题目内容
The metric assigned to each network depends on the type of protocol. Some simple protocol, like RIP, treats each network as equals. The (91) of passing through each network is the same; it is one (92) count. So if a packet passes through 10 network to reach the destination, the total cost is 10 hop counts. Other protocols, such as OSPF, allow the administrator to assign a cost for passing through a network based on the type of service required. A (93) through a network can have different costs (metrics). For example, if maximum (94) is the desired type of service, a satellite link has a lower metric than a fiber-optic line. On the other hand, if minimum (95) is the desired type of service, a fiber-optic line has a lower metric than a satellite line. OSPF allow each router to have several routing table based on the required type of service. （94）是（）
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The usual way to ensure reliable delivery is to provide the (16) with some feedback about what is happening at the other end of the line. Typically, the protocol calls for the receiver to send back special (17) frame bearing positive or negative (18) about the incoming frames. If the sender receives a positive acknowledgement about a frame, it knows the frame has arrived safely.On the other hand, a negative acknowledgement means that something has gone wrong, and the frame must be transmitted again. An additional complication comes from the possibility that hardware troubles may cause a frame to (19) completely. In this case, the receiver will not react at all, since it has no any reason to react. It should be clear that a protocol in which the sender transmits a frame and then waits for an acknowledgement, positive or negative, will hang forever if a frame is ever lost due to, for example, (20) hardware. （18）是（）
WLANs are increasingly popular because they enable cost-effective connections among people and applications that were not possible in the past. For example, WLAN-based applications can enable fine-grained management of supply (11) to improve their efficiency and reduce (12) . WLANs can also enable entirely new business processes. To cite but one example, hospitals are using WLAN-enabled point-of-care (13) to reduce errors and improve overall patient care. WLAN management solutions provide a variety of other benefits that can be substantial but difficult to measure. For example, they can protect corporate data by preventing (14) through rogue access points.They can improve overall network management by integrating with customers’ existing systems. Fortunately, it isn’t necessary to measure these benefits to justify investing in WLAN management solutions, which can quickly pay for themselves simply by minimizing time- (15) deployment and administrative chores. （15）是（）
Serialization delay and (1) delay are the two components of network delay that are improved by increasing bandwidth. Serialization delay, i.e. the amount of time it takes to put the (2) on the wire, and queuing delay (depth of the queue) are improved by increasing the (3) from a 128Kbps circuit to a T1. However, three other components of delay, routing/switching delay, distance delay, and protocol delay are components that can not be positively affected by an (4) in bandwidth. If the circuits are not over-utilized, then increasing the bandwidth to improve the (5) of the application will only result in an increased bandwidth with no positive effects on performance. （3）是（）
The usual way to ensure reliable delivery is to provide the (16) with some feedback about what is happening at the other end of the line. Typically, the protocol calls for the receiver to send back special (17) frame bearing positive or negative (18) about the incoming frames. If the sender receives a positive acknowledgement about a frame, it knows the frame has arrived safely.On the other hand, a negative acknowledgement means that something has gone wrong, and the frame must be transmitted again. An additional complication comes from the possibility that hardware troubles may cause a frame to (19) completely. In this case, the receiver will not react at all, since it has no any reason to react. It should be clear that a protocol in which the sender transmits a frame and then waits for an acknowledgement, positive or negative, will hang forever if a frame is ever lost due to, for example, (20) hardware. （19）是（）
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