DCNs need to be scalable and efficient to connect tens or even hundreds of thousands of servers to handle the growing demands of cloud computing.
Major problems faced by the three-tier architecture include, scalability, fault tolerance, energy efficiency, and cross-sectional bandwidth.
The three-tier architecture uses enterprise-level network devices at the higher layers of topology that are very expensive and power hungry.
Fat tree DCN employs commodity network switches based architecture using Clos topology.
[3] With the advent of cloud paradigm, data centers are required to scale up to hundreds of thousands of nodes.
[3] Fat tree DCN architecture delivers 1:1 oversubscription ratio and high cross section bandwidth, but it suffers from low scalability limited to k=total number of ports in a switch.
DCell offers immense scalability, but it delivers very poor performance under heavy network load and one-to-many traffic patterns.
[1] The fat tree DCN delivers high throughput and low latency as compared to three-tier and DCell.
One of the major reasons for DCell's low throughput is very high over subscription ratio on the links that interconnect the highest level cells.
[5] Energy efficiency is one of the major challenges of today's information and communications technology (ICT) sector.
Around 15.6 billion kWh of energy was utilized solely by the communication infrastructure within the data centers worldwide in 2010.
[21] Moreover, fat tree and DCell architectures use commodity network equipment that is inherently energy efficient.