Untethering the User from the Device with SIP

Those of you (like me) of “a certain age” might remember that your first work telephone was probably an analog 2500 set.

It was fine for making and receiving calls, but that was about it. It had no Bluetooth integration for a headset or a display for caller ID. If you knew the flash codes you might be able to perform a conference or transfer, but who remembered those? I certainly didn’t.

Still, for the most part, it was good enough for the times. This was especially true since we had nothing better to compare it to. We had very similar analog telephones at home and so our expectations weren’t very high. You can’t miss something you’ve never had.

As time went by, that analog telephone was replaced with a digital set that supported advanced telephony features without you having to remember all those awkward flash codes. Through simple button clicks, you could conference, transfer, hold, park, and retrieve calls. It had a display for calling name and number. You also had non call feature such as forward and that annoying voice mail light.

However, even with the arrival of better technology, not a lot had changed. You were still tied to that phone number and therefore your desk. Mobility was a long cord and was talking on the phone while you read an email.

Related article: What Today’s Birthday of the Telephone Means to Me

My identity was still a number on a phone that never moved.

As the PC became more and more a part of our work lives, it began taking on a larger role in how we communicated. We combined voicemail access with our email system. Instead of dialing a number and entering a password, we pointed, clicked, and listened.

The PC also introduced the world to the first wave of unified communications. I installed my first integrated soft-phone, presence, and instant message application onto my PC sometime in the 1990’s. While it was advanced for its time, it was mostly built on proprietary protocols and offered few integration options. Even worse, I was still tied to my desk. Nothing had changed in that regard.

The invention of the notebook PC helped with mobility, but even that had significant limitations. It was too heavy for handheld access and it required a wired or wireless network for connectivity to the outside world. It did me no good if I was trying to work from one of my kid’s baseball games. Even if there was a 3G or 4G network flying through the air, my PC had no way to connect to it.

Untethering the user

These days, the PC is not the end-all, do-all device that it once was. I spend as much, or sometime more time on my smart phone and tablet. Not only do they provide me with email, calendar, business applications, and those point-and-click voicemails, but I also get enterprise communications. SIP has allowed my mobile devices to become enterprise voice-enabled by simply downloading an application and pointing it at my company’s SBC.

More importantly than having a few more devices to carry around, my communications identity has become untethered from those pieces of metal and plastic. Communication is delivered to my phone. At the same time, it can also be delivered to my PC, iPhone, and iPad. I am no longer just a telephone number married to a desk. I am rooted when I need to be rooted. I am mobile when I need to be mobile. You can reach me using my old fashioned telephone number. You can also reach me via my SIP name. My desk has become anywhere I happen to be at any given moment in time.

The SIP REGISTER command is used to “bind” a user name to a device. Depending on the capabilities of your SIP system, you might be able to simultaneously register several devices to the same name. For instance, Avaya allows you to register up to ten devices for a single user name. Now, when that user is called, more than one device can be alerted and the user chooses which one to answer. For me, I answer my 9641 when I am sitting at my desk and my One-X Mobile or Flare when I am out and about — same name or number, multiple devices, my choice.

By now, everyone should know that SIP is media agnostic. It’s essential that folks realize that this registration flexibility makes it device and location agnostic, too. Openness to all ways to communicate on all device types makes SIP the protocol for unified communications.

Any device, any time, any media…same user

Separating a user from his or her devices and telephone numbers is extremely powerful. Not only do I get the aforementioned mobility and device independence, but I also get flexibility in the ways you can communicate with me. You can send me voice, video, or instant message using the exact same name. I don’t have to give you a list of different names, methodologies, or devices. I don’t need to tell you that from 8:00 to 10:00 I will be on this device at this location and from 10:00 to 1:00 I will be on a different device at another location. I don’t have to change names throughout the day in order to be reachable. The same name will find me wherever I am, on whatever device I am using, on any network I happen to connect to, and with any media type.

