TCP functions at the Open Systems Interconnection(OSI)transport layer, or Layer 4. Its chi

Question

TCP functions at the Open Systems Interconnection(OSI)transport layer, or Layer 4. Its chief responsibility is to ensure reliable end-to-end connectivity. IP, located one layer （1）, at the OSI network layer, or Layer 3,communicates the addresses of each packet’s sender and receiver to the routers along the way .Routers and Layer 3 switches can read IP and other Layer 3 protocols. This information, combined with routing tables and other network intelligence, it takes to get across the room or around the world（2）TCP/IP.

The routing process begins with an IP address that is（3）to the sending end station. End stations may be assigned permanent IP addresses or they may borrow them as needed from a Dynamic Host Configuration Protocol(DHCP)server or other service. If the sending end station determines that the destination address is not local, the packet goes to a first-hop router, typically one that is close and has been reassigned to the（4）. The router inspects the packet’s IP address and performs a route table lookup to see if the destination end station resides on the local(physically connected)network, typically called an IP subnet. An IP subnet usually is assigned to each of the router’s network interfaces. If the destination IP address is local, the router searches an internal store of IP addresses and local-device media access control(MAC)addresses. This store is known as the Address Resolution Protocol(ARP) cache. ARP is the universal tool for（5）IP addresses to MAC addresses. If the destination’s MAC address appears, the router installs that MAC address in the packet header(removing its own MAC address because that’s no longer needed)and sends the packet to the destination end station.

（1）A. up

B. down

C. sideward

D. back-fence

（2）A. via

B. through

C. by

D. through out

（3）A. special

B. especial

C. unique

D. particular

（4）A. accepter

B. sender

C. router

D. server

（5）A. searching

B. looking

C. locating

D. matching

Answer 1

正确答案：B,A,C,B,D
TCP完成开放系统互连（OSI）模型中传输层，即第四层的功能。它的主要责任是确保端至端之间的可靠连接。IP位于下一层，在 OSI的网络层，即第三层，把每个包的发送者和接收者地址告诉一路上各个路由器。路由器和第三层交换器可以读出IP和其他的第三层协议。这些信息与路由表以及其他网络智能结合在一起,能通过 TCP/IP在整个房间或围绕地球进行传递。 路由过程始于对发送端站而言是唯一的一个IP地址，端站可以被分配永久的IP地址，或者按需要从动态主机配置协议（DHCP）服务器或其他服务中借用。如果发送端站确定目的地址不在本地，该包就被送到第一跳路由器，一般来说，该路由器是在附近的，并已被预先分配给发送者。该路由器检查包的IP地址，查找路由表，看看目的端点是否位于本地网络，它通常叫做IP子网，IP子网一般被分配到路由器的每个网络接口上。如果目的IP地址为本地的，该路由器就搜寻存储着IP地址和本地设备介质访问控制（MAC）地址的内部存储器,这个存储器叫地址分辨协议（ARP）高速缓存。ARP是把IP地址映射到 MAC地址的通用工具。如果目的 地的MAC地址出现了，该路由器就把这个MAC地址装进包的报头中（取掉自己的MAC地址,因为不再需要它了），把该包送到目的端站。