Ultra Ethernet: UEC 1.0 for AI Fabrics
Ultra Ethernet is the open, multi-vendor path to InfiniBand-class AI networking on standard Ethernet. The UEC 1.0 specification, released in June 2025, defines the Ultra Ethernet Transport (UET) with packet spraying, multi-path RDMA, out-of-order delivery, selective retransmission, and both sender- and receiver-based congestion control. It does not require a lossless PFC fabric. IP Infusion is a member of the Ultra Ethernet Consortium, and OcNOS-DC runs lossless RoCEv2 AI fabrics with DLB in production today.
Packet spray across every path
A single RDMA message between two GPUs is sprayed packet-by-packet across all four spine paths at once. The fabric tolerates out-of-order arrival and the destination UEC NIC reassembles in order. No flow-pinning, no hash collisions, no idle uplinks.
What the Ultra Ethernet Transport adds
RoCEv2 works, but it inherits older design constraints: one hashed path per flow, network-wide PFC pause, and window-restart loss recovery. The UEC 1.0 specification keeps the standard physical Ethernet you can buy from anyone and replaces the upper layers with a transport (UET) built for 1k to 100k GPU jobs.
Packet spraying
A single message is sprayed across every available path at once. No flow pinning, no ECMP collisions, so fabric utilisation approaches the theoretical maximum during a collective.
Multi-path RDMA
RDMA is carried over many parallel paths rather than one, so a large transfer is no longer capped by the bandwidth of a single hashed link.
Out-of-order delivery
The fabric is allowed to reorder. The UEC NIC reassembles in order before delivery, so applications and the GPU never see disorder.
Selective retransmission
Lost packets are recovered selectively rather than restarting the RDMA window, collapsing the tail-latency penalty of any in-fabric loss.
Modern congestion control
Both sender- and receiver-based schemes replace coarse PFC pause as the primary tool. UET does not require a lossless PFC fabric; pause becomes a backstop, not the front line.
Open and multi-vendor
UET runs on standard Ethernet from any vendor. The consortium, whose members span silicon, NIC, switch, and cloud companies, publishes the spec openly.
UEC, RoCEv2, and InfiniBand, axis by axis
RoCEv2 runs most AI fabrics in production today. Ultra Ethernet is the standards-based path forward as UEC-capable NICs ship, and InfiniBand remains the single-vendor specialist. Which axis matters depends on the workload and the timeline.
| Axis | RoCEv2Ethernet, today | Ultra EthernetUET, open multi-vendor | InfiniBandsingle-vendor |
|---|---|---|---|
| Path use | One hashed ECMP path per flow; parallel paths can sit idle. | Packet spray across every available path in parallel. | Adaptive routing built into the spec. |
| Loss handling | Lossless via PFC + ECN + DCQCN; relies on network-wide pause. | Tolerates loss and reorder; does not require a lossless PFC fabric. | Lossless by credit-based flow control. |
| Reordering | In-order delivery only. | Out-of-order delivery, reassembled in order at the NIC. | In-order delivery. |
| Retransmission | Window-based recovery taxes tail latency. | Selective retransmission of only the lost packets. | Link-level recovery. |
| Congestion control | DCQCN with ECN marking. | Both sender- and receiver-based control at the endpoints. | Credit-based at the link. |
| Ecosystem | Multi-vendor Ethernet at every layer. | Open, multi-vendor; any vendor can build to the UEC 1.0 spec. | Effectively single-vendor for NIC and switch silicon. |
| OcNOS-DC status | Production today on Tomahawk 4 / Tomahawk 5. | IP Infusion is a UEC member; OcNOS-DC runs RoCEv2 in production today. | Not applicable; separate fabric and tooling. |
What OcNOS-DC runs in AI fabrics today
OcNOS-DC runs a production lossless RoCEv2 fabric today with PFC, ECN, DCQCN, and sub-millisecond DLB on Broadcom Tomahawk 4 and Tomahawk 5 switches. IP Infusion is a member of the Ultra Ethernet Consortium.
Lossless RoCEv2
PFC pauses per-priority traffic before buffers overflow, ECN marks packets early, and DCQCN buffer profiles are tuned for RDMA collective traffic.
Dynamic load balancing
DLB reads live ASIC queue depth and rebinds flowlets to less-loaded paths in under a millisecond, so large flows stop colliding on one uplink.
Tomahawk 4 / 5 silicon
Runs on Broadcom Tomahawk 4 (25.6T) and Tomahawk 5 (51.2T) open switches from Edgecore and UfiSpace.
PFC deadlock watchdog
A per-port, per-priority watchdog detects paused-queue cycles and drains the queue before jobs hang.
Streaming telemetry
PFC pauses, ECN marking, DCQCN thresholds, and buffer depths stream over gNMI with OpenConfig YANG for tuning during cluster bring-up.
Vendor-neutral path
Pairing OcNOS-DC with open hardware keeps the NIC, GPU, and switch choices with the cluster owner, so no single vendor owns the AI fabric.
Build on RoCEv2 now, plan for UEC as NICs ship
Real fabrics do not switch overnight. RoCEv2 carries production AI training today, and UEC-capable NICs bring a multipath transport to standard Ethernet as they ship.
- RoCEv2 today. Production-grade for clusters built right now. OcNOS-DC ships pre-tuned RoCEv2 on Tomahawk 4 / Tomahawk 5. Most fabrics in production in 2026 are RoCEv2.
- UEC as NICs ship. UEC-capable NICs bring packet spray and selective retransmission to scale-out clusters. Cluster owners pick the NIC vendor.
- InfiniBand stays specialist. Single-vendor performance with separate cabling, management, and ecosystem. UEC brings comparable transport techniques to standards-based, multi-vendor Ethernet.
Open Ethernet for AI fabrics, on OcNOS-DC today
Ultra Ethernet brings multipath transport techniques to standard, multi-vendor Ethernet. IP Infusion is a member of the Ultra Ethernet Consortium, and OcNOS-DC runs lossless RoCEv2 with DLB in production today.
A consortium member
IP Infusion is a member of the Ultra Ethernet Consortium, which publishes the Ultra Ethernet specification openly.
Production RoCEv2 now
OcNOS-DC delivers lossless RoCEv2 with PFC, ECN, and sub-millisecond DLB today on validated open hardware from vendors such as Edgecore and UfiSpace.
Your choice of NIC
OcNOS-DC runs on open Broadcom Tomahawk 4 and Tomahawk 5 hardware and leaves the NIC and GPU choice with the cluster owner.
Ultra Ethernet, answered
What is Ultra Ethernet (UEC)?
Is IP Infusion a member of the Ultra Ethernet Consortium?
How is Ultra Ethernet different from RoCEv2?
Does OcNOS support Ultra Ethernet today?
Do I need new hardware for Ultra Ethernet?
What are packet spray and out-of-order delivery?
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