I will admit that there are certain aspects of the past that I am sad to see go away. I still love the rich sound of a vinyl record played through a tube amplifier. However, I do not miss being tied to my desk all day long. I love being able to pick when, where, and how I choose to do my job and that’s a very good thing.

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This article originally appeared on SIP Adventures and is reprinted with permission.

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How to Realize Huge Cost Savings for Enterprise Telecom

This case study shares the steps taken by Avaya to reduce a sizeable telecom bill by 50%. The methods are trending tactics used by a wide range of organizations, and in combination have proven to produce especially favorable results. Keeping in mind that most IT operation budgets are flat, cost savings of this size can give your organization a greater opportunity to invest in innovation.

When every penny counts, internal telecommunication expenses must be closely accounted for. It’s a large expense and pain point for many organizations, and adopting change in this area is often associated with fear and uncertainty.

In reality, these fears disappear with a pinch of planning and excellent execution. Prioritizing telecom costs as a business initiative, establishing expectations, and determining a reasonable timeframe are some of the leading difficulties in taking on a project of this magnitude. These steps can have a great impact on the overall success of the project.

  1. Hire an expert to properly analyze your costs.

    There are many nuances in telecom, so if your organization does not have an expert internally, then it would be worthwhile to hire a third-party consultant to analyze the cost. They can provide better financial estimates of the cost and savings to ensure adequate ROI.

  2. Centralize trunking.

    To make it simple, paying for fewer circuits reduces cost. At Avaya, we reduced our total internal global telecom costs by 50% and got a 40% overall reduction of IT operational spending by doing so. Pay close attention to the amount of money paid in relation to the locations and compare centralized trunking cost to your current expenses. There are also considerations based on regional laws—for example, telecom laws in India may prevent this practice altogether.

  3. Reduce local trunking.

    Gartner estimates that “network architects and procurement managers can leverage SIP trunking services to slash enterprise telecom expenses by up to 50%.” As we all know, telecom does not come cheap, so these are results that cannot be ignored. Since IT operating budgets are often flat, this method can be a valuable way to extract savings from existing expense.

Gartner further suggests that, “enterprises should leverage the competitive SIP trunking market as U.S. service providers are reducing rates to win new business and retire their legacy TDM networks.” Needless to say, if you have yet to board the SIP train, you should strongly consider doing so now.

Previously at Avaya, all locations had their own local trunking and now we are saving cost by routing calls through a central location. In fact, SIP trunk consolidation provided an average savings of ~40% per month over PSTN trunks. We did it by implementing Avaya Aura to connect sites between a WAN used for both voice and data.

The Benefits Speak for Themselves

Consider what your company could do with these savings. We chose to reinvest 20% of our savings towards innovation and new capabilities. Gaining support from your colleagues should be a bit easier with these proof points in your back pocket and a strategic plan of action.

Understanding SIP PRACK for Avaya Aura

As many of my readers know, every few months I teach a two and a half day class on “all things SIP.” My students are exposed to everything from “why SIP” to the nitty-gritty of SIP requests, responses and call flows. I even speak about some of the more esoteric topics such as To and From tags, the Replaces header, nonce values and TR-87.

Included in the esoteric list is the PRACK (Provisional Response Acknowledgement) method. PRACK wasn’t in the original SIP specification and was introduced later in RFC 3262. It came about after it was realized that some user agent servers need to know that a provisional response was received by a user agent client. Before PRACK, 1xx responses sent using UDP might get lost, and the sender would never know. PRACK adds a layer of reliability to an otherwise unreliable call flow.

I previously addressed PRACK in my article “Ducks Go Quack. SIP Goes PRACK.” Although I addressed most of the pertinent material, I was short on examples and real-life call flows. As I walked my most recent students through live calls on my company’s Avaya system, I happened to notice a few PRACKs and decided it was time to update my old article.

