CSC/ECE 506 Fall 2007/wiki4 001 a1

Current Supercomputer Interconnect Topologies

Gigabit Ethernet

Ethernet is defined by IEEE Standard 802.3. It is implemented by networking protocols that allow 1GB of data to be transfered at a speed of up to 1 GB per second. 1 GB Ethernet is currently being replaced in the marketplace with the faster 10GB Ethernet. The standard defines the use of data frame collision detection rather than collision avoidance. CSMA/CD is used to describe the method Ethernet protocols allow communication. This stands for Carrier Sense Multiple Access with Collision Detection. If two stations operating Gigabit Ethernet send data frames which collide, the following protocol is followed according to Standard 802.3:

Main procedure
  1. Frame ready for transmission.
  2. Is medium idle? If not, wait until it becomes ready and wait the interframe gap period (9.6 µs in 10 Mbit/s Ethernet).
  3. Start transmitting.
  4. Does a collision occur? If so, go to collision detected procedure.
  5. Reset retransmission counters and end frame transmission.

Collision detected procedure
  1. Continue transmission until minimum packet time is reached (jam signal) to ensure that all receivers detect the collision.
  2. Increment retransmission counter
  3. Is maximum number of transmission attempts reached? If so, abort transmission.
  4. Calculate and wait random backoff period based on number of collisions.
  5. Re-enter main procedure at stage 1.

Ethernet

Myrinet

Myrinet is a platform developed by Myricom to run on Ethernet LAN clusters that provides 5-10 times lower latency than Ethernet over TCP/IP. Users of Myrinet interconnects include the University of Illinois, Indiana University, the University of Southern California, Vanderbilt University, and Los Alamos National Laboratory.

Sources

[1] top500.org interconnect usage (Share %), performance statistics (Rmax Sum)

[2]IEEE 802.3 Ethernet Standard

[3] Ethernet protocol summary on Wikipedia

[4] Myrinet article