Why I Still Get Excited About Session Border Controllers

I remember my first DVD player. I couldn’t tell you the exact year I bought it, but it must have been sometime in the 1990s. However, I do remember that it cost me around $400 and it wasn’t even the most expensive one on the market. There were quite a few that went for more than $1000.

Times have certainly changed. I recently went to the Best Buy website and found a player with way more features than my old one for less than $30. On Ebay I can pick it up for half that. Clearly, run-of-the-mill DVD players have lost all of their luster.

I will venture to say that the same holds true for session border controllers (SBCs). It wasn’t that long ago that Acme was the only game in town and they could charge as much as they wanted to. $200,000 for a basic SBC was not out of the question.

Like DVD players, the SBC world is a very different place than it was a few short years ago. Not only have the costs dropped significantly, but there are several vendors to choose from. The basic functionality of five years ago has become table stakes today. We have gone from the days of SIP trunks to and from a carrier, to a multifunctional security and routing device that goes well beyond a TDM replacement box.

In fact, we can’t even call them boxes anymore since most vendors offer virtual versions of their products. The SBC is moving beyond an appliance that sits in the telecom room to a slice of memory, processor, and storage in an enterprise’s virtual server farm.

Does all this mean that SBCs are no longer exciting (at least to communications geeks like us)? Absolutely not. Instead, rather than getting all worked up about trunks, NAT, and deep packet inspection, I look for features that make one vendor’s product standout from the others.

Does that mean that we can ignore topology hiding, B2BUA functionality, and high availability? Absolutely not. It’s just that those features are now the commodity aspects of an SBC. I expect them to be there and it shouldn’t be a question of availability. You don’t ask if a car has tires, do you? Neither should you have to ask if an SBC does header manipulation. It’s expected that it does.

Over the next couple of pages I would like to point out some of the SBC features that do excite me. I clearly will not catch them all, but let this be a starting place.

Size Matters

I will start with capacity. Since the dawn of the SBC, the number of simultaneous sessions an SBC could support was the first question you asked when deciding which one to buy. You would be foolish to put money into an SBC that topped out at 96 sessions when you absolutely needed 150. You could buy all the license packs you wanted, but you can’t squeeze more sessions from a box that has reached its limit.

That’s why I was so thrilled to read that the new Sonus SWe virtual SBC supports an unlimited number of sessions. Yes, you heard me right – an unlimited number of sessions. This means that you can start the SBC as a 25 session pilot before configuring it for thousands of production trunks. Of course, you might need to increase the horsepower of your virtual slice, but that’s not the same as going out and buying a new SBC. One virtual SBC can do it all cost effectively.


Speaking of sessions, every vendor sells session capacity as licenses. If you want 50 sessions, you buy 50 licenses. If you want 50 sessions on one SBC and 75 sessions on another, you buy the appropriate number for each box. Each SBC is individually licensed.

However, what happens if that 50 session SBC suddenly needs 55 sessions? Can you borrow five sessions from the 75 session box if it’s only using 60? Until now, the answer was “no.” If you want 55 sessions on the 50 session SBC, you contact your dealer to purchase an additional five.

This changes with Genband’s enterprise licensing for their Q10, Q20, and Q-Flex products. With their SBCs, you determine the maximum number of licenses you need for your entire enterprise and all your SBCs can then share in that pool. This allows you to more efficiently balance your capacity requirements across geography and multiple time zones.

SIPPING-19 and Beyond

With all the excitement around SIP and its ability to transform the way we communicate with one another, you may be surprised that the SIP standards body, the IETF, only defines 19 different telephone features.  That’s right, only 19.  In fact, they have a name, SIPPING-19, and they are the only features that a SIP phone is required to support.  Specifically, they are:

  1. Call Hold
  2. Music on Hold
  3. Consultative Hold
  4. Find Me
  5. Transfer Instant Message
  6. Transfer Attended
  7. Transfer Unattended
  8. Call Park
  9. Call Pickup
  10. Automatic Redial
  11. Click to Dial
  12. Message Waiting Indicator
  13. Call Forward Unconditional
  14. Call Forward Busy
  15. Call Forward No Answer
  16. 3-Way Conf Party Added
  17. 3-Way Conf Party Joins
  18. Incoming Call Screening
  19. Outgoing Call Screening

Trust me when I tell you that an Avaya SIP phone can support many more than that. While I don’t know the exact number, it’s probably closer to 700 than 19. It does that with a combination of SIP, other protocols, and access to Avaya specific data such as the 46xxsettings.txt file.

This is where the Avaya Session Border Controller for Enterprise (ASBCE) comes in. Unlike other SBCs that support generic SIP phones and SIPPING-19, the ASBCE has been tailored to deal with the specifics of remote Avaya SIP physical and soft phones. I won’t bore you with the technical details, but in addition to core SBC functionality, the ASBCE also actc as a reverse proxy. This enables the http access required by Avaya SIP endpoints for configuration and Personal Profile Manager (PPM). No other SBC on the market today can do that.

Buy One, Get One Free

Who doesn’t love a BOGO? Thankfully, when it comes to SIP and Microsoft Lync, two SBC vendors give you exactly that. Sonus (SBC 1000 and SBC 2000) and AudioCodes (Mediant 800 and Mediant 1000) combine SBC functionality with that of a Lync Survivable Branch Appliance.  This allows branch offices to use a single appliance for all their Microsoft edge SIP activity.

AudiCodes takes it even further by enabling their Mediant 800 with 3G/4G WAN backup capability. This is an extra level of survivability that no other similar product gives you.

To understand more about SBAs, please see my article, The Microsoft Lync Survivable Branch Office.

Browning Your Bread

Don’t get me wrong. I am not discounting the core functionality of an SBC. I am simply stating that some aspects have become like toasters. You expect a toaster to evenly brown your bread and shouldn’t be surprised when it does. While not exactly toasters, SBCs have a commodity aspect to them that just needs to be there. Yes, each vendor will claim that their product does that core functionality better than the competition, but for many enterprises, those differences are irrelevant.

What you want is to be excited. You want a solid core with a little something extra thrown in.

Thankfully, there is enough out there to thrill even me.

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