This actually can lead to a very interesting discussion about TCP friendliness, which I didn't have space to elaborate in paper:

1. The Trend of Selfish Applications:
TCP's poor performance is not only an object of research study. More and more applications have chosen to ignore the notion of TCP friendliness and use selfish application-level optimization techniques such as opening many parallel connections (as in modern web browsers and GridFTP), contacting multiple servers in parallel (in BitTorrent), or modifying TCP to use a very large initial window size. In fact, some CDN providers use selfish optimization of TCP to accelerate data transfer from CDN servers to end users on the public Internet. This trend indicates that often, applications prefer higher performance regardless of potential TCP unfriendliness. Although we recommend use of PCC only when it is isolated from legacy TCP, it is likely that due to PCC's robust high performance, some or many users (especially those suffering in network environments that are challenging for TCP) will use PCC as another selfish performance optimization technique. Legacy TCP users, on the other hand, will unfortunately suffer from performance degradation when competing with PCC and other selfish optimization techniques under FIFO queue based network.

What happens next in this tussle? One possibility is a slow arms race towards selfish high performance rate control. If done through adoption of PCC using our safe utility function, it will actually avoid a ``tragedy of the commons'' situation as we have shown. But more immediately, network owners (ISPs) will likely take action to avoid complaints.

2.ISP response to selfishness:

o maintain legacy TCP users' satisfaction, network operators can respond to selfishness by deploying flow-level or customer-level resource isolation at the point of congestion. Of course this requires hardware support, but it is feasible for two reasons. First, unlike protocols like XCP and RCP, an ISP can deploy resource isolation as a local change at an individual congested device, requiring no signaling or packet header changes or explicit feedback to end-hosts. Second, the belief that per-flow FQ is infeasible for high speed switching hardware is now a misconception, with merchant silicon supporting hundreds of thousands of flows at hundred-gigabit speeds. Even by 1999, early implementations used limited hardware (less than 33Mhz FPGA or CMOS) to support FQ on multi-gigabit links. Today, an off-the-shelf EZchip NP-4 supports 256K flows with 100 Gbit throughput, VSC2202 supports 500K flows with Gigabit Ethernet throughput, and so on. We obtained a quote of $25 for the VSC2202, of which the cost of the FQ logic itself is only a fraction.} In certain cases resource isolation is already deployed; cellular networks for example use separate queues for each user.

3. Towards a new architecture?

The above trends suggest that in-network resource isolation may be increasingly deployed as a consequence of the continuous tussle between applications optimising selfishly and ISPs protecting their infrastructure with means that are feasible to deploy. We argue that this process is actually (slowly) evolving the Internet towards a fundamentally better architecture: end-hosts focus on optimising their desired performance, while the network's job is to isolate resources across users. This architecture offers a clean separation of concerns. End-hosts in this architecture deal with what they can directly observe and control, leading to simple, clean designs and the flexibility to express their heterogenous objectives and even safely evolve to new end-to-end protocols. Similarly, the network deals with what it directly observes and cares about, i.e., competition between users or flows. Our evaluation has already demonstrated the flexibility that results from this architecture.