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1. Basic knowledge of LAN networking
1. Main features of LAN
- The coverage area is small, usually a building or a group of buildings.
- Usually owned solely by an organization.
- The internal data transfer rate is much higher than the wide area network.
2. LAN standard
The currently used standards mainly include 802.1, 802.3, 802.11, and 802.16. 1EEE 802 standard includes the local area network reference model and the relationship between the model and the OSI reference model (OSI/RM) (see figure). The local area network reference model only corresponds to the physical layer and data link layer of the OS1 reference model, and divides the data link layer into a media access control (Media Access Control, MAC) sublayer and a logical link control (Logical Link Control, LLC) sublayer .
Correspondence between IEEE 802 and OSI Reference Model
3. Switched LAN
Each port of the switch in switched Ethernet is in an independent collision domain, and the terminal host connected under the port monopolizes the bandwidth of the port. The forwarding technology has two types: shortcut switching and store-and-forward switching. Switched network technology has brought the development of LAN into a new stage and brought new life to LAN.
4. Virtual local area network technology
Virtual local area network (VLAN) is based on switching technology, and the nodes in the local area network are divided into several "logical workgroups" according to the nature and needs of work, and a logical workgroup is a virtual local area network. The implementation principle of VLAN is very simple. Through the control of the switch, when the data packets sent by the members of a certain VLAN pass through the switch, the switch will only send them to other members of the same VLAN, and will not send them to computers other than the members of the VLAN.
The main advantages of VLAN are:
① The broadcast domain is limited to one VLAN, which saves bandwidth and improves network processing capabilities;
②VLANs cannot communicate directly, that is, users in one VLAN cannot communicate directly with users in other VLANs, but need to pass routers or layer-3 switches to enhance the security of the LAN;
③VLAN can be used to divide different users into different workgroups, and the users of the same workgroup do not have to be limited to a fixed physical range, thus making network construction and maintenance more convenient and flexible.
There are several types of virtual local area network division methods.
(1) Based on switch port division.
This division is to divide the ports of the switch into different VLANs, each VLAN subnet is relatively independent, and several ports on multiple switches can be divided into a logical subnet. This method is the most commonly used and simplest division method.
(2) Based on MAC address division.
The MAC address is the physical address of the network card connected to each network device in the network. The MAC address of every network card in the world is fixed on the network card and is unique. This division method is to divide different MAC addresses, and divide one or more MAC addresses that meet the requirements into a logical subnet.
(3) Based on network layer address division.
This division method is based on the network layer address of each host, that is, the network layer addresses that meet the requirements are divided into a logical subnet.
(4) Division based on IP broadcast groups.
Promptly an IP broadcast group is exactly a VLAN, and the method for this division expands VLAN to promptly an IP broadcast group is exactly a VLAN, and the method for this division expands VLAN to wide area network.
Second, the basic concept of integrated wiring
1. The composition of the integrated wiring system
(1) Workspace subsystem.
An independent area where terminal equipment needs to be installed should be divided into a work area, and the work area subsystem should be composed of the information socket module of the wiring subsystem, the connecting cable and adapter extending to the terminal equipment. The area of a working area is generally calculated as no more than 10m 2 , and the number of telephones and computer terminal equipment is set according to user needs.
(2) Horizontal (wiring) subsystem.
The horizontal (wiring) subsystem shall consist of information sockets in the work area, distribution cables and optical cables from the information socket modules to the wiring equipment in the telecommunication room, wiring equipment in the telecommunication room, equipment cables and jumpers, etc.
(3) Vertical (trunk) subsystem.
The vertical (trunk line) subsystem shall consist of wiring equipment and jumpers in the equipment room, as well as connecting cables between the equipment room and the wiring room on each floor. It is the nerve center of the integrated wiring system, and its main function is to connect the main distribution frame system with the distribution frame system of each floor.
(4) Building group subsystem.
The building group subsystem shall consist of backbone cables and optical cables connecting multiple buildings, building group distribution equipment and equipment cables and jumpers.
(5) Subsystem between equipment.
The equipment closet is where network management and information exchange takes place at appropriate points in each building. The equipment room subsystem mainly includes building incoming equipment, telephone switches, computer hosts and other equipment, as well as security wiring equipment.
(6) Management subsystem.
The management subsystem includes wiring equipment, input and output equipment and other components in the handover room. It is set in the room of the wiring equipment on each floor, and can also be applied to the subsystem of the equipment room.
2. Advantages of integrated wiring
(1) Compatibility: It is the primary feature of integrated wiring, which means that it can be applied to a variety of application systems, and it is completely independent and has nothing to do with the application system.
(2) Flexibility: It adopts a modular design and uses standard connecting parts and transmission cables, so all channels are common.
(3) Economy: Unified planning and unified installation and construction of various network cables reduce unnecessary repeated wiring and repeated construction, save wire materials, make the whole system an organic whole, facilitate centralized management and maintenance, and reduce future maintenance costs.
(4) Openness: It uses an open system structure, conforms to internationally popular standards, supports all communication protocols including ISO/IEC 8802-3 and ISO/IEC 8802-5, and can integrate different transmission media and different equipment from different manufacturers into one system.
