TopCOn 本次讲座的主要内容: 1、GTS-330系列全站仪操作技术要点 2、拓普康全站仪与微机的数据通讯

中国科学院——院友通讯（2020年第4期，总第34期）

第10章模块化程序设计 一、模块化程序设计概述 二、段的定义 三、模块间的通讯 四、模块的连接 五、源程序综合举例

Packet Multiple Access SHARED UPLIN TERMINAL APPL TERMINALL TRANS NET LLC DLC MAC

Routing Must choose routes for various origin destination pairs o/d pairs) or for various sessions Datagram routing: route chosen on a packet by packet basis Using datagram routing is an easy way to split paths Virtual circuit routing: route chosen a session by session basis Static routing: route chosen in a prearranged way based on O/D pairs Eytan Modiano

Used for analyzing network performance In packet networks, events are random Random packet arrivals Random packet lengths While at the physical layer we were concerned with bit-error-rate, at the network layer we care about delays How long does a packet spend waiting in buffers?

Modulation Representing digital signals as analog waveforms Baseband signals Signals whose frequency components are concentrated around zero Passband signals Signals whose frequency components are centered at some frequency fc away from zero Baseband signals can be converted to passband signals through modulation Multiplication by a sinusoid with frequency fc Eytan Modiano

Channel Coding When transmitting over a noisy channel, some of the bits are received with errors Example: Binary Symmetric Channel (BSc) Pe= probability oferror Q: How can these errors be removed? A: Coding: the addition of redundant bits that help us determine what was sent with greater accuracy

Source coding Source Encode Channel Alphabet alphabet Source symbols Letters of alphabet, ASClI symbols, English

Sampling Given a continuous time waveform, can we represent it using discrete samples? How often should we sample? Can we reproduce the original waveform?