Service specific coordination function for transparent assured delivery with AAL5 (SSCF-TADA5)

Abstract

One of the main issues emerging in satellite networks is the efficient and assured delivery of data. TCP/IP over ATM over poor quality links is known to fail catastrophically. The major source of this failure is that TCP incorrectly assumes all loss or corruption of data is due to network congestion, so TCP reacts inappropriately. In general, two approaches can be considered. In the first approach, TCP distinguishes between congestion and non-congestion errors and handles the non-congestion errors properly. In the second approach, TCP is shielded from non-congestion errors, so that it doesn't invoke unnecessary congestion control mechanisms. In this paper, a service specific coordination function for transparent assured delivery with AAL5 (SSCF-TADA5) is described. SSCF-TADA5 operates to guarantee the transparent assured delivery of data in TCP/IP over ATM over degraded physical link conditions such as those encountered on a satellite radio link, which is characterized by long propagation delay, high error rate with burst errors, and low throughput. Therefore, TCP is totally shielded from non-congestion errors resulting from poor physical link conditions. SSCF-TADA5 coordinates between the user plane AAL5 service interface and the service specific connection oriented protocol (SSCOP), thereby forming a new service specific convergence sublayer (SSCS) supporting classical IP over ATM. We discuss the design of SSCF-TADA5, and then compare TCP/IP performance with and without SSCF-TADA5. The results of the test show that assured delivery with SSCF-TADA5 significantly mitigates the degradation in the most severe cases, which combine high error rate with high channel utilization.