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Monitorização Vídeo

Básicos

Internet CCTV GUIDE - video transmission
Until quite recently, the main interest of constructors, designers and installers was concentrated on image recording - currently the decisive significance in modern surveillance installations have issues related to transmission of video information.
Due to security reasons and tendency towards cost reduction (necessity of employing professional staff), surveillance system centers are situated in some distance from the protected buildings and places, thus the leading role of good quality video transmission.
Nowadays, there are two parallel technologies of video transmission: analog and digital, however they are used for realization of different functions - analog transmission in local area systems, digital - for longer distances.
ANALOG VIDEO TRANSMISSION
Advantages
Cheap and popular devices, simple installation and operation.
Disadvantages
Limited transmission range, susceptibility to interferences and impact of attenuation of transmission line, limited access for larger group of scattered users.
Use: In local area surveillance installations, at short transmission distances and in low budget installations.
Building analog transmission system.Image processed by a camera to electric continuous signal may be transmitted through various transmission media - the most popular are:
  • Copper cables,
  • Optical fibers,
  • Electromagnetic waves (radio, laser, infrared)
  • copper cables,
  • optical fibers,
  • electromagnetic waves (radio, laser, infrared)
Transmission systems consist of the basic elements:
  • camera - processing image to electric signal;
  • converter - it adjusts input and output signal to the type of used transmission medium - it can be: transmitter, modulator, transformer, filter, adapter;
  • transmission channel;
  • receiver (monitor) - device processing electrical signal back to optical form.
Analog transmission media
Coaxial cable
Cabo Coaxial (75 ohm): TRISET-113 1.13/4.8/6.8 [1m]
Basic element of the cable is its copper core.It is surrounded by following layers:
  • isolator layer,
  • metal shield (mostly copper, in net or coating form) securing the inner wire from outer EM field,
  • outer protective layer, separating cable from environment.
Typical coaxial cables used for signal transmission are characterized by wave impedance of 75 ohm.
Advantages of coaxial cables:
  • they match for typical inputs/outputs of video equipment,
  • metal shield secures from signal "leakage" and protects against interferences,
  • possibility of using preemphasis and deemphasis.
Disadvantages of coaxial cables:
  • non-zero resistance of metal shields causes voltage drops - due to return currents: when there is difference in mass potential of camera and receiver, it effects in insertion of interfering voltage into transmission line, and as the consequence - horizontal strips in image (fixed or moving, depending on difference of potential - fixed or variable),
  • environmental electromagnetic interferences, not always sufficiently attenuated by the shielding, causing deterioration in image quality,
  • amplification of signal in transmission line also amplifies interferences (it is not possible differential amplification).
Basic cables parameters:
  • signal attenuation expressed in dB/100m, depending on frequency (growing with it)
  • line capacitance (caused by relation between wire and shield working as capacitor's plates), measured in F/m, usually pF/m,
  • shielding efficiency, showing ability of suppressing outer EM field, shown in dB,
  • resistances: of outer (shielding) and inner (core) conductors, in ohms.
Areas of application
Transmission of single signals on short distances, with low level of environmental interferences. Using 75 ohm impedance cable, connections between cameras and monitors may be realized at distances from 100 - 500/600 meters. The maximal distance is strongly related to quality of the cables used - 600m distance can be achieved using the copper cable TRISET-113 E1015.
We don't recommend cheap copper-plated cables - when using them, quality of transmission dramatically decreases.
Depending on the cable type, above 100 - 500 m distances it is recommended to use signal amplifiers - M1840. We should remember that color cameras are more sensitive to so called "cable lengthening" - initial symptom is decrease in color saturation.
Pair of copper wires (twisted-pair cables)
Pair of copper wires covered with isolation and twisted spirally around themselves. Usually grouped in set of four pairs in common sheath (UTP/FTP cables). Individual wires can be distinguished due to different colors.
UTP/STP cables are used for transmission of one to four video channels. Typical connector - RJ45.
Advantages of twisted-pair cables:
  • ability to transmit a few signals through one cable (four or ten paired),
  • smaller size of UTP/STP cable than of typical coax,
  • wide area of applications (phone networks, computer networks, surveillance networks),
  • high resistance to outer interferences - disturbances affect both wires equally and there is possible mutual neutralization due to use of differential amplifiers at the ends of transmission line.
Disadvantages of twisted pair-cables:
  • necessity of using comparatively complicated transmitting/receiving systems, especially for longer distances,
  • necessity of using matching resistors (of half the impedance of the pair, connected in series with each pair),
  • 50 ohm impedance - necessity of using matching circuits at video inputs/outputs.
Areas of application
Connection of surveillance installation via existing telecommunications cable networks (i.e. telephone, LAN) that usually have not utilized all pairs.
Additional parameters and more detailed description of features you may find here.
Twisted-pair transmission systems:
- "single signal" transformers:
The system keeps good quality of color image. It is also possible to transmit several signals when using adequate number of sets (e.g. via one shielded FTP cable) without image quality loss. The system is sensitive to cable length, colors distinctly fade out with length increase.
- "multiple signal" transformers:
Description of TR-4 transformer - M1667.
Quality of image is very good no matter the number of transmitted signals is. Some weak reflections may occur when using cameras with large number of frames per second. When total length of cable exceeds 300m, color loss can be observed (till complete loss).
- transmitters:
The system has been designed for specific lengths of the cable, for which transmission quality is optimal, on account of wave adjustment of receiver and transmitter (in the case of other transmission distances blurs and reflections occur in the image). For the transmitter, the acceptable distance is up to 1800 m, but significant image quality decrease appears at distances above 900 m (sharpness and chrominance fade-out). Regulated in the receiver value of signal bias doesn't improve quality, significantly increasing image brightness only, till dark details fade out completely (can be only used in the case of B/W surveillance, in low light conditions).
In none of the above mentioned systems electromagnetic interferences coming form inductive or other electrical devices (e.g. drill, cell phone) influent image quality.
During practical tests of transmitting systems with matching transformers, it has been determined that good transmission parameters are achieved at distances up to 300m.
Optical fiber
These glass fibers (cores) are surrounded with glass coat. Lower light reflection factor in the core allows to achieve total inner reflection of transferred light rays, generated by laser that is controlled by electrical impulses.
Main types of optical fibers are: single mode and multi-mode. The second one can be additionally divided into step and graded, that is in which the change of light refraction factor between the core and the coat occurs rapidly or fluently. It causes slowdown or acceleration of rays on the medium borders, so difference of ways for particular wavelengths and as the result - chromatic dispersion.
Main parameters of glass fibers are: size, attenuation, number of modes, ability of multiplexing (rays of different colors), reflection attenuation (coming from terminals and conjunction places) and maximum propagation time.
Advantages of optical fibers:
  • immunity to electromagnetic interferences
  • no generation of electromagnetic interferences
  • no stray currents
  • no differences of potentials
  • low attenuation - presently the lowest achieved value is 0.16 dB/km.
  • high durability, around 25 years
  • high transmission speed.
Disadvantages of optical fibers:
  • high price
  • some problems with making terminals and joints
  • expensive signal converters
Areas of application:
- systems requiring high bandwidth or long transmission distance,
- CCTV systems built in high interference environment and for long transmission distances.
Ethernet Media Conversor ULTIMODE M-403M (duas fibras monomodo até 40 km)Ethernet Media Conversor ULTIMODE M-403M (duas fibras monomodo até 40 km)Switch TP-Link TL-SF1008D (8 portas)
Example application of L11041 media converters


