and required complete reboot.

Easy to use and customize

Our analysis of installation was limited to setting up the soft phone on the client PCs and did not address setting up the PBX or server with which the soft phone operates. Likewise, we did not include a management rating because it is a function of the PBX or server on which the soft phone resides, rather than the soft phone.

With one exception, all the soft phones were installed and operational in less than 5 minutes. With minimal perusal of help files and "quick start" references that came with most products, we quickly accessed basic features. On a scale of 10, with 10 being most difficult, the technical expertise required to install the soft phones was a 2.

Cisco received high marks for its Web-based installation, which requires no CDs or loading components. The administrator sets up the soft phone, saves it to a configuration file, loads it on the CallManager and sends the URL to the user, who downloads the soft phone configuration to the PC. Administrators can also use a tool for bulk creation of extensions and user names, which are available directly from a URL.

The Siemens optiClient 360 installation proved the most arduous because it required installation of three components: optiClient 350 (used for base-level connection to the H.323 gatekeeper) and optiClient 360 software, both installed on a file or applications server; and the optiClient software installed on the local PC.

What's more, after the soft phone component is installed locally, access to the server-based resources required to run it must be mapped manually on the local PC. Siemens says end users typically wouldn't be involved in installing the first two components, but mapping components on the local machine is time-consuming nonetheless.

The Mitel 5822 earned points for a graphical user interface identical to a Mitel hard phone, thus facilitating the learning curve for end users. It also supports several languages. But configuring buttons and speed dial settings was cumbersome. Particularly annoying was that it didn't automatically label speed dial and features buttons after reprogramming them.

All of the soft phones offered extensive support for customizing the user interface (view all user interfaces).

The SwyxIt was a standout in this area, offering more than 27 "skins" to change the soft phone's appearance and 23 different ring tones. Siemens' "floating toolbar," which appears in Outlook, gives users access to the Outlook address book to place and accept calls.

For configuration, Alcatel earned its high rating chiefly for its flexible user interface. The 4980 icon could be docked, hidden, always in view on the screen, an icon on the system tray, or a "normal" view of the phone on the screen. The user had options to customize buttons, change fonts and colors, and use multiple languages.

Siemens took a unique approach to its soft phone interface, opting for a "communications circle" rather than a view that resembled a phone. Users can drag-and-drop a speed-dial button directly into the circle to instantaneously start a call. The circle also displays different types of borders, depending upon which features are enabled and the state of calls in progress. Reviews were mixed on this approach; one lab tester found this interface the easiest to use, while others thought it was so different that it might put users off.

While Cisco gained points because of its view on the screen is identical to the Cisco IP phone, it consumed a lot of screen real estate. The user could collapse it down to get smaller views. For example, the handset could be removed, leaving only the keypad. But this approach wasn't as convenient as those offered by Alcatel and Swyx in which the "phone" could be "hidden" from view until needed.

In addition to inferior voice quality compared with regular phones, another impediment to widespread use of soft phones in the short term is the learning curve that must occur as users move from regular to PC-based phones. Another downside is the possibility that end users could be overwhelmed with all the available options. While it's fun to set up unusual ring tones (such as bongs, screeches and animal noises) and change "skins" to alter the look and feel of the user interface, it's sometimes difficult to figure out what to use among the many available options.

In the final analysis, it's the integration with popular business applications (Outlook, Lotus Notes and others) and network features that allow streamlining and integration of communications functions that will make soft phones attractive to enterprise users.