Posts categorized "SIP"

Join Me On VUC Today At Noon US EDT To Talk IPv6, IoT, WebRTC and more...

Today at 12 noon US Eastern (in about 3.5 hours), I'll be part of a panel on the VoIP Users Conference (VUC) talking about IPv6, WebRTC, the Internet of Things (IoT) and much, much more... you should be able to watch it live at or embedded here:

VUC host Randy Resnick had a scheduled guest be unable to attend and so he asked a group of us to come on for what he is calling a "VUC Vision" session. I will be on there, as will, I believe, Tim Panton and a number of others. I expect the discussion should range over good variety of topics. It should be a good time... you're welcome to join in the discussion.

It's probably best to also join the IRC backchannel where links are shared, questions are answered and other comments occur. You also can visit the Google+ event page for the VUC session today where there may be additional links and info.

If you won't be at your computer, you can also call in via:

  • sip:[email protected]
  • +1 (646) 475-2098

The session will of course be recorded so you can listen/watch later.

Vuc vision 20141003

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How Do We Define 'SIP' For Telecom In 2014?

Sip question"What is a minimum set of specifications that a vendor must implement to be able to say that it is SIP-compliant?"

A friend asked me that question and my response was:

It depends.

and even more unfortunately:

I don't know.

It turns out to be a challenging question to answer... and it led me to ask:

  • How do we define what "SIP" is for telecommunications in 2014?
  • How do we help vendors move their products/services to be based on SIP?
  • As we talk about "turning off the PSTN" and "moving all telecom to IP", how can we make it easier for companies to switch to using SIP?

The reality is that being "SIP-compliant" does turn out to depend upon where in the larger SIP interconnection ecosystem the vendor is located.

Is the vendor:

  1. a SIP client, in terms of a "hard" phone, a softphone, or other application that is seeking to connect to a SIP server?
  2. a SIP server seeking to connect to a SIP "service provider" to have connectivity out to the PSTN and other SIP networks?
  3. a SIP service provider seeking to interconnect with other SIP service providers and to the PSTN?
  4. a middlebox such as a firewall or session border controller (SBC) seeking to be in the middle of a SIP communication stream?
  5. an application that interacts with SIP systems in some way? (ex. call recording, IVR, networking monitoring)

To be "SIP-compliant" really means you need to figure out what amount of "SIP" you need to implement to play your part in the larger picture. Particularly when the SIP "architecture" we describe isn't the pretty little picture we use:

Sip architecture

but rather a much more complex reality:

Sip architecture reality

Unfortunately, the "Session Initiation Protocol" (SIP) is no longer just good old RFC 3261 and a few friends. RFC 3261 provided a radical new way to do telecommunications... it was "HTTP for voice"... it was simple, easy and pretty amazing. If you have a moment, go back and read RFC 3261. It's a remarkable document and set of ideas.

However, there were two factors that started to complicate "SIP":

  • the "Internet" community kept thinking of new and innovative ways that they could do more with SIP-based telecommunications; and
  • the traditional telecom companies/vendors kept wanting to bring across more and more legacy PSTN functionality into the world of SIP, typically without changing that PSTN functionality so that they wouldn't have to change their business models or processes.

This combination set SIP up to slowly become more and more of an accretion of various hacks and kludges designed to either enable SIP to unleash new possibilities and/or to take over key functionality from the PSTN.

But in doing so it became so much harder to define what "SIP" was.

Back around 2008/2009, Jonathan Rosenberg tried with his "Hitchiker's Guide to SIP" that was published as RFC 5411 in February 2009:

Now consider that this contained about 26 pages worth of documents to be referenced... and this was back in 2009! In the 5 years since, the "Realtime Applications and Infrastructure (RAI)" area of the IETF has been extremely busy and a similar document today would be be MUCH longer.

But does such a long list really help?

Going back to to my list of different roles within the SIP ecosystem, do we need more narrower lists for each role? A SIP client connecting to an IP-PBX may not need to implement all of the same specifications as a SIP service provider connecting to the PSTN.

What is the minimum set of SIP specifications for each role?

