Infiniband vs Ethernet: Detailed Insights into Latency, Performance, Scalability, and Cost

Introduction to InfiniBand and Ethernet

InfiniBand and Ethernet are two dominant networking technologies in modern AI and high-performance computing (HPC) environments. InfiniBand has long been valued for its ultra-low latency and high bandwidth, making it a preferred choice for demanding workloads. However, Ethernet is steadily advancing, particularly with innovations like Ultra Ethernet, which aims to enhance its performance for large-scale AI applications. Both technologies have their strengths, and the choice between them depends on specific requirements such as performance, scalability, and cost.

InfiniBand vs. Ethernet: Architecture

InfiniBand Architecture

InfiniBand leverages a point-to-point, switch-based architecture with links capable of reaching speeds up to 800 Gbps, ensuring ultra-low latency of less than 1 microsecond. This is made possible by its efficient link-layer protocol, which uses LIDs (Local Identifiers) instead of IP addresses for routing, significantly reducing protocol overhead and accelerating packet transmission.

InfiniBand's flow control operates on a credit-based system, where the sender only transmits data when the receiver's buffer has available space, preventing congestion and packet loss. It also features end-to-end flow control, ensuring stable data transmission across multiple hops, and making it highly reliable for data-intensive tasks. The architecture includes a robust Quality of Service (QoS) mechanism using virtual lanes (VLs) and service levels (SLs) to prioritize traffic, ensuring latency-sensitive data is transmitted with higher priority.

InfiniBand supports scalable topologies like fat-tree and full mesh, making it ideal for large compute clusters. Additionally, it supports RDMA (Remote Direct Memory Access), enabling direct data transfers without CPU intervention, further reducing latency. These capabilities have made InfiniBand a preferred technology for high-performance data centers, scientific computing, and financial applications, especially in scenarios with extreme performance demands.

Ethernet Architecture

Ethernet is the world’s most widely used networking technology, known for its flexibility, cost-efficiency, and broad compatibility. Its switch-based architecture allows point-to-point connections between multiple devices, with speeds ranging from 1 Gbps to 800 Gbps to meet the growing demands of high-bandwidth applications. Built on the TCP/IP protocol stack, Ethernet offers extensive network compatibility, though this layered structure introduces more overhead compared to InfiniBand, leading to slightly higher latency.

Ethernet uses IP addresses for routing and complex protocols like BGP (Border Gateway Protocol) for flexible data transmission in large networks. Its flow control mechanisms include traditional and Priority Flow Control (PFC), which can pause traffic at specific priority levels under high load without impacting other traffic. The fine-grained control helps Ethernet operate in data center environments needing efficient traffic management. Ethernet also utilizes Explicit Congestion Notification (ECN) to manage congestion so the sender can adjust traffic before packet loss occurs.

 

Ethernet’s Quality of Service (QoS) features enable traffic classification and prioritization using DSCP (Differentiated Services Code Point) and Weighted Fair Queuing (WFQ), ensuring that real-time applications like voice and video receive the necessary bandwidth and low-latency processing, even in busy networks. Ethernet's scalability is another strength, supporting network topologies like star and tree, making it highly adaptable for large-scale deployments. With the addition of RoCE (RDMA over Converged Ethernet), Ethernet is narrowing the latency gap with InfiniBand, positioning itself as a viable option for low-latency scenarios.

InfiniBand vs. Ethernet: Latency

InfiniBand Latency

Due to its native RDMA protocols and lack of TCP/IP overhead, InfiniBand has ultra-low latency of 1-2 microseconds. Without the CPU, data may be transferred between nodes' memory regions. InfiniBand's cut-through switching technology lowers latency than Ethernet's store-and-forward switching, forwarding packets when the destination is found.

Hardware-based flow control and deterministic queuing minimize congestion and packet loss in InfiniBand for throughput at ultra-low latencies. In large-scale implementations, SHARPv4 allows FP8-precision data operations inside the network for lower needless data transfer and latency. In the ongoing InfiniBand vs. Ethernet debate, InfiniBand's architectural benefit is obvious in AI and HPC applications where quick inter-node communication is needed.

Ethernet Latency

Ethernet latency varies depending on the standard, with performance improving as speed increases. However, the TCP/IP overhead contributes to delay, as operations like packet construction, acknowledgment, and error checking can cause up to 100 microseconds of latency in high-throughput scenarios. Additionally, in multi-hop Ethernet networks, each switch introduces further delays.