(5) Advancement: All wiring links are configured according to eight-core twisted pair, and adopt the latest communication standard. The voice trunk part adopts copper cable, and the data part adopts optical cable to provide sufficient bandwidth capacity for simultaneous transmission of multiple multimedia information
(6) Reliability: High-quality materials and combined crimping form a set of high-standard information transmission channels. The general wiring system of the building adopts a star-shaped physical topology structure, point-to-point connection, any line failure will not affect the operation of other lines, and it also provides great convenience for line maintenance and emergency repair, thus ensuring the reliable operation of the system.
3. Design level of integrated wiring
(1) Basic integrated wiring system.
The basic integrated wiring system scheme is an economical and effective wiring scheme. It supports voice or integrated voice/data products, and can fully transition to data asynchronous transmission or integrated wiring system. Its basic configuration is as follows: each work area has an information socket; the distribution cable of each work area is a 4-pair twisted-pair cable; clamp-type handover hardware is used; the trunk cable of each work area has at least 1 pair of twisted-pair wires.
Its characteristics are: it can support all voice and data transmission applications; it is convenient for maintenance personnel to maintain and manage; it can support the transmission of products and equipment of many manufacturers and special information.
(2) Enhanced integrated wiring system.
The enhanced integrated wiring system not only supports the application of voice and data, but also supports image, video, video, video conferencing, etc. Its basic configuration is as follows: each work area has at least 2 information sockets; the distribution cables of each work area are two 4-pair twisted-pair cables; clamping or plug-in handover hardware is used; the cables of each work area have at least 2 pairs of twisted-pair wires.
Its features are: each work area has two information sockets, which are flexible, convenient, and fully functional; any socket can provide voice and high-speed data transmission; it is convenient for management and maintenance.
(3) Integrated integrated wiring system.
The integrated wiring system is a wiring system that incorporates twisted pair wires and optical cables into buildings. Its basic configuration is as follows: configure 62.5um optical cables in the main line or horizontal wiring subsystem of the building complex; equip 4 pairs of twisted pairs in the cables of each work area; there should be more than 2 pairs of twisted pairs in the trunk cables of each work area.
Its features are: the introduction of optical cables, suitable for large-scale intelligent buildings, and the rest of the features are the same as the basic type or enhanced type.
4. Integrated cabling system standard
(1) ANSI/TIA/ΕΙA-568-A
(2) TIA/EIA-568-B.1, TIA/EIA-568-B.2 and TIA/EIA-568-B.3 standards.
(3) International standard ISO/IEC 11801.
(4) Domestic standards
5. Wiring real questions over the years
Wiring related knowledge points
1. 双绞线Can avoid electromagnetic interference.
2. 嵌入式插座Used to connect twisted pair wires. (not connected to the floor distribution frame)
3. 多介质插座It is used to connect copper cables and optical fibers (write other errors), to meet the needs of users for "optical fiber to the desktop".
4. 建筑群子系统It can be any combination of various wiring methods ("generally connected with twisted pair" is wrong).
5. STPIt is more expensive and complicated than UTP, but it has strong anti-interference ability and small radiation.
6. When used as a horizontal wiring system cable, the length of the UTP cable should usually be within 90meters.
7. 管理子系统It is installed in the wiring room on the floor to provide the means to connect with other subsystems.
8. For 高速率终端the solution that can use optical fiber directly to the desktop.
9. 适配器It is a digital-to-analog conversion or data rate conversion device for connecting different signals.
10. Among the laying methods adopted by the wiring subsystem of the building complex, the most favorable method for cable protection is 地下管道布线(in-pipe wiring), the better one 巷道布线, and the most unfavorable one 直埋布线.
11. ISO/IEC 18011 is not the standard for integrated wiring system.
12. The integrated wiring uses the method of changing, adding, exchanging and extending cables in the management subsystem to change the cable routing.
13. Two ways of point-to-point combination and branch combination are often used for trunk cable laying.
Relevant real questions over the years
Question 1: In the following description about the integrated wiring system, the wrong one is ( ).
A. Twisted pair twisting can reduce electromagnetic interference
B. Embedded mounting socket is used for连接楼层配线架
C. Multimedia sockets are used to connect copper cables and optical fibers
D. For building complex subsystems, in-pipe wiring is the most ideal way
Correct answer: B
Reference analysis:
[Analysis] The purpose of twisting the twisted pair is to minimize the external electromagnetic radiation and external electromagnetic interference. Flush mount sockets are used连接双绞线的, and multimedia information sockets are used to connect copper cables and optical fibers. New buildings usually use embedded (concealed) information sockets, while existing buildings use surface-mounted (surface-mounted) information sockets. The wiring subsystem of the complex can be overhead wiring, roadway wiring, direct buried wiring, and underground pipeline wiring. To sum up, it can be seen that the description in item B is wrong.
Question 3: In the following description about the integrated wiring system, 错误的是( ).
A. Twisted pair twisting can reduce electromagnetic interference
B. The management subsystem is set in the wiring room on the floor
C. Multimedia sockets are used to connect copper cables and optical fibers
D. For direct buried wiring of building complex subsystems最理想的方式
Correct answer: D
Reference analysis:
[Analysis] The building group subsystem can be overhead wiring, roadway wiring, direct buried wiring, underground pipeline wiring, or any combination of these four wiring methods. Option D is wrong.
