In the New IP, agility is essential to streamlining operations, speeding new services and allowing networks to adapt to the unpredictable and highly varied workloads created by cloud computing. But we've been talking about network and service agility for decades. The real challenge is how to make the network more agile so we can reap the resulting benefits.
I recently attended Light Reading's New IP conference in San Jose, Calif. All of the keynote presenters highlighted the need for agility in the network (except the cyber security dude who just scared everybody), and I'm happy to report that there are many new technologies and techniques being implemented to make networks smarter and more agile.
For example, in the IP transport infrastructure alone -- the routers, switches and optical transport gear -- there are several notable developments that make the network more agile and efficient. The layers are being integrated. The optical layer is becoming more flexible. And we're introducing new tools to make the whole thing easily consumable through applications.
Let's start by looking more deeply at IP and optical cross-layer integration or vertical agility. Like many "new" ideas in networking, the notion of tightly coupling the IP and optical layers is not really new. IP routing and optical transport proponents have been trying to usurp control of the other layer and integrate its basic functions in their platforms for years. The problem is that neither group completely understood the complexity and nuance of the other group's technology causing the resulting architectures to be mostly one dimensional and sub-optimal. (See my blog on this topic: An IP Traveler in the Land of Optics.)
For a truly agile and optimized infrastructure we need to maintain the best features of both the IP and optical layers and link them together thoughtfully. This is necessary because the scaling challenges and optimization constraints of the two layers are fundamentally different.
The IP layer is designed to route packets of digital information one at a time, forwarding 100s of millions of packets per second without interruption or delay. To do this IP routers maintain a routing information base (RIB) that determines which outgoing interface should be used for each packet based on a variety of information, including network topology, constraints, reachability and administrative policies.
A router in a large scale network must maintain an RIB with millions of entries while in constant communication with 1,000s of other routers and monitoring 100s to 100,000s of physical and logical links. The resulting router control plane is designed to robustly handle a huge information volume with constantly changing state (as an aside, it's worth noting that modern router designs have separate control and forwarding planes to ensure that packet forwarding is isolated from network state changes).
Whereas the IP layer is designed for routing packets of digital information, the optical layer is designed to efficiently route photonic signals, or wavelengths, from a transmitter to a receiver across a network of fiber optic cables, filters, splitters, amplifiers, multiplexors and other components that manipulate the signal. Similar to the IP layer, the optical layer control plane uses administrative policy and topology information to route wavelength connectivity throughout the network. However, it must use unique constraints and algorithms that track wavelength signal impairments to ensure end-to-end integrity of the wavelength connection.
Most proposals for integrating the IP and optical layers are one-sided and dumb down the other layer. They either use a simple optical layer to connect routers or add basic IP and/or Ethernet packet functionality to an optical system. While this approach may work for specific use cases it cannot deliver optimal performance at both the IP and optical layers. The end result is usually higher cost and less flexibility.
A more thoughtful approach to integrating the IP and optical layers is to maintain independent IP and optical control and introduce cross-layer communication via a standard interface, such as generalized multi-protocol label switching (GMPLS) user to network Interface (UNI). It's a mouthful to say, but it does the job of linking the two layers without sacrificing intelligence or replicating functionality. The end result is a much more efficient IP and optical network with cross-layer communication.
By communicating across the layers we can avoid replication of functionality, such as link or node resiliency resulting in significant benefits. A recent Bell Labs study revealed up to 40% cost savings can be achieved through these techniques while also liberating a third of deployed network capacity. In addition, we avoid duplication of functionality which allows engineers to focus on making both the IP and optical layers more agile and programmable instead of replicating features and functionality. This is leading to new innovations in IP and optical networking, such as:
- In IP networks a good example is segment routing which enables edge-to-edge control and optimization of IP traffic flows with very little control or forwarding state in the IP core.
- In optical transmission we are now enabling truly agile photonic networks using the concept of CDC-F optical networks. An acronym for Colorless, Directionless and Contentionless with Flexgrid support, CDC-F defines technologies which provide complete flexibility in routing wavelengths throughout the network, making the network more programmable and SDN ready.
Optimally linking the layers for efficient communication is just the first step. As these new capabilities emerge we are completely rethinking how we build IP and optical networks. By bringing together IP and optical expertise we truly understand the cost, performance and agility relationships between the layers for the first time. This is leading to new and innovative network architectures that are far more agile, scalable and cost effective... and much better positioned to handle software-defined networking.
— Stephen Vogelsang, vice president, Strategy & CTO – IP Routing and Transport Business Division, Alcatel-Lucent, special to The New IP