SIPconnect sipforumThe good news is that for the second role I mention, the SIP server to SIP service provider, the SIP Forum has done some outstanding work with their SIPconnect initiative. You can find more info at:

You can download the SIPconnect 1.1 technical specification and see the great amount of work they have done. The idea is that ultimately any "SIPconnect-compliant" IP-PBX or other SIP server can connect to any "SIPconnect-compliant" SIP service provider. It should "just work" with a minimum amount of testing. The goal is to allow the more rapid deployment of SIP-based IP-PBXs and making this part of the interconnection puzzle work that much better.

So if you are a vendor of a SIP server, whether you call it an IP-PBX, a call server, or whatever... or you are a SIP service provider seeking to connect to SIP servers at your customers - in either case you have SIPconnect that you can use to be "SIP-compliant".

But what about the other roles?

What if a vendor has multiple products?

What if a service provider or enterprise is just trying to get "SIP" products to work together? What should they specify beyond the vague statement that a product should support "SIP"?

Now, there are other organizations that have attempted to answer this question. The 3GPP has a list of SIP specifications and the GSMA seems to have similar documents. The ITU-T has many recommendations but since they rename everything it's hard to understand what really links back to SIP - and many of the ITU recommendations are only available to members and so you can't easily view them.

Which brings me back to these questions:

  • Do we need a new IETF document that aims to update RFC 5411 with a newer list and perhaps "profiles" of what would be needed for different roles?
  • Is this something the SIP Forum or some other organization should take on?
  • Has someone else already created a concise list/document/specification and I just haven't yet found it?

And perhaps the even larger question:

  • Do you believe this is an issue that we collectively should be working on as an industry to help make the deployment of SIP easier?

What do you think? How do we define SIP in 2014? What should we do? I'd love to hear your comments either in response to this post here on this blog or out on social media where this is posted. (Thanks!)

An audio commentary on this post is also available:

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SIPNOC 2014 Begins Today In Virginia - I am speaking about TLS and SIP (and DANE)

SIP Forum SIPNOC 2014 OverviewToday I'm back at the Hyatt Dulles in Herndon, Virginia, for the fourth SIP Network Operators Conference (SIPNOC) event. These SIPNOC sessions are great because they bring together the people actually operating the SIP-based networks that make up our telecommunications infrastructure. SIPNOC continues to be THE best place I've found to interact with the people actually taking SIP standards and making them happen in the "real world".

I've been to all four SIPNOCs - and I continue to find them outstanding events, not only because of the excellent technical content, but also because of the people.

In many cases, these are the "phone guys" (and gals) who have found their way to IP. The "Bellheads" of the age-old "Bellhead vs Nethead" debate. The "telcos". The people who have been doing telecom for decades... and are now evolving to IP.

In other cases, the people here are the new contenders. The cable companies are here - and they are strongly challenging the legacy telcos, and they are creating entirely new IP-based infrastructures. The "Internet Telephony Service Providers (ITSPs)" and "SIP Trunking" providers are here, too... companies that are reimagining what telecom can be in an IP space. Newer vendors... newer application providers... etc.

It's a wonderful mix of people.

All here talking about telecom in the age of the Internet... sponsored by the SIP Forum.

As I mentioned in a post yesterday on the Deploy360 blog, I will be speaking today at SIPNOC 2014 about TLS for SIP. The abstract for my talk is:

With concerns about large-scale pervasive monitoring on the Internet, many groups are encouraging the increased use of Transport Layer Security (TLS, what we used to call “SSL”). While SIP has had TLS support for quite some time, it is often not used. This session will look at concerns of using TLS with SIP and discuss opportunities for providing higher security for SIP-based communication. The session will also outline some newer innovations such as the DANE protocol that when coupled with DNSSEC can provide a higher level of trust for TLS encryption.

This relates largely to the "TLS for Applications" work we are doing within Deploy360, as well as our advocacy for the use of the DANE protocol to add a layer of trust to TLS/SSL certificates.

As I note in that Deploy360 post, I'm delighted to see on the SIPNOC agenda that speaking before me will be Carl Klatsky from Comcast providing a case study of the lessons they have learned so far in moving to IPv6!

