Benefits of Distributed Collapsed Backbones

What is a Network Backbone?

Network backbones come in two broad varieties: “distributed” and “collapsed”.

A distributed backbone has a core consisting of multiple switches or routers chained together, typically in a ring.

A collapsed backbone has a central device at the hub of a star network. In medium to large networks, this central device is a chassis switch.

Each of these two designs has its advantages and disadvantages, and some environments are better suited to one design in particular. However, there are some network environments which could utilize the benefits of both options combined–particularly if they could avoid the disadvantages of both options.

This white paper discusses how to create a network design that combines both distributed and collapsed backbones. This combined design is called a distributed collapsed backbone.

To understand how such a design works, it is necessary to first consider some of the characteristics of these two designs, to understand their benefits and downsides, and to understand the environments to which each is most suited.

Distributed backbones

The standard model of a distributed backbone network consists of a core ring of routing/switching nodes, each of which is the hub of its own local star network or its own local ring, which then extends out to a local access layer.

In some cases, there may be servers connected locally to most of the backbone nodes. In other cases, the servers are all located at a single node at the ‘head end’ of the distributed backbone.

In either case, traffic from the users local to each node enters the backbone via that node, and at least some of the traffic traverses through other backbone nodes to reach its destination. Thus, the links within the backbone carry traffic to and from destinations throughout the network, not simply to and from destinations that are local to the nodes at each end of the link.

A distributed backbone design is especially suited to physically spread out environments, for example a campus network that connects distinct departments into a unified network.