CCTV. Video surveillance and IP networks.
Child of two revolutions
Are you used to the abbreviations IP, RTP, QoS, DiffServ, PoE?
It looks like you are looking at the prospect of introducing IP devices into your video surveillance system.
Well, you are not alone.
All over the world, there is a mass migration from analog cameras to digital ones transmitting video signals over IP networks.
In essence, a second revolution in the ideology of building video surveillance systems is currently taking place.
The first revolution was the transition from storing video in analog form to digital.
The benefits of such a transformation were quickly appreciated by specialists: searching video archives, which previously required days of work, began to be carried out almost instantly.
Perhaps the advantages of the second revolution are not so noticeable, but they are still significant enough that the only subject of dispute at present is the period of complete disappearance of analog solutions.
It seems incredible, but only five years ago it was necessary to prove the relevance of video transmission over IP networks.
«Security people» said: «Why do we need this?», administrators were afraid of overloading their networks.
Many integrators of that period did not consider information security an attractive area of financing at all.
A heated discussion unfolded on the pages of professional journals.
As noted at the time, the problem was the lack of awareness among specialists in related fields: “IT companies know how networks are structured, but they consider security to be the domain of narrow specialists; telecommunications companies know all about data transmission; security companies know very well how important it is and know how to ensure it.
But for the successful implementation of IP technologies for ensuring security, they must closely cooperate.”
It can be said that IP video surveillance systems installed in recent years are precisely the result of such cooperation.
We will try to tell you what an IP video camera is, consider the main advantages of transmitting video over IP for video surveillance systems, and the technical solutions used.
What is an IP video camera
A modern network camera is, in fact, a combination of a digital video camera and a specialized computer.
A digital camera can be of a very different class.
For example, the resolution of the recorded image varies from 640 x 480 to 2050 x 1550 and more. There are cameras designed for daytime shooting and for working in low light conditions, etc. Most cameras are equipped with an analog output.
The computer part of IP video cameras is of greatest interest.
First of all, these are network capabilities: cameras usually have an Ethernet port, a built-in web server, an FTP client, an e-mail client, support for network protocols TCP/IP, ARP, HTTP, FTP, SMTP, NTP, PPPoE, DHCP, DNS, DDNS.
When connecting to the network, all that remains is to assign it a web address.
Cameras usually implement multicast technology: video images can be transmitted simultaneously to dozens of consumers.
And in other respects, the cameras are similar to a specialized computer with good capabilities: they usually implement a change in the compression algorithm, resolution, frame rate of the recorded video, various digital processing operations, such as changing the levels of brightness, contrast, saturation, sharpness and hue, scaling, rotation and mirroring of the image.
Add to this a possible built-in motion sensor and encryption of transmitted video data and be amazed at the weight of a typical network video camera — about 100 g (!).
By the way, the widespread opinion about the bulkiness of the digital video stream is not entirely true.
In fact, everything depends on the image quality and frame rate. Thus, the MPEG-4 standard provides for video transmission rates up to 4.8 kbps.
Only advantages…
Let's consider the advantages of network cameras for video surveillance systems over analog solutions.
1. Probably the most important consequence of the transition to digital video cameras is the intellectualization of the video surveillance system.
Users are offered new, previously fundamentally impossible services, which ultimately lead to a new quality of the system. Such services include the ability to record only upon motion detection, detection of abandoned objects, built-in information storage facilities. It becomes possible to scale individual sections of the image, recognize objects, etc.
2. The ability to power over a network cable is also a significant competitive advantage of IP video cameras. This eliminates the need to lay a separate power cable, as is the case with an analog camera.
In addition, the use of PoE power supply technology (Power over Ethernet — IEEE 802.3af standard) allows for uninterruptible power supply centrally. However, this may cause a problem.
The fact is that video cameras are often located in remote locations, and the limitation of PoE technology is the distance of 100 m between the equipment room and the power consumer.
But here media converters come to the rescue, which are usually designed to connect fiber optic and copper cables.
In this case, a fiber optic cable is laid from the center to the media converter, in the converter the signals are converted for transmission via a copper cable, and the latter, together with the connected power supply, is deployed to the IP video camera. Naturally, there should be a power «socket» near the media converter.
3. The undoubted advantage of IP video cameras is their higher resolution compared to analog ones.
The maximum resolution of a TV signal (with an aspect ratio of 4:3) is 833 x 625 at a frame rate of 25 Hz. The resolution of a digital camera can be more than 10 times higher. This sometimes allows you to use one network video camera instead of several analog ones.