Fiber-optic video transmission tests - are described in this article
Kinds of modulation used in analog video transmission systems
Modulation is employed in order to make signal independent of channel interferences and adapt it to long transmission distances. It is realized by changing the original signal, mainly its amplitude and frequency.
In analog video transmission systems there are used amplitude modulations: two-band DSB-AM and pseudo one-band with partially attenuated carrier VSB-AM. With the use of VSB-AM modulation channel spacing is not required - on condition of low differences between them. If we want to allow larger differences of signal level than 3dB (up to 8dB for some receivers) we must use larger channel spacing, equal two or more channels. In the case of DSB-AM modulation, the modulated signal occupies wider band, therefore it is needed to provide channel spacing equal at least two channels. It causes worse use of available transmission band, so the lower total network bandwidth.
Other kind of modulation used in wireless video transmission is FM - frequency modulation. It consists in continuous change of frequency of carrier signal having constant amplitude, so that its power remains unchanged. This kind of modulation is more resistant to interferences and has much higher energetic efficiency. In order to correct S/N ratio, there can be used additional signal processing - preemphasis and deemphasis (additional amplification in transmitter and attenuation in receiver of higher frequencies of the band).
Modulators enable adjustment of electric signals to transmission conditions (i.e. change of transmission frequency into specific channel). Industrial modulators cover UHF band used in television transmissions: 470-862 MHz (channels 21- 69). Reception of the signals is possible on standard TV sets.
TV Modulador TERRA MT41
Transmissão de vários sinais de vídeo com a utilização de moduladores

