(第1空)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，increasing 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.