Transport Protocol for Asymmetric Communication
Communication channels with asymmetric uplink/downlink bandwidth are very common nowadays. Popular residential access technologies, such as Digital Subscriber Line (DSL), often divide available bandwidth in an asymmetric manner, where the downlink bandwidth is much higher than uplink bandwidth. Other systems may employ two separate communication channels as uplink and downlink, where the downlink channel has much higher bandwidth than the uplink one. For example, in rural area, systems may use satellites or TV-like broadcast for downstream and use analog modem for upstream traffic. While this asymmetry might be desirable in server-client based applications, it is less ideal for peer-to-peer based ones. This is because a client may exhaust it uplink bandwidth without utilizing its downlink bandwidth, which gets simply wasted.
One nature question is: Can we allocate the, otherwise idling, downlink bandwidth for uplink usage, so that the uplink bandwidth is increased? In 2001, from information theory aspect, Adler and Maggs media:AM01.pdf showed that using a properly-designed protocol, the downlink bandwidth can be used to accelerate upload speeds. Note that, they did not propose a real network protocol that can be used in the wild. Instead, their work (and several other extended works) strived to prove the feasibility of dynamically reallocating bandwidths in a mathematic way. Moreover, previous works presented several upper bounds of the upstream bandwidth improvement. See media:Gagie06.pdf (and the references therein) for a brief survey.
To our best knowledge, there has been no practical protocols in the literature, which support this kind of bandwidth reallocation. Using such a protocol can increase the bandwidth utilization of the residential (the-last-mile) links. It can be even more helpful in rural area, such as deserts, where uplink bandwidth is limited by the infrastructure and likely to be low. Hence, designing and implementing a transport protocol for asymmetric communication, ideally a TCP drop-in, has potential to benefit a large number of users all over the world.