The received images have good quality, without interferences and distortions, for all available channels (21 - 69). Measurements were made for 100m coaxial cable. Above this length (e.g. 200 and 300 m), at transmitted frequencies (470 - 862 MHz), attenuation of the cable was to high to receive an usable image.
More about modulators (also catalog pages) - here
Wireless transmissions
Sistemas atualmente populares usam 5.8 GHz, menos vulnerável a interferências de 2,4 GHz. Eles são utilizados em situações em que é difícil a instalação de cabos, bem como em sistemas de vigilância (acontecimentos temporários, conjuntos, locais de construção menores etc.)
Vamos descrever as questões relacionadas a este modo de transmissão no exemplo de CAM5816h M1558 transmissor e receptor de sinais de áudio / vídeo. Outros kits podem ser encontrados aqui.
Sistema de Transmissão Wireless: CAM5816h 5.8GHz (audio e video, exterior, 3km)
CAM5816h 5.8 GHz - transmissor
Sistema de Transmissão Wireless: CAM5816h 5.8GHz (audio e video, exterior, 3km)
CAM5816h 5.8 GHz - receptor
O M1558 sistema de transmissão sem fio CAM5816h foi projetado para transmitir sinais de vídeo e áudio analógico e em distâncias de até 3 km e é dedicado principalmente para aplicações em CCTV analógico. O conjunto é composto por transmissor (Tx) e receptor (Rx) utilizando a banda ISM não licenciada (5725 MHz - 5875 MHz). Além da transmissão sem fio de vídeo e som em sistemas de CCTV profissional, o conjunto pode ser usado sempre que alguém precisa de confiança, ligações de longo alcance AV.
O conjunto assegura vídeo / áudio de transmissão de alto desempenho, mesmo em ambientes de alta interferência. Isso permite usá-lo em muitos várias instalações, como sistemas de monitoramento de vídeo em cidades, fábricas, em estacionamentos, em parques, empresas e muitos outros.
O usuário pode escolher um dos oito canais não sobrepostos, evitando alguns dos mais congestionadas. Com vídeo e de fácil montagem de alta qualidade (não há problema com a mudança da localização da câmera e um transmissor, se necessário), o equipamento de um insubstituível em muitas situações onde as soluções com fios não são econômicos ou viável. O conjunto CAM5816h também pode ser um ótimo complemento para qualquer sistema de CCTV com fio existente, permitindo, de forma transparente alargar a sua gama, sem interferência na fiação instalada anteriormente.
Principais características
  • estável, transmissão de alta qualidade de PAL / NTSC vídeo
  • 8 canais não sobrepostos (vídeo e áudio)
  • antenas direcionais de alto ganho para garantir um funcionamento estável
  • Variar até 3 km
  • Possibilidade de dispor as ligações compostas por dois ou mais conjuntos (no caso de não visibilidade entre os pontos de extremidade ou distâncias de mais de 3 km)
  • Banda livre de industrial, Wi-Fi, Bluetooth, interferências de radiotelefonia
  • Transmissão em tempo real dos sinais originais (sem processamento digital - sem atraso para compressão e empacotamento)
  • Fácil de instalar e completamente livre de manutenção
  • Caixas resistentes com antenas direcionais integradas
DIGITAL VIDEO TRANSMISSION
Digital video transmission is the base and future of modern telecommunications installations. Its application area is much larger than just surveillance systems and it concerns also such issues as: telephony, education, e-commerce, advertisement and many more aspects of modern economy.
Basic knowledge of the features of digital transmission is a necessary condition to work in any of telecommunications branches, including the field of surveillance systems.
The main issues of digital transmission are:
  • signal processing, i.e. conversion from analog to digital form - digitalization and compression,
  • transmission issues.
Digitalization and compression
One of main problems digital transmission meets is the fact that converted signal would cover much wider bandwidth after the conversion from analog to digital form than it does being transmitted in original analog shape. Therefore special compression is used, which partially eliminates from the digitalized form the information that is not perceptible by humans or inessential.
Fora do MJPEG, MPEG-4 e métodos de compressão H.264, o último é o mais eficiente e popular agora.
MPEG compression, for the reason of more expensive codecs and weak adaptation to existing data transmission networks, is used for professional transmission rather e.g. in broadcast television systems.
Distortions.
For every kind of compression there is a limit, below which even small increase of compression factor causes significant quality decrease. Distortions are becoming visible then. The reason is rejection of too much data concerning edges, shapes, small details, colors.
Transmission issues
