Introduction to SCPS-TP

The Space Communications Protocols Specification (SCPS) defines a set of revisions to the Internet protocols to enable them to operate properly over stressed communications links. It extends normal TCP/IP to become an ’upgraded’ TCP. XipLink is an independent, high performance implementation of the SCPS-TP standard, with further extensions and enhancements for satcom and wireless link optimization. SCPS has been selected as the standard TCP Acceleration mode for all networks, as well as other inernational governments and companies.

XipLink was the first independent implementation of SCPS-TP from the specification. It was also the first in-kernel implementation of SCPS, and remains the most scalable solution today.

SCPS-TP addresses any IP communications link with significant round trip delay or loss not due to network congestion. Many of the unusual characteristics of satellite links are also found in terrestrial wireless scenarios; in fact, the secondary design goal for SCPS was to improve the performance of wireless links in military tactical environments.

With SCPS-TP, the bandwidth of an existing link will be utilized to a significantly higher percentage and more efficiently. This translates directly to faster data transfer and/or accommodating more connections (or customers) with the existing link infrastructure. The SCPS-TP advantage grows dramatically as link quality decreases. The SCPS transport layer, SCPS-TP, is compatible with Internet applications and the Internet itself. It can take the place of the TCP stack in a user’s PC, or be deployed as a pair of gateways across a stressed communications segment in a conventional IP network.

SCPS was actually designed as a protocol suite, with an SP security layer, FP file transfer, and NP network protocol (a scalable IP in fact). However, with the evolution of the Internet and supporting protocols, these other SCPS layers have become less relevant. We recommend normal IPSec instead of SCPS-SP, for example.

Wireless data communications differ significantly from the wired Internet with respect to:

  • Bit-error rate
  • Round-trip delay
  • Continuity of connectivity
  • Forward and reverse link capacity
  • CPU and memory capacity
  • Communications goals
  • Primary source of data loss

More information on SCPS can be found at www.scps.org