Question 9: In the following description about integrated wiring, 错误的是( ).
A. Twisted pair twisting can reduce electromagnetic interference
B. Compared with UTP, STP has less external electromagnetic radiation
C. The multi-media socket is used to connectUTP和STP的
D. When used as a horizontal wiring system cable, the length of the UTP cable should usually be within 90 meters
Correct answer: C
Reference analysis:
[Analysis] The information sockets of the work area subsystem can be roughly divided into embedded mounting sockets (dark sockets), surface mounting sockets, and multimedia information sockets (optical fiber and copper cables). Among them, the embedded installation socket is used to connect twisted pair (UTP, etc.): the multi-media information socket is used to connect copper cable and optical fiber to solve the user's demand for "fiber to the desktop". In the integrated wiring system, the horizontal wiring subsystem mostly uses category 5 (or category 5 super, or category 6) 4 pairs of unshielded twisted pairs. The length of the twisted pair cable should be within 90m, and the information socket should be connected internally as a fixed line. Therefore, option C is wrong.
Question 32: Which of the following descriptions about integrated wiring is correct ( ).
A. Trunk cable laying 必须adopts point-to-point combination
B. The multimedia information socket is used to connect5类双绞线和6类双绞线
C. When the terminal has a high speed requirement, the horizontal subsystem can be laid directly to the desktop using optical fiber
D. Use 工作区子系统the method of changing, adding, exchanging and extending cables in the computer to change the cable routing correctly
Answer: C
Reference analysis:
[Analysis] The laying of trunk cables usually adopts point-to-point combination and branch combination. Multimedia sockets are used to connect copper cables and fiber optics. Users can change cable routing by changing, adding, exchanging, and extending cables in the management subsystem. So choose option C.
Question 2: In the following description about the integrated wiring system, 错误的是().
A. STP is more expensive than UTP
B. For high-speed terminals, the solution of directly connecting optical fiber to the desktop can be used
C. Commonly used between building group subsystems双绞线连接
D. Multimedia sockets are used to connect copper cables and optical fibers
Correct answer: C
Reference analysis:
[Analysis] The subsystem of the building group is composed of cables connecting the buildings除了双绞线，还有光缆和电器保护设备等.
Question 10: Which of the following descriptions about integrated wiring is correct ( ).
A. The adapter has the function of converting different data rates
B. Compared with STP, UTP prevents external electromagnetic radiation能力更强
C. The multi-media socket is used to connectUTP和STP的
D. For the building complex subsystem, 巷道布线法yes 最理想way
Correct answer: A
Reference analysis:
[Analysis] Adapters are used to connect digital-to-analog conversion or data rate conversion devices of different signals. Compared with UTP, STP, FTP and SFTP twisted-pair cables, they are shielded cables with shielding layer, which have the characteristics of preventing external electromagnetic interference and preventing external radiation, so option B is wrong. Multimedia socket, as the name suggests, is a device used to connect two different media, copper cable and optical fiber, so option C is wrong. For the building group subsystem, because in the building group environment, underground roadways are usually used between buildings. Although the cost of laying cables in the roadway is low, safe and reliable, it is easily damaged by the heat or hot water of the hot water pipe, so it is not an ideal wiring method. In the building group wiring system, the more ideal wiring method is the wiring method in the pipeline. Therefore option A is correct.
Question 11: Among the following standards, 不是which is the standard for integrated cabling system ( ).
A、ISO/IEC 18011
B.、ANSI/TIA/EIA 568-A
C. GB/T 50311-2000 and GB/T 50312-2000
D、TIA/EIA-568-B.1, TIA/EIA-568-B.2和TIA/EIA-568-B.3
Correct answer: A
Reference analysis:
[Analysis] The integrated wiring system standards are: ANSI/TIA/EIA 568-A released by the TR41.8.1 working group in 1995, which defines the voice and data communication wiring system; GB/T 50311-2000 and GB/T 50312-2000 are national standards for integrated wiring system engineering formulated by our country. ISO/IEC 118011 was formulated and issued by the joint technical committee ISO/IEC JTC1 in 1995. This standard includes related components and test methods into international standards, so it is not a standard for integrated wiring systems, so question A is selected.
Question 39: Which of the following descriptions about the wiring subsystem of the building complex is correct ( ).
