In recent years, Internet companies such as Google, Microsoft, Facebook, and Amazon (as well as their counterparts in Asia and Europe) have built massive data centers, each housing tens to hundreds of thousands of hosts, and concurrently supporting many distinct cloud applications (e.g., search, e-mail, social networking, and e-commerce). Each data center has its own data center network that interconnects its hosts with each other and interconnects the data center with the Internet. In this section, we provide a brief introduction to data center networking for cloud applications.
The cost of a large data center is huge, exceeding $12 million per month for a 100,000 host data center. Of these costs, about 45 percent can be attributed to the hosts themselves (which need to be replaced every 3–4 years); 25 percent to infrastructure, including transformers, uninterruptible power supplies (UPS) systems, generators for long-term outages, and cooling systems; 15 percent for electric utility costs for the power draw; and 15 percent for networking, including network gear (switches, routers and load balancers), external links, and transit traffic costs. (In these percentages, costs for equipment are amortized so that a common cost metric is applied for one-time purchases and ongoing expenses such as power.) While networking is not the largest cost, networking innovation is the key to reducing overall cost and maximizing performance.
The worker bees in a data center are the hosts: They serve content (e.g., Web pages and videos), store e-mails and documents, and collectively perform massively distributed computations (e.g., distributed index computations for search engines). The hosts in data centers, called blades and resembling pizza boxes, are generally commodity hosts that include CPU, memory, and disk storage. The hosts are stacked in racks, with each rack typically having 20 to 40 blades. At the top of each rack there is a switch, aptly named the Top of Rack (TOR) switch, that interconnects the hosts in the rack with each other and with other switches in the data center. Specifically, each host in the rack has a network interface card that connects to its TOR switch, and each TOR switch has additional ports that can be connected to other switches. Today hosts typically have 40 Gbps Ethernet connections to their TOR switches Each host is also assigned its own data-center-internal IP address.
The data center network supports two types of traffic: traffic flowing between external clients and internal hosts and traffic flowing between internal hosts. To handle flows between external clients and internal hosts, the data center network includes one or more border routers, connecting the data center network to the public Internet. The data center network therefore interconnects the racks with each other and connects the racks to the border routers. Figure 6.30 shows an example of a data center network. Data center network design, the art of designing the interconnection network and protocols that connect the racks with each other and with the border routers, has become an important branch of computer networking research in recent years.
About the Authors
Jim Kurose is a Distinguished University Professor of Computer Science at the University of Massachusetts, Amherst. He is currently on leave from the University of Massachusetts, serving as an Assistant Director at the US National Science Foundation, where he leads the Directorate of Computer and Information Science and Engineering.
Dr. Kurose has received a number of recognitions for his educational activities including Outstanding Teacher Awards from the National Technological University (eight times), the University of Massachusetts, and the Northeast Association of Graduate Schools. He received the IEEE Taylor Booth Education Medal and was recognized for his leadership of Massachusetts' Commonwealth Information Technology Initiative. He has won several conference best paper awards and received the IEEE Infocom Achievement Award and the ACM Sigcomm Test of Time Award.
Dr. Kurose is a former Editor-in-Chief of IEEE Transactions on Communications and of IEEE/ACM Transactions on Networking. He has served as Technical Program co-Chair for IEEE Infocom, ACM SIGCOMM, ACM Internet Measurement Conference, and ACM SIGMETRICS. He is a Fellow of the IEEE and the ACM. His research interests include network protocols and architecture, network measurement, multimedia communication, and modeling and performance evaluation. He holds a PhD in Computer Science from Columbia University.
Keith Ross is the Dean of Engineering and Computer Science at NYU Shanghai and the Leonard J. Shustek Chair Professor in the Computer Science and Engineering Department at NYU. Previously he was at University of Pennsylvania (13 years), Eurecom Institute (5 years) and Polytechnic University (10 years). He received a B.S.E.E from Tufts University, a M.S.E.E. from Columbia University, and a Ph.D. in Computer and Control Engineering from The University of Michigan. Keith Ross is also the co-founder and original CEO of Wimba, which develops online multimedia applications for e-learning and was acquired by Blackboard in 2010.
Professor Ross's research interests are in privacy, social networks, peer-to-peer networking, Internet measurement, content distribution networks, and stochastic modeling. He is an ACM Fellow, an IEEE Fellow, recipient of the Infocom 2009 Best Paper Award, and recipient of 2011 and 2008 Best Paper Awards for Multimedia Communications (awarded by IEEE Communications Society). He has served on numerous journal editorial boards and conference program committees, including IEEE/ACM Transactions on Networking, ACM SIGCOMM, ACM CoNext, and ACM Internet Measurement Conference. He also has served as an advisor to the Federal Trade Commission on P2P file sharing.
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