  User Datagram Protocol (UDP) is a commonly used protocol for data
transmission in small embedded systems. UDP as such is unreliable and packet
losses can occur. The achievable data rates can suffer if optimal packet sizes
are not used. The alternative, Transmission Control Protocol (TCP) guarantees
the ordered delivery of data and automatically adjusts transmission to match
the capability of the transmission link. Nevertheless UDP is often favored over
TCP due to its simplicity, small memory and instruction footprints. Both UDP
and TCP are implemented in all larger operating systems and commercial embedded
frameworks. In addition UDP also supported on a variety of small hardware
platforms such as Digital Signal Processors (DSP) Field Programmable Gate
Arrays (FPGA). This is not so common for TCP. This paper describes how high
speed UDP based data transmission with very low packet error ratios was
achieved. The near-reliable communications link is used in a data acquisition
(DAQ) system for the next generation of extremely intense neutron source,
European Spallation Source. This paper presents measurements of UDP performance
and reliability as achieved by employing several optimizations. The
measurements were performed on Xeon E5 based CentOS (Linux) servers. The
measured data rates are very close to the 10 Gb/s line rate, and zero packet
loss was achieved. The performance was obtained utilizing a single processor
core as transmitter and a single core as receiver. The results show that
support for transmitting large data packets is a key parameter for good
performance.
  Optimizations for throughput are: MTU, packet sizes, tuning Linux kernel
parameters, thread affinity, core locality and efficient timers.
