Andrew Prokop
Andrew Prokop has been heavily involved in the world of communications since the early 1980s. He holds five United States...
Read Full Bio >>

Andrew Prokop | August 24, 2015 |


Taking SIP Beyond Dial Tone

Taking SIP Beyond Dial Tone I have a question for all you No Jitter readers: What is SIP used for?

I have a question for all you No Jitter readers: What is SIP used for?

If you are like most people in the communications industry, you will tell me that SIP is used to make telephone calls. Some of you might also mention point-to-point or multiparty video, but in general, most people think of SIP as a way to make some sort of call -- SIP for physical, soft, and mobile telephones and telephone-like devices.

While these are certainly valid uses of SIP, the notion of making calls only scratches the surface of what it can do. I often wonder how different our impressions would be if the inventors of SIP had chosen to pioneer a different use case. Would we still think of it as a replacement for TDM telephony if the first SIP-enabled devices had been electrocardiogram monitors?

If you have been following my articles, you may have picked up that for many years I was a software developer working on SIP endpoints and backend services. During that time, I wrote thousands of lines of Java and C++ code that established and managed SIP calls. However, I also wrote just as many lines that had nothing to do with calling.

For instance, I once worked on a project that used SIP to create a shared whiteboard/drawing space. Think of extending the Microsoft Paint program across the Internet; two people could play with the same drawing canvas at the same time. SIP was used to send commands and graphics coordinates to draw lines, curves, points, and write text.

Around the same time, I did something similar for a network chess program. This application used SIP to convey chess moves from one PC to another across a LAN or WAN.

One of my more interesting creations was a method to pass clipboard data between different PCs. A user was able to do a copy (Ctrl+C) on one PC, and another user could paste (Ctrl+V) that data on a different PC. How did that data get from one machine to the other? With SIP, of course.

The point is that SIP can be used for things far beyond dial tone. While it's certainly true that telephony is currently the largest user of SIP, there may come a day when voice traffic has been dwarfed by other forms of media.

Peeling Back the Onion

I divide the major uses of SIP into three different camps. First, there are the session management aspects. These involve creating SIP sessions in order to pass data between endpoints. My chess game is an example of this. A SIP INVITE message is used to establish a session between two players. Contained within that INVITE is Session Description Protocol (SDP) information that defines the IP address, port, and protocol used to transmit chess moves and control signals. The game ends with a SIP BYE message. These are the same messages you would use for any voice or video session.

I also lump instant messaging into this form of communication, but instead of an INVITE request, SIP employs the MESSAGE request. Within the body of a MESSAGE request is the IM text. However, unlike the previous form of conversations, no session is established, yet data is passed between two users.

The next big class of SIP applications do not rely on INVITE or MESSAGE requests. Here, SIP SUBCRIBE, PUBLISH, and NOTIFY requests are used to create a client/server relationship between different entities. This bond informs the server of who is interested in something and notifies the client when that something has changed. For example, a SIP telephone subscribes to the voice mail status of its registered user. When a new voice mail arrives for the user, the SIP client is notified and the device can display informative text, or in the case of an old school SIP telephone, illuminate a red light.

SIP subscriptions are amazingly powerful and allow you to go well beyond dial tone and media streams. I've seen SIP used to subscribe to a user's class-of-service options. This allowed an administrator to set permissions and capabilities for a user (e.g. this user has the ability to create six-party conference calls) and have that user's end point visually display the change (e.g. un-gray the conference button on a soft phone). Users can also subscribe to address books to be informed of new entries. A SIP-based alarm system might notify first responders that an emergency condition has gone into effect.

You are undoubtedly familiar with the most popular use of subscriptions. Those presence jellybeans on your Lync or Skype for Business client turn different colors based upon SIP SUBSCRIBE and NOTIFY messages.

How about using SIP to remote control your house? As far-fetched as that might sound, someone created a design to do just that. If you want to see just how far you can move SIP away from telephone calls, take a look at this proposal. A quick glance through the document will show you clever uses of MESSAGE, SUBSCRIBE, and NOTIFY.

I've done extensive work with Avaya SIP telephones and discovered that they use different subscriptions to enable traditional PBX functionality not currently defined within SIP. Lamps are lit, features enabled, and soft key labels are changed because of NOTIFY messages. A typical Avaya SIP telephone subscribes to at least five different events. A contact center telephone adds yet another subscription for agent-specific activities. If you were to trace the packets in and out of busy Avaya Session Manager, you might see as many NOTIFY messages as you see INVITE requests.

