| 安防网络最大的坑，竟然是交换机? |
| 添加时间：2017/11/27 16:51:32 浏览次数： |
| 安防自模拟转IP之后，网络在安防的应用越来越重要，也越来越复杂。笔者在安防网络领域从业多年，发现行业内的技术人员走了很多弯路，无论是安防厂商、集成商还是最终用户，对交换机如何选型及视频卡顿的原因存在不少误解。 After the security simulation to IP, the application of the network in security is more and more important, more and more complex. The author has worked in the security network field for many years, and found that the technical personnel in the industry have taken many detours, whether security vendors, integrators or end-users, there are many misunderstandings about how to choose the switch and video caton. 市面上流传的很多所谓选型经验和文档，其实都是满满的坑，比如最近某篇《一个交换机到底能带几台摄像头》……，所以，今天我把这些常识性错误简单总结一下。 Many of the so-called "selection experience and documents" circulated on the market are actually filled with pits, such as a recent article, "how many cameras can a switch take?" So, today I'm going to summarize these common mistakes. 误区1：盲目根据交换容量计算摄像机带机数量 Error 1: blindly calculate the number of camera tape according to exchange capacity 这种算法，就是把交换机的交换容量简单除以摄像头的码流，然后计算出带机数量。 The algorithm divides the exchange capacity of the switch by simply dividing the bitstream of the camera, and then calculates the number of machines. 如果根据这个理论，一台24口全千兆非网管交换机每个端口速率都是1000Mbps，下连端口只要合计接入不超过250路4M码流的摄像机就没有问题，那整台交换机就可以带几千路？ If according to this theory, a 24 Gigabit Ethernet switch, each port speed is 1000Mbps, the lower port as long as the total access to no more than 250 4M stream video camera will be no problem, then the whole switch can take thousands of road? 估且按所谓的实际性能一般只有理论值的 60~70%，那每个下连端口也可以合计接入不超过150路就没有问题，整机怎么着也可以带1000多路？ According to the so-called actual performance, generally only theoretical value of 60~70%, then each under the port can also total access no more than 150, there will be no problem, how can the whole machine with 1000 channels? 可实际情况是这样吗？ But is that the case? 照这个逻辑，千兆傻瓜机和网管机带机能力也没啥区别了。当我们按照这个理论去分析视频卡顿的网络原因，会分析到你怀疑人生。 According to this logic, there is no difference between Gigabit machines and network management machines. When we follow this theory to analyze the reasons for the video Caton network, will analyze you doubt life. 最后发现，网络的各个节点的带宽设计完全没有问题，流量根本不存在瓶颈，交换机运行状态看起来很正常的，可视频就是卡卡卡，马赛克花花花，怎么解释？ At last, the bandwidth design of each node of the network is no problem, no traffic bottlenecks, the operation of the switch state looks very normal, but the video is Ka Kaka, flower flower mosaic, how to explain? 误区2：交换机的实际性能一般只有理论值的 60~70% ？ Error 2: the actual performance of the switch is generally only theoretical value of 60~70%? 很多人，甚至是交换机厂家的售前，会在做安防方案的时候，跟你说，交换机实际转发性能只有理论值的60%~70%，所以，计算待机数量要留余量。 Many people, even before the switch manufacturers, will be doing security programs, to tell you that the actual forwarding performance of the switch is only theoretical value of 60%~70%, so calculate the number of standby to stay margin. 笔者从事数通领域工作17年，在设备厂家待过，也在芯片公司待过，至少在这有限的从业期间，还从未见过哪家芯片公司推出的某一款芯片的实际性能（交换容量）达不到理论值的。 I engaged in the field of work for 17 years, in the equipment manufacturers have been, but also in the chip company to stay, at least in this limited period of employment, has never seen any chip company launched a chip of the actual performance (switching capacity) can not reach the theoretical value. 24口全千兆交换芯片，交换容量必须≥48Gbps【24（24个端口）X1G（1000M）X2（全双工）=48G】，否则就达不到线速转发，我想没有哪一家芯片设计公司会犯这种低级的常识性错误，也没有哪一家正规交换机厂商会把一款达不到线速转发性能的交换机推向市场（机箱式交换机线卡存在阻塞比另当别论）。 24 full Gigabit switch chip, exchange capacity must be greater than or equal to 48Gbps [24 (24 port) X1G (1000M) X2 (full duplex) =48G], otherwise it is not up to the line speed forwarding, I think there is no a chip design company will make common sense this mistake, there is no a formal a switch manufacturers will reach the line speed forwarding performance switches to the market (box type switch line card is blocked than another). 如果你真遇到过交换机的交换容量达不到理论值，只有60~70%的性能，那恭喜你，你成功购买了一台次品，这种次品正规厂商想做都做不到，因为只有研发设计或者生产制程有缺陷，并且没有经过专业测试就直接市场销售的才有可能出现这种产品。