Network Fundamentals Author: Awa Date: 2004-10-22http: //www.net130.com
§1 Computer Network Basic Knowledge One. The concept of computer network: understanding and definition of the concept of "computer network", with the development of the computer network itself, people have put forward a variety of different perspectives. Early computer systems are highly concentrated, all devices are installed in a separate large room, and then the batch and time-time system, multiple terminals connected in the time-time system must follow the primary computer. In the middle of the 1950s, many systems will geographically dispersed multiple terminals to a central computer through communication lines, so that the first generation of computer networks have been viewed. The first generation computer network is a remote online system-centered remote online system. Typical applications are aircraft ticketing system consisting of more than 2,000 terminals in a computer and in the United States. Terminal: External equipment for a computer includes a CRT controller and a keyboard, no GPU and memory. As the remote terminal increases, the front-end machine FEP is added before the host. At that time, people defined the computer network as "Connected to the purpose of transmitting information, implement remote information processing or near-step resource shared", but such a communication system has a prototype of communication. The second-generation computer network is interconnected by a number of hosts through communication lines, providing services for users, and has launched in the late 1960s, typical representatives are ARPANETs assisted by the US Department of Defense Senior Research Program. The host is not connected to the line directly, but the interface message processor IMP is connected to the interconnection. IMP and the interconnected communication lines are responsible for communication tasks between hosts, constitute communication subnets. The host of the communication subnet is responsible for running the program, providing resource sharing, forming a resource subnet. When the two host communication, the understanding of the content of the information, the information representation form, and the response signal in various situations must comply with a common agreement, called the protocol. In the ARPA network, the protocol is divided into several levels, how to lay layers, and the sum of the protocols used in each layer, referred to as the network architecture, the architecture is an abstract concept, and the specific implementation is through specific hardware. And software is done. The second generation network in the 1970s and 1980s was developed rapidly. The second generation network is centered on communication subnet. During this period, the network concept is "the aggregate of the computer with independent functions that can be shared with the purpose of interacting resources", forming the basic concept of a computer network. The third generation computer network is an open and standardized network with a unified network architecture and follows international standards. IS0 issued 0Si / RM in 1984. The model is divided into seven levels, also known as the 0Si seven-layer model, recognized as the foundation of the new generation of computer network architecture. Late the foundation for the popularization of the LAN. ┌ ┌ 开 开 开 生产 生产 生产 生产 应用 应用 应用 发展 发展 发展 发展 发展 应用 电 应用 应用 应用 应用 应用 应用 应用 电 电 电 电 应用 应用 应用 应用 应用 应用 应用 应用 应用 性 应用 应用 应用 应用 应用 应用 应用 应用 应用 应用 应用 应用 应用 应用The architecture of the layer has different characteristics, such as the local area network to save costs without the storage forwarding, but is connected to the online computer by a single broadcast channel. The fourth-generation computer network has begun, and the development of local area network technology has matured. Fiber optics and high-speed network technology, multimedia, intelligent networks, the entire network is like a large computer system that is transparent to the user, developed to Internet represented by Internet . Computer Network: A system that implements resource sharing and data communication using a computer system with independent work capabilities through communication devices and lines. As seen from the definition involves three aspects: (1) at least two computers interconnect. (2) Communication equipment and line media. (3) Network software, communication protocol and NOS two. Classification of computer networks: A lot of standards for computer network classification, such as topology, application protocols, etc.
However, these standards can only reflect the characteristics of the network, and the classification standards that can be used to reflect the nature of the network technology are distributed distance, divided into LAN, MAN, WAN, and Internet. 1. LAN: A few meters - 10 km small machine, the microcomputer has developed a lot of promotion, the configuration is easy, the rate is high, 4 Mbps-2Gbps. Located in a building or one unit, there is no diameter problem, does not include a network layer. 2. Urban Net: 10 km - 1,100 km to the LAN of a city, using IEEE802.6 standard, 50kbps - l00kbps, located in a city. 3. WAN: Also known as telematics, hundreds of kilometers - km. Earlier, leased lines, connected to IMP and lines, constitute a mesh structure, solve the path problem, the rate of 9.6kbps - 45Mbps such as: the Ministry of Posts, China, ChinaPac, and CHINADDN network. 4. Internet: Not a specific network technology, it is a high-level technology that will be uniformly unified in some protocol.
