The paper is presented by Prof. Mark Handley (University College London). This paper has received a SIGCOMM 2017 Best Paper Award.
The talk starts by describing three goals in DC networks:
- low latency between hosts
- receiver prioritisation
- predictable high throughput
One of the key ideas in this paper is the use of packet trimming when a switch queue fills up. This idea proposed as Cut Payload (CP) in this paper (worth checking out):
P. Cheng, F. Ren, R. Shu, and C. Lin. Catch the whole lot in an action: Rapid precise packet loss noti cation in data centers. In Proc. Usenix NSDI, 2014.
In NDP, the authors addressed the shortcomings of CP with the following changes:
- An NDP switch maintains separate queues for data packets and higher priority trimmed header packets. This provides low latency similar to lossless Ethernet, without the collateral damage caused by pausing.
- An NDP switch performs weighted round robin between the high and low priority queues. This can eliminate congestion collapse.
- An NDP switch decides wether to trim a newly arrived packet or the data data packet at the end of the low priority queue. This breaks up phase effects.
On top of presenting a switch queuing algorithm, NDP proposes a per-packet multipath forwarding and a novel transport protocol.
- NDP provides very low flow completion time.
- NDP provides much better isolation between different workloads than mechanisms such as DCQCN (that rely on lossless Ethernet for low delay).
- Incast: While other solutions have also tackled this problem well (see figure below), the important part is that NDP solves the incast problem using only 8 packet buffers.
You can check out the great animations that were presented during the talk here.
The talk was followed by a lively Q&A, with questions on fairness (NDP ensures fairness), network topology (NDP requires a Clos topology) and failure awareness (NDP handles link failures by maintaining scores for links).