Transport Protocol for Asymmetric Communication
Communication channels with asymmetric uplink/downlink bandwidths 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. Other systems may employ two uni-directional communication channels, where the downlink channel has much higher bandwidth. For example, in rural area, network systems may employ satellites or TV-broadcasts for downlink traffic and use analog modem for uplink traffic. While this asymmetry is desirable in server-client applications, it is less ideal for peer-to-peer applications. 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 the upload speed. Notice that, they did not propose an actual network protocol that can be used in the wild. Instead, they strived to prove the feasibility of dynamically reallocating bandwidths. Extended works in the literature have also reveal the upper bound of the potential improvement on upstream bandwidth. See media:Gagie06.pdf for a brief survey and references.
To our best knowledge, there has been no practical protocol in the literature, which supports dynamic bandwidth reallocation. Using such a protocol can increase the bandwidth utilization of the residential (last-mile) links. It is even more useful 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.
