Location: Home Page > Article Article

Knowledge networks are social networks that bring together knowledge participants. It can create and transfer knowledge between individuals, organizations and outside organization, and people can collaborate and share information through a knowledge network. The goal is to connect technology with people and realize an effective combination of intellectual capital, structural capital and client capital. It can be divided into an internal knowledge network and an external knowledge network. The former emphasizes sharing of knowledge between employees and organizations within organization, while latter emphasizes sources of knowledge outside organization, including communities, national and social relationships, and competitors. Below is a collection of samples for learning basics of wireless networking compiled by editor, which you can refer to.

Basic knowledge of wireless networks (1)

1. What is a wireless network?

Generally speaking, so-called wireless communication, as name suggests, uses radio waves to transmit data. From point of view of application, it is completely similar to use of wired networks. The biggest difference between them is that transmission medium is different.

Also, because it is a wireless network, it has many advantages over wired networks in terms of installation and mobility.

2. What are benefits of a wireless network over a wired network?

Its portability and convenience are not available on wired networks. In terms of cost, it can greatly reduce wiring costs as well as modification and clearance costs. In fact, space used is much more flexible.

3. Does wireless network affect human body?

Because wireless network transmission power is much weaker than that of ordinary mobile phones, wireless network transmission power is about 60-70mW, while transmission power of mobile phones is about 200mW, and use method is not like a mobile phone.human body, so there is no security considerations.

4. If you want to set up a wireless network, what basic equipment do you need?

Typically, basic equipment for setting up a wireless network is a wireless network card and access point (AP) so that network resources can be shared wirelessly with an existing wired architecture.

5. Will there be interference when using wireless network or affect operation of other devices?

Basically, frequency band used by wireless network belongs to 2.4GHz ISM high frequency band. Electrical equipment used in daily life, office, etc. will not interfere with each other because there are many of them. frequency differences, and wireless network itself has a total of 12 channels available for tuning, so you don't have to worry about natural interference.

6. What is ISM frequency range?

Answer: The ISM (Industrial Scientific Medical) frequency band (2.4-2.4835 GHz) is mainly open to industry, science, medicine and three major institutions. This frequency band is determined by US Federal Communications Commission (FCC). ) Come out, this refers to Free License, and there is no so-called restriction on authorization.

7: What is spread spectrum?

Spread spectrum technology is mainly divided into two methods: "frequency hopping technology" and "direct sequence".

These two technologies were used by Army during World War II to ensure stability and privacy of communications signals in harsh environment of war.

To a non-specific receiver, beat signal generated by Spread Spectrum is just impulse noise to it. Thus, it is a relatively secure communication technology in general.

8: What is frequency hopping spectrum?

Frequency Hopping Spread Spectrum (FHSS) technology is synchronized and simultaneous, accepting both ends to transmit signals with a certain type of narrowband carrier. beat signal is just impulse noise.

The signals triggered by FHSS can be specially designed to avoid noise or non-repeating one-to-many channels, and these frequency hopping signals must comply with FCC regulations using more than 75 frequency hopping and frequency hopping signals. The maximum time interval (Dwell Time) to next frequency is 400 ms.

9: What is a Direct Sequence Spectrum?

Direct Sequence Spread Spectrum (DSSS) is to use more than 10 chips to represent original signal "1" or "0", to make original signal higher power, narrower frequency becomes lower power frequency with a wider frequency.

The number of chips used per bit is called expansion chips, a higher value of expansion chips can increase noise immunity, and a lower value of expansion factor can increase number of users.

In general, spread factor in DSSS is quite small, for example, spread factor used in almost all 2.4 GHz wireless LAN products is less than 20.

In IEEE 802.11 standard, its spreading factor is only 11, but according to FCC regulations it must be greater than 10, and in experiment, best spreading factor is around 100.

10. How wide can a wireless network cover?

The range covered by a typical wireless network depends on whether environment is open or not. If there is no external antenna, field of view is about 250 m. If it is a semi-open space, there are partitions. area, about35~50 m,

Of course, when adding an external antenna, distance may be longer. This is related to gain of antenna itself, so it needs to be planned according to needs of customers.

11: What is wireless privacy while using?

