If you’re a regular reader of this blog, you know I always prefer knowledge over recipes. Unfortunately, it’s pretty hard to build that knowledge using the widely available training materials, which often just blast you with a barrage of facts that you’re supposed to memorize and deliver at the certification exam.
How about turning your training into a South Park episode?
Read more ...Scale-out cloud-applications continue to be the most disruptive force to traditional network architectures in the data center. They demand an open and uncompromised cloud network, unshackled by monolithic and the prehistoric proprietary networks.
Our customers and partners are reshaping this traditional networking industry. Previously burdened by monolithic software and underperforming hardware, the new evolving bifurcation of computing architectures for modern cloud-based applications has resulted in key trends and drivers for this evolution including:
1. Unstructured data is everywhere. Whether from users, applications or machines, it is growing exponentially with no vertical or industry being spared. One current obstacle to working with large data sets is the use of relational databases and desktop statistics/visualization packages that require massively parallel software running on hundreds, or even thousands of servers.
2. New workloads are changing the notion of separate SANs. This impacts the role of networking and IP storage, where virtual machine mobility sustains multiple gigabits of throughput by default with multicore processors.
3. Cloud intensive applications such as content distribution, and new infrastructure technologies such as containers and Hadoop clusters are pushing the envelope of what is possible with massively parallel transactions. These new large-scale data analytics have given birth to converged Continue reading
When a researcher uses the Mininet network simulator to create a network of hosts and switches connected to an SDN controller, he or she may wish to be able to see what the simulated network topology looks like.
The POX SDN controller includes a component that will send network topology data to the Gephi data visualization platform, which can the show a graph of nodes and links representing the network topology. In this post, I will show how to set up POX and Gephi so we can see the network topologies created using the topology options in the Mininet command.
While we work through this tutorial we will also see how the POX SDN controller, which does not offer a native Northbound API, can use POX components to provide northbound interfaces.
This tutorial assumes you already have the following. I include links to relevant posts if you need to review any of these requirements.
Have you ever wondered just "how" OFDM subcarriers are able to be spaced so tightly together without any guard band in-between? Most Wi-Fi textbooks will simply state that the spacing of the subcarriers allows the harmonics to overlap, thus canceling out any interference.
OFDM subcarrier spacing creates "nulls" canceling out inter-carrier interference (ICI) without the need for guard bands or expensive bandpass filters
OFDM divides a given channel into many narrower subcarriers. The spacing is such that the subcarriers are orthogonal, so they won’t interfere with one another despite the lack of guard bands between them. This comes about by having the subcarrier spacing equal to the reciprocal of symbol time. All subcarriers have a complete number of sine wave cycles that upon demodulation will sum to zero.
This tells us that the spacing of the subcarriers is directly related to the useful symbol time (more specifically, the amount of time the transmitter spends performing IFFT). Because of this relationship, the resulting sinc frequency response curves from each subcarrier create signal nulls in the adjacent subcarrier frequencies thus preventing inter-carrier interference (ICI). OFDM is a form of frequency division multiplexing (FDD), which typically requires guard bands between carriers and specialized hardware Continue reading