My third and final class of SIP-enabled applications use the INFO message. INFO is used to carry application level information along a SIP signaling path. For example, some older SIP telephones use INFO to send DTMF digits. INFO is also used to carry mid-call signaling messages between PSTN gateways.

The biggest user of INFO may be a SIP offshoot protocol called TR-87. TR-87 enables first- and third-party call control of SIP entities. Back in the day, I used TR-87 between a Microsoft Office Communications Server (OCS) and a Nortel CS1000. The OCS client sent INFO messages to instruct the Nortel IP telephone to make a call and the Nortel system used INFO messages to tell the OCS client that the call had been placed. These back-and-forth command and status messages implemented what was referred to as Remote Call Control (RCC).

TR-87 was still available in Microsoft Lync 2013, but the story is more complicated with Skype for Business. From the Microsoft website:

Remote call control was a feature in previous versions of Lync Server which enabled users to control their PBX phones with their Lync. In Skype for Business Server, this feature has been replaced with Call Via Work.

Remote call control users in your organization who are homed on Front End Servers running Lync Server can continue to use remote call control, even if they are using a Skype for Business client. However, for any users homed on Skype for Business Server, remote call control is not supported.

Mischief Managed

I hope this helps you see that the power and reach of SIP extends past that of simple telephone calls. Transformational technologies are constantly evolving, and I expect SIP to do the same. There are old problems that still need to be tackled and new challenges that must be met. SIP won't be the answer to everything, but it will continue to play a big part in the world of real-time, unified communications.

Andrew Prokop writes about all things unified communications on his popular blog, SIP Adventures.

Follow Andrew Prokop on Twitter and LinkedIn!
Andrew Prokop on LinkedIn


June 20, 2018

Your enterprise may have adopted SIP Trunks, but are you up to date on how the latest technology is driving evolution in approaches?

In this webinar, youll learn how the new generation of SI

June 6, 2018

The two largest strategic vendors-Cisco and Microsoft-have been busy making changes to their enterprise communications roadmaps, incorporating collaboration applications as fundamental components.

May 23, 2018

If Cisco is a critical strategic supplier for you, then its vital for you to understand the most recent announcements around Webex Teams, and how to build your migration path for the next generatio

