B4

TLDR

B4 is a private WAN that connects Google’s data centers and is characterized by massive bandwidth needs, elastic traffic demand, and full edge‑server control enabling rate limiting and demand measurement. The paper presents the design, implementation, and evaluation of B4. B4 uses a software‑defined networking architecture with OpenFlow‑controlled simple merchant‑silicon switches and a centralized traffic‑engineering service that routes flows across multiple paths to achieve near‑100 % link utilization. Over three years of production deployment, B4’s traffic‑engineering service achieved near‑100 % utilization while balancing capacity and application priority, and the authors report lessons learned and future work.

Abstract

We present the design, implementation, and evaluation of B4, a private WAN connecting Google's data centers across the planet. B4 has a number of unique characteristics: i) massive bandwidth requirements deployed to a modest number of sites, ii) elastic traffic demand that seeks to maximize average bandwidth, and iii) full control over the edge servers and network, which enables rate limiting and demand measurement at the edge. These characteristics led to a Software Defined Networking architecture using OpenFlow to control relatively simple switches built from merchant silicon. B4's centralized traffic engineering service drives links to near 100% utilization, while splitting application flows among multiple paths to balance capacity against application priority/demands. We describe experience with three years of B4 production deployment, lessons learned, and areas for future work.