Practical expansion of video signal transmission began together with the use of networks based on TCP/IP protocol (especially Internet). Digital video transmission in computer networks has big advantage - it allows to transmit coherently all signals related to remote control of objects or places: alarm signals, control signals, video data, voice data.
An extension of transmission abilities in computer networks is streaming transmission.
Streaming can be established between two points or between single source and multiple receivers. Stream transmission consists in simultaneous sending of multiple digital data (video, voice and other digital information e.g. control data), then received in continuous stream form. The transmitted data can used even before it is downloaded completely. In the case of Internet streaming, the data coming from the network to a computer is directed to specific devices - for example graphic or sound cards - responsible for processing, and immediately removed after displaying or playing. For playing back a file, the elements have to be transmitted consecutively as well as adequately buffered. To ensure this, the "player" and the server have to communicate with each other, to settle to which moment data has been already played, in order to enable the player to gather adequate portion of data, allowing fluent playback in moments when network bandwidth decreases.
Common TCP protocol does not fit this kind of communication (although it is used for that), but the future of streaming is clear thanks to new protocols, specially prepared for this purpose:
  • UDP (User Datagram Protocol)
  • RTSP (Real Time Streaming Protocol)
  • RTP (Real Time Protocol)
Basic terminology of TCP/IP network protocols
IP address
Address of a computer in TCP/IP network is called IP address. Usually when we enter IP address we use dot-decimal notation (e.g. 195.13.38.254).
Computer connected to the network may have fixed IP address (so called fixed IP) or variable address being assigned e.g. at each connection via modem. There is also possible assignment of IP address for some time period (e.g. once/24h). Dynamic IP address assignment is performed by DHCP protocol (Dynamic Host Configuration Protocol). This protocol is commonly used for the reason that it allows automatic IP configuration for work in specific environment.
Besides public addresses (being "seen" in the Internet), an Internet provider may use private addresses (so called non-routing) from pools 192.168.x.x, 172.16.x.x and 10.x.x.x. These addresses are used in local area network, usually connected to the Internet by the means of a router, masking the inner network with one external routing address.
MAC address.
MAC address (Media Access Control) consists of 48 bits. We can divide it into two basic parts: LAN card manufacturer code assigned by IEEE, and unique factory number. MAC address is used for identification of individual LAN card in the local network and may be used e.g. for limitation of Internet access for the specific device.
Active network devices
Equipamento passivo (ou seja, os componentes do cabeamento estruturado, cabos conectores, quadros de distribuição / caixas) conecta dispositivos de rede ativas:
  • Regenerator (repeater) é usado para o conjunto de determinados segmentos de rede, mas também restaura recebido (distorcida para a razão de atenuação ou crosstalk cabo). Pode juntar-se os segmentos de rede com diferentes meios de transmissão usados.
  • Switch -- Switches também restaura os sinais transmitidos. O pacote de transmissão é realizada apenas para a saída quando o receptor está ligado. Switch aprende-lo de endereços MAC de placas de rede e pacotes transferências designado para o destinatário especificado, este comportamento faz com diminuição de tráfego de rede. Switches trabalhar em sistema full-duplex (transmissão simultânea em ambos os sentidos).
  • VLAN switch - Tipo de interruptor que permite a criação virtual de rede LAN. Esta rede permite a otimização da intensidade do tráfego de pacotes em particular segmentos de rede.
  • Bridge - É usado para a transmissão e possivelmente filtragem de dados entre duas redes, no entanto estas redes não têm de utilizar o mesmo meio de transmissão. A ponte segue endereços MAC colocados em pacotes que estão sendo enviados a ele. Tanto uma ponte e um interruptor agir da mesma maneira, e que a diferença (além do fato de que as pontes têm duas portas, interruptores até dezenas) entre eles é bastante sutil - por exemplo, o modo de envio do pacote.