Basically, GEMPLEX wireless network technology adopts DSSS system, which has function of anti-tethering. In addition, with double protection of data encryption function (WEP40bits), its security is quite complete.

12. What is a bridge (access point)?

Answer: The access point, commonly known as network bridge, as name suggests, is used as a bridge between traditional wired LAN and wireless LAN, so any PC equipped with a wireless network card can share wired network. through TD. Resources of a local network or even a global network.

In addition, access point itself also has a network management function that can perform necessary control on PC connected to wireless network card.

13. How many workstations can access point support at same time?

Theoretically, it can support CLASS C, but in order for workstation itself to have enough bandwidth to use, it is generally recommended that access point support about 20-30 workstations as best condition.

14: What is roaming feature?

Just like a mobile phone, it can move between different base stations, and a wireless workstation can also move between different access points. As long as ESSID definitions of access point groups are same, natural wireless network workstation can move freely in radio area covered by waves.

15. If wireless network equipment is installed outdoors, how can it prevent lightning strikes?

In general, a wireless network can be equipped with lightning protection equipment, which can be installed on wireless network equipment to alleviate damage to system caused by external surges.

16. What is access control?

Answer: Essentially, each wireless network card has a set of unique hardware addresses, so-called MAC address, which can be determined using an access control table. The card can enter this access point, and some cards are rejected to enter system, so that a control mechanism can be implemented that can prevent outsiders from accidentally entering network and stealing resources.

17. What is ASBF?

ASBF (Auto Scale Down Function), this feature is a unique feature of Gemplex AP that ensures that wireless LAN always has best connection quality. network cards must be designed according to IEEE 8 specifications02.11.

18. What is power management?

Since laptop needs to be charged after about 2 hours of use, and if other peripherals are used at same time, it will consume more power, so this function is designed to effectively manage power consumed by wireless network card. .

In other words, it can timely control when DATA is being sent or received, it is in "wake state", otherwise it is in power off mode.

19. Does length of wire used by antenna affect transmission quality?

Generally speaking, length, material, and impedance matching of wire used in an antenna will affect signal to a certain extent, and most obvious one is gain attenuation.

Generally speaking, 20 feet will attenuate signal by about 1.2 dBi, and an average attenuation of 8 dBi will cut original transmission distance in half. Therefore, length and quality of wire are most important in application of wireless products. Can not be ignored.

20. When setting up a directional antenna, is there a tool that can provide guidance on optimizing signal quality?

Gemplex's Bridge itself provides a set of link quality calibration software routines that are presented on screen as graphic curves. Users can clearly see current signal strength and adjust position of antenna. best.

21. What is Ad-hoc?

Represents a special mode of wireless network application. A group of computers can be connected to each other and share resources without using an access point.

22. What is infrastructure?

An application model that combines wired and wireless LAN architectures. With this architecture model, network resources can be shared. This app requires a hotspot.

23. What is BSS?

A special Ad-hoc LAN application called Basic Service Set (BSS). A group of computers can form a group by specifying same BSS name, and this BSS name is called BSSID.

24. What is ESS?

Infrastructure application. One or more BSSs may be defined as an extended service set (ESS). Users can navigate and access any data in BSS on ESS. Access points must be configured with same ESSID and channel to allow roaming.

25: What is SNMP?

"Simple Network Management Protocol", a network management communication protocol, through SNMP software can connect to SNMP-enabled devices, and can collect all device information and execute other integrated applications. Gemplex Wireless LAN Product There is support for this feature.

Basic knowledge of wireless networks (2)

1.Network Protocol

l What is a protocol

Protocols are rules and procedures for communication and behavior on network.

l Three elements of agreement

n Protocol syntax: The sending machine sends data to target host according to a specific syntax.

n Protocol semantics: receiver can understand sender's data.

n Timing: A sends data to B, does B receive it, does A respond, and A decides whether to send data again according to response. This is also an interactive relationship.

l If one computer on network uses same protocol as another computer, two computers can exchange information.

l Two hosts using different protocols cannot communicate with each other and must be translated through a gateway in order to communicate.

