SCPS (commonly pronounced as "skips"), are the Space Communication Protocol Standards. Their origins go back to the mid-1990s, when elements of NASA, the US Air Force and the National Security Agency jointly commissioned the development of a specialized suite of data transfer protocols expressly designed for the stressed environment of space and wireless communications.

At the time, both DoD and the space science community were experiencing a common problem. For virtually every new mission employing stressed wireless communication, new protocols were being developed from scratch for the express requirements of that mission. This led to a great deal of added expense, inefficiency, duplication and contradiction of effort. What is more, there was virtually no importance being placed on standardization and interoperability. What was needed was a common set of networking protocols that could provide high-performance in high-stress environments, and could serve as the singular standard for wireless communications. Recognizing this need, DoD and NASA funded an international R&D effort aimed at creating and standardizing these protocols.

When the study began, there were several protocol options being considered, including GOSIP, the Space Station Communication Protocols, and the then fledgling Internet standards. There were also a number of custom protocols being developed at the time, but these were not given any serious consideration since "rolling your own" protocol was the very problem the SCPS effort was trying to eliminate. The momentum the Internet was gaining at the time was very compelling, and ultimately the Internet suite was chosen as the basis for SCPS.

In 1993, an elite team of protocol engineers was assembled with representatives from throughout the international space science community, charged with the research and development of these stressed protocol standards. But, the SCPS researchers quickly discovered performance problems in running Internet protocols over errored, asymmetric, high-latency links. Bit efficiency and bandwidth efficiency were a serious limitation, and it was clear that augmentations to the Internet protocol suite would necessary for it to become an accepted standard.

The Performance Objectives

Their goals in modifying these protocols were fairly straightforward; create a set of protocols that offer:

• the best possible use of limited bandwidth
• high link utilization
• power conservation
• prioritization of traffic
• tolerance of intermittent connectivity
• high forward/return link asymmetry
• adaptation to the environmental stress of wireless networks

And perhaps most important of all, these protocols had to be based on current Internet protocols and fully interoperable with IETF standards. It was generally agreed that the development of any new protocols that were not based on current Internet standards would become yet another proprietary solution, and would do little to uncomplicate the standardization and interoperability issues plaguing the wireless community. The engineers went to work with these objectives in mind, and after about a 3-year development effort the SCPS suite of protocols were born.

The technology far exceeded expectations in terms of the throughput, reliability and efficiency it achieved in transporting Internet traffic over stressed links. What was previously considered impossible not only worked, but could be done by simply modifying the existing IETF standards. The SCPS suite of protocols have since been tested under a variety of operational and environmental conditions and have consistently produced remarkable results. Not only does SCPS mitigate the throughput degradation associated with latency and asymmetry, but it employs a series of error-resistant technologies that provide rapid recovery from packet loss. The primary focus of SCPS to date has been in satellite communications, but it has also been integrated into wireless LAN/WAN environments and mobile wireless telemetry platforms, where it has produced similar performance benefits.

SCPS as a DoD Standard

In addition to the performance objectives, the SCPS consortium was looking to establish these protocols as an international standard for the wireless networking community. Today, the SCPS suite has been adopted as a standard by the International Standards Organization (ISO) and the Consultative Committee on Space Data Systems (CCSDS). But by far the broadest adoption of the SCPS standard has been within the US Department of Defense. It currently bears the advisory standards designator Mil-Std-2045-44000, issued by MilSatCom/Military Protocols over Satellite (MPOS). SCPS is also a standard within TIA-1008-A Internet Protocols over Satellite (IPOS) and registered in the DoD Information Technology Standards Registry (DISR). It is the most commonly specified acceleration requirement in DoD, covering fixed and mobile satellite and terrestrial wireless networking.

Global Protocols and the SCPS Effort

Global Protocols employs many of the original members of the SCPS development effort, including the author of the SCPS Green Book and developer of the SCPS Transport Protocol. Today, we are the primary contributor to the evolving DoD standard for SCPS implementations, and work closely with military customers, DISA and their supporting contractors to ensure that vendor implementations of SCPS meet the DoD's evolving acceleration requirements.

SkipWare® and SCPS RI

SkipWare® is Global Protocols' expert implementation of the SCPS-Transport Protocol. It should not be confused with the reference implementation (RI) distributed by Mitre Corp., nor should they be mistaken for other vendors' proprietary SCPS implementations.

SkipWare is by far the largest implementation of SCPS in the DoD, and as a result SCPS and SkipWare have become almost synonymous. However, there are significant performance and feature differences between the RI, other vendors' SCPS implementations, and Global Protocols' products. When the term "SCPS" is used, it is important to know the context in which the term is applied, and what specific implementation is being referenced in order to ensure that program requirements are properly met.

What is the SCPS Reference Implementation?

The SCPS Reference Implmentation (RI) was the original blueprint code for what is today the SCPS standard. The RI is maintained and distributed by the Mitre Corporation through funding provided by NASA/JPL. Anyone seeking to build their own SCPS implementation, integrate SCPS onto a network hardware platform, or simply evaluate the protocols, is encouraged to first review this open-source distribution.

How do I get the SCPS-RI?

To obtain a copy of the SCPS-RI, please contact the NASA Project Manager at NASA/JPL.

What will I receive?

The SCPS-RI is provided as C source code, intended to be compiled on a FreeBSD platform. Users are required to build their own binaries for the gateway code. The RI is less than 1 Mb in size and can usually be sent as an email attachement. It contains readme files to assist in the build and the configuration settings.

What can Global Protocols, Inc. provide in the way of SCPS-RI support?

While Global Protocols does not directly support the RI code, our staff is intimately familiar with the code and its performance. Global Protocols offers consulting services to clients seeking support and consulting while working with SCPS-RI.