September 29, 2023
In recent years, pace of development of PoE power supply technology has become stronger and stronger. With a number of advantages such as simplified installation and deployment of electrical equipment, energy saving and security, PoE power supply has become a new favorite in scenarios such as wireless coverage, security monitoring and smart grids. In technical exchanges, most confusing issue is POE.
Today, editor will share with you important metrics of PoE switches and help you understand technical parameters of PoE switches, so that users can choose more suitable PoE switch products for themselves.
1. Switch category
1. Network construction method
Access level switch, aggregation level switch, master level switch
2. Model OST
Second level switch, level three switch, level four switch... level seven switch
3. Switch manageability
Managed switches, unmanaged switches. The difference lies in support of network management protocols such as SNMP/RMON
2. How to identify standard and non-standard PoE switches
1. Standard POE Switch: Complies with IEEE802.3af and 802.3at standards. This is a standard POE switch (commonly known as 48V). POE kit includes Power Sourcing Equipment (PSE) and receiving device. equipment (PD, Power Device) consists of two parts, poe switch is a kind of PSE equipment. The PSE is device that supplies power to terminals and is also POE Power over Ethernet process manager. PD is terminating device receiving power (national standard 48V device contains a PD chip).
2. Non-standard POE switch: On contrary, it is a non-standard POE switch ("non-standard", called "non-standard", is commonly known as 24V, but non-standard has 48V, 24V, 12V, 5V, etc.).
To determine whether switch is a normal switch or a PoE switch, method is very simple, you can judge by appearance of product with naked eye. Look at product label. Items supplied by conventional manufacturers will have product labels, usually on bottom of product. Read product information on label carefully and you will be able to judge one or two. Look at switch panel, if above information is not on bottom label, then look at panel. Some brands print name and model of switch on PVC panel, and LED indicators on panel often also have PoE logo.
3. Look at power parameters
A PoE switch that uses an external power supply will often have detailed labels on power adapter. Based on voltage of power supply, if it is 48V, it is a PoE switch. normal switch.
Switches with built-in power supply do not display power supply options, but some products have wattage rating on product label. PoE switch.
Third, main reference parameters of switch
1. What is data rate? Line speed refers to number of bits transmitted per second on a switch port, and unit of measurement is bps (bits per second, that is, how many bits are transmitted per second, and a bit is a binary number of 0 or 1). ).
2. What is bandwidth of backplane? The thermal switch backplane bandwidth is maximum amount of data that can be processed between switch interface processor or interface card and data bus. The backplane bandwidth refers to overall communication capacity of switch, and unit of measurement is Gbps, also called communication bandwidth. Therefore, only modular switches (which have expandable slots and can change number of ports flexibly) have this concept, fixed port switches do not.This concept is supported, and backplane capacity and switching capacity of fixed port switches are equal. The backplane bandwidth determines upper limit of connection bandwidth between each card (including cards that have not been installed in an expansion slot) and switching mechanism. Due to different architectures of modular switches, backplane bandwidth may not fully and effectively reflect actual performance of switch. Fixed port switches do not have a backplane bandwidth concept.
Calculation formula: number of ports x corresponding port speed x 2 (full duplex)
24 x 100M ports+2 Gigabit ports: 24*2*100+2*2*1000=8.8Gbps
3. What is throughput? Bandwidth (also known as total packet rate) refers to amount of data successfully transmitted by a network, device, port, or other medium per unit of time (measured in bits, bytes, etc.), i.e. throughput. refers to maximum data rate that a device can receive without dropping frames.
4. What is cost of package? For network equipment, in addition to important bandwidth metric, packet rate, also known as burst rate, is another main metric for measuring performance of network equipment. Packet rate generally refers to full duplex throughput of 64-byte data packets, which includes both bandwidth index and packet rate index.
The following calculates maximum packet rate for a port with a data rate of 1000 Mbps. 1000 Mbps=1,000,000,000 bps/(84*8 bits)≈1,488,095pps=1.488MppsAccording to this algorithm, etc., you can get packet rate for following common line ports speeds:10 Gigabit. line rate port burst rate 14.88MppsGigabit port packet rate 1.488Mpps100Mbps port packet rate 0.1488Mpps
Packet rate = number of Gigabit ports × 1.488Mpps + number of 100Mbps ports * 0.1488Mpps + number of other types of ports * corresponding calculation method.
24 100M ports, 2 Gigabit ports: 2*1.488+24*0.1488≈6.6Mbps
5. Wire-speed exchange: It refers to data exchange without bottlenecks according to data rate of network link. Its implementation, firstly, depends on ASIC chip, and completes analysis of protocol and data packet with special hardware, rather than through switch CPU with software. The implementation of media speed switching also depends on distributed processing technology, and data streams of multiple switch ports can be processed simultaneously. Therefore, LAN switch can be considered as a parallel processing device that combines CPU, RISC and ASIC.
6. PoE power supply capacity Since this is a PoE switch, parameters related to performance of its power supply are power of PoE power supply, including PoE power standard and total PoE power. PoE power standards include af and at standards. The former allows a maximum port power of 15.4W, while latter allows a maximum port power of 30W, so PoE switches that support at standard are better.
4. Power supply process of a standard POE switch
1. Detection: The poe switch first outputs a very small voltage and detects a power receiving device that supports IEEE802.3at/af standard chip (a chip that supports IEEE802.3at/af standard is referred to as "PD").
2. PD Classification: After detecting a PD, poe switch classifies PD device and evaluates power of PD device.
3. Power supply: During startup period (typically less than 15µs), poe switch supplies power to PD from low voltage until voltage required by PD is sufficient to provide stable and reliable DC power. for PD device.
4. Power off: If PD is turned off, poe switch will quickly (typically within 300-400ms) cut off power to PD and repeat detection process to determine if cable connector is connected to PD. Total PoE power is usually clearly stated in product manual, indicating maximum power that entire PoE switch can provide.
5. What to look for when choosing a POE switch
1. There are many types of PoE switches, number of ports is 4, 8, 16, 24, transfer rate is 100Mbps and gigabit, power is 100W, 200W, 300W, 400W. The baud rate must be selected correctly.
2. The quality of network cable is critical to a successful PoE power supply. Generally, Category 5e network cable, Category 6 network cable, and Category 6e network cable are recommended. The inner material of network cable is also very important. Do not use aluminum wire, copper-plated aluminum wire, copper-plated iron wire, iron core wire, etc. It is best to use oxygen-free copper network cable.
Distance within 80 meters. Theoretically, distance to PoE power supply is 100 meters, but considering quality of market network cable and influence of environment, actual distance to power supply should be within 80 meters. as much as possible.
3. Avoid choosing non-standard PoE switches. The reason non-standard ones still exist is because of low cost, although non-standard ones may be used in some places. However, non-standard PoE switches carry a potential security risk, such as burning out network devices connected to them. When using a non-standard PoE switch, its power supply voltage must match voltage of powered device.
POE power supply is just one method of power supply for many engineering projects. There are many other methods, each of which has its own application.
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