§ 2 Basic composition of the LAN, the characteristics of the LAN: LAN distribution range is small, small investment, simple configuration, etc., has the following characteristics: 1. High transmission rate: generally 1 Mbps - 20Mbps, fiber high speed network up to 100Mbps, 1000Mbps 2. Supports more types of transport media. 3. Communication processing is generally completed by the NIC. 4. The transmission quality is good, the error rate is low. 5. Rule topologies. Second, the composition of the local area network: LAN is generally consisting of four parts: the server, user workstation, and transmission media. 1. Server: Running Network 0s, providing service functions such as hard disk, file data, and printer sharing, is the core of network control. From the application, a highly configured normal 486 compatible machine can be used for file servers, but from the improvement of the overall performance of the network, especially from the system stability of the network, it is preferred. The current common NOS mainly has three kinds of NetWare, UNIX and Windows NT. NetWare: Popular version V3.12, V4.11, V5.0, low hardware requirements, similar to DOS, improved technology, reliable, support multiple workstations and protocols, suitable for local area network * as a system, as a file server, Print server performance is good. Unix: A typical 32-bit multi-user NOS, primarily applied to Super Small Machines, on the mainframe, currently available in UNIX SUR4.0. Support network file system services, providing data, etc., powerful, not easy to master, complex command, is launched by AT & T and SCO. Windows NT Server 4.0: A full platform system for distributed graphics applications, interfaces are similar to Win95, easy to install and manage, and integrate Internet network management tools, broad prospects. The server is divided into file servers, print servers, database servers, on the Internet, and Web, FTP, E-mail, etc. Server. Network 0s move towards the development of multiple communication protocols, a variety of network cards, and workstations. 2. Workstation: You can have your own 0s, independent work; through running workstation network software, access server share resources, common DOS workstations, Windows95 workstations. 3. NIC: Connect the workstation server to the network, realize resource sharing and communication, data conversion, and electrical signal matching. Classification of NIC (NTC): (1) Rate: 10Mbps, 100Mbps (2) Bus Type: ISA / PCI (3) Transmission medium interface: single port: BNC (fine cable) or RJ-45 (twisted pair) 4. Transmission medium: currently commonly used transmission media has twisted pairs, coaxial cables, fibers, and the like. (1) Twisted pair (TP): Pack of a pair of twisted pairs in an insulating jacket, in order to reduce interference, each pair to reverse each other. Divided into non-shielded twisted pair (UTP) and shielded twisted pair (STP). UTP in the LAN is divided into three types, 4, 5, and more than 5 types.
Take AMP as an example: 3 categories: 10Mbps, leather, skin note "CAT3 ', box" 3 ", 305 m / box, 400 yuan / box 4: There are not many 5 categories: (Super 5) 100Mbps, 10Mbps, skin thickness, turns, skin note "CAT5", on the box, 305 meters / box, 600-700 yuan / box (100 meters per section, 4 relay Maximum 500 m) STP: Internal and UTP, outsourced aluminum foil, Apple, IBM network product requirements use STP twisted pair, high rate, expensive price. (2) Coaxial cable: from a hollow outer cylinder conductor Composed with a central wire in the central axis, separated by an insulating material between the two conductor. It is divided into thick cables and cables according to the diameter. Thick cable: long transmission distance, high but cost, use in large local network dry lines, connection The terminal is terminally connected. A. The strip is connected to the external transceiver. B. The transceiver is connected to the network card. C. NIC must have a AUI interface: 500 meters per segment, 100 users, 4 The repeater can reach 2500 meters, the transceiver is 2.5 meters, the transceiver cable is up to 50 meters. Third cable: the transmission distance is short, relatively inexpensive, used in T-head, connected to the BNC network card, two end safety 50 Euro terminal resistance Each section of 185 meters, 4 repeater, maximum 925 meters, 30 users per segment, the T-head between the T-head is 0.5 meters. According to the transmission frequency band, the baseband and broadband transmission are divided into baseband and broadband transmission. Baseband: Digital signal, signal accounts for the entire channel A signal can be transmitted in the same time. Broadband: transmitted signals of different frequencies. (3) Optical fiber: Apply optical principle, generating a beam from the optical transmitter, turn the electrical signal to the optical signal, then import the optical signal into the optical fiber At the other end, the optical receiver is received by the optical receiver, and it is changed to the electrical signal, and the decoded is decoded. Divided into single-mode fiber and multimode fiber. Insulation confidentiality. Single mode fiber: The laser is a light source, only one optical path, the transmission distance is long, 2 km or more. Multi-mode optical fiber: luminous, low-speed short distance, 2 km. Third, computer network software system:
