U-Net: Protected, User-Level Networking Interface

Last modified 13-Jan-1998 by M. Welsh

This is the release documentation for U-Net, a low-latency communication mechanism over ATM and Fast Ethernet. U-Net is a research product of the Systems Group at the Cornell University Computer Science Department and Matt Welsh at UC Berkeley.


U-Net is a protected, user-level network architecture for low-latency and high-bandwidth communication. ATM, Fast Ethernet, and Myrinet are the network media supported with this release. Benchmarks have demonstrated round-trip (ping-pong) latencies of as low as 60 microseconds (Fast Ethernet) and 65 microseconds (ATM) for 40-byte messages. The full bandwidth of the physical network can be exploited using small messages (800 - 1000 bytes).

The primary application for U-Net is low-latency communication in workstation clusters, for parallel and distributed computing tasks. The Active Messages communication layer and Split-C parallel language have both been ported to U-Net, and demonstrate that a cluster of workstations communicating via U-Net can rival the performance of commerical MPPs.

The U-Net ``philosophy'' is that low-latency communication can be obtained using off-the-shelf, commodity components and widespread network media (such as ATM and Fast Ethernet). U-Net also suggests that direct, user-level access to the network interface (removing the kernel from the critical path of communication) is vital for obtaining low latency. This approach also allows applications to implement their own communication protocols and tailor their own communication patterns and needs.

Unlike other user-level network architectures, U-Net stresses protection. While it is possible to simply write device registers from a user application, this does not allow multiple applications to share the network interface, or enforce protection boundaries between them. The U-Net interface allows the network device to be shared and enforces protection between applications, so that one (malicious or buggy) application cannot affect the communication of others, or cause the system or network interface to crash.

The U-Net design is described in the SOSP '95 paper referenced below.


The following release documents are available:


Please see the following sites for introductory and conceptual information about U-Net.

Contact Information

The following people are involved with the U-Net project. Feel free to get in touch if you have questions or problems. Matt Welsh is the contact point for general questions about the U-Net software release for UNIX.