Author Archives: Russ

Low Latency Networking

Low latency is coming to a network near you. In fact, it’s probably coming to your network, whether or not you realize it.

While bandwidth has always been the primary measure of a network, and cross sectional or non-contending bandwidth for data center fabrics, further research and reflection has taught large scale network operators that latency is actually much more of a killer for application performance than lack of bandwidth—and not only latency, but its close cousin, jitter. Why is this?

To understand, it is useful to return to an example given by Tanenbaum in his book Computer Networks. He includes a humorous example of calculating the bandwidth of a station wagon full of VHS tapes, with each tape containing the maximum amount of data possible. For those young folks out there who didn’t understand a single word in that last sentence, think of an overnight delivery box from your favorite shipping service. Now stuff the box full of high density solid state storage of some kind, and ship it. You can calculate the bandwidth of the box by multiplying the number of devices you can stuff in there by the capacity of each device, and then dividing by roughly Continue reading

Administravia 030818: Added Navigation

I was asked by a reader to add categories and links for videos; I actually added three new categories, one for short videos, another for long videos, and a third for written posts. You can find these under the bottom menu item on the left. I am having a problem with the menu not showing up correctly, so I move the resources under the third menu item, as well.

Finally, I added a new archive page, which shows you all the posts in the “left” category across the three years this blog has been “in production.” I couldn’t figure out how to narrow things down so pictures and other stuff are not included, so there is more on the page than needed right now, but it’s a start.

DFS and Low Points

On a recent history of networking episode, Alia talked a little about Maximally Redundant Trees (MRTs), and the concept of Depth First Search (DFS) numbering, along with the idea of a low point. While low points are quickly explained in my new book in the context of MRTs, I thought it worthwhile to revisit the concept in a blog post. Take a look at the following network:

On the left side is a small network with the nodes (think of these as routers) being labeled from A through G. On the right side is the same network, only each node has been numbered by traversing the graph, starting at A. This process, in a network, would either require some device which knows about every node and edge (link) in the network, or it would require a distributed algorithm that “walks” the network from one node to another, numbering each node as it is touched, and skipping any node that has already been visited (again, for more details on this, please see the book).

Once this numbering has been done, the numbers now produce this interesting property: if you remove the parent of any node, and the node can still reach Continue reading