Haha, as for what’s going on, you’ll know after you look at their respective working principles!
How wired Internet access works
Each Cable Modem needs to be registered at the front end before use.
The front-end device CMTS is a device that manages and controls Cable Modem. Its configuration can be completed through the Consol interface or Ethernet interface. The configuration process through the Consol interface is similar to the Cable Modem configuration, and is performed item by line command. The configuration through the Ethernet interface requires the use of special software provided by the manufacturer, such as HiSpeed_NMS configuration software.
The configuration contents of CMTS mainly include: downlink frequency, downlink modulation method, downlink level, etc. The downlink frequency can be set arbitrarily within the specified frequency range, but in order not to interfere with the signals of other channels, it should be selected at the specified frequency point by referring to the channel division table of the cable TV. For example, select the center frequency of DS34 channel 682MHz. The choice of modulation method takes into account the transmission quality of the channel. In addition, the IP addresses of DHCP and TFTP servers, the IP address of CMTS, etc. must also be set.
After the above settings are completed, if there is no fault in the middle line and the attenuation of the signal level meets the requirements, start the DHCP and TFTP servers to establish a normal communication channel between the front end and CableModem.
Generally speaking, the downlink output level of CMTS is 50~61dBmV (110~121dBμV), the received input level is -16~26dBmV; the received level range of Cable Modem is -15~15dBmV ;The level of the uplink signal is 8~58dBmV (QPSK) or 8~55dBmV (16QAM). After the uplink and downlink signals are attenuated by HFC network transmission, the level values ??should meet these requirements.
The upstream channel interface and the downstream channel interface in the CMTS equipment are separated. When used, they need to be mixed into a signal through high and low pass filters, and then sent to the coaxial cable. In actual use, branch distributors can also be used to complete signal mixing, but this will cause greater interference to the upstream and downstream channels within the CMTS equipment.
After the channel between CMTS and Cable Modem is established, Simple Network Management Protocol (SNMP) can be used for network management. SNMP is a general network management program. For CMTS and Cable Modem equipment from different manufacturers, the management information base (MIB) files provided by the manufacturers need to be loaded into SNMP to manage the corresponding equipment. You can also use line commands for management, but the operation is not intuitive and prone to errors.
How wireless Internet access works
Although the standards and specifications followed by various wireless networks are different, there are only two types of transmission methods, namely radio waves. method and infrared method. Among them, infrared transmission is the most widely used wireless network technology at present. Almost all the home appliance remote controls we use use infrared transmission technology. As a wireless LAN transmission method, the biggest advantage of infrared transmission is that it is not interfered by radio waves, and the use of infrared is not restricted by the State Radio Regulatory Commission. However, the transmission quality of infrared transmission is greatly affected by distance, and the penetrability of infrared to non-transparent objects is also very poor, which directly results in the infrared transmission technology not being able to play a leading role in computer wireless networks; compared to Below, the application of radio wave transmission is much wider. Based on the positioning of this article, the author only briefly introduces the modulation method of radio waves.
1． Spread spectrum method
In this method, the spectrum of the data signal is expanded several times or even dozens of times before being transmitted. Although this approach sacrifices frequency band bandwidth, it improves the anti-interference ability and security of the communication system.
Wireless LANs that use spread spectrum generally choose the ISM frequency band, where ISM is taken from the first letters of Industrial, Scientific and Medical respectively. The emission frequencies of many industrial, scientific research and medical equipment are concentrated in this frequency band.
For example, the American ISM frequency band consists of three frequency bands: 902MHz~928MHz, 2.4GHz~2.48GHz, and 5.725GHz~5.850GHz. If the transmit power and bandwidth radiation meet the requirements of the US Federal Communications Commission (FCC), you can use the ISM band without submitting a special application to the FCC.
2． Narrowband modulation method
As the name suggests, in this modulation method, the data signal is directly transmitted without any expansion. Compared with the spread spectrum method, the narrowband debugging method occupies less frequency band and has high frequency band utilization. However, wireless LANs that use narrowband modulation occupy dedicated frequency bands and therefore require approval from the national radio management department before they can be used. Of course, users can also directly choose the ISM band to avoid band application. However, the problem is that when nearby instruments or communication equipment are also using this frequency band, it will seriously affect the communication quality and the reliability of the communication cannot be guaranteed.
Currently, WLANs based on the IEEE 802.11 standard all use spread spectrum.
Features
Usually the transmission media of computer networking mainly relies on copper cables or optical cables to form a wired LAN. However, wired networks are subject to wiring restrictions in many situations, and the construction and renovation projects are very large. Moreover, wired LAN still has defects such as easy damage of lines and immovable network nodes. Especially when connecting nodes that are far apart, laying dedicated communication lines is difficult, expensive, and time-consuming. These problems have formed serious bottlenecks for the rapidly expanding Internet demand and restricted the development of the Internet.
The emergence of WLAN has fully solved a series of problems caused by the inherent defects of wired networks. Compared with wired networks, WLAN has the following specific advantages.
Easy to install: During the network establishment process, the network cabling has the longest construction period and the greatest impact on the surrounding environment. The establishment of a wireless LAN reduces or even eliminates this complicated workload. Generally, only one or more wireless access (Access Point) devices are placed in the area to establish network coverage.
●Flexible use: In a wired network, the placement of network equipment is limited by the location of network information points. Once a WLAN is built, any location within the signal coverage area can easily access the network for data communication.
●Economic savings: Due to the lack of flexibility of wired networks, designers often have to consider future expansion needs as much as possible and preset a large number of low-utilization access points when planning the network. , causing a waste of resources. And once the development of the network exceeds the expected plan, the overall transformation will also be a considerable expense. The emergence of WLAN has completely solved this planning problem, fully protected users' investment, and is also very simple to modify and maintain.
●Easy to expand: Like wired LAN, WLAN has a variety of configuration methods, which can be flexibly selected and reasonably matched according to actual needs. In this way, WLAN can be used whether it is a small network with a few users or a large network with thousands of users, and can provide features such as "roaming" that wired networks cannot provide.
At present, the data transmission rate of wireless LAN can reach 54Mbps, which is very close to the transmission rate of wired LAN, and its transmission distance of up to 20km is beyond the reach of wired LAN. As a supplement and extension of wired LAN, WLAN makes computers mobile and can quickly and conveniently solve network connectivity problems that are difficult to achieve in wired networks, becoming the dominant direction of network development in the future.