Hardware Disaggregation: Truly SDN-Optimized Network Elements?

Rick Talbot
Rick Talbot

Summary Bullets:

  • SDN orchestration opens the door to network element disaggregation – performing wavelength, TDM and packet switching and optical transport in separate network elements.
  • Operators will need to choose between the best-of-breed benefits of network element disaggregation versus the shared powering, cooling and management of P-OTPs.

Much of the discussion around NFV has addressed separating virtual functions from physical devices. However, the capabilities introduced by SDN set the stage to present an even more radical possibility for the network.

SDN can orchestrate the separate traffic forwarding functions – wavelength switching, TDM (SONET/SDH/OTN) switching, packet switching and optical transport – which are often provided in a single packet-optical switching platform (P-OTP). This orchestration allows the forwarding functions to be provided by separate hardware elements, yet managed, and optimized, in an end-to-end network. Why would we now disaggregate elements that the optical networking industry has spent years to aggregate as packet-optical transport platforms?

  • Costs. Operators likely pay more for P-OTPs that support all four functions at each platform site than platforms that provide just the required functions at specific sites because a multi-function platform costs more to design and manufacture than a single-function platform.
  • Performance. Operators likely sacrifice best-of-breed components when they employ a platform that provides multiple traffic forwarding functions.
  • Innovation. Related to the best-of-breed concept, advances in transport element hardware occur one function at a time, not four (wavelength, TDM and packet switching and optical transport) simultaneously.
  • Vendor Choice. Vendor lock-in is less likely when multiple vendors can supply the network elements, even if the same vendor supplies a given function across the network.

An example of the last point is the optical transport advances designed into the recently introduced custom data center interconnection (DCI) transport platforms. These single-function (optical transport) devices offer generally twice the capacity per rack-unit (RU) of P-OTPs, while consuming significantly lower power. However, it is unlikely that a P-OTP vendor would (or could) employ these capabilities in the optical transport functions of their platforms. Similarly, packet switch vendors (and white box switch vendors) are likely to be able to exceed the packet switching capacities of the P-OTPs.

Of course, P-OTP vendors can point to savings provided by their combined-function platforms:

  • Low cost of interconnecting elements over a backplane;
  • Common power supply, cooling (fans) and operating system; and
  • Single element management system.

In addition, they tend to be the established service provider infrastructure vendors, so they would assert that they (and their traditional solutions) are more reliable than competitors (and their solutions).

For the time being, SDN technology, as well as standards, likely lack the maturity to support network element disaggregation, and the design of a disaggregated transport network will probably be quite complex, even when SDN technology is mature and standards are in place. However, as operators employ data center techniques in their next-generation central offices, they will find the potential savings offered by network element disaggregation difficult to ignore. Eventually, the full benefit of SDN may not be fully realized without such disaggregation.

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