It's kind of fun to scan my list of presentations and look back at what I've spoken about at the past SIPNOC events:

SIPNOC 2011 (employed at Voxeo)
1. SIP Adoption and Network Security
2. Lessons Learned in Large-Scale SIP Interoperability
SIPNOC 2012 (employed at Voxeo)
1. SIP and IPv6 – Can They Get Along?
2. Panel Discussion: SIP Adoption and Network Security
3. BOF: SIP and IPv6
SIPNOC 2013 (employed at Internet Society)
1.IPv6 And SIP – Myth or Reality?
2. Who are You Really Calling? How DNSSEC Can Help
3. Panel Discussion: Anatomy of a VoIP DMZ (moderator)
SIPNOC 2014 (employed at Internet Society)
1. Is It Time For TLS For SIP? (also includes some DNSSEC/DANE)

It's nice to have someone else talking about IPv6 this year!

Of course, you'll also find me in the VoIP security BOF tonight... and listening to the other sessions. Unfortunately I have something else happening tomorrow evening back in New Hampshire and so I'm only here at SIPNOC today and will be flying back tomorrow. The SIPNOC event continues all day tomorrow and half a day on Thursday.

Sessions are underway now... here is photo proof:

Sipnoc2014 start

Unless you happen to be located in the DC area, it would be very hard for anyone to join into this year's SIPNOC event... but if you work with SIP or VoIP networks, I would strongly encourage you to put SIPNOC 2015 on your calendar for next year!

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Can We Create A "Secure Caller ID" For VoIP? (Join Tomorrow's STIR BOF To Learn More)

Can we create a "secure Caller ID" for IP-based communications, a.k.a. voice-over-IP (VoIP)? And specifically for VoIP based on the Session Initiation Protocol (SIP)? Can we create a way to securely identify the origin of a call that can be used to combat robocalling, phishing and telephony denial-of-service (TDOS) attacks?

That is the challenge to be undertaken by the "Secure Telephone Identity Revisited (STIR)" group meeting tomorrow morning, July 30, 2013, at 9:00 am in Berlin, Germany, as part of the 87th meeting of the Internet Engineering Task Force (IETF). The meeting tomorrow is a "Birds Of a Feather (BOF)", which in IETF language is a meeting to determine whether there is sufficient interest to create a formal "working group" to take on a new body of work within the IETF. The proposed "charter" for this new work begins:

Over the last decade, a growing set of problems have resulted from the lack of security mechanisms for attesting the origins of real-time communications. As with email, the claimed source identity of a SIP request is not verified, and this permits unauthorized use of source identities as part of deceptive and coercive activities, such as robocalling (bulk unsolicited commercial communications), vishing (voicemail hacking, and impersonating banks) and swatting (impersonating callers to emergency services to stimulate unwarranted large scale law enforcement deployments). This working group will define a deployable mechanism that verifies the authorization of the calling party to use a particular telephone number.

The agenda for tomorrow's STIR meeting begins with a presentation by Henning Schulzrinne, now CTO of the US Federal Communications Commission (FCC) but also a long-time IETF participant and one of the co-authors of the original RFC 3261 specification for SIP. Henning will be laying out the problem statement and there will be a discussion of the proposed scope of the IETF work. He'll be followed by presentations of potential solutions by Jon Peterson, Eric Rescorla and Hadriel Kaplan and then a discussion of the proposed charter and the work to be done. Given the intense debate that has occurred on the STIR mailing list over the past weeks I expect tomorrow's session to be one where some points will receive a great amount of passionate debate and discussion. (If you are interested in listening in or participating remotely in tomorrow's STIR meeting, see the information later in this article.)

Revisiting Previous SIP Identity Work

As some background, the Internet Architecture Board (IAB) laid out some of the challenges to "secure origin identification" in IP-based communication last November and took a very high-level look at the overall issue. Next, in preparation for what became this STIR effort, Jon Peterson, Henning Schulzrinne and Hannes Tschofenig authored a draft problem statement and requirements document.

The "Revisited" part of the group name is a nod to the fact that this whole issue of asserting "identity" has been explored within the SIP community in the past. Way back in 2006, RFC 4474 defined what has been called "SIP Identity" and provided a method for cryptographically signing certain SIP headers to identify the origin of a call. Unfortunately, RFC 4474 turned out not to work well with the way SIP was actually deployed and so usage has been virtually non-existent. An effort to update that document, what is called "RFC4474bis", has also been proposed and some of those ideas may be incorporated into the new proposed work for the STIR group.

