单项选择题 Which protocols are found in the network layer of the OSI reference model and are responsible for path determination and traffic switching?（）

单项选择题 Data transfer is slow between the source and destination. The quality of service requested by the transport layer in the OSI reference model is not being maintained. To fix this issue, at which layer should the troubleshooting process begin?（）

单项选择题 Which layer in the OSI reference model is responsible for determining the availability of the receiving program and checking to see if enough resources exist for that communication? （）