A. Among the four laying methods that can be used, roadway wiring for cable protection is better than direct buried wiring
B. Among the four laying methods that can be used, the best way to protect cables is overhead wiring
C. The cables connecting the building complex subsystems between the buildings usually use coaxial cables or shielded twisted pairs
D. ISO/IEC 50211-2000 provides engineering design specifications for integrated wiring system of buildings
Correct answer: A
Reference analysis:
[Analysis] Roadway wiring method: using the underground roadway between buildings to lay cables, not only the cost is low, but also the original safety facilities can be used to provide protection for the cables. Because there are hot water pipes in the underground roadway, the cables may be scalded. Underground Pipeline Routing: An underground system of pipes and manholes used to interconnect buildings within a network. Since the pipe is made of corrosion-resistant material, this method provides the best mechanical protection for the cable and minimizes the chance of cable damage and repair. Direct buried wiring method: In this method, except for the part of the cable passing through the foundation wall, the rest of the cable has no pipeline protection and is most vulnerable to damage. Overhead wiring method: use the original poles for wiring. This wiring method is low in cost, but has poor confidentiality, security and flexibility. The cables used to connect the building complex subsystems usually use twisted-pair cables. The integrated cabling system standards are: ANSI/TIA/EIA568-A issued by the TR41.8.1 working group in 1995. It defines the voice and data communication cabling system: TIA/EIA-568-B.1. TIA/EIA-568-B.2 and TIA/EIA-568-B.3 are the three versions after ANSI/TIA/EIA568. GB/T50311-2000 and GB/T50312-2000 are national standards for integrated wiring system engineering formulated by our country. So choose option A
Question 15: In the detailed analysis of network requirements, in addition to including overall network requirements analysis, integrated wiring requirements analysis, network availability and reliability analysis, and network security requirements analysis, the work that needs to be done is ().
A. Network project cost estimation
B. Network project schedule
C. Selection of network hardware equipment
D. Analysis of network bandwidth access requirements
Correct answer: A
Reference analysis:
[Analysis] The detailed analysis of network requirements mainly includes:网络总体需求分析、综合布线需求分析、网络可用性和可靠性分析、网络安全性需求分析、网络工程造价估算等. On the basis of completing the first four detailed analysis and preliminary design schemes, it is necessary to make a preliminary estimate of the system construction project cost that meets the design requirements.
Question 17: In the following description about the integrated wiring system (PDS), the error is ( ).
A. The equipment configuration of PDS project refers to the configuration of various distribution frames, wiring subsystems, transmission media and information sockets, etc.
B. When performing two services on a single information outlet, a Y-shaped adapter should be used
C. The length of the twisted-pair cable in the horizontal wiring subsystem should be within 90m
D. The network topology 组合逻辑describes the adjacency relationship of network elements
Correct answer: D
Reference analysis:
[Analysis] The network topology of the integrated cabling system is composed of various network units, which are combined and configured according to technical performance requirements and economic rationality.组合配置包括组合逻辑和配置形式。组合逻辑描述网络功能的体系结构;配置形式描述网络单元的邻接关系,即说明交换中心(或节点)和传输链路的连接情况. Therefore, the statement of option D is wrong.
Question 20: Among the following descriptions about integrated wiring components, the correct one is ().
A. Twisted pair twisted 不能to reduce electromagnetic interference
B. The multi-media socket is used for连接UTP和STP的
C. Compared with STP, UTP prevents external electromagnetic radiation能力更强
D. When used as a horizontal wiring system cable, the length of the UTP cable should usually be within 90 meters
Correct answer: D
Reference analysis:
[Analysis] The purpose of twisting the twisted pair is to make对外的电磁辐射和遭受外部的电磁干扰减少到最小. Multimedia sockets are used to connect铜缆和光纤的. STP is shielded twisted pair, UTP is unshielded twisted pair.与STP相比, UTP防止对外电磁辐射的能力较弱. When UTP cables are used as horizontal cabling system cables, their length should generally be within 90 meters. So choose option D.
Question 22: Which of the following descriptions about integrated wiring is wrong ( )
A. The multimedia information socket is used to connect twisted pair and coaxial cable
B. The laying of trunk cables often adopts point-to-point combination and branch combination.
C. When the terminal has high-speed access requirements, the horizontal subsystem can be directly laid to the desktop using optical fiber
D. Change cable routing by changing, adding, exchanging, and extending cables in the management subsystem
Correct answer: A
Reference analysis:
[Analysis] The multimedia information socket is used to connect optical fiber and coaxial cable. Therefore choose option A.
Question 25: In the following description about integrated wiring, 错误的是( ).
A. The multimedia information socket is used to connect optical fiber and copper cable
B. The laying of trunk cables often adopts point-to-point combination and branch combination.
C. When the terminal has a high-speed requirement, the horizontal subsystem can be directly laid to the desktop using optical fiber
D. 工作区子系统Change, add, exchange, and expand cables in the computer to change cable routing
Correct answer: D
Reference analysis:
【Analysis】管理子系统Changing, adding, exchanging, and extending cables are used to change cable routing, and option D is wrong.
Question 28: Which of the following descriptions about integrated wiring is correct ( ).
A. When the terminal has high speed requirements, the horizontal subsystem can be 铜缆laid directly on the desktop
B. The multimedia information socket is used to connectUTP和STP
C. The laying of trunk cables usually adopts point-to-point combination and branch combination.
D. You can 工作区子系统change, add, exchange, and expand cables in the Internet to change the cable routing
Correct answer: C
Reference analysis:
[Analysis] When the terminal has a high speed requirement, the horizontal subsystem can be laid directly to the desktop using optical fiber. Multimedia sockets are used to connect optical fiber and copper cables. Cable routing can be changed by changing, adding, swapping, and extending cables in the management subsystem. So choose option C.
