Ideas for using software-defined networking (SDN) in a telecom network — or cable, or mobile — have been emerging for some time. What's interesting this year is that they seem to be getting more specific.

In the last couple of weeks, vendors have announced a few examples that are at least in beta test, so we thought we'd group them here for discussion.

Granted, it's very easy for a vendor to dream up theoretical use cases; we expect reams of those to pile up during the next year. But these applications are plausibly useful; in fact, one has kind of been in place for years, albeit without an "SDN" label. See what you think.

1. Microwave Backhaul: Adjusting the Aperture

Accedian's Dynamic Performance Optimization is kind of the opposite of a bandwidth-on-demand machine, in that it throttles bandwidth down automatically. It's a technology intended for the microwave backhaul links in mobile networks, a setting where bandwidth can fluctuate rapidly.

That instability is on purpose. Modern microwave radios adjust to interference by trading off quadrature amplitude modulation (QAM) levels (i.e., the number of bits sent at once) for signal-to-noise ratio. Under heavy interference, the radio could throttle down the QAM rate, effectively hitting the brakes, to get a cleaner signal out.

But the router at the head-end, which is receiving this signal, doesn't know this has happened. Its bandwidth pipe is still open and now underutilized. The problem is compounded by the fact that microwave radios get cascaded, meaning a signal can go through a series of radios.

So, Accedian is proposing DPO, which lets the head-end switch/router dynamically change its bandwidth "aperture," CEO Patrick Ostiguy says. Accedian aims to develop DPO as a multivendor technology so that a router can peer through the entire chain of microwave radios.

DPO uses signal reflections to continually check the available bandwith. The key is to react immediately; Ostiguy likens it to a hand pulling back from a hot stove before the brain realizes what happened. "It's not optimal to take 15 minutes to talk about it and optimize the network at a holistic level," he says.

Similar ideas have come up in wireless (the self-optimizing network, or SON) and in cable (pre-Doscis cable modems did similar bandwidth-shaping).

DPO, which Accedian says is in beta test, mostly applies outside North America, where LTE networks are being built out and there aren't copper or fiber networks available to use for backhaul.

2. Broadband Access: Knocking Off the Caps

Instead of carriers instituting bandwidth caps, it would be nice to just react by charging the heaviest users or rationing out bandwidth. But carriers can't necessarily do that in real time, partly because of the antiquated management and operations support systems (OSS) software running their networks.

"Whenever they try to do anything that's going to collect a lot of data for a real-time fix on what's happening in the network, there are a whole lot of obstacles," says Steve Collins, vice president of marketing and business development for Active Broadband Networks. "Most often, they just kind of punt" by enforcing caps.

Active Broadband's alternative is its Dynamic Broadband Service Manager (DBSM), which can do that real-time monitoring. In August, DBSM got an SDN boost, using OpenFlow to control bandwidth on particular traffic flows or to make policy-dependent changes to those flows. The company is also touting DBSM's ability to see across multiple access networks. "This is going to be more important as you see the cable guys move into fiber" or, possibly, as telcos acquire cable assets, Collins says.

2.5. Cable Broadband

Active Broadband deployed something similar to DBSM in 2008 for a very large cable company (Comcast, but Active Broadband isn't saying that out loud), and it's still in use. We thought about counting that as a separate use case, but that felt like cheating; plus, it feels weird to count a 2008 application as "SDN."

3. Optical Transport: Switching Data Centers

Last week, ADVA Optical Networking, IBM, and Marist College demonstrated what they say is the first case of automated optical provisioning between data centers — meaning, data-center servers telling the WAN to set up an optical link.

In the demo, a Floodlight SDN controller sent configuration commands to IBM switches. Then, a virtual machine, while running a live video, got migrated from one data center to another. This could be useful for a broadcast network that has one site go down, for instance; they would have to "go to three different departments to do what we did in 40 seconds," says Todd Bundy, business development director at ADVA.

By turning wavelengths into an on-demand service, a carrier or enterprise could avoid having to lease or build nailed-up network connectivity. In the broadcaster's case, that bandwidth would go unused most of the time.

One key development here was writing software to translate OpenFlow commands into SNMP for the optical control plane. OpenFlow doesn't yet have an agent that can deal with the unpredictable impairments inherent to the optical network, Bundy says.

Plenty More to Come

Obviously, this is a snapshot, not a comprehensive list. Other examples emerged even last year — Verizon experimenting with SDN for traffic management, or the bandwith-on-demand trial that Infinera did with ESnet. Feel free to use the comments space to tell us about any interesting transport cases we've missed.