Congestion Control in New Storage Architectures Q&A

We had a great response to last week’s Webcast “Controlling Congestion in New Storage Architectures” where we introduced CONGA, a new congestion control mechanism that is the result of research at Stanford University. We had many good questions at the live event and have complied answers for all of them in this blog. If you think of additional questions, please feel free to comment here and we’ll get back to you as soon as possible.

Q. Isn’t the leaf/spine network just a Clos network?  Since the network has loops, isn’t there a deadlock hazard if pause frames are sent within the network?

A. CLOS/Spine-Leaf networks are based on routing, which has its own loop prevention (TTLs/RPF checks).

Q. Why isn’t the congestion metric subject to the same delays as the rest of the data traffic?  

A. It is, but since this is done in the data plane with 40/100g within a data center fabric it can be done in near real time and without the delay of sending it to a centralized control plane.

Q. Are packets dropped in certain cases?

A. Yes, there can be certain reasons why a packet might be dropped.

Q. Why is there no TCP reset? Is it because the Ethernet layer does the flowlet retransmission before TCP has to do a resend?

A. There are many reasons for a TCP reset, CONGA does not prevent them, but it can help with how the application responds to a loss.  If there is a loss of the flowlet it is less detrimental to how the application performs because it will resend what it has lost versus the potential for full TCP connection to be reset.

Q. Is CONGA on an RFC standard track?

A. CONGA is based on research done at Stanford. It is not currently an RFC.

The research information can be found here.

Q. How does ECN fit into CONGA?

A. ECN can be used in conjunction with CONGA, as long as the host/networking hardware supports it.

 

 

New Webcast: Data Center Congestion Control

How do new architectures being deployed in today’ s data centers affect IP-based storage? Find out on September 15th in our next SNIA Ethernet Storage Forum live Webcast, “Data Center Congestion Control,” where we will discuss new architectures and a new congestion control mechanism called CONGA. Developed from research done at Stanford, CONGA is a network-based distributed congestion-aware load balancing mechanism. It is being researched for use in next generation data centers to help enhance IP-based storage networks and is becoming available in commercial switches. This Webcast will dive into:

  • A definition of CONGA
  • How CONGA efficiently handles load balancing and asymmetry without TCP modifications
  • CONGA as part of a new data center fabric
  • Spine-Leaf/CLOS architectures
  • Affects of 40g/100g in these architectures
  • The CONGA impact on IP storage networks

Discover the new data center architectures that will support the most demanding applications such as big data analytics and large-scale web services. As always, this Webcast will be live. I encourage you to register today and bring your questions.