Fourth, several working modes of the local area network: 1. Dedicated Server Structure: (Server-Baseb) is also known as the "Workstation / File Server" structure, which constitutes a workstation access server file with one or more file servers and one or more file servers to share storage devices. The file server naturally uses a shared disk file as the main purpose. For general data transfer, it is already enough, but when the application system used by the database system and other complex and increasing users, the server can no longer bear such a task, because with the increase of users, The procedures for each user service also increase, each program is running independently, which is extremely slow, thus generating client / server mode. 2. Client / Server Mode: (Client / Server) One or several larger computer concentrations for the management and access of shared databases, called the server, and disperse other application processing work to other microcomputers on the network. , Constitute a distributed processing system, the ability of the server control management data is rising by the file management method to the database management mode, so the server C / S is also referred to as a database server, focusing on data definition and access security and restore. , Concurrent control and transaction management, implement database management functions such as selection retrieval and index sorting, it has enough ability to transfer to the client through the part of the data required by the user after handling, not the entire file, Reduce the transmission load of the network. The C / S structure is the development of database technology and the result of universal application and the development of local area network technology. 3. Alternative network: (Peer-to-peer) is the same as dedicated Server and C / S on topology. In the equation network structure, there is no dedicated server that each workstation can both serve both client functions.
§3 Network interconnection equipment If the microcomputer is connected to each other due to the popularity of the microcomputer, there is a local area network, then due to the universal application of the network, in order to meet each other's communication and resource sharing, The interconnection between the network has led to the network. This section describes the hardware devices of general network interconnection. When the network is interconnected, you must solve the following problem: how to connect two networks physically. A network how to implement visits and communications with another network, how to solve differences in agreements, how to deal with speed and bandwidth, solve these problems, coordinate, and convert mechanisms are repeaters, bridges , Routers and gateways, etc. Solving the difference between the network with hardware: l. Repeater: After the transfer medium exceeds the length of the network segment, the distance of the repeater can extend the network, the weak signal is reproduced, the IEEE 802 standard specifies up to four in the four The relay is connected to five network segments. The repeater works in the physical layer and does not provide network segment isolation. 2. Special repeaters: hubs and switches (Multi-port repeaters): (1) Hub: It is a device that focuses together with a communication line, which is equivalent to the bus, working in the physical layer. It is the most widely used connection device in the local area network, divided into three types of independent HUB, modular HUB, and stacked HUB according to the configuration form. Intelligent HUB improves the shortcomings of general HUB, increasing bridge capability, filtering out frames that are not self-designed, increase the bandwidth of network segments, and has network management capabilities and automatic detection ports connected to PC network card speed capability . There are commonly 10M, 100M equity HUBs on the market. (2) Switch: The destination address of the switching Ethernet packet will be sent to the destination from the original port. When sending an Ethernet port to a different destination port, you can transfer these Ethernet bags at the same time to improve the network. The effect of actual throughput. The exchanger can establish multiple transmission paths at the same time, so the obvious effect can be received on the network segment of the connection multiple servers. Mainly used in Union of Hub, Server or Distributive Traverse. Classify the exchanger by technology: Direct switch: (CUT-THROUGH): Once you receive the target address in the packet, you will start forwarding before receiving the full frame. Applicable to an environment with low rate port and collision error rate. Storage Forward: (Store-and-Forward): Verify that the received frame is confirmed, and the filter is broken. Applicable to environments where different rate ports and collisions are collissed, and the bit is high. Application Note: (1) Select 10 / 100M to adapt to the switch. (2) The switches of two or more technologies are selected. 3, Bridge: (1) Filtering and forwarding. (2) Learning function. (3) Connect different transmission media, no path selection capabilities. 4. Router: A device that implements network interconnection between multiple networks and media is a more complex network interconnection device than the bridge. Main features: (1) Packet forwarding, providing the best path to connect the network of different hardware technology. The packet format and packet length conversion are performed if necessary. (2) Provide isolation, division, each of the ports of the router is a separate subnet. (3) Provide a reasonable WAN access. (4) Support the backup network path, support mesh network topology, switches, bridge requirements, and loop topologies. Internet all kinds of local area networks and wide area networks. Suitable for large switched networks. After using ROUTE, the shape of communication subunit is integrated, forming a larger network, from a macro perspective, can believe that the communication subnet is actually a network composed of a router, and the communication between the router Implemented through communication capabilities of various communication subnets.
