S-PACK stands for Selective Packet Acknowledgment, but was internally nicknamed Super Packet because of the implementation details. The basic concepts behind S-PACK are similar to TCP sack (selective acknowledgment) and, its send a lists of retransmission requests and acknowledgment in a bundles. It is also what I call a “rude protocol”. By rude protocol I mean when facing increased packet loss and latency instead of backing down, it became more aggressive! Some test versions were so aggressive that one implementation would go as far as bursting 100 Mbps of randomized source IP TCP like packets (Spoofed) at the destination address briefly to deliberately clog the routers and force what ever ongoing tcp connections were taking place to stall, then it would start it’s transmissions before they would start to ramp up again. This would allow S-PACK to have a clean connection to start sending through and the remaining tcp connections (that haven’t failed) would share the remainder. Fortunately most versions were not that rude, and would just use the required data rate + lost data with as little extra overhead as possible. Still in a heavy packet loss link it had a hard coded upper limit that could be as high at the outbound links. The results were on a saturated T1 of 1.5 Mbps we could start up and take 1Mbps leaving the remaining connections only 0.5 Mbps. This was Important though for live Internet events where even the network management people saw our Cybercasts as the most important traffic at that moment, and if some other QOS methods were available they would have used them also.

The first commercial public use for S-pack was with the live Internet cybercast of Arthur C. Clarke from Sri Lanka in March 17, 1997 to UIUC near Chicago, a 12 Hr time difference. The protocol gave us a clean 60 Kbps of video over the small countries totally Internet connectivity of 64 Kbps. Before we started transmitting the line was seeing 90% packet loss with ping regularly and was almost unusable for anything. It even amazed me that we were getting a smooth clean video stream across that link.

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