Message-level Ordering Transportation

Motivation

1. Connection-level transmission control requires that different messages must be delivered in order, resulting in head-of-line blocking;
2. The connection-level transmission control usually needs to cooperate with the flow-by-flow ECMP strategy, so as to minimize the disorder degree when the data packets arrive at the receiving end. This coarse-grained load balancing strategy reduces network utilization;
3. Datagram-level transmission control cannot guarantee the reliability of data transmission and the in-order delivery of different packets within the same message.

The operation rate of Mellanox CX5 declines when concurrent connnection scales.

Overview

Based on the problems existing in the existing RDMA transmission control scheme, we propose an RDMA transmission control method with message-level ordering. Strict priority between messages is often unnecessary, and the introduction of sequence control between messages can easily lead to head-of-line blocking, and also indirectly reduce network resource utilization. In fact, what needs to be strictly guaranteed is the order between different packets within a message. This solution realizes reliable transmission at the message level and the sequential delivery of data packets in the message, which greatly alleviates the problem of head-of-line blocking, improves the load balancing effect, and reduces the complexity of application development.