TCP and UDP work fine over terrestrial networks where packet loss and latency isn't a problem, but both have problems over wireless links where packets may be lost or latency is high. Researchers at MIT and its Lincoln Laboratory, together with colleagues at the Hamilton Institute in Maynooth, Ireland, have developed a data-coding technology they say could more than double bandwidth on satellite Internet connections. The improvements could be most noticeable to TV news viewers because it would reduce dropped frames and glitches on IP-based transmissions from overseas correspondents.
TCP offers error correction and ensures the packets arrive in the correct order and intact, but the high latency present in satellite links limit data capacity. UDP does not require handshaking, but offers no error correction. The data coding the researchers are developing is a variant on TCP. Instead of the back and forth handshaking required for TCP links, it sends mathematical functions describing multiple packets so that a receiving device, such as a satellite terminal, can solve for the missing packets without requesting a repeat transmission.
Inmarsat plans to test the coding technology in 2014. Ammar Khan, design authority at Inmarsat, said, “We are hoping it would give us clean video with fewer disruptions. You transfer more packets than what you normally would, but you don’t have to retransmit.” This could increase throughput by as much as 20-fold in conditions where data losses are exceptionally large.
So far, the technology has been tested in lab simulations that simulate the high latency and data losses found on satellites. Khan noted, “We’ve efficiently juiced a lot from all the other technologies we’ve used. Network coding is a strong contender to boost further what we can do.”
The satellite transmission work expands on work Muriel Medard and colleagues at MIT have been pursuing to improve Wi-Fi and other terrestrial networks and even to improve efficiency on wired connections in data centers. Details are available in the paper Network Coded TCP (CTCP) Performance over Satellite Networks.