In this paper, we analyze a model for transport control protocol (TCP) along with a non-adaptive virtual queue (VQ) and an adaptive virtual queue (AVQ) management policy. In the class of transport protocols, we focus on compound TCP as it is the default protocol in the Windows operating system. We start by conducting a local stability analysis for the underlying fluid models. For the VQ policy, we show that small virtual buffers play an important role in ensuring stability, whereas the AVQ policy could readily lose local stability as the link capacity, the feedback delay, or the link's damping factor gets large. With both the queue policies, the protocol parameters of compound TCP also influence stability. Furthermore, in both the models, we explicitly show that as parameters vary the loss of local stability would occur via a Hopf bifurcation. For the AVQ policy, we are also able to analytically verify if the Hopf bifurcation is super-critical, and determine the stability of the bifurcating limit cycles. Packet-level simulations, conducted over two topologies, using the network simulator (NS2) confirm the existence of stable limit cycles in the queue size.

Transport protocols that use explicit rate feedback are a promising alternative to the algorithms which use implicit, packet loss based feedback. A key issue in the design of rate controlled communication networks is how new flows may be admitted at a fair and high starting rate. In this paper, for the management of new flows we present a modified NetFPGA Rate Control Protocol (RCP) implementation for a recently proposed admission management process at the routers. Using this implementation, we perform an evaluation of the admission of new flows in rate controlled networks. We conduct experimental tests across a range of bandwidth-delay product environments, and also deal with the arrival of a large number of flows. Our work serves to exhibit that the proposed admission management process appears to be an attractive method for dealing with the admission of new flows while maintaining small queues. Additionally, the algorithm allows the routers to maintain a specified target link utilisation. A consequence of such small queues is that buffers, in routers, may be dimensioned to be much smaller than the current, bandwidth-delay product, buffer sizing rule.