CA6140车床831008拨叉零件的数控加工工艺及钻20、Φ50孔夹具设计含5张CAD图-版本1
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CA6140车床831008拨叉零件的数控加工工艺及钻20、Φ50孔夹具设计含5张CAD图-版本1,ca6140,车床,零件,数控,加工,工艺,20,50,夹具,设计,cad,版本
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Network architecturesThe term architecture is commonly used today to describe networks. A network architecture, such as illustrated in Fig.1.7, describes the components in the network, how they operate , and what form they take . A network encompasses hardware, software, data link controls (DLC), Standards, topology, and protocols.1. hardwareThe physical equipment in the network is referred to as the hardware. Typical of such equipment are computers, modems, telephone, terminals , machines, controllers, and the like.2. SoftwareSoftware consists of programs, procedures, and sometimes, associated documentation of the operation of the communication system. Communications software (CSW), application programs (AP), network control programs (NCP), operating system (OS), and database management system (DBMS) are examples of software.3. ProtocolsA protocol defines how network components establish communications, exchange data, and terminate communications. A protocol is essentially a formal set of conventions, or rules, between communicating processes about of messages to be exchanged. Handshaking and line discipline are also protocols. To make implementation and usage more convenient in sophisticated networks, higher-level protocols may use lower-level in a layered fashion.4. Data link controls A data link consists of electronic equipment such as electronic devices, terminals, and machines and the interfacing circuits that are operating in a particular way to permit information to be exchanged between installations. The specific method of operation is defined by transmission codes, transmission modes, and direction control.There are two major categories link control protocol in use today:(1) Asynchronous, in which bit streams are transferred at fixed rates with the transmitter and receiver operating in synchronization by the clock. (2）The flow of date to and from the many points and links within the network must be controlled and orderly. The sending and receiving sites must sequencing of the messages being transmitted among all users. The connection path between sits is usually shared by more than one user, as multipoint configuration. A multi-point line, sometimes called a multi-drop line, is a communications line having several subsidiary controllers that share time on the line under the control of a central site.Date line controls provide for all these needs. They manage the flow of data messages across the communications path, or links. In essence, they are special kinds of protocols consisting of a combination of software and hardware located at each site in the network. Through a communication link, the DLC protocol pro-vides for the reliable interchange of information between data terminal equipment. Typical DLC functions in the network are the following:Synchronizing the sender and receiver 1) Controlling the sending and receiving of data2) Detecting and recovering transmission errors between two points3) Maintaining awareness of link conditions4) Topologies Topology describes the surface layout the elements comprising the communications network-that is, it is the shape of the system. Communication system may be implemented in a variety of ways. typical communication system are telephone lines, radio wave links, networks, serial connections, parallel connections and power line system modulations. The choice of topology depends on factors such as cost, response time, throughput, capacity, load sharing, and capacity needs.5. Local area networksA local area network (LAN) is a communications network operating in a local area. It extends from several hundred to several thousand feet within a building or other facility. A LAN is owned and operated by an individual or organization and is, therefore, not subject to regulation by either the federal communications commission (FCC) or the state Public Utility Commission (PUS). A LAN is a means of connecting various types of equipment for the purpose of sharing resources and communicating in a distributed processing environment, as illustrated in fig .1.8. that is , all device that must communicate with one another in a CIM environment can be tied together though some form of common interface such as a LAN .An effective LAN has specific characteristics. Typical of these are the following: Is in a moderate-sized geographic area (office, laboratory, building, factory, industrial complex, or campus, for example) Has medium to high sped data channel(s) Provides reliable communications Is owned and used by a single organization Connects independent devices rather than a device and its peripherals A LAN usually has four major components that serve to transport data between end users: user workstation, protocol control logic. medium interface, and physical path.6. User workstationThe user workstation is used to accomplish an application. The station can be anything from a word processor to a mainframe computer.