The basic content of network transmission
Network transmission refers to a series of lines (fiber, twisted pair, etc.) through the adjustment of the circuit according to the network transmission protocol to communicate the process. Where the network transmission needs the medium, that is, the network between the sender and the recipient of the physical path, which has a certain impact on the network data communication. Common transmission media are: twisted pair, coaxial cable, fiber, wireless transmission media. Network protocol is the network (including the Internet) to pass, manage some of the norms of information. As people communicate with each other is to follow certain rules, the mutual communication between computers requires common compliance with certain rules, which are called network protocols. Network protocols are usually divided into several levels, communication between the two sides only in the common level can be linked to each other.
Transmission media is also known as transmission media. Divided into guided transmission medium and non-directional transmission medium. Guided transmission media are: metal conductors and fiber conductors and other cable form. Non-directional transmission medium: shortwave, microwave, Bluetooth, satellite and light waves and other radio waves, for the wireless transmission form?
First, twisted pair cable (TP):
In order to reduce the degree of interference of the signal, each pair of twisted pairs in the cable is usually twisted by two insulated copper wires, and therefore, it is called a pair of twisted pairs. For twisted pair. Twisted-pair cables are divided into unshielded twisted pair (UTP) and shielded twisted pair (STP). Currently available on the market UTP is divided into three categories, four categories, five categories and five categories of four categories: 3 categories: transmission rate support 10Mbps, outer protective rubber is thin, the skin marked "cat3" 4: Not commonly used in Category 5 (Category 5): transmission rate support 100Mbps or 10Mbps, the outer protective rubber thicker, the skin marked with "cat5" super 5 type twisted pair in the transmission signal than the ordinary type 5 twisted pair attenuation Smaller, more anti-interference ability, in the 100M network, the interference level is only ordinary 5 class 1/4, the current less application. STP is divided into three categories and five categories, STP internal and UTP the same, outsourcing aluminum foil, anti-interference ability, high transmission rate but expensive. Twisted pair is generally used for star wire mesh connection, both ends installed RJ-45 head (crystal head), connecting the network card and hub, the maximum cable length of 100 meters, if you want to increase the scope of the network, Strand can be installed between the repeater, up to 4 repeaters can be installed, such as the installation of four repeaters with five network segments, the maximum transmission range of up to 500 meters.
Second, coaxial cable:
Consists of a hollow outer cylindrical conductor and an inner conductor located on the central axis, with the inner conductor and the cylindrical conductor and the outside being separated by an insulating material. According to the different diameter, can be divided into two kinds of thick cable and cable: thick cable: long transmission distance, good performance but high cost, network installation, maintenance difficulties, generally used for large local area network trunk, Device. (1) The thick cable is connected to the external transceiver. (2) The AUI cable is connected between the transceiver and the network card. (3) The network card must have AUI interface (15-pin D-type interface): 500 meters each, 100 users, 4 repeaters up to 250 meters, the minimum between the transceiver 2.5 meters, the transceiver cable up to 50 meters. Thin cable: connected with the BNC card, both ends of the 50 ohm terminal resistance. With T-head, T-head between the minimum 0.5 meters. Thin cable network length of each line up to 185 meters, each line up to 30 users access. Such as the use of four repeaters connected to five segments, the maximum network distance of up to 925 meters. Thin cable installation easier, lower cost, but the daily maintenance is not convenient, once a user failure, it will affect the normal work of other users. According to the different transmission band, can be divided into baseband coaxial cable and broadband coaxial cable two types: baseband: digital signal, the signal occupies the entire channel, the same time can send a signal. Broadband: transmit signals of different frequencies.
Is composed of a group of optical fibers used to spread the beam, small and flexible transmission medium. The optical signal is generated by the optical transmitter, the electrical signal is converted into an optical signal, the optical signal is introduced into the optical fiber, and the optical signal received by the optical fiber is received by the optical receiver at the other end, and it is converted into an electrical signal. Decode and then deal with. Compared with other transmission media, the optical insulation performance of the fiber is good, the signal is small, the bandwidth is wide, the transmission speed is fast and the transmission distance is large. Mainly used to require a longer transmission distance, wiring conditions, special trunk connection. Divided into single-mode fiber and multi-mode fiber: single-mode fiber: the laser as a light source, only a light path, transmission distance, more than 2 km. Multimode fiber: by the diode light, low speed short distance, less than 2 km. In the case of
Network transmission unit is MBPS, your computer below the connection speed is written below. It represents the frequency of the signal transmitted a second, but this frequency is not what we usually say byte (referred to as B), B that is the space occupied by the file, is the size of the meaning.
1T = 1024GB 1GB = 1024MB 1MB = 1024KB 1KB = 1024B (byte) 1byte = 8 bit 1 bit = 00000000 (8 binary numbers, which is why we often say why the computer only deals with 0 and 1)
Analysis of Transmission Distance of Network Camera
Most of the engineers in the network camera wiring installation process will encounter a network camera transmission distance problem, the network camera in the recent transmission can use the most simple network cable for transmission, but if the distance is relatively far, the network camera should How to solve this transmission problem, the following, made a detailed analysis.
Network cameras, are using network cable (twisted pair) transmission, and the current market is the most common network cable over Category 5 twisted pair, the following are the regular manufacturers of the national standard ultra-Category 5 twisted pair as a discussion (Amp , A Dan, Far East, Southeast Asia and other brands).
Due to the limitations of the cable (twisted pair) itself, the specification requires twisted pair transmission distance of less than 100 meters. Therefore, in the actual use of network cable connection, the cable line transmission distance of not more than 100 meters.
As the network cable can be extended through the switch and other transmission distance, the network transmission can also use optical fiber for long-distance transmission. So for the network camera, the transmission distance is not limited, theoretically can be infinite distance transmission.
100 meters above the network transmission program
However, in the actual use of the process, often encountered more than 100 meters distance, the need to use cable transmission, what is the solution to this situation? Optical fiber transmission can solve the problem of long-distance direct transmission, but because of its high cost, technical requirements are too high and other reasons, not practical, the following will not be discussed.
1, use the switch to extend
In the middle of the transmission every 90-100 meters, add a switch, you can achieve the increase in the transmission line distance. This refers to the switch refers to the regular manufacturers with network relay function of the switch, the market below 50 yuan of the switch does not generally take the network relay function, can not be used to achieve the transmission distance increases.
This method can generally increase the 3-4 switches to achieve the network transmission distance to 400 meters. But this way, because the need to increase the switch in the middle, and the switch requires power, may cause inconvenience such as construction.
2, use the network extension to extend.
Network Extender, also known as Cable Extender. Is a kind of equipment that can extend the transmission distance of the cable, including the transmitter and the receiver. Use the network extender to increase the transmission distance of the cable to 300-700 meters. Since the transmitter and receiver of the network extender are both ends of the network cable, and both ends of the general situation also have power, so this way in some conditions than the use of switches more practical.
3, the use of wireless bridge connection
Use wireless connection (that is, the general said that the wireless bridge, wireless microwave belong to this), how far away from the choice of transmission equipment, the general wireless bridge equipment support 4-5 km or more.
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