4. Gateway: It is used to interconnect a completely different network. Main function: Turn a protocol into another protocol, turn a data format into another data format, turn a rate into another rate to seek unity. Provide a central intermediate interface. In the Internet, the gateway is a computer device that defines whether the information issued by the user can deliver the information sent by the user according to the IP address of the user's credit, and it also transmits the outside world to the local network computer.
§4 Basic knowledge of the INTERNET network 1. The development of the Internet network: Internet network originated from the 1969 US Department of Defense Advanced Research Program Association to assist in the development of 4 nodes composed of ARPA networks. In 1987, the NSF (National Science Foundation) used the form of tendering, and three companies such as IBM have established a new WAN, and the computer network of other departments of the United States has incorporated into this network, forming the current Internet main network ANSNET. In April 1994, the computer network information center (CNIC, CAS) of the Chinese Academy of Sciences officially accessed into the Internet. At present, my country has initially built four backbone WAN, namely the CHINANET of the Ministry of Post, CERNET, the Academy of Sciences, China's CSTNET, China's ChinaGBN These four nets are directly connected to the Internet. In April 1997, the interconnection between CHINAGBN, CERNET, and CSTNET network. Second, Internet and Intranet: L, Internet Network: Put the computer network, data communication network, and public telephone network, physically connected via router and various communication lines, and then use TCP / IP protocol to implement different types of networks. Communication between communication is a "network network", the foundation of the Internet is the foundation of various computer networks and communication networks. The INTERNET network is to solve the problem: (1), between the two networks to be physically connected through the intermediate device, which is two networks, solving the hardware 'interconnect' of low-level physics', that is, router or IP gateway. (2) Intermediate equipment To achieve packet exchange and diameter, protocol conversion, etc., to solve the high-level logical software "interconnection", the TCP / IP protocol. The Internet web can be abstract to apply TCP / IP technology networks connected by routers. 2: TCP / IP: Totel TCP / IP is the core of this set of protocols (or protocol stack). The functionality of this group of protocols is to use the hardware differences between the existing physical networks, block or isolate the hardware differences of specific network technology, and establish communication between hosts of different physical networks. Communication. 3, intranet: Network established for implementation (TCP / IP protocol) in a unit or enterprise. It can be a local area network or a wide area network. Third, IP address and subnet mask: 1, IP address: Internet network is interconnected by different physical networks, and the inter-communication between different networks must have corresponding address identity, this address ID is called an IP address. . The IP address provides a unified address format consisting of 32bit, which is not convenient to use binary use, and the user uses the "point part decimal" mode. The IP address uniquely identifies the number of the network and the location of the network, according to the size of the network, the usage IP address is divided into the following three categories: A: This type of address is characterized by 0, the first byte represents the network No., second, third, fourth byte represent the host number in the network, the number of networks is small, up to 126 network numbers, up to 16777,214 host numbers in each network. 0 ******* ******* * ******* * ******** L-126 0-255 0-255 1-254 B: This type of address The characteristics are the beginning of binary L0, first, the second byte means the network number, the second, three bytes represent the host number in the network, up to 16384 network numbers, up to 66534 host numbers in each network.