Question 29: Among the four laying methods that can be used in the wiring subsystem of the building complex, 最有利和最不利the methods of cable protection are ( ).
A. Roadway wiring and overhead wiring
B. In-pipe wiring and direct buried cloth
C. Overhead wiring and in-pipe wiring
D. Overhead wiring and direct buried wiring
Correct answer: B
Reference analysis:
[Analysis] Roadway wiring method: use the underground roadway between buildings to lay cables, which is not only low in cost, but also can use the original safety facilities to provide protection for the cables. Because there are hot water pipes in the underground roadway, the cables may be scalded. Overhead wiring method: use the original poles for wiring. This wiring method is low in cost, but has poor confidentiality, security and flexibility. Direct buried wiring method: In this method, except for the part of the cable passing through the foundation wall, the rest of the cable has no pipeline protection and is easily damaged. Pipeline routing: An underground system consisting of pipes and manholes used to interconnect buildings within the network. Since the pipe is made of corrosion-resistant material, this method provides the best mechanical protection for the cable and minimizes the chance of the cable being repaired. So choose option B.
3. LAN interconnection equipment
1. Repeater
The repeater is the simplest network interconnection device, which mainly completes the function of the physical layer, and is responsible for transmitting information bit by bit on the physical layer of the two nodes, and completing the functions of signal replication, adjustment and amplification.
The characteristics of the repeater are as follows:
- Only the signal on the transmission medium can be received, amplified, shaped and forwarded.
- The effect is only to increase the transmission distance, and will not change the structure and content of the frame.
- Several connected network segments still belong to this local area network, as long as any node in this local area network sends data, other nodes can receive this data, and they share a conflict domain.
2. Hub
A hub is a connection device used in a local area network, which has multiple ports and can connect multiple computers. In the local area network, the hub is often used as the center, and all scattered workstations and servers are connected together to form a star-shaped local area network system. The advantage of the hub is that in addition to its ability to interconnect multiple terminals, it will not affect other nodes when the line of one node fails in a star structure.
Hubs are divided into: active hubs (Active Hub) and passive hubs (Passive Hub). Active hubs draw energy from the power source to regenerate the signal. A passive hub can only separate a signal for several users, it does not regenerate the signal, so it does not extend the length of the cable, but only allows two or more hosts to be connected to the same cable segment, and attenuates the signal.
The main characteristics of the hub are as follows:
(1) The hub works at the physical layer. When all nodes are connected to a hub through twisted pair, they still implement the CSMA/CD media access control method, and all nodes can accept the data sent from a node, so all nodes connected to a hub share a collision domain.
(2) A hub has multiple ports, and each port is connected to an adapter on a workstation with two pairs of twisted pairs through an RJ-45 plug.
3. Hub-related real questions over the years
Related knowledge points of BGP:
1. Work on 物理层, connected to a hub 所有结点共享/属于（不是独立）一个冲突域.
2. 只有一个结点Data can be sent every time, while other nodes are in the state of receiving data (multiple nodes can receive data frames at the same time). When a node connected to a hub sends data, 该节点将执行CSMA/CD (不是CA)介质访问控制方法.
3. In the network link 串接一个集线器可以监听该链路中的数据包.
4. The hub 不是基于MAC地址/网卡地址/IP 地址完成数据转发(基于MAC地址的是网桥或交换机等), but the source node uses a pair of sending lines to broadcast the data through the bus inside the hub.
5. Hub use 双绞线连接工作站.
Question 1: In the following description about hubs, 错误的是( ).
A. All nodes connected to the hub belong to a collision domain
B. When the nodes connected to the hub send data, they will execute the CSMA/CD media access control method C. By connecting a hub in series
in the network link, the data packets in the link can be monitored
D. Multiple nodes connected to a hub不能同时接收数据帧
Correct answer: D
Reference analysis:
[Analysis]结点通过双绞线连接到一个集线器上,当其中一个结点发送数据的时候,任何一个结点都可以收到消息, so the serial hub in the link can monitor the data packets in the link. Since the hub works at the physical layer, only one node can send data at a time, while other nodes are in the state of receiving data. All nodes connected to a hub share a collision domain, and these nodes implement the CSMA/CD medium access control method.
A. The hub 基于MAC地址completes the data frame forwarding
B. The nodes connected to the hub use the CSMA/CD algorithm when sending data
C. By connecting a hub in series in the network link, the data packets in the link can be monitored
D. All nodes connected to a hub share a collision domain
Correct answer: A
Reference analysis:
[Analysis] It is generally believed that the hub works at the physical layer and can only receive, amplify, shape and forward the signal waveform on the transmission medium, without involving the structure of the frame, and does not do any processing on the content of the frame. The network interconnection device that completes data forwarding based on MAC address identification is a bridge or a switch. Since all nodes connected to a hub share a collision domain, the nodes connected to the hub still need to implement the CSMA/CD medium access control method when sending data. After obtaining the right to send data, the source node uses a pair of sending lines to broadcast the data through the bus inside the hub. If a hub is connected in series in the network link, the data packets broadcast in the link can be monitored. So option A is wrong.