There have also been other efforts such as the "P-Asserted-Identity (P-A-I)" defined in RFC 3325. The challenge here, though is that theoretically P-A-I is supposed to be limited to usage within a trusted network, although in practice it may be seen by other networks. There have also been several efforts to define or document identifiers for billing purposes (including my own P-Charge-Info) although these efforts are trying to solve a slightly different problem.

The point here really is that the STIR effort is drawing upon a rich body of "SIP identity" work that dates all the way back to some early drafts in 2002. Much thought has been given to this issue and many of the people involved with STIR have also been involved with earlier efforts and understand well some of the challenges faced by that past work.

An Important Difference

One important difference between STIR and earlier "SIP identity" efforts is that initially the STIR effort is only focused on telephone numbers. The draft charter explicitly states this:

As its first work item, the working group will specify a SIP header-based authorization mechanism to verify the originator of a SIP session is authorized to use the claimed source telephone number, where the session is established with SIP end to end. This is called an in-band mechanism. The mechanism will use a canonical telephone number representation specified by the working group, including any mappings that might be needed between the SIP header fields and the canonical telephone number representation.

and later:

Expansion of the authorization mechanism to identities using the user@domain form deferred since the main focus of the working group is to develop a solution for telephone numbers.

Previous "identity" work was also undertaken to include a "SIP URI" or "SIP address" and while the ultimate STIR mechanism (or a variant thereof) might also work for SIP URIs, the focus in this initial work is all around securing the origin identification of telephone numbers.

This initial focus makes a great amount of sense given that so much of the SIP traffic today is a result of telecom service providers moving their regular calls to telephone numbers off of the legacy PSTN networks and over to IP networks where they use SIP. Additionally, a great amount of the "problem" traffic seen in VoIP today can be created by attackers who use simple VoIP software to generate their calls to regular telephone numbers.

Remotely Participating In Tomorrow's STIR BOF

If you are interested in participating in the meeting (or at least listening in) on Tuesday, July 30, the meeting will go from 9:00 - 11:30 local time in Berlin, Germany. Berlin is in Central European Summer Time (CEST) which is UTC+2 (and 3:00 am US EDT / midnight US PDT for my friends back in the USA).

You can hear the audio stream at:

You can also join the Jabber chat room at:

The slides and other meeting materials can be found at (and note that materials may not be uploaded until shortly before the session and so you may need to refresh your browser):

Alternatively you can use the "MeetEcho" conferencing system that integrates the audio, the slides and the Jabber chat room at:

More information about participately remotely can be found on the IETF 87 Remote Participation page.

To get the most out of the meeting, you'll also want to read these three Internet Drafts that will be part of the solutions being discussed:

.... and be prepared for what should be a LIVELY discussion!

If you are unable to participate remotely, the session will be recorded and you will be able to listen to the archived audio stream, view the Jabber chat logs and also playback the MeetEcho recording.

Getting More Involved

Beyond listening to tomorrow's BOF session, the best way to get involved - either to actively participate or to at least monitor the effort - is to join the STIR mailing list at:

The list is open to anyone to join. There are no membership or corporate requirements or fees - anyone with an email address may participate.

WARNING! - As can be seen in the list archive, there is currently a large volume of discussion and it will probably continue for some time. If you do join the mailing list you may want to consider setting up rules to sort the STIR email into a folder - or just prepare for the volume to be added to your inbox.

The other way to be involved is to monitor and read the documents that are created for the STIR effort. Newer documents are being created with "stir" in the document name and so they can be easily found at:

Other documents that are useful to understand this effort are linked to earlier in this article and can also be found in the text of the proposed STIR charter. After tomorrow's STIR BOF session there will be more information about how the effort will proceed within the IETF. The meeting tomorrow should result, I expect, in the recommendation to go ahead with formally creating a working group and undertaking this work, but we'll see what outcome occurs.

Can a method of secure origin identification for SIP-based VoIP calls be created? Given that basically all telecom traffic is in the process of moving to be based on IP, the need for a secure origin identifier is very clearly here - and many of us do believe we can develop a system that will work in today's environment.

What do you think? Are you ready to join in and help?

Update: Added the additional charter text about "Expansion of the authorization mechanism to identities..."

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At SIPNOC 2013 This Week Talking About VoIP And IPv6, DNSSEC ... and Security, Of Course

Sipnoc 2013 logoOne of the conferences I've found most interesting each year is the SIP Network Operators Conference (SIPNOC) produced by the SIP Forum, a nonprofit industry association. Part of my interest is that it is only an educational conference, i.e. there's no massive exhibit floor or anything... it's all about education. It also brings together pretty much all the major players in the "IP communications" space - certainly within North America but also from around the world.