  • Router - é usado para conectar algumas redes juntos, administrar e filtrar o tráfego entre elas. Os dois mais populares áreas de aplicação são a conexão de rede LAN para rede WAN (geralmente a Internet) e conexão de algumas LANs juntos. Os roteadores geralmente têm várias portas que trabalham em diferentes tecnologias (por exemplo, Ethernet, Frame Relay e ATM) e pode fazer conversões entre eles. Os roteadores podem reconhecer os endereços de destino dos pacotes e decidir onde e como eles devem ser enviados. Além disso, os roteadores também podem realizar muitas outras funções, tais como firewall. Eles são feitos como autónomos, dispositivos especializados ou implementados em computadores com software adequado.
Kinds of networks
  • LAN (Local Area Network) - rede local projetado para unir estações de computador juntos, geralmente colocado na pequena área. Ele permite a troca de comunica e arquivos entre os usuários, compartilhando recursos disponíveis na rede, tais como dispositivos I / O por exemplo, impressora de rede. Hoje em dia as LANs são baseadas no tecnologias: Ethernet, Token Ring ou FDDI.
  • WAN (Wide Area Network) - rede em grande escala, esticado em grande área geográfica - uma região, país, continente, ou o mundo inteiro. WAN junta LANs em conjunto, utilizando linhas telefônicas, circuitos alugados, fibra óptica ou links de satélite. A mais conhecida e a maior WAN é a Internet.
  • WLAN (Wireless LAN) - tipo de rede de computador em que a informação não seja transferido por fios, como na LAN, mas com a utilização de ondas de rádio. O mais eficiente padrão 802.11n WLAN é agora, utilizando a banda de 2,4 GHz e permite transmitir dados com velocidades de até 300 Mbps. WLAN também pode ser criado usando a tecnologia Bluetooth, no entanto, é bastante ineficiente. WLANs estão sendo cada vez mais populares em grandes blocos de escritórios, hotéis, aeroportos, restaurantes, pubs.
Virtual networks
VLAN (Virtual Local Area Network) - a network of computers that behave as if they were connected to the same LAN even though they may actually be physically located in different segments of the Web.
To separate such group of devices in traditional Ethernet network, adequate topology would have to be used. VLAN allows avoiding these limits, and guarantees that devices that belong to different VLAN sub-networks can't communicate with each other, so they are secured from access of unauthorized persons.
Virtual Private Network. Another way of limiting unauthorized access to a network. Advanced techniques of encryption and protocol tunneling are used to establish secure connection. The use of existing network i.e. the Internet for transmission of private data allows to significantly reduce costs - and taking special measures - to keep the same security level as in private networks.
VPN enables secure access to resources of the protected network for authorized remote users. They may be company workers, also when traveling, staff of surveillance center etc.
Network security.
Risks that occur in a computer network can be divided into following classes:
  • access of unauthorized people to data transmitted in the network or saved on computers connected to it,
  • access of unauthorized people to other resources (e.g. computing power),
  • data loss caused by malicious actions from outside
  • data fake (it mostly concerns e-mail correspondence).
All bugs and failures of systems and protocols can be used to threaten security of a network. The invaders usually make use of:
  • eeaknesses of TCP/IP protocol, allied protocols and also net services (DNS, SMTP),
  • software bugs,
  • mistakes of the administrator or the user of the network.
Video transmission devices in surveillance systems
The use of digital transmission broke through series of barriers within surveillance installations, enabling high flexibility and effectiveness through:
  • long distance image transmission (ability of remote viewing of current events as well as recorded material and control over whole monitoring equipment and performed operations)
  • working in whole network,
  • extended ability of control and automation,
  • easy cooperation with alarm and telecommunications systems (ability of joining surveillance systems with other systems, e.g. alarm system, fire alarm, e-mail or SMS notification).
Depending on users' requirements, digitalization and compression can be performed:
  • during recording (in digital recording systems)
  • in dedicated devices (video servers)
  • in cameras with built-in web servers (mostly using HTTP protocol)
  • via web cameras (connected to USB ports of computers).
Network DVR: ULTIMAX-204 (H.264, 4 canais)
H.264 Video Server: ACTi TCD-2100
Câmara IP 2MP: Sunell SN-IPC54/14EDN (standard, ONVIF, CMOS, 1080p)
4-channel DVR
ULTIMAX-1304 H.264
H.264 video server
ACTi TCD-2100
2Mpx camera
Sunell
Antena TV UHF: DIPOL 44/21-60 Tri Digit
Diagrama de blocos de um sistema de monitoramento distribuído de uma cadeia de supermercados,
com gravação local em DVRs e acesso remoto aos dados de vigilância através da Internet

