计算机网络第1章：计算机网络及其参考模型.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Network Topologies—Cellular Physical Perspective The cellular topology is for wireless technology Sometimes the receiving nodes move (e.g. cell phone), and sometimes the sending nodes move (e.g. satellite) Logical Perspective Nodes communicate with each other directly (though sometimes extremely difficult), or communicate only with their adjacent cells, which is extremely inefficient. Computer Network Reference Model Overview of Computer Network OSI Reference Model TCP/IP Model Network Topology Network Devices LAN Devices in a Topology Hosts—devices connected directly to network segment printers, computers, servers, FAX, copier Hosts—not part of any layer, but the functions of the OSI model are performed in software inside host LAN Devices in a Topology NICs – Layer 2 Carries a unique code called a MAC address Is used to control data communication for the host on the network Translates parallel signal produced by computer into serial format to send over the network Transceiver used to convert signals as well as send and receive bits Provides the host’s access to the medium 至局域网 串行通信 硬件地址 适配器 （网卡） CPU 和 存储器 生成发送的数据 处理收到的数据 把帧发送到局域网 从局域网接收帧 计算机 IP 地址 并行 通信 NICs – Layer 2 Media – Layer 1 Carries a flow of information in bits The means by which signals travel from one networked device to another Repeaters – Layer 1 regenerate (amplify) and retime network signals at the bit level to allow them to travel a longer distance on the media perform no filtering used to extend the length of the network clean, amplify, and resend signals that are weakened by long cable Hubs – Layer 1 used to regenerate and retime network signals propagate signals cannot filter traffic cannot determine the best path used as network concentration points sometimes called multiport repeaters Repeaters/Hubs - Differences Repeater typically has only two