单选题
The network layer provides services to the transport layer. It can be based on either______. In both cases, its main job is ______ packets from the source to the destination. In network layer, subnets can easily become congested, ncreasing the delay and ______ for packets. Network designers attempt to avoid congestion by proper design. Techniques include______ policy, caching, flow control, and more. The next step beyond just dealing with congestion is to actually try to achieve a promised quality of service. The methods that can be used for this include buffering at the client, traffic shaping, resource______, and admission control. Approaches that have been designed for good quality of service include integrated services (including RSVP), differentiated services, and MPLS.
单选题
A. virtual circuits or datagrams B. TCP or UDP C. TCP or IP D. IP or ARP