March 12, 2018
An effective E-911 implementation doesn't just happen; it takes a solid strategy. Tune in for tips from IT expert Irwin Lazar, of Nemertes Research.
March 9, 2018
IT consultant Steve Leaden lays out the whys and how-tos of getting the green light for your convergence strategy.
March 7, 2018
In advance of his speech tech tutorial at EC18, communications analyst Jon Arnold explores what voice means in a post-PBX world.
February 28, 2018
Voice engagement isn't about a simple phone call any longer, but rather a conversational experience that crosses from one channel to the next, as Daniel Hong, a VP and research director with Forrester....
February 16, 2018
What trends and technologies should you be up on for your contact center? Sheila McGee-Smith, Contact Center & Customer Experience track chair for Enterprise Connect 2018, gives us the lowdown.
February 9, 2018
Melanie Turek, VP of connected work research at Frost & Sullivan, walks us through key components -- and sticking points -- of customer-oriented digital transformation projects.
February 2, 2018
UC consultant Marty Parker has crunched lots of numbers evaluating UC options; tune in for what he's learned and tips for your own analysis.
January 26, 2018
Don't miss out on the fun! Organizer Alan Quayle shares details of his pre-Enterprise Connect hackathon, TADHack-mini '18, showcasing programmable communications.
December 20, 2017
Kevin Kieller, partner with enableUC, provides advice on how to move forward with your Skype for Business and Teams deployments.
December 20, 2017
Zeus Kerravala, principal analyst with ZK Research, shares his perspective on artificial intelligence and the future of team collaboration.
December 20, 2017
Delanda Coleman, Microsoft senior marketing manager, explains the Teams vision and shares use case examples.
November 30, 2017
With a ruling on the FCC's proposed order to dismantle the Open Internet Order expected this month, communications technology attorney Martha Buyer walks us through what's at stake.
October 23, 2017
Wondering which Office 365 collaboration tool to use when? Get quick pointers from CBT Nuggets instructor Simona Millham.
September 22, 2017
In this podcast, we explore the future of work with Robert Brown, AVP of the Cognizant Center for the Future of Work, who helps us answer the question, "What do we do when machines do everything?"
September 8, 2017
Greg Collins, a technology analyst and strategist with Exact Ventures, delivers a status report on 5G implementation plans and tells enterprises why they shouldn't wait to move ahead on potential use ....
August 25, 2017
Find out what business considerations are driving the SIP trunking market today, and learn a bit about how satisfied enterprises are with their providers. We talk with John Malone, president of The Ea....
August 16, 2017
World Vision U.S. is finding lots of goodness in RingCentral's cloud communications service, but as Randy Boyd, infrastructure architect at the global humanitarian nonprofit, tells us, he and his team....
August 11, 2017
Alicia Gee, director of unified communications at Sutter Physician Services, oversees the technical team supporting a 1,000-agent contact center running on Genesys PureConnect. She catches us up on th....
August 4, 2017
Andrew Prokop, communications evangelist with Arrow Systems Integration, has lately been working on integrating enterprise communications into Internet of Things ecosystems. He shares examples and off....
July 27, 2017
Industry watcher Elka Popova, a Frost & Sullivan program director, shares her perspective on this acquisition, discussing Mitel's market positioning, why the move makes sense, and more.
July 14, 2017
Lantre Barr, founder and CEO of Blacc Spot Media, urges any enterprise that's been on the fence about integrating real-time communications into business workflows to jump off and get started. Tune and....
June 28, 2017
Communications expert Tsahi Levent-Levi, author of the popular blog, keeps a running tally and comprehensive overview of communications platform-as-a-service offerings in his "Choosing a W....
June 9, 2017
If you think telecom expense management applies to nothing more than business phone lines, think again. Hyoun Park, founder and principal investigator with technology advisory Amalgam Insights, tells ....
June 2, 2017
Enterprises strategizing on mobility today, including for internal collaboration, don't have the luxury of learning as they go. Tony Rizzo, enterprise mobility specialist with Blue Hill Research, expl....
May 24, 2017
Mark Winther, head of IDC's global telecom consulting practice, gives us his take on how CPaaS providers evolve beyond the basic building blocks and address maturing enterprise needs.
May 18, 2017
Diane Myers, senior research director at IHS Markit, walks us through her 2017 UC-as-a-service report... and shares what might be to come in 2018.
April 28, 2017
Change isn't easy, but it is necessary. Tune in for advice and perspective from Zeus Kerravala, co-author of a "Digital Transformation for Dummies" special edition.
April 20, 2017
Robin Gareiss, president of Nemertes Research, shares insight gleaned from the firm's 12th annual UCC Total Cost of Operations study.
March 23, 2017
Tim Banting, of Current Analysis, gives us a peek into what the next three years will bring in advance of his Enterprise Connect session exploring the question: Will there be a new model for enterpris....
March 15, 2017
Andrew Prokop, communications evangelist with Arrow Systems Integration, discusses the evolving role of the all-important session border controller.
March 9, 2017
Organizer Alan Quayle gives us the lowdown on programmable communications and all you need to know about participating in this pre-Enterprise Connect hackathon.
March 3, 2017
From protecting against new vulnerabilities to keeping security assessments up to date, security consultant Mark Collier shares tips on how best to protect your UC systems.
February 24, 2017
UC analyst Blair Pleasant sorts through the myriad cloud architectural models underlying UCaaS and CCaaS offerings, and explains why knowing the differences matter.
February 17, 2017
From the most basics of basics to the hidden gotchas, UC consultant Melissa Swartz helps demystify the complex world of SIP trunking.
February 7, 2017
UC&C consultant Kevin Kieller, a partner at enableUC, shares pointers for making the right architectural choices for your Skype for Business deployment.
February 1, 2017
Elka Popova, a Frost & Sullivan program director, shares a status report on the UCaaS market today and offers her perspective on what large enterprises need before committing to UC in the cloud.
January 26, 2017
Andrew Davis, co-founder of Wainhouse Research and chair of the Video track at Enterprise Connect 2017, sorts through the myriad cloud video service options and shares how to tell if your choice is en....
January 23, 2017
Sheila McGee-Smith, Contact Center/Customer Experience track chair for Enterprise Connect 2017, tells us what we need to know about the role cloud software is playing in contact centers today.