2. Common transfer protocols

l NetBEUI

n Microsoft NetBIOS extension

n supports all Microsoft networking products

n fast and small

n Easy setup

n is for small, non-routable networks

n is located at third and fourth layers of OSI network model, namely network layer and transport layer

lIPX/SPX

On a Netware host

n faster

n can be routed, but routing effect is not very good at large network scale

l Nwlink IPX/SPX compatible

n IPX/SPX compliant protocol

n is used to connect to Netware

n average speed, average size

n routable

n With Nwlink, Windows 2000 computers can communicate with other network devices using IPX/SPX.

lTCP/IP

n The only recognized protocol on Internet

n complies with RFC standards

n slow speed, large size

n is routable and can still perform better routing at large network scale

3. How to choose a transfer protocol

l Communication can only take place if same protocol is used

n If server sets any protocol, host must set appropriate protocol for communication.

n If one computer needs to communicate with other computers, it must first check which protocol is installed on other computer, and same protocol can be set before communicating.

n If company is very small, network only provides internal file transfer, no router, and no Internet connection, NetBEUI protocol should be selected.

n When users on network need to conduct business or communicate over Internet, TCP/IP protocol should be installed.

n If you have a Netware server on your network, you must install NWLINK protocol.

l Comparison of three protocols

n NetBEUI is like a racing car, fast, not routable

n NWLINK, IPX/SPX are similarfor family cars: speed is higher, but routing range is limited.

n TCP/IP is like a big truck, routing effect is good, range is wide, but speed is slow

Basic knowledge of wireless networks (3)

1. Network expansion

l Shared network

n bandwidth sharing

The logical structure n is a bus type structure

n How to use a bridge to connect to a networkSegmentation?

2. Bridge

l Bridge characteristics

n operates at second layer of OSI model, data link layer

n According to MAC address (hardware address) of target NIC in header of data packet, data packet

n can isolate traffic and be used for network segmentation (or separation of subnets of second level, separation of collision domains)

n is an unconditional broadcast frame, cannot isolate a broadcast

n Create a routing table with MAC address of source NIC

n There can only be one signal on network at a time

Summary of how bridges work

n The bridge operates in OSI model and at second layer (data link layer). It can understand layer 2 data packet header and decide how to send packet according to destination address in packet header. (MAC address of network card).

n The bridge automatically creates a table of MAC addresses connected to each port according to source address of layer 2 data packet. When bridge receives a data packet, it sends data packet to corresponding port.

n If data packet received by bridge is a broadcast frame, it will be unconditionally sent to all ports. Bridges cannot isolate broadcast frames, so a bridged network cannot form a loop.

n If bridge cannot find port where packet's destination MAC address is, it will send packet to all ports.

3. Router

l Router Features

n works in OSI model and at third, network layer

n Create data frames according to target network number (Net ID)

n is route to group of cars

n can isolate broadcast messages to prevent broadcast storms (Broadcast Storming), used for network segmentation (separation of subnets of third level, separation of broadcast domains)

n Routing type: static and dynamic

n The router does not translate protocol, but performs work with data frames between different network segments of routed protocol

How routers work

n On a network, host sends data packets, and data packets are transmitted to router through network cable.

n The router checks Layer 3 header of data packet, which contains IP address of destination host.

n Routerreads destination address, reads network number in destination address, and selects a route according to network number.

n routers can isolate broadcasts. After router sees broadcast frame, it simply discards it, so router can form a loop.

n Routed protocols: IPX/SPX, TCP/IP.

n Non-routable protocols: NetBEUI, DLC (no network number. Host number in structure).

n A router does not perform protocol translation, but rather handles data frames between different network segments of same routable protocol.

n The Routing Table concatenates destination network number to determine what data packet looks like.

4. Toggle

l A switch is a device similar to a bridge or router.

l Switch Features:

n The overall speed is high.

I. ASIC (Application Specific Integrated Circuit)

ii. Application of ASIC (Application Specific Integrated Circuit) to implement data packet processing in hardware so that data frames can be directly transmitted through multiple segments in a faster and more efficient way.

n Implement multiple channels at same time.

iii. A switch is a combination of several bridges. Thus, switch is like a flyover, which can realize multi-channel.

n Each port is isolated as a collision domain to achieve exceptional throughput.

n allows full duplex operation.

5. Gateway

l Protocol translation software. Usually used for seventh layer.

l Different protocols for same task.

l For specific tasks.