I'll be there this week in Herndon, Virginia, talking about how VoIP can work over IPv6 and how DNSSEC can make VoIP more secure. The sessions I am directly involved with include:

  • Panel Discussion: Anatomy of a VoIP DMZ
  • VoIP Security BOF
  • Panel Discussion:  IPv6 and SIP - Myth or Reality?
  • Who Are You Really Calling? How DNSSEC Can Help

There are quite a range of other topics on the SIPNOC 2013 agenda, including a number of other talks related to security.  

It should be quite a good show and I'm very much looking forward to it.  I'm particularly looking forward to my "DNSSEC and VoIP" talk on Thursday as that is a topic I've not presented on before... but I think there is some quite valuable potential about using DNSSEC with VoIP.

If you are there at SIPNOC this week, please do say hello!

P.S. While SIPNOC is not being livestreamed, you may find some people tweeting using the hashtag #SIPNOC.

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VUC Today: The Jitsi VoIP Softphone - Join The Call To Learn More!

JitsiWhat is new with the Jitsi softphone these days? What new capabilities does it have as it continues to expand its support of SIP, XMPP and other protocols?

I've long been a fan and user of Jitsi, in part because it supports IPv6 and is the only VoIP softphone I know of right now that supports DNSSEC, something I'm continuing to experiment with, so I'm looking forward to today's "VoIP Users Conference (VUC) call at 12 noon US Eastern - about 2.5 hours from now.

You can watch it live via a Google+ Hangout On Air, or call in (potentially using Jitsi!) via:

  • sip:[email protected]
  • +1 (646) 475-2098

There's also an IRC backchannel where links are shared, questions are answered and other comments occur.

And for those of you using Google+, there is a Google+ Event you can join.

It should be a good show! (And yes, you can watch it / listen to it later...)

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Oracle Buys Acme Packet For $2 Billion To Gain SIP Session Border Controllers (SBCs) And More

AcmepacketFascinating news today out of Oracle that they have purchased Acme Packet in a transaction estimated to be around $2 billion US. For those of you not really tracking the VoIP security space, Acme Packet is probably the world's largest vendor of "session border controllers (SBCs)", devices that are used to securely and reliable interconnect VoIP networks. SBCs also provide a very important role in helping with interoperability of Session Initiation Protocol (SIP) signaling between the SIP products and networks of different vendors.

As Andy Abramson writes, the fascinating aspect of this acquisition is this:

This is an interesting grab by one of the tech world's true giants because it sqaurly puts Oracle into a game where they begin to compete with the giants of telecom, many of whom run Oracle software to drive things including SBC's, media gateways and firewall technology that's sold.

This acquisition does put Oracle VERY firmly into the telecom sector at a carrier / large enterprise level, as Acme Packet's products are widely used within that tier of companies. As the news release notes:

"The company's solutions are deployed by more than 1,900 service providers and enterprises globally, including 89 of world's top 100 communications companies."

Acme Packet has also long been recognized as a leader by analyst firms such as Gartner. People from Acme Packet, in particular Hadriel Kaplan, have also been extremely involved with industry efforts such as the SIP Forum and standards activity in the IETF.

As far as integration, Oracle already has a wide array of "communications" products, including several unified communications (UC) products that could potentially interact with Acme Packet products extremely well. Beyond all of that, though, this acquisition will have Oracle being a strong player in providing telecom infrastructure as we continue to collectively move to basing all our communications on top of IP.

Congratulations to my friends at Acme Packet and Oracle... and I wish them the best as they proceed down the path to completing this acquisition.

More information here:

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Next SIPit Test Event Feb 18-22 - Deadline of Feb 4 For Registration

SipitAre you a vendor of SIP-based products and services? Do you have software or hardware (or cloud-based products) that use SIP? If so, are you planning to attend the next SIPit test event planned for February 18-22, 2013, in Raleigh, North Carolina?

The SIPit events are an outstanding place to test your SIP implementations. Where else will you have so many other vendors also testing their equipment? It's a great place to go, test... and iterate your code even while you are there so that you can test again.