A. By adding a hub in the network, the IDS connected to the hub can obtain and analyze data packets.
B. By connecting a hub in series in the network link, you can listen to the data packets in the link
C. All nodes connected to a hub share a conflict domain
D. The hub is the one 基于MAC地址that recognizes and completes data forwarding
Correct answer: D
Refer to analysis:
[Analysis] The hub does not have the MAC address table that the switch has, so when it sends data, it is not targeted, but it is sent by broadcasting, and all nodes connected to a hub form a collision domain. By cascading a hub in a network link, you can monitor the data packets in the link. Nodes connected to the hub implement the CSMA/CD media access control method when sending data. So choose option D.
Question 2: In the following description about hubs, 正确的是().
A. The hub is 基于IP地址the one that recognizes the data forwarding.
B. The hub 每个端口构成一个独立的冲突域
. C. When a node connected to the hub sends data, D. By connecting a hub in series 只有目的结点能够收到
in the network link, you can monitor the data packets in the link
Correct answer: D
Reference analysis:
[Analysis] It is generally believed that the hub works at the physical layer, and can only play the role of receiving, amplifying, shaping and forwarding the signal waveform on the transmission medium, without involving the structure of the frame, and not doing any processing on the content of the frame. The network interconnection device that completes data forwarding based on MAC address identification is a bridge or a switch. Since all nodes connected to a hub share a collision domain, the nodes connected to the hub still need to execute the CSMA/CD media access control method when sending data. After obtaining the right to send data, the source node uses a pair of sending lines to broadcast the data through the bus inside the hub. If a hub is in-line in a network link, it will listen for packets broadcast on that link. Therefore option D is correct.
A. Isolate the collision domain
B. Complete frame forwarding according to the MAC address
C. Use twisted pair to connect the workstation
D. Implement the CSMA/CD media access control method
Correct answer: C
Reference analysis:
[Analysis] A hub is the central device of Ethernet. All nodes are connected to a hub through a twisted pair. When a node sends data, all nodes can receive data, so the hub still works at the physical layer, and all nodes connected to a hub belong to the same collision domain. In any time period, only one node can send data frames, while other nodes can only be in the receiving state. The CSMA/CD media access control method works at the data link layer.
A. When deploying IDS in the network, you can use a hub instead of a tap (TAP)
B. When a node connected to a hub sends data, it will execute CDMA/CD方法
C. Each node connected to a hub has 独享a collision domain
D. The hub is the one 基于IP地址that recognizes and completes data forwarding
Correct answer: A
Refer to analysis:
[Analysis] When deploying IDS in the network, a hub can be connected in series in the network link to monitor the data packets in the link, and the hub can be used instead of the tap (TAP). Nodes connected to the hub implement the CSMA/CD medium access control method when sending data. All nodes connected to a hub share a collision domain. The hub does not have the MAC address table that the switch has, so when it sends data, it is not targeted, but it is sent by broadcast. So choose option A.
A. The hub works. 网络层
B. When a node connected to the hub sends data, all nodes can receive it.
C. A hub is connected in series in the network link or 交换机all can listen to the data packets in the link.
D. Each node connected to a hub forms a 独立的collision domain
Correct answer: B
Reference analysis:
[Analysis] The hub works when物理层,a node connected to the hub sends data, and all nodes can receive the hub based on broadcasting to complete data forwarding, that is to say, when it wants to send data to a node, it does not directly send the data to the destination node, but sends the data packet to all nodes connected to the hub. All nodes connected to a hub form a shared collision domain. So choose option B.
Question 3: Using Sniffer on a port of a network device can capture all the communication flows of different ports belonging to the same VLAN. This kind of device is ( ).
A. Layer 2 switch
B. Layer 3 switch
C. Router
D. Hub
Correct answer: D
Reference analysis:
[Analysis] Layer 2 switches work at the data link layer, and Layer 3 switches and routers work at the network layer. Monitoring a port can only obtain the communication flow between this port and other ports. The hub works on the physical layer. All nodes connected to a hub share a collision domain. When a node sends data, all nodes can receive it, so all communication ports can be captured on one port. Therefore option D is correct.
3. Bridge
(1) Bridge Definition
A bridge is a device that connects two LANs, works at the data link layer, to be precise, it works at the MAC sublayer, and it can complete the connection of network systems with the same or similar architecture. The bridge is designed for storing and forwarding data in various LANs. It can connect different LANs together to form an extended LAN.
(2) Working principle
The working principle of the network bridge is relatively simple. Generally, two network cards connected to different types of LANs are inserted into a computer, such as an Ethernet card and a token ring network card, and the corresponding network card drivers are installed respectively. After completion, the computer becomes a network bridge for connecting Ethernet and token ring network. Because the frame structure, media access control method and transmission rate of different types of LANs are different. Therefore, the network card on the computer used as a network bridge can independently complete its own frame sending and receiving functions, and the network bridge software can complete the functions of receiving, forwarding and address filtering. The network card and bridge software complete the basic functions of the bridge under the control of a CPU, so that the bridge realizes the interconnection of different frame structures, media access control methods and speed networks. At present, the network bridge used for heterogeneous LAN interconnection is no longer important, because the mainstream technology of LAN basically adopts the Ethernet standard. The bridge also undertakes important maintenance work, that is, constructing and maintaining the MAC address table. The relationship between the physical addresses of different nodes and the forwarding ports of the bridge is recorded in the MAC address table. The bridge relies on the MAC address table to determine whether the frame needs to be forwarded and where to forward it.
