ITEXPO begins in:   New Coverage :  Asterisk  |  Fax Software  |  SIP Phones  |  Small Cells
May 2006
Volume 1 / Number 3


Henning Schulzrinne was a member of technical staff at AT&T Bell Laboratories, Murray Hill and an associate department head at GMD-Fokus (Berlin) before joining the Computer Science and Electrical Engineering departments at Columbia University, New York. His research interests encompass real-time, multimedia network services in the Internet and modeling and performance evaluation. Protocols co-developed by him — including SIP — are now Internet standards, used by almost all Internet telephony and multimedia applications. His research interests include Internet multimedia systems, quality of service, and performance evaluation.

I had the chance to ask Professor Schulzrinne a few questions on the matter of SIP’s role in enterprise communications.

GG: Recent news announcements from some of the leading companies in the Enterprise IP Communications space have all been focused on support for SIP. Cisco, Avaya, Sphere, IBM, 3Com, and Microsoft have all been making headlines with their SIP initiatives.

Why the recent focus on SIP for enterprise applications?

HS: I suspect that there are probably several reasons, such as enterprise managers having been burned before by proprietary systems. However, in this particular case, one reason is that many vendors seem to specialize into each of the core components of an enterprise IP communications systems, such as Ethernet phones, proxy servers, PSTN gateways and border devices, such as VoIP-enabled firewalls. Even many companies that offer products across this spectrum may not offer the precise equipment that a particular company needs, such as conference room-quality speaker phones or 802.11 phones. For example, we recently rolled out a SIP-based system for the Department of Computer Science at Columbia, which includes two brands of desk phones, a software infrastructure from one major vendor, a soft phone made by a small company, and ATA devices for fax machines made by yet another specialized vendor.

GG: What benefits does SIP offer the enterprise?

HS: There are probably two core benefits, namely having a standards-based technology and using a mature technology that has been widely tested. A standards-based technology makes it far easier to evolve a system, without having to do forklift upgrades every few years. In the past, it has been fairly common that upgrades were postponed as long as possible as such an upgrade would be extremely disruptive and might have involved replacing hundreds or thousands of hardware devices, along with the central infrastructure and maybe even the wiring. Now, it should be possible to slowly evolve the infrastructure as needs evolve and functions get added. For example, as managers get their late-model IP phones with color screens, older phones can then migrate down to users having more modest needs (or that simply rank lower on the organizational totem pole).

Having a standards-based technology also makes scaling much easier, e.g., when two organizations are merging. The technology itself is now fairly mature; unlike many proprietary systems, issues such as scaling and security have been addressed, even if they are not always implemented yet. Longer term, currently only SIP offers an integrated vision of communications that includes not only voice and video, but also instant messaging, presence, and advanced services.

GG: What’s your take on SIP Trunking?

HS: SIP trunking avoids the need to run PSTN gateways locally to make any outside calls, so this is clearly a step in the right direction of an all-IP, end-to-end SIP infrastructure. Ideally, SIP trunking should not require any new protocol mechanisms or infrastructure, just the inbound and outbound delivery of calls destined for calls to the outside. Longer term, the combination of ENUM or URL-based routing will reduce the need for the explicit notion of trunks. After all, we don’t use e-mail trunking to send messages from one company to another.

The market for SIP trunking services seems to be fairly young, particularly for smaller to mid-size enterprises, as service providers appear to be more interested in selling IP Centrex hosted services rather than just gateway services. Besides the possibly lower per-minute costs, the ability to have more burst capacity seems very attractive. For example, in my department, we have a PRI, for about 200 users, which is usually more than enough capacity. However, we’d like to be able to host larger teleconferences, without jeopardizing the ability of others in the department to make and receive calls. We have plenty of IP bandwidth, hundreds of Mb/s for the campus, but cannot justify buying an additional PRI for the occasional use it would get.


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