(1) Protocol control logic A protocol control logic takes user is information and converts it to a protocol that can move the LAN network to reach the desired location , the protocol logic also controls the LAN and provides for the end user is access to the network .（2) Medium InterfaceThe medium interface function generates the electrical signals to be transmitted on the LAN the interface is between the path the protocol logic can take several forms, typical of which are CATV (cable television) taps , infrared diodes for infrared path , microwave antennas, or complex laser-emitting semiconductors for optic fibers.(3) Physical Path A LAN is path may consist of coaxial TV cables, coaxial bade-band cables, twisted pair of wires, optic fibers, and microwaves. Cable TV coaxial cable is used in many networks because it has a high capacity, a very good signal-to-noise ratio, low signal radiation, and low error rates.(4) Manufacturing Automation ProtocolThere are many types and sizes of networks. Some LAN systems are owned by an organization and are confined to the premise of that organization. Others are owned by national or international public networks that may be accessed by the user. In many case, LAN systems may also connect to public networks and be able to access them.Network are also connected in several configurations (topologies) , as seeing in Fig .1.9.Each topology can constitute an entire network or can be just a portion of a large network .A star network is a centralized network in which each device is connected virtually to a central controlling point.A ring network, sometimes called a loop, is a network in which each device is connected to the next in sequence in a closed, circular fashion. This topology has two possible paths, one in each direction.A bus network is a topology that consists of a single shared line to which all devices are connected.In a hierarchy network, a central root node has over the entire network. The secondary nodes attached to the root can be front-end processors (EEP) that in turn connect to tertiary nodes of lesser significance. The hierarchy can consist of a large computer that has overall of several smaller control devices connected to their own terminals.A multiply connected topology requires that there be at least two paths between any pair of nods to assure availability and reliability m the event of failure one path or node.The unconstrained network occurs most commonly. The term unconstrained merely means that the configuration is not restricted to one specific kind of connection.Many LAN systems are available today. All use either base-bands, broad-bands, or both, in a base-band, the line is pulsed, as in the on/off conditions. Because these pulses are still the square wave direct current, they require no additional special handling or modulation, which makes the process relatively inexpensive, it is impossible to mix voice and data unless the analog voice signals have been previously digitized. The broadband technology requires a conversion process and is therefore more expensive. The advantages gained are that voice, video, and data can all be sent on the same channels. Facilities can be shared through assignment of frequency channels to allow all devices to operate simultaneously. Popular modulation and multiplexing techniques can be used because a wide range of frequencies is available. 网络建筑学现在在今天，建筑学这个术语通常用来描述网络系统。例如图表1.7所示的，建筑描述了一个网络的各个组成部分他们之间是如何的操作以及以一种什么方式进行连接的。一个网络系统包括硬件、软件、数据线控制端、技术规范和数据传输的协议。1、 硬件网络系统中的物理组成部分叫做硬件；电脑、调制解调器、电话机、接线端、机器、控制端等等是这种设备的典型。2、 软件软件包括一系列程序、步骤，有时还有通讯系统操作的相关文档。通讯软件CSW、应用程序AP、网络控制程序NCP、操作系统OS和数据库管理系统DBMS是软件的例子。3、 指令指令规定网络系统各个组成部分是如何的建立通讯、传输数据和停止通讯的。实际上，一条指令是在通讯过程中关于信息被交换的形式和内容的一系列的习惯或规则。转移和排准则也是指令。为了使执行和运用在复杂的网络系统中更方便，高级指令可以用同一级的低级指令来实现。4、 数据连接控制一个数据连接有允许以数字化的形式自动传输信息的电子设备组成。他是一个安装的装备的集合，比如说：电子设备、终端机器和那些一特殊方式运行的允许信息在不同的设备之间被交换的界面电路。这种运行的特殊方式被界定为传输密码、传输方式和反方向控制。在今天使用的主要有两种连接控制协议：（1） 异步的方式，用这种方式小的数据流被一定和接受以一种异步比率。（2） 同步的方式，小的数据流被移动以一种固定的比率随着时间转换和接收操作同步进行。数据在网络系统之中的很多点和线之间的传输流动可以被控制和排序。反发送和接收站必须了解在所有的用户间被翻译的信息的辨认行为和序列站一站之间的连接线路，像多点格局一样，通常被多个用户共同使用。多点连接有时又称之为复合连接是在中心站控制下有若干个在连接上共享时间的补充控制者的一种交流。数据连接控制为下列所有的需要提供服务，他们管理者数据信息在交流通路或连接之间的流动。实质上，他们是本网络系统中各个站点中的软件和硬件联合而构成的特殊种类指令。通过交流链接，数据连接指令在数据接线端设备之间提供可靠的内部交流信息，在网络系统中数据控制的典型作用如下：1） 使和接收同步进行；2） 控制数据的发送和接收；3） 检测和改善点与点之间的翻译误差；4） 布局。布局描述了构成通讯网络系统的各个单元的表面规划，也就是说，是网络系统的外形。通讯系统可以由很多方法实现。典型的通讯系统是电话连接、无线电连接、网络系列连接、并列连接和电源连接一同调整。布局的选择取决于，比如，成本、反应时间、生产量、电容、承载量和生产量需求等因素。5、 局域网局域网是在局部地区操作的网络系统，它在建筑物或其他设备中由几百英尺扩展到几千英尺。局域网是由私人或组织团体拥有和操作的。因此，它不是由联邦通讯委员会和国家公共事业控制的项目。局域网是为了在一个缓缓前进的环境里边共享资源和交流的目的而连接各种类型的设备的一种工具正如图表1.8所示。也就是说，所有的装置必须在一个能够有连接在一起的通过一个常用形式的通讯口接收的界面环境和其他的相交流，像局域网。一个有效的局域网有一些具体的特点，典型的是以下这些： 在中型的地理地区，办公实验室，建筑物、工厂、工业综合体、校园等。 有中高速的数据传输频道。 提供可靠的交流。 被当各机构拥有和使用。 以独立的装置相连接，而不是一个装置和
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