The National Institute of Advanced Industrial Science and Technology (AIST,), an independent administrative institution, has released software PSPacer 1.0 for accurate network bandwidth control and traffic smoothing. PSPacer 1.0 realizes accurate bandwidth control and smoothing on the ordinary personal computer (PC) based on the Linux operating system (OS) without requiring special purpose hardware. The PSPacer 1.0 suppresses bursty traffic, improves the efficiency of long-distance wide-bandwidth communications through the internet and contributes to improving the quality of stream delivery.

In the PSPacer-based communications, the packet transmit spacing is uniform ensuring stable communications.

In the Internet Protocol (IP) communications, bursty traffic often occurs, sending a greater number of packets in a short interval and temporarily exceeding the available bandwidth. Under such a situation, buffers for switches and routers in the network overflow, causing some packets lost and effective communication performance markedly degraded. In the ordinary PC and streaming servers, the onset of bursty traffic is unavoidable, to deteriorate the quality of communications. In order to suppress bursty traffic, smoothing is needed to ensure equally spaced packet transmission in compliance with available bandwidth.

The GTRC-AIST has noticed the possibility of ensuring efficient communications by smoothing bursty traffic, and has developed and been utilizing a smoothing hardware. For the purpose of extending this technology to versatile use, smoothing software PSPacer has been developed.

The development work of PSPacer has been partly supported by a grant from the Ministry of Education, Sports, Culture, Science and Technology (MEXT) of Japan through the NAREGI (National Research Grid Initiative) Project.

Up to now, the control of packet transmit interval with software has been made through the timer interruption. The timer interruption provided by the Linux and other operating systems gives spacing 1 to 10 ms, which is not small enough for accurate control of transmit interval. On the other hand, shortening interval of timer interruption increases the processor burden, providing unfavorable effects to computation and communication performance of the computer.

The PSPacer 1.0 controls transmission intervals through the transmission of additional packet (gap packet) between adjacent packets without timer interruption. The transmit interval can be controlled accurately by adjusting the number and size of gap packets. As the gap packets are discarded at the input ports of switches and routers, they do not affect the network.

With the PSPacer 1.0, it is possible to provide bandwidth control and smoothing for each of 100 or more connections by use of ordinary PC. In case of gigabit Ethernet, the transmission bandwidth can be set for a range from 8 kbps to 930 Mbps for each of IP communication connections, and the packet transmission interval can be controlled at an accuracy of time for 1-byte data transmission in accordance with the bandwidth.

The PSPacer 1.0 is installed as a loadable kernel module for the Linux platform, to be ready for being introduced independent of the device driver. After the installation of the PSPacer 1.0, all that's required is to specify (1) the packet allocation rule with IP address and port No., (2) the communication interface for bandwidth control and smoothing and (3) the allocated maximum bandwidth. Applications to use the network are not required to be changed. The software also supports IPv6.

With the PSPacer 1.0, variations in transmission bandwidth are kept at the minimum level, and the possibility of buffer overflow is reduced. For this reason, it is possible to drastically augment the utilization efficiency of the network physical bandwidth.

The PSPacer 1.0 can be effectively used for the following applications.

1. Long-distance wide-bandwidth TCP/IP communications: In the TCP/IP, which is  widely used in the internet communications, the maximum volume of data to be transmitted is controlled in accordance with roundtrip time. For this reason, bursty traffic may easily occur in the long-distance network where the latency is large. With the PSPacer 1.0, it is possible to utilize 90 % or more of network bandwidth even in the intercontinental communications with very large latency.
2. Multiple communications through one-and-same path: When multiple traffics are carried through one-and-same path in the network as in case of stream delivery, it may occur that bursty traffics in each of communications are summed up readily going beyond the available bandwidth. With the PSPacer 1.0, each traffic does not surpass the setup bandwidth making it possible to utilize the network bandwidth to the maximum extent.

The PSPacer 1.0 is distributed as open source software under the terms of the GNU General Public License (GPL), and can be downloaded from GridMPI