The following screenshots were gathered using the Avaya traceSM utility. I simply started traceSM on a live Aura system, let it run for a few minutes, and then stopped it after I noticed a few PRACK messages fly by. This was simply because I was unsure as to when Avaya uses PRACKs and when it does not.  In other words, “When in doubt, trace it out.”

prack1

Let’s start at the beginning. PRACK messages aren’t just sent out-of-the blue. The sender of an INVITE message must indicate that it is capable of sending PRACKS. It does that by including the header in the INVITE message:

Supported: 100Rel

This tells the recipient that, if requested, it will send PRACK messages for 1xx Responses.

The following shows an INVITE with such a header.

prack2

Now that the user agent server knows that PRACK messages are possible, it will include headers similar to the following in all 1xx Responses it wants to be PRACKed:

Require: 100Rel

Rseq: 1

The Requires header with a value of 100Rel tells the user agent client (the sender of the INVITE) that a PRACK is expected for this response. It’s important to know that the user agent server (the sender of the Response messages) has to request the PRACK. It’s not an automatic process and must be initiated with an Rseq header.

The value in Rseq is used by the user agent client when it creates a PRACK message. The user agent server is responsible for setting and incrementing this number.

The following 180 Ringing indicates that it expects a PRACK.

prack3

Upon receipt of this 180 Ringing, the user agent client must respond with a PRACK message. Of interest to this article is the Rack header. This header must contain the Rseq value sent in the previous 180 Ringing. Additionally, it will indicate the original INVITE session’s CSeq number. Look back at the INVITE in this call flow, and you will see a CSeq value of 1 (one). Therefore, the Rack will look as follows:

Rack: 1 1 INVITE

prack4

Next, the user agent server will send a 200 Ok for the PRACK. This tells the user agent client that the PRACK was received and processed.

prack5

For grins, I will now show you the 200 Ok for the original INVITE. Note that it does not have a Rseq header and 100Rel is not in the Requires header. Why not? That’s because this is not a provisional response. PRACKs are only sent for 1xx responses.

prack6

Mischief Managed

Before I close things out, I want to address the question I hinted at near the top of this article.  When does Avaya use PRACK?

While I honestly don’t know all the permutations, it appears that an INVITE from an Avaya endpoint will always indicate that it supports PRACK (Supported: 100Rel).  However, as you just learned, it’s the recipient of the INVITE that indicates if PRACK messages are required.

In the example above, the Avaya Modular Message voice mail server requests PRACK messages.  Additionally, PRACK is used when direct media is enabled.

There is a good chance that PRACK is used in other situations, but I am going to have to start up a few more traceSM sessions to learn where they show up.

That’s about all I really need to say about PRACK. I invite you to take a look at the RFC if you want to learn about any PRACK subtleties I might have missed, but for all practical purposes, I’ve said all that needs to be said. I hope you had as much fun today as I did. As is often the case, I learned something in the process of writing this article, and that’s always a good thing.

Understanding Avaya Aura SIP Registration

“Let’s start at the very beginning/a very good place to start/when you read you begin with A B C/when you sing you begin with Do Re Mi.”

I have always loved musicals, and Rogers and Hammerstein’s “The Sound of Music” is high on my list of favorites. Sure, it’s corny and far from historically accurate, but that doesn’t bother me in the least. I’m always willing to set aside any sense of reality for good singing, romance and adventure, and “The Sound of Music” has them all.

So … what does this have to do with unified communications? REGISTER, of course. Like Do Re Mi, you begin SIP with REGISTER.

This article is a continuation of the concepts I presented in A Close Look at Avaya Aura IMS Call Processing and An Even Closer Look at Avaya Aura IMS Call Processing, and I’d suggest you take a look at those before tackling this one.

Can you get SIP devices to communicate without REGISTER? Absolutely. In fact, when I teach my SIP class, the students put their SIP clients into point-to-point mode, which does not require REGISTER. This means that clients send SIP requests and responses directly to the other clients, not through a proxy. The clients can do everything all by themselves.

