计算机新技术
1. computer Networks: A large numbers of separated but interconnected computers do the job . These systems are called Computer Networks.
2. Distributed System: In a distributed system, a collection of independent computers appears to its use as a single coherent system,it means existence of multiple autonomous computer is transparent to the users.
3. Distinction: between a computer networks && distributed system: Lies with software rather than hardware
In a computer network, this coherence model and software absent.
二.Magnetic Media 1. Principle
2. Data safety Analysis 3 ultrium技术:(1)高容量和高性能(2)开放性标准的存储格式 4. Virtual Storage 虚拟存储
NASC (Network Attached storage ) 5. 传输介质
(1) Twisted pair 双绞线 (2) Coaxial Cable 同轴电缆 (3) Optical fiber 光纤
6. Radio Transmission 无线电传输
(a ) In the VLF, LF, and MF bands, radio wares follow curvature of the earth
(b ) In the HF band
7. Advantages over terrestrial systems (1) They can cover large areas (2) Inherent broadcast capability (3) Easy development
8. Communication Satellites 卫星通信 (1) Geostatronary Satellites 同步
(2) Medium —Earth Orbit Satellites 中轨 (3) Low —Earth Orbit Satellites 低轨 距地面距离运行周期
低数百千米~5000km 2~4h 中500~20000km 4~12h
高 36000km 24h
1
are the
1. Web-scale problems 2. Large data centers
3. Different modals of computing 4. Highly —interactive web applications PB: 1015 Byte
层次,Software area a sener SaaS
PaaS(platform) IaaS
Infora structure
The Mobile Telephone System: Generation: Analog Voice Digital Voice
Digital Voice and Data
Hand off: (1)Hard hand off,(2)Soft hand off P 55 D-Amps: Digital Advanced Mobile Phone System
(1) GSM: Global System for Mobile Communications 欧洲提出 (2) GSN(2): 美国提出
Advanced Mobile Phone System(AMPS) …………………..P54
(a) Frequencies are not reused in adjacent cells 相邻频带频率不能一样 (b) To add more users, smaller cells can be used 讲一个蜂窝单元划分为多个蜂窝小单元。
蜂窝通信系统的组成:移动台MS ,交换网络子系统MSS ,无线基站子系统BS
1、 同步轨道:geosynchronous orbit (GEO)
Advantages:
1、 large area coverage
2、 satellite relation is synchronous to earth 3、 three satellites can cover the whole global 4、 low system complexity Disadvantages:
1、 long propagation delay
2、 high transmission power is required 2、 Medium Earth orbit (MEO) Advantages:
1、 slightly longer propagation delays
2、 slightly higher transmission power required
3、 more expensive than LEOs but cheaper than GEOs 3、 High Elliptical Orbit (HEO )
Advantages :
1、 maximum time spent over populated northern hemisphere 2、 large area coverage over the northern hemisphere
Network System : Human computer interaction:
Human computer interaction is a discipline concerned with the design ,evaluation and implementation of interactive computing systems for human use and with the study of major phenomena surrounding them 。
WPAN(Wireless Personal Area Network) 802.15 1. Bluetooth IEEE 802.15.1
数据率:720kb/s 通信范围:10m
使用TDM 方式、扩频调频、FASS 技术组成不同基站的网络(piconet )
Piconet 1 Piconet 2
Active slave Bridge slave Parked slave
活动节点 只响应主节点激活命令
Two Piconet can be connected to from a scatternet. 最多有255个从节点, 最多有7个活动节点 Bluetooth Application (1) LAN Access
(2) Cordless telephone 无绳电话 2. WPAN : IEEE 802.15.4 通信距离短(10~80m),传输速率低,成本低廉 无线局域网 WLAN: 802.11
基本服务集 BSS(Basic Service Set)
服务区 BSA(Basic Service Area) 结构:1. 自主网络(无IP ) 2. 有AP 特点:1无中心节点(AP ); 2多路径选择
3不受影响,结构灵活 缺点:路由复杂
Ethernet: uses CSMA/CD
CSMA/CD: Carrier Sense Multiple Access with Collision Detection. 原理:(1)发送CS (载波):检测信道是否空闲 (2)没有(空闲)传送:free (3)繁忙(busy ):等待
计算:I —persistent 随机时间
The Briary Exponential Backoff Algorithm 二元后退指数算法 计算等待时间长度:最大 1023倍单位时间 等待时间:{0,1,2,、、、,1023} {0,1,、、、,2n -1} 210-1=1023 n: number of channel collision 冲突一个 21—1=1 {0,1}随机选择 0:不等待,发送第二个载波
1:等待一个时间单位,发送………….
冲突2个 22—1=3 {0,1,2,3}随机选择其中一个数 0: 1: 2: 3:
n>10时,等待时间不会变大,1023为最大,但n 可继续增加 当n=16时,仍为冲突,不再继续,会放弃 10(10Mb/s) Base T(双绞线) F (光纤)
A bit Ethernet
1. Use standard Ethernet frame Format: 标准以太网结构
2. Allows for point--to —point,Link and shared broadcast channels.
3. In shared mode,CSMA/CD is used: short distances between nodes to be efficient.
4. Uses hubs, called here “Buffered Distributers”
5. Full —Duplex at 1Gbps for point —to —point links . 、
802.1
第四页
△GSM VS D-AMPS: Same : using FDMA
Difference : channel capacity 信道带宽(GSM : 200kHz . D-AMPS : 30kHz )
△第三代 Third-Generation Mobile Phones : Digital voice and Data P62. 三种标准 : WCDMA ( Wideband CDMA ) CDMA2000 TD-SCDMA ( Time Decision 同步 ) △Text :
1.In your opinion what are the advantages of 3G ? P62
2.P55. Sometimes 移动用户从一个频段切换到另一个,会被暂时打断,why?
△P68 Ethernet :
“dominant” LAN technology : 使用原因 1. cheap
2. first widely used LAN technology
3. simpler , cheaper than token LANs and ATM 4. kept up with speed race : 10/100/100Mbps △Bytes ☆画图
时间同步 从这里开始计算 有效数据 ★计算最小帧长度: 6+6+2+46+4=50+14=64
△Ethernet Technologies : 计算传输距离
200M
网络传输速率 10Mb/s , 不加中继器是200M △已知能够按接收最小值的传输距离(不经过中继器) Rode 个数 100m 4个 500m
第七页
接入方式: 1. 固定接入: fixed access 2. 移动接入: mobility access 3. 便携接入: portable access 4. 游牧接入: nomadic access
△无线城域网 WMAN ( Wireless Metropolitan Area Network ) 802.16 WiMax : Worldwide Interoperability for Microwave Access 代表WMAN 接入 WiFi :
WLAN 接入