(4) Main features
① The bridge can interconnect two networks using different data link layer protocols, different transmission media and different transmission rates.
②The bridge realizes the communication between interconnected networks by receiving, storing, address filtering and forwarding .
(5) Classification of bridges
①According to the different connection lines of the bridges, they are divided into ordinary LAN bridges, remote bridges and wireless bridges.
②According to the number of ports, it can be divided into dual-port bridge and multi-port bridge.
③ According to different frame forwarding strategies, it is divided into transparent bridge and source routing bridge.
(6) Spanning tree
When the topology changes, the bridge should be able to discover its change and automatically generate a new spanning tree. The spanning tree algorithm assigns a unique identifier to each bridge, and this identifier is composed of the bridge's MAC address and a priority. The port of each network bridge is assigned a unique identification in the network bridge, which is called "port identification".
The following concepts are used in the spanning tree algorithm.
- Path cost: Each port of each bridge has a path cost, which is the cost of transmitting frames on a LAN through that port.
- Root port: Each bridge has a path with the least cost to the root bridge, and the port used by the first hop above the path is the root port.
- Root Path Cost: For each bridge, the cost of the path with the least cost to the root bridge (the path starts from the bridge's root port) is the bridge's root path cost.
- Designated Bridge, Designated Port: In each LAN, a bridge is selected as the designated bridge. The port of the designated bridge that is used to connect the bridge to the LAN is called the designated port. Each network segment has only one designated port, and other ports are blocked, also called blocked ports.
Low frame forwarding rate and broadcast turmoil are the two main problems of the bridge; frame forwarding rate and frame filtering rate are the main parameters to evaluate the performance of the bridge.
4. Switch
A switch is a network device that is based on MAC address identification and can complete the function of encapsulating and forwarding data packets. The main functions of the switch include physical addressing, supporting network topology, error checking, frame sequence, and flow control. At present, the switch also has some new functions, such as support for VLAN (virtual local area network), support for link aggregation, and some even have a firewall function.
交换机与网桥的主要区别:网桥的端口数量相对较少,一般不超过24个,交换机的硬件系统经过专门设计,可以实现多个端口并发连接,支持多达128个端口; 网桥通常在一台计算机上配置而成,内部结构一般只有一个CPU,通过软件完成帧的接收、存储、地址过滤与转发等功能,其性能受结构限制,交换机一般使用为帧转发专门设计的ASIC芯片,或采用多CPU并发工作的结构,因而交换机的帧过滤和转发速率要高于网桥;网桥在发送数据帧前,通常要接收到完整的数据帧并执行帧检测序列FCS后,才开始转发该数据帧,交换机具有存储转发和直接转发两种帧转发方式。
4. Ethernet networking
1. Introduction to Ethernet Standard
IEEE 802.3 defines the protocol standard of Ethernet physical layer and media access control sublayer. Although the media access control sublayer of Ethernet adopts the same frame structure and unified CSMA/CD method, the physical layer technology can be different. The physical layer of standard Ethernet adopts IEEE 802.3 x Type-y-Name naming rules. Among them, x indicates the transmission rate, and the unit is Mbit/s; y indicates the maximum length of the network segment, and the unit is 100m; Type indicates whether the transmission mode is baseband or frequency band; Name indicates the name of the LAN.
2.10BASE-T standard Ethernet networking
In 10BASE-T Ethernet, computers can be easily connected into a local area network through unshielded twisted pair, RJ-45 interface and hub. This networking method, which takes the hub as the center to connect devices, is a breakthrough in the structure of the traditional bus-type shared Ethernet, but its medium access control still adopts the CSMA/CD method. Since the hub is a physical layer interconnection device, the nodes connected to it are still in a "collision domain", and only one node can send data frames at a time, while other stations can only receive data frames.
3. Fast Ethernet networking
(1) Overview of Fast Ethernet.
The Fast Ethernet protocol standard IEEE 802.3u was released in 1995 by the IEEE 802 committee. This standard uses the IEEE 802.2 standard and the CSMA/CD method in the LLC sublayer and MAC sublayer respectively , but it redefines the physical layer standard. On the basis of keeping the traditional Ethernet frame structure and media access control mode unchanged, the transmission rate is increased to 100Mbit/s, and 10Mbit/s and 100Mbit/s automatic negotiation mechanism is provided.
(2) Fast Ethernet media dedicated interface MI.
The 100BASE-T standard defines a Media Independent Interface (MII). As shown in Figure 5-9, MIL separates the MAC sublayer from the physical layer, so that when the physical layer realizes a transmission rate of 100Mbit/s, the transmission medium and signal encoding method will not affect the MAC sublayer. MI functions include: provide carrier sense signal and collision detection signal upward through the interface of MAC sublayer; exchange control information with the hub downward and support 10Mbit/s and 100Mbit/s rate interface
MII interface of Fast Ethernet
(3) The physical layer standard of Fast Ethernet.