4. A digital image is sharper than an analog one.
The advantage of progressive scanning of network cameras is especially obvious when shooting moving objects, which come out sharp. Interlaced scanning of analog cameras leads to blurring of moving parts of the image.
If we consider that progressive scanning is also used in LCD monitors, it becomes beyond competition.
5. The introduction of digital video cameras increases the reliability of the system as a whole. After all, in the case of using analog cameras, the failure of the digital video recorder leads to the unavailability of information from several cameras at once. In the case of a digital camera, such a «bottleneck» does not exist.
6. When using IP video cameras, the video surveillance system becomes easy to manage, expand and upgrade. Moreover, as a rule, it is possible to use existing cable networks, and existing computers as video archives.
Variety of protocols and solutions
Video transmitted in real time places very serious demands on the communication channel. These are requirements for both bandwidth and acceptable signal delay.
It would seem that the optimal solution for transmitting a video signal should be a dedicated transmission channel that provides synchronous communication. However, the mainstream in this area turned out to be in a completely different direction: for transmission, the video signal is broken down into small packets, and they are transmitted in asynchronous mode.
At the same time, it is not guaranteed that the packet with number N will arrive at the receiver earlier than the packet with number N + 1. These are the features of the IP protocol.
Probably, a student who proposed a similar solution for video transmission 30 years ago would have received a solid and well-deserved F.
The UDP protocol, which is not connection-oriented, is used to transport packets. Its peculiarity is the lack of control over packets lost during transmission and their retransmission – since in the case of video this would lead to unacceptable delays.
Of course, the IP and UDP protocols themselves cannot ensure high-quality video transmission. Other solutions are used for this, some of which we will consider.
The RTP protocol was developed to transmit real-time traffic that is sensitive to delays. Within the framework of this protocol, the data type is determined for each datagram, a sequence number and a timestamp are entered.
All this helps to correctly assemble the signal at the reception, regulate the delay time.
However, it should be borne in mind that RTP alone does not guarantee high-quality and timely delivery of video (i.e. proper quality of service — QoS). For this, the RTP protocol control protocol — the RTCP protocol — is used.
If we draw an analogy with communication systems, then RTCP packets are service signals that are periodically or as problems arise sent over the network.
They provide feedback from the receiver to the transmitter.
For example, when the load increases (and therefore the quality of RTP packets deteriorates), an IP video camera can increase the degree of video signal compression.
Naturally, organizations do not build IP networks only for video transmission. The main type of traffic is data that does not require real-time delivery.
And if so, then the idea of prioritization arises: real-time traffic should be transmitted first.
This idea led to the emergence of the resource reservation protocol RSVP, which allows reserving network resources to obtain the necessary QoS for real-time traffic (integrated service model — IntServ).
RSVP is primarily implemented in routers, but IP video cameras also need to know how to reserve the necessary bandwidth.
In the case of a large IP network, the RSVP protocol has a number of shortcomings that forced the IETF to develop other principles for ensuring a given QoS — the differentiated services (DiffServ) model.
This model introduces the concept of a class of service based on the placement of the «type of service» (ToS) field in the IP packet header.
For example, a similar approach is implemented in the technology of multiprotocol label switching (MPLS), which is now considered as the basis for creating next-generation networks (NGN).
However, MPLS equipment is still quite expensive, so in the case of a small-sized enterprise network, it is better to focus on RSVP with various extensions.
IP or not IP?
But is it worth spending money on switching to new technology? In my opinion, there is no clear answer. By and large, in this case it is necessary to perform a risk assessment, estimate the probability and amount of damage due to a malfunction of the previous video surveillance system and compare the result with the costs of the new system.
In addition, it is necessary to take into account the possible reduction in «observers» (and, consequently, their wage fund) with the transition to IP.
Apparently, if the analog-digital video surveillance system was created recently, there are no complaints about its operation, and no expansion is planned, then it makes sense to continue to operate it.
At the same time, do not forget to monitor new IP video, because sooner or later the time will come when it will no longer be possible to live the old way.
If the video surveillance system is created from scratch or is subject to significant expansion, then, in my opinion, there is no alternative to switching to IP technologies.
By the way, an additional effect of such The transition may also include modernization of the enterprise's computer network.