The registration deadline is Feb 4, 2013 for SIPit 30, so you need to act soon if you want to attend.

Olle Johansson posted a great set of slides about why you should go to SIPit:

And reaching back to 2009, here's a video interview I did with Robert Sparks about the SIPit test events:

If you are a vendor of SIP products or services, I would strongly encourage you to consider attending the next SIPit. It's a great way to make sure your SIP works as best as it can.

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Last Day To Submit Speaking Proposals for SIPNOC2013

Sipnoc 2013Got a great idea for a talk to give to an excellent gathering of SIP/VoIP network operators? Have a new way of handling security? Have a case study you'd like to present for how you solved an operational issue?

The SIP Network Operators Conference (SIPNOC) is an outstanding event happening in Herndon, Virginia, USA, from April 22-25. It brings together network operators working with SIP / VoIP networks for several days of talks, networking (of the human kind) and education. I've gone the past two years, speaking about IPv6, and they are truly excellent conferences. Not too big, not too small... and with an extremely high quality of people both attending and speaking.

If you think you'd like to present, TODAY, January 25, 2013, is the end of the call for presentations for SIPNOC 2013. They are seeking presentations on topics such as (see the CFP for more detail):

  • Peering
  • SIP Trunking
  • Congestion Control
  • Applications/content Development
  • Interoperability
  • Call Routing
  • Security
  • Monitoring/Troubleshoooting and Operational Issues
  • Testing Considerations and Tools
  • Availability/Disaster-Recovery
  • WebRTC and SIP
  • SIP-Network Operations Center Best Practices
  • Standardization Issues and Progress
  • FoIP/T.38 Deployment
  • User-Agent Configuration
  • IPv6 Deployment Challenges
  • Emergency Services
  • Scaling and Capacity Issues
  • HD-Voice Deployment Challenges
  • Video Interop Issues

They are seeking individual talks, panel sessions, research sessions and BOFs.

Even if you just have an idea for a session, I'd encourage you to submit a proposal so that the SIPNOC 2013 Program Committee will know of your interest and can reach out to you for more details. More info about the process can be found on the CFP page.

If you aren't interested in speaking, but are now intrigued by SIPNOC and would like to be learning from all the excellent sessions, you can go to the SIPNOC 2013 main page and find out information about how to register and attend.

If you work at or for a telecom/network operator who is involved with SIP and VoIP, I highly recommend SIPNOC as a conference you should attend - you'll learn a huge amount and make great connections.

P.S. I have no affiliation with SIPNOC other than being a speaker there in the past. SIPNOC is a production of the SIP Forum, a great group of people focused on advancing the deployment and interoperability of communications products and services based on SIP.

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The Fascinating Interest in Using Google Voice With SIP Addresses

Why are so many people interested in using Google Voice with SIP? Is this a sign that people really want to use SIP-based services for VoIP? Is this all hobbyists or people looking to play around with Google Voice? Or is it people trying to solve real interconnection issues? What are people trying to do with Google Voice and SIP?

All these questions came to my mind today when I dipped into Google Analytics and noticed that for the month to date in November 2012, my old (March 2011) post about Google Voice and SIP addresses continues to receive a large amount of traffic:

Ga googlevoiceandsip

Slightly over 3,000 pageviews in the first 13 days of November - and if I go back a bit I see over 71,000 pageviews since January 1, 2012. In fact, it's had about 232K pageviews since I wrote it over 1.5 years ago, and has accounted for almost 25% of all traffic to this site in that time.

And this particular article was just one in a series of articles I wound up writing about Google Voice and SIP as we all collectively tried to figure out what was going on.

Digging into the traffic sources to the page, almost all of it this month comes (somewhat predictably) from search. The search terms, at least the ones we can see (since Google now shows "Not Provided" for all searches done over SSL), show a range of interest in SIP:

Ga googlevoiceandsip search

And all of this for a service from Google Voice which seemed to be a temporary service and subsequently stopped working... kinda, sorta... and then did work... and then didn't work. (And I just checked... and it doesn't work for me right now.)

I find all this interest fascinating. I hope it's a good sign that people out there do want to see more usage of SIP addresses.

And I do hope that at some point Google will open up the connection again and let us connect in to Google Voice numbers using SIP URIs. It would be a great move.

Meanwhile, I'll continue to be fascinating by all the traffic still coming to those old articles...

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