- 100BASE-TX: Use 2 pairs of Category 5 unshielded twisted-pair wires, one pair is used for data transmission and the other pair is used for reception; 4B/5B coding mode is adopted, and full-duplex mode is used; the maximum network segment length is 100m.
- 100BASE-FX: Two optical fibers are used, one for data transmission and the other for reception; data transmission adopts 4B/5B-NRZI coding mode; it works in full-duplex mode; the maximum network segment length is 415m. ·
- 100BASE-T4: Use 4 pairs of Category 3 unshielded twisted pairs, 3 pairs are used to transmit data, and one pair is used to detect conflicting signals. Data transmission adopts 8B/5T encoding method; it works in half-duplex mode; the maximum network segment length is 100m.
(4) Working mode.
There are two working modes of Fast Ethernet, half-duplex and full-duplex. Since Fast Ethernet adopts full-duplex mode and point-to-point connection, the coverage distance of its transmission medium is only limited by the strength of the transmission signal, not by the size of the conflict window. In addition, a switch that supports full duplex can realize the interaction between different speeds and the mixed insertion of network cards with different speeds.
(5) Automatic negotiation.
The functions of Fast Ethernet auto-negotiation include: automatically determine whether the peer device of the unshielded twisted pair is using a full-duplex 100Mbit/s working mode or a half-duplex 10Mbit/s working mode; publish the working mode of the remote connected device to other nodes; exchange working mode related parameters with the remote connected device, coordinate and determine the working modes of both parties; automatically select the shared highest performance working mode. For example, when the network card of a host and the switch used to connect the host both support 100BASE-TX and 100BASE-T4, they will automatically negotiate to the highest performance 100BASE-TX mode. The function of auto-negotiation can only be applied in the Ethernet using twisted pair, and it can be realized by exchanging the "basic link code word" defined by 100BASE-T between the devices at both ends of the link. The time required for the negotiation process should be within 500ms. It should be noted that in 100BASE-T half-duplex mode, because the CSMA/CD mechanism is still used, the size of the collision window remains unchanged, but the transmission rate is increased by 10 times, so the maximum cable length should be reduced to 1/10 of that of 10BASE-T; but in 100BASE-T full-duplex mode, due to the exclusive cable and point-to-point connection mode, it is no longer restricted by the CSMA/CD mechanism, so the supported networking range can be larger.
The priority order of auto-negotiation is: 100BASE-TX or 100BASE-FX full-duplex mode, 100BASE-T4, 100BASE-TX half-duplex mode, 10BASE-T full-duplex mode, 10BASE-T half-duplex mode.
5. Network structure design of integrated wiring system
1. The network topology of the integrated wiring system
The network topology structure of the so-called integrated wiring system refers to an actual logical representation of the network layout of the integrated wiring system, which expresses various units used in the structure, such as wiring components, transmission media, wires, connecting hardware, and the connection diagram between them. The network topology of the integrated cabling system includes various network units, and these network units are combined and configured according to the principles of economical rationality and technical performance requirements.
2. The main components of the integrated wiring system
(1) Connect the device.
The connection equipment of the integrated wiring system mainly includes: communication outlet (TO), transfer point (TP), floor distribution frame (FD), main distribution frame (BD) in the building, and building group distribution frame (CD), among which TP is an optional part.
(2) Transmission medium. There are two types
of transmission media commonly used in integrated wiring systems: twisted pair and optical cable, which should be selected according to actual needs in application.
① twisted pair.
Twisted pair is the most commonly used transmission medium in integrated wiring engineering, which can transmit analog signals and digital signals, and is especially suitable for short-distance information transmission. Twisted pair wires are generally formed by twisting two copper core wires with a diameter of 0.40-0.65mm (commonly 0.5mm) according to the specified twisting moment. Among them, the purpose of twisting is to minimize the external electromagnetic radiation and the external electromagnetic interference suffered.
Twisted pair wires are divided into two types: unshielded twisted pair wires and shielded twisted pair wires. The unshielded (UTP) twisted pair cable has no metal shielding layer to the outside, which makes it less resistant to electromagnetic interference. It is bent and pulled by external forces during use, which can easily lead to damage to the balanced lay length. At the same time, this kind of cable is easy to radiate and leak when transmitting information, and the safety is poor; but because of its small size, light weight, good elasticity and low price, it is the most commonly used communication medium in structured cabling systems . The shielded (STP) twisted pair cable has a layer of metal foil on the outside, which has good anti-interference performance, but it has the disadvantages of high price, large volume, heavy weight, and difficult construction.
② Optical fiber (cable).
Optical fiber refers to a network transmission medium that uses glass fibers to transmit network data in the form of light pulses. In the integrated wiring system, two working wavelengths are often used: 0.85um (0.8-0.9um) and 1.30um (1.25-1.30um).
3. General wiring engineering equipment configuration
In the engineering design of the integrated wiring system, the equipment allocation problem required by the system should be considered simultaneously, that is, according to the building intelligent scale of the unit to which the project belongs and the relevant system composition, determine the types and quantities of the distribution frame, wiring subsystem, transmission medium and information socket (that is, the communication outlet) that the project needs to be equipped with.