November 06, 2023
With transition from analog security to IP networking, use of networking for security is becoming more and more common. To solve problems such as network surveillance video freezing, many articles cite their own experience. In fact, this experience will reveal some common sense errors in practical application. Regardless of security vendors, integrators, or end users, greatest misunderstanding of these security stakeholders regarding security network occurs at switch.
Misunderstanding 1: Blind calculation of number of cameras based on switching capacity
This algorithm is simply to divide switching capacity of switch by camera bitstream and then calculate number of cameras.
If, according to this theory, speed of each port of a 24-port gigabit unmanaged switch is 1000 Mbps, and downstream ports are connected to cameras with no more than 250 channels of 4-Mb streams, there will be no problems. then whole switch Can you pass a thousand roads?
According to this logic, there is no difference in power of a gigabit fool machine and a network management machine. When we analyze network causes of video freezes according to this theory, we will analyze what you doubt in your life.
In end, it was found that throughput pattern of each node in network is fully functional, and there are no traffic bottlenecks at all. The operation status of switch seems to be normal, but video stutters and mosaic, how to explain this?
Misconception 2: Actual switch performance is typically only 60-70% of theoretical value
Many people, even switch manufacturer pre-salespeople, will tell you when designing security solutions that actual switch performance is only 60-70% of theoretical value, so you should leave a margin in calculations. from reserve.
A security officer who has worked in industry for almost 20 years said that he had never seen actual performance (switching capacity) of a chip produced by this company fall short of theoretical value. 24-port full-gigabit switching chip, switching capacity must be ≥ 48Gbps [24 (24 ports) X1G (1000M) X2 (full duplex) = 48G], otherwise it will not reach wire speed, I do not think there is any chip design company will make such low level common sense mistakes and no conventional switch manufacturer will market a switch that can't deliver wire speed performance (chassis switch line card blocking ratio is another matter). ).
Misconception 3: Choose switches based on experience
At present, when various network equipment manufacturers are involved in security network projects, in addition to selecting models based on port specifications and switching capacity, most important method is to select models based on experience of past projects.
However, we often encounter a situation where same switch is used in different projects, and network scales of these projects are similar, number of cameras and bitstreams is similar, and network scheme is same. Project A is good, project B is also good, but project C will get stuck. After contacting manufacturer about replacing switch, it will be numbered immediately, but after a while it will hang again.
One possible reason is that video transmitted by switch is at too much risk, congestion occurs at aggregation or kernel level, and packet loss occurs. Obviously, problem lies in unreasonable selection of switches.
How to choose a radio button?
1. According to code stream and number of cameras, select characteristics of switch and design network layout.
At present, quality of security practitioners is gradually increasing, and choosing right switch is most basic quality. However, when designing a solution, it is recommended to take into account situation of traffic bursts, it is recommended that bandwidth usage of switch port does not exceed 70%, but it is better to control it within 60%.
2. Choose a managed switch with as much cache as possible.
A cache can reduce packet loss caused by congestion. Theoretically, if cache is large enough, there will be zero packet loss and video will not freeze due to network issues. As a rule, higher-end switches and switches with richer service features have a larger cache. For same 24-port gigabit switch, non-network management cache can have only a few hundred KB, while switch's three-level cache can have tens of M. Therefore, when budget is sufficient and cost is acceptable, try to choose a managed switch with a large cache.
It should be noted that no matter how switch is chosen and network is designed, no manufacturer can guarantee that their products and solutions will never get stuck in any security project, so we should not be too extreme with switch. Chase. Only by constantly improving optimization scheme and equipment for maintenance after operation and maintenance, safety network can achieve satisfactory results.
