Several techniques have been developed to meet the demand for faster and more efficient access to the Internet. Different applications have different networking requirements. For example, real-time interactive voice requires a low latency network path, but does not require high bandwidth. QoS refers to the ability of a network to provide improved service to selected network traffic over various underlying technologies including Frame Relay, SONET, and IP-routed networks. In particular, QoS features provide improved and more predictable network service by providing the following services: Supporting dedicated bandwidth, improving loss characteristics, avoiding and managing network congestion, shaping network traffic, setting traffic priorities across the network. This paper introduces various tcp protocol problems and their solution used in avoiding and managing network congestion.