However, point-to-point without REGISTER has a serious downfall. The clients are required to know the IP addresses of all the other clients they wish to communicate with. While this is fine in a limited classroom environment, it becomes unwieldy after you grow beyond a handful of endpoints.

As an analogy, imagine having to know the IP address of everyone you wanted to send an email to. That’s the same problem you have if you don’t use REGISTER. It’s simply not practical.

The Tie that Binds

REGISTER associates a user’s identification, or Address of Record (AOR), with one or more locations. Note that I said locations. You are not limited to registering an AOR to a single device. Personally, I routinely register my AOR to a physical desk phone and multiple SIP soft-clients. Avaya Aura supports up to ten such registrations per user. That’s enough to make even the most device-crazy nerd happy.

You bind an AOR to an IP address with a Contact header.  For example, one of my soft clients might tell a SIP registrar that aprokop can be reached at 192.168.0.14 with this Contact header.

Contact: Andrew Prokop <SIP:aprokop@192.168.0.14>

Registrations are time-based and will eventually expire. This requires the client to periodically refresh a REGISTER with a new REGISTER. Actually, new isn’t the correct word to use for this. Subsequent REGISTER messages must contain the same Contact, To, From, call-ID and From Tag as the original registration. This allows the SIP registrar to know that it’s simply a refresh and not a new registration for the same AOR.

Note that CSeq will increment with each REGISTER sent.

Keeping Things Secure

I might tell my communications system that I am Andrew Prokop, but it would be foolish to trust me at face value. That’s why SIP allows a REGISTER to be challenged.

Before I go through a REGISTER challenge, allow me to define something known as a nonce.

Nonce stands for Number Once and is an arbitrary number used only once in a cryptographic communication. The recipient of a nonce will use it to encrypt his or her credentials. Number Once refers to the fact that encryption with this nonce can only be done one time. If someone were to sniff the LAN and obtain someone’s encrypted password, it won’t do them any good because it can only be used in a single transaction. It becomes stale and useless immediately after its first use.

A REGISTER flow is fairly simple and follows these steps:

  1. A user sends a REGISTER to the SIP registrar. For Avaya Aura, this is a Session Manager. The To and From headers contain the user’s AOR. The user specifies the number of seconds the registration should be valid in the Expires header. This value can be later raised or lowered by the registrar.
  2. The registrar returns a 401 Unauthorized response with a WWW-Authenticate header.  This header contains data that must be used to encrypt the user’s communications password. Specifically, it contains a nonce along with the name of the encryption algorithm that the client must use.
  3. The user sends a second REGISTER to the SIP registrar. This REGISTER contains an Authorization header. Within Authorization is the user’s encrypted password.
  4. If the correct password is received by the registrar, a 200 Ok response is sent to signify a successful registration. An Expires header may be present with a different value than what the user requested. This is the time the registration will be valid as determined by the registrar’s policies.

A registration is removed by sending a REGISTER with an Expires header value of 0 (zero).

In a picture, we have this.

Reg1Using the traceSM tool on an Avaya Aura Session Manager, I captured the following trace that shows a REGISTER, the challenge and a REGISTER with encrypted credentials.  Take a look at the headers, and you’ll see that they’re doing exactly what I said they would do.

Reg2 Reg3 Reg4

 

In the case of my daily work life, my various SIP devices will each send a REGISTER, be challenged and resend the REGISTER with the encrypted credentials. They periodically refresh their registrations to ensure that I am able to make and receive calls on all my devices until I am finished for the day.

Speaking of finished for the day, that’s about all I have to say about REGISTER. It’s not that complicated once you understand the basics. Just keep in mind that while registration isn’t absolutely mandatory, it enables a secure, scalable and easy to manage SIP solution.

… And these are a few of my favorite things!

Andrew Prokop is the Director of Vertical Industries at Arrow Systems Integration. Andrew is an active blogger and his widely-read blog, SIP Adventures, discusses every imaginable topic in the world of unified communications. Follow Andrew on Twitter at @ajprokop, and read his blog, SIP Adventures.