Lunch & Learn: Digital Telephony at Princeton

Voice over Internet Protocol, how it works

Voice over Internet Protocol, how it works (Photo credit: Wikipedia)

Voice over Internet Protocol (VoIP) refers to a family of hardware and software technologies that deliver voice communications over the internet rather than the public, switched telephone network. To make it work, technologists have to convert traditional analog signals into a digital format and then translate that signal into IP packets for transmission over a private or public network.

At the October 28 Lunch ‘n Learn, Dave Wirth, Manager of Operations within the Office of Information Technology’s (OIT) Networking/Telephony group, reviewed the technology, its present implementation at Princeton, and the University’s plans for the future.


VoIP systems have actually been in use at Princeton, mostly by members of OIT’s staff, for seven years. The experimental equipment, primarily technologies that interfaced with our existing telephone switch, permitted us to learn a great deal, says Wirth, but as we upgrade our current switch, all of that equipment is now being replaced. The new VoIP trial will be taking place at 701 Carnegie Center, the new home for OIT on Canal Point Road.
There are many myths about VoIP, emphasizes Wirth. Such services are not totally free, VoIP lines cannot survive electrical blackouts, and dial-up Internet connectivity will not generally provide satisfactory quality.
Princeton is relying on an advanced yet simpler VoIP interface, SIP (Session Initiated Protocol). Says Wirth, SIP is modular and scalable, easier to design and update, and internet friendly. From the users’ perspective, one of the most attractive benefits of SIP is the ability to make a call based on an e-mail or IM address rather than always needing a telephone number.
There are advantages to tradition telephony. The conventional handsets are less expensive, and our present telephone systems are remarkably reliable; by contrast VoIP systems rely on hardware platforms that have not benefitted from the years of experience
of the telephone companies. We will now have to worry about echoes, latency, and jitters. As a result, alarms and 911 calls may continue to rely on traditional copper circuits for quite some time.
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With old systems, you call a number. With new systems, you call a person. Philosophically, that’s a big difference, emphasizes Wirth. IP systems will offer more attractive pricing, far more features, and for most users better and richer ways of communicating. With VoIP, you can purchase phones from a wide variety of vendors, and you can combine voice, data, and images on the same network. The result over time will be a range of interesting and compelling applications for personal and departmental communication and collaboration.

Primarily to ensure the best voice quality and for security reasons, the possibility of viruses and denial of service attacks, Princeton has chosen to keep its data and VoIP networks separate. In addition to being able to test various new applications for eventual use on campus, the VoIP system will permit staff in the new building to retain their 258 campus extensions.

So what’s in it for users? There are intriguing benefits, including conferencing, call forwarding, and auto redial features that normally cost more money. Among the new features, there are distinctive ring tones, and everyone will have a display in their phone to view CallerID and to view a phone log of recent calls that supports Click-to-Call, the ability to click on a name or number and connect. Among other features, staff will gain the ability to set up ad hoc conferences and to set up global and personal directories.

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When will these benefits extend to the rest of campus? The infrastructure is demanding and so, new construction like the Chemistry building will be the first to benefit, says Wirth. The rest of us, unfortunately, will have to wait.
A podcast and the presentation are available.

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