Interconnection Networks

• The overall performance of a cluster system can be determined by the speed of its processors and the interconnection network. Many researchers argue that the interconnection network is the most important factor that affects cluster performance.
• Regardless of how fast the processors are, communication among processors, and hence scalability of applications, will always be bounded by the network bandwidth and latency.
  • The bandwidth is an indication of how fast a data transfer may occur from a sender to a receiver.
  • Latency is the time needed to send a minimal size message from a sender to a receiver.
• In the early days of clusters, Ethernet was the main interconnection network used to connect nodes. Many solutions have been introduced to achieve high-speed networks. Key solutions in high-speed interconnects include Gigabit Ethernet, Myrinet, and Quadrics.
  

  Table 8.1: Data Rate, Switching Method, and Routing Scheme for Interconnection Networks.

  Interconnection	Network Data Rate	Switching	Routing
  Ethernet	10 Mbit/s	Packet	Table-based
  Fast Ethernet	100 Mbit/s	Packet	Table-based
  Gigabit Ethernet	1 Gbit/s	Packet	Table-based
  Myrinet	1.28 Gbit/s	Wormhole	Source-path
  Quadrics	7.2 Gbyte/s	Wormhole	Source-path

  
  
• While Ethernet resides at the low end of the performance spectrum, it is considered a low-cost solution. Other solutions add communication processors on the network interface cards, which provide programmability and performance. Table 8.1 shows the relative performance and other features of different high-speed networks.