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?（）

A. presentation
B. session
C. transport
D. network
E. physical

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? （）

A. transport
B. network
C. presentation
D. session
E. application

单项选择题A company implements video conferencing over IP on their Ethernet LAN. The users notice that the network slows down, and the video either stutters or fails completely. What is the most likely reason for this?（）

A. minimum cell rate (MCR)
B. quality of service (QoS)
C. modulation
D. packet switching exchange (PSE)
E. reliable transport protocol (RTP)

单项选择题What must be set correctly when configuring a serial interface so that higher-level protocols calculate the best route?（）

A. bandwidth
B. delay
C. load
D. reliability

单项选择题When configuring a serial interface on a router, what is the default encapsulation?（）

A. atm-dxi
B. frame-relay
C. hdlc
D. lapb
E. ppp