Traditional network layer packet forwarding relies on the information provided by network layer (1) protocols, or static routing, to make an independent (2) decision at each hop within the network. The forwarding (3) is based solely on the destination (4) IP address. All packets for the same destination follow the same path across the network if no other equal-cost paths exist. Whenever a router has two equal-cost (5) toward a destination, the packets toward the destination might take one or both of them, resulting in
空白（2）处应选择（）Traditional network layer packet forwarding relies on the information provided by network layer (1) protocols, or static routing, to make an independent (2) decision at each hop within the network. The forwarding (3) is based solely on the destination (4) IP address. All packets for the same destination follow the same path across the network if no other equal-cost paths exist. Whenever a router has two equal-cost (5) toward a destination, the packets toward the destination might take one or both of them, resulting in
空白（1）处应选择（）
The network layer provides services to the transport layer. It can be based on either___20___. In both cases, its main job is ___21___ packets from the source to the destination.
In network layer, subnets can easily become congested, ncreasing the delay and ___22___ for packets. Network designers attempt to avoid congestion by proper design. Techniques include___23___ 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___24___, and admission control. Approaches that have been designed for good quality of service include integrated services (including RSVP), differentiated services, and MPLS.
A transport layer protocol has several responsibilities. One is to create a process-to-process (program-to-program) communication, TCP uses port (1) to accomplish this. Another responsibility of a transport layer protocolis to create a (2) and error-control mechanism at the transport level. TCP uses a sliding(3) protocol to achieve flow control. It uses the acknowledgment packet, time-out, and retransmission to achieve(4) control. The transport layer is also responsible for providing a connection mechanism for the application program. The application program sends (5) of data to the transport layer. It is the responsibility of the transport layer at the sending station to make a connection with the receiver.
空白（2）处应选择（）The TCP protocol is a（）layer protocol.
The presentation layer is concerned with the (1) and semantics of the information exchanged between two systems. The processes in two systems are usually exchanging information in the form of character(2), numbers, and so on. The information should be changed to bit (3) before being transmitted. Because different computers use different encoding systems, the presentation layer is responsible for(4) between these different encoding methods. The presentation layer at the sender changes the information from its sender-dependent format into a common format. The presentation layer at the receiving machine changes the common format into its(5)-dependent format.
空白（5）处应选择（）我来回答:
