Answer: C

The transport layer is responsible for reliable data delivery. This layer implements a flow control mechanism that can detect congestion, reduce data transmission rates and increase transmission rates when the network appears to no longer be congested (e.g., TCP flow controls). The network layer is not correct because congestion control occurs based on router implementations of flow control at the subnet level (i.e., source quench messages sent out when router memory or the buffer reaches capacity), however, no message exists to cancel or discard messages, which actually may increase congestion problems. Session layer and data link do not have any functionality for network management.   _{Your Comment}