On the Road to IP and Optics Convergence

Next Generation Communications Blog

On the Road to IP and Optics Convergence

By: Peter Bernstein, Senior Editor

For what seems like ages now the communications industry has been talking about convergence. We have already gone through many phases as networks move from TDM to being end-to-end Internet Protocol (IP) with voice traffic increasingly being carried on converged networks.  Indeed, the popularity of Voice-over-IP (VoIP) and the coming of Voice-over-LTE (VoLTE) on mobile networks is the future.  

That said, convergence is not just about IP but is also about the transformation of global network infrastructures in the wired world, with legs into the wireless one as well, of IP and Optics.  And, as Steve Vogelsang, VP Strategy and CTO, IP Routing and Transport Business Division, Alcatel-Lucent noted in a recent TechZine blog, IP and optics: Time to make nice, “Let’s face it. The future of the communications industry requires a convergence of IP and optics. So maybe it’s time to give each other some overdue respect."

Vogelsang starts with the acknowledgment that: “Optical networking is very different from IP networking. The base system designs and some of the underlying technology are similar, but the design goals and resulting optimizations are quite different.” He continues by saying reality is that, “IP and Optics are destined to come together. “

Vogelsang then goes on to provide four insightful observations about IP and Optical convergence that are good food for thought.  The four are:

  1.   Optics, as we all know, is in the physical layer. That’s physical as in “physics.” As in the really tough math. 
  2. The coherent optical transmission world is no longer digital. The information being transported is digital, but it is encoded into analog signals using increasingly sophisticated algorithms.
  3. To maximize the transmission capacity of each fiber, we’re optimizing every part of the optical transmission system by turning constants into variables. Wavelengths are tunable. The grid that defines the “color” of wavelengths is now flexible (e.g. FlexGrid), allowing variable bandwidth allocations per signal (i.e., the colors of the wavelength rainbow are no longer all the same width). In addition, the modulation used to encode digital bits into analog is variable. The FEC algorithm and number of error correction bits is variable. And, the photonic switching layer is becoming more diverse, allowing signals to be routed in any direction and reused. 
  4. As we converge the IP and optical layers, there are problems to be solved. What looks like an optimal routing decision to a router might not work out that way at the optical layer.

Vogelsang proceeds to delve into an interesting discussion as to what needs to be addressed to get to IP and optical convergence.  He notes that:  “The first problem to solve is automating the optical layer, because much of what happens, even today, involves hands-on setup. ROADMs were a great start, but they only allow automation of the middle of the route, but not the ingress and egress points. Next-generation ROADMs solve a lot of these issues by making them colorless, directionless, contentionless (CDC) and, for networks over 100 Gbit/s, flexible (CDCF). But the key will be getting the routing layer to talk intelligently to the optical control layer and vice versa.”

How the network of the future gets to being ultra-broadband, including that of mobile operators, is going to be through IP and Optical integration in almost every part of the infrastructure.  And, while we are not there yet, as Vogelsang says, “There is a lot of sophisticated and tricky maneuvering happening at the optical layer, which few IP engineers recognize or understand. While that was OK in the past, it is entirely insufficient today.”  It is the reason the title of his posting about now being the time for IP and optical engineers to “make nice” is not just an observation but should be construed as a call to action. 

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