10 ****** ******* * ******* ******** 128 1 191 0-255 0-255 1-254 C: Characteristics of this type of address It is the beginning of the binary 110, the first, second, three bytes represent the network number, the fourth byte represents the host number in the network, the number of networks is more, can have 2097152 network numbers, up to 254 in each network. Host number. 110 ***** ******** ******** ******** 192-233 0-255 0-255 1-254 IP address stipulations: The network number cannot be At the beginning of 127, the first byte cannot be all 0, and it cannot be all L. The host number cannot be all 0, and it cannot be all L. 2. In order to quickly determine which part of the IP address represents the network number, which part represents the host number, determine if the two IP addresses belong to the same network, the result of the subnet mask generated, the subnet mask is given according to the format of the IP address Out. The default sub-mask mask of a, b, and Class C is as follows: A: 255. O. O. 0 B: 255.255.0. O C: 255.255.255.0 Using subnet mask to determine the network number and host number of the IP address to perform and calculate with the corresponding subnet mask with the corresponding subnet mask, and can distinguish between the network number portion and the host number portion. Such as 10.68.89.1 is a class A IP address, so the default subnet mask is 255.0.0.0.0, O, which is converted to binary and operate, and the network number is 10. For example, 202.30.152.3 and 202.30.152.80 are Class IP addresses, the default sub-mask is 255.255.255.0, and the two network numbers are obtained after being operated, and the two hosts are obtained. Located on the same network. Another function of the subnet mask is used to divide the subnet. In practical applications, there is often a problem that the network number is not enough. You need to divide a variety of subnets in a certain type of network. The method used is to divide some of the binary bits of the host number identification section to identify subnets. 3, gateway address: In the Internet network, the gateway is an intermediate device connected to the internal network and other nets on the Internet, also known as "router". The gateway address is a channel address that can be understood as the internal network and Internet information. Fourth, domain name system and DNS server: 1. Domain name system: Compared with IP addresses, people prefer to use a string with a certain meaning to identify the computer on the Internet. Therefore, in the Internet, users can use a wide variety of Method to name your own computer so that you may have an opportunity to rename on the Internet, such as providing the WWW service host named WWW, the host that provides E-mail service is named Mil, this is not the only identifier Internet The host location of the network. In order to avoid repetition, the Internet Network Association adopted a method of adding a post after the host name, this suffix name is domain name, used to identify the region of the host, and the domain name is obtained by the application. In this way, the host on the Internet online can be unique with the "host name. Domain name". Such as: www. Tongji. EDIJ. The WWW is the host name in the CN name, named by the server administrator, tongji. Edu.cn is a domain name, and the server administrator can apply for legal use.
The domain name has a certain regional hierarchical relationship, the general structure is "regional hierarchy. Organization name. Country name", Tongji said Tongji University, EDU said the national education institution department and CN represent China. Www. Tongji. EDU. The CN represents the WWW host of Tongji University in China. The Internet Association stipulates that there are seven categories of institutional domain names, respectively: COM: Commercial Organization. EDU: Education Institutions. INT: International Organization. GOV: Government agency organization. Mil: Military Organization. NET: Network organization organization. 0RG: Non-profit organization organization. Geographic country domain names, different names for different countries: CN China US US JP Japanese Fr France AU Australia CA Canada UK United Kingdom 2, DNS Server: Provides computer systems that mutual conversion services between host domain and IP addresses. There are two domain name parsing methods: repeated transfer query parsing and recursive analysis. V. Web Server: Web Server is also known as WWW (World Wide Web) server, the main function is to provide online information browsing services. As shown below: (1) The application layer uses the HTTP protocol. (2) HTML document format. (3) Browser Uniform Resource Locator (URL). 6. E-mail Server: E-mail server mainly provides email mail service. Methods of email: (1) Apply for an E-Mail mailbox. (2) Set an E-mail server: I. Mailbox name (account name); II. Send, receive an email server address; III. Enter your email address.
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