同理，包转发率也是如此。 If you really met the exchange capacity switch is not up to the theoretical value, only the performance of 60~70%, then congratulations, you successfully purchased a defective, the defective regular vendors do not want to do, because only the design or production process defects, and without professional testing on the direct sales market this is possible products. In the same way, packet forwarding rate is the same. 误区3：根据经验进行交换机选型 Error 3: switch type selection based on experience 目前各个网络设备厂商在涉足安防网络项目时，除了按端口规格选型，按交换容量选型，还有最重要的一个手段，就是根据以往的项目经验选型。 At present, each network equipment manufacturer in the security network project, in addition to the selection of port specifications, according to exchange capacity selection, there is one of the most important means, that is, according to the previous experience of the project selection. 可是我们常常遇到这样的情况，同一款交换机在不同项目中，并且这些项目网络规模差不多，摄像机数量及码流也差不多，组网方案也是一样的。 But we often encounter such a situation, the same switch in different projects, and these projects network scale is similar, the number of cameras and streams are almost the same, networking program is the same. A项目是好的，B项目也是好的，可是C项目就会出现卡顿，WHY？ The A project is good, the B project is also good, but the C project will appear Caton, WHY? 立马联系厂家换一台，一换就好了，嗯，看来真是运气不好。可是过段时间又出现卡顿了，WHY？ Immediately contact manufacturers for a change, just like, well, it seems to be bad luck. But over time and Caton, WHY? 不断的换设备，重启设备，调整网络结构等。反复折腾，也许好了，也许还是会随机卡顿，搞的筋疲力尽，最终也无法定论，甚至一线网络品牌厂家也给不出一个准确原因。 Changing equipment, restarting equipment, adjusting network structure and so on. Fiddle, maybe, maybe will be randomly Caton, exhausted, and ultimately can not be conclusive, even a network brand manufacturers also did not give a precise reason. 首先，我们先来简单的剖析一下视频流传输的基础原理： First of all, let's first briefly analyze the basic principles of video stream transmission: 视频流是由I帧和P帧组成，其中I帧为超大帧，在网络传输的过程，I帧的任何一个报文的丢失，就会导致视频无法成像，同时，由于视频的实时性要求，一般采用UDP的传输机制，即丢包不重传，所以，基本上网络只要出现丢包，就会卡顿。 The video stream is composed of frames and P frames, which I frame super frame, in the process of network transmission, the loss of any one message I frame, will lead to the video image, at the same time, due to the real-time requirements, generally use the transmission mechanism of the UDP, which is packet loss retransmission, so basically network as long as there will be loss, carlton. 其次，再来简单介绍一下交换机的交换原理： Secondly, the exchange principle of the switch is briefly introduced: 当某个100M端口向另一个100M端口传输1M的数据流时，是以100M的速率传输了1/100秒。如果这1/100秒时有另外一个100M端口也向同一个100M端口传输1M的数据流，虽然两个端口加起来数据流只有2M，远没有达到100M的带宽瓶颈，但也会拥塞。 When a 100M port transfers the data stream of 1M to another 100M port, it transmits 1/100 seconds at the rate of 100M. If there is another 100M port in the 1/100 seconds, the 1M data stream is transmitted to the same 100M port. Although the two ports add up to only 2M, the data stream can not reach the bandwidth bottleneck of 100M, but it will also be congested. 同理，1000M端口在同一时间点只能接受一个1000M端口传输数据，但可以同一时间点接受10个100M端口传输数据，但超过10个，也会拥塞。 Similarly, the 1000M port can only accept a 1000M port to transfer data at the same time point, but can accept 10 100M ports at the same time to transmit data, but more than 10, it will also congestion. 所以，流量（带宽）与速率是二个概念，不能混为一谈。无论传输的数据流有多大，传输的速率都是100M或1000M，只是不同数据流大小传输所需的时间长短不同罢了。当速率相同的情况下，两个及以上的端口在同一时间点向同一端口传输时，就会拥塞。此时缓存如果能够 Therefore, traffic (bandwidth) and speed are two concepts, can not be confused. No matter how large the data stream is, the rate of transmission is 100M or 1000M, but the time required for the transmission of different data streams is different. When the rate is the same, two or more ports at the same time point to the same port transmission, congestion will be. At this point, if the cache can |
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