Tier-1 carrier perspectives provided an early highlight of the SDN & OpenFlow World Congress, held this week in Bad Homburg, Germany. The general message was that the capabilities of software-defined networking (SDN) are desired right now, but that the technology hasn't reached a carrier-grade level yet.

In the meantime, some carriers are already shaking up their operations to prepare for an SDN future. Possibly the most extreme of these is Deutsche Telekom CTO Axel Clauberg, who gave an opening keynote on Wednesday.

Clauberg gave an update on TeraStream — a very long-term project, aiming to build the network DT will use at the end of the decade, replacing the old networks (even the original telephone network, expected to be decommissioned around 2018).

This doesn't mean completely cleaning house — old OSSs will still linger around the network, for instance. But instead of directly supporting them all, DT expects to use an OSS Gateway that can translate to those old and (presumably, by 2020) dying languages.

Likewise, the teeming hordes of protocols around the network could be narrowed down to just a handful: IPv6, DHCP, Ethernet transport (at 100-Gb/s at first), and some kind of tunneling protocol, Clauberg said.

The optical network is being reduced to "cheap passive splitters," with all the intelligence being handled by routers. In Croatia, which is DT's showcase for trying out TeraStream's new ideas, the carrier recently showed interoperability between Alcatel-Lucent and Cisco gear, both vendors working toward this new type of optical network. "It will be cheaper, in the not-too-distant future, to build a 100-Gb/s network than it is today building a 10-Gb/s network," Clauberg said.

This network will be Layer 3, even in the data center, because the scale of a large carrier calls for routing, he said. "Layer 3 is our paradigm; that's the key to our simplicity approach."

OpenFlow is probably going to be DT's protocol of choice eventually. While it waits for the protocol to mature, however, DT is using Netconf to configure network equipment. It's also using Yang as the high-level language for defining services. Tail-f's NCS product is helping do all of this and is a bit part of DT's controller, Clauberg said.

"There is no carrier-grade SDN today," Clauberg said. "If you want to run OpenFlow in the wide-area, you have to invest a lot. That's what Google did."

Colin Bannon, chief architect with BT Global Services, offered what he called an "exploration" — not a strategy map, but more a sketch of big-carrier life that he'd like vendors to consider.

Massive carriers such as BT have some problems that go well beyond what a data-center sees. The speed of light actually matters, for instance, because it messes with the latency requests that come in for around-the-world connections. (Seriously. Bannon said he sometimes has to gently remind customers about the laws of physics.)

BT's primary goal is to adhere to customers' service-level agreements (SLAs). To that end, the feedback loop promised by SDN — where network provisioning is informed by current network conditions — "is what we want first," he said. "That's the game-changer, to allow that feedback loop and allow us to attain not just the SLA but the service experience around the apps."

That's going to take some time to fully develop. In the meantime, Bannon sees Layer 3 MPLS as a solid stopgap option.

"I think MPLS has a lot of life in it," he said. "We need an option to leverage MPLS that has a service-rich set of functionality whether it be OAM [operations, administration, and maintenance], traffic engineering, fast convergence, fast reroute — those are all important to us to provide that end-to-end, iron-clad SLA."

(Like Clauberg, Bannon thinks a carrier is best served by a Layer 3 network. Later, over lunch with SDxCentral and others, he pointed out how this contrasts with the Layer 2 approach to network overlays that VMware is touting with its NSX product.)

Bannon likes SDN, and he thinks NFV will be huge, but he summed up his talk as a "plea from the trenches ... to think about this incremental model," one that takes into account the existing network. Vendors do mention this factor, but it carries more weight coming from a customer, especially one with a network operating at such massive scale. Such a beast can't shed its coat easily.

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