RoCE (RDMA over Converged Ethernet) addresses these inefficiencies by enabling direct memory access over Ethernet, reducing CPU overhead, and bypassing TCP/IP. RoCEv2 improves RoCEv1 by supporting IP routing and overcoming the limitation of requiring the same L2 network. This makes RoCEv2 more flexible for large data centers and environments spanning multiple network segments while retaining the core advantages of RDMA, such as zero-copy data transfer. In this process, data moves directly from the application’s memory to the destination host without CPU intervention, significantly reducing latency and CPU resource consumption. Data Center Bridging technologies like PFC (Priority Flow Control) and ETS (Enhanced Transmission Selection) further create lossless Ethernet fabrics, reducing latency for specific traffic types. However, due to Ethernet’s processing complexity, it remains slower than InfiniBand in most high-performance computing (HPC) and AI workloads.

InfiniBand vs. Ethernet: Performance, Scalability, and Flexibility

Ethernet

Ethernet, especially 400GbE and 800 GbE, boasts outstanding performance figures. Such developments have helped AI workloads and hyperscale settings. Ethernet's lower latency because of RoCEv2 renders it competitive for numerous HPC applications. 

Also, Ethernet's backward compatibility allows it to be added to existing data centers. Scaling up doesn't need a total infrastructure upgrade since most companies use standard Ethernet switches and NICs. Ethernet can manage high traffic levels without congestion due to its non-blocking switch designs and leaf-spine structures. ECMP, or Equal-Cost Multi-Path Routing, helps load balance connections for greater performance under high loads.

InfiniBand

InfiniBand supports 800Gb/s and 1600Gb/s lines with ultra-low latency and high bandwidth. InfiniBand fabrics can link thousands of nodes and network cards in a two-tier design. HPC clusters need this scalability to sustain low-latency inter-node communication. 

InfiniBand's credit-based flow control may encounter challenges during microbursts or unexpected traffic scenarios, especially under severe loads. However, InfiniBand typically uses Explicit Congestion Notification (ECN) and adaptive routing to redirect traffic, alleviate congestion, and maintain performance. These techniques are generally effective in high-load environments, ensuring efficient traffic management and sustained performance. However, in large clusters, physical layer failures in optical components can still pose a bottleneck, potentially affecting the promise of a lossless network. When it comes to failover, Ethernet generally achieves faster failover speeds—about 30 times quicker—but InfiniBand maintains an advantage in delivering low latency and high throughput in heavy computational environments, making it suitable for applications that require consistent, high-performance communication.

Cost Considerations of Infiniband and Ethernet

InfiniBand

Hardware influences InfiniBand's cost, including high-end switches, HCAs, and optical or DAC/AOC connections for low-latency, high-bandwidth settings. Standard InfiniBand switches may cost over $20,000 per unit, based on port density and cooling (air or liquid). 

Plus, InfiniBand cables (e.g., QSFP56 for HDR or OSFP for NDR) cost more than Ethernet cables owing to their designs and fast speeds. Because each interruption needs costly optical transceiver replacements, InfiniBand networks have high maintenance costs. In multi-tier InfiniBand setups, scaling needs huge infrastructure investment, so MLNX-OS for InfiniBand switches and Fabric Manager raise expenses.

Ethernet

Meanwhile, Ethernet uses scale to decrease costs. 800Gb/s Ethernet switches cost $1,000 to $10,000, depending on feature set and port count. Ethernet adapters and NICs are accessible and cheaper than InfiniBand HCAs, with basic 100GbE adapters costing $400 to $1,800. 

Ethernet's widespread usage facilitates commodity hardware integration for lower operating costs. What is more, Ethernet's quicker failover than InfiniBand decreases downtime costs in big installations. Ethernet's compatibility with regular routers and switches simplifies infrastructure and cuts maintenance costs with cheaper, off-the-shelf parts.

Conclusion

Choosing between Ethernet and InfiniBand should be based on your specific performance, scalability, and cost requirements. In many cases, both technologies can be deployed together in a hybrid network setup, allowing organizations to leverage the strengths of each. We UfiSpace focus on Ethernet-based solutions for AI networking. Welcome to learn more at our AI solution page.