Bandwidth of a link is the main factor that limits image transmission. Each compressed frame of an image from B/W camera occupies about 7.5KB (Kbytes) so singular camera transmits 7.5kB/s or 60Kbps at 1 frame/s (1 fps) recording speed.
The figures below show rough calculations of possible number of employed cameras depending on available transmission bandwidth:

Link type

Channels (possible number of cameras)

Modem connection

1 camera at 1 fps.

Digital channel 256kbps

1 camera at 3 fps or 3 cameras at 1 fps.

Ethernet 10 Mbps

50 cameras at 1 fps.

Ethernet 100 Mbps

400 cameras at 1 fps.

Digitalization in webcameras
Web camera is a camera integrated with system that changes analog signal to digital form, and thanks to built in Ethernet interface, allows to transmit signal further - in the form of IP packets. It enables remote viewing trough the network. It is commonly used in simple image sharing systems e.g. from ski slopes etc.
View of the device. Wi-Fi camera with bidirectional audio transmission and possibility of WPA-PSK data encryption
Digitalization in web servers
Video web server is a device changing analog signal from cameras to digital form, and thanks to built-in Ethernet interface allows for further data transmission in the form of IP packets. The device can be connected to LAN, to cable modem or to xDSL modem. Traffic generated by the device to the Internet depends on the viewing size and the quality chosen by the user. Managing system automatically chooses number of frames per second, depending on available transmission capability. It is usually within 512 - 3000 Kbps range.
An example of such a device can be one-channel video web serverP1401 K2131. To "video in" we can connect camera or other video signal source, and then transmit the converted and compressed signal through the network. The included software enables remote registration on a computer. The web server also allows audio transmission.
CPD-560 digital recorder with built-in network module
Web servers also support larger number of cameras, e.g. SED-2300QK2111 - 4-channel video server. Access to real time images is possible for any authorized network user (privilege limited by password) - with Internet Explorer (ver.6.0 or later).
Back view of 4-channel web server
The video server has 4 alarm connectors (inputs/outputs). Alarm events, in fact connected with them screenshots, may also be sent to e-mail address/es or by FTP protocol. There is also possibility to control PTZ cameras.
Recording may be performed on any computer within the network, having installed the included software.
Digitalization during recording.
There are on the market two main groups of devices used for digital recording:
  • digital recording cards mounted in PC computers (GeoVison, AD),
  • independent digital recorders - stand-alone devices with built-in dedicated operating system and data carrier (HDD or/and DVD/CD-RW) on which video data is recorded).
DVR cards.
We will present the basic features of DVR cards on the example of M8205 card. The card uses TCP/IP protocol and client-server architecture, and ensures remote access - via LAN, Dialup, ISDN, Internet.
Maximal number of simultaneous remote connections - 5.
Connection with ADACS server (the same applies to other card servers) can be established in two ways: through client software or with Internet browser (with Java support).
When connecting to the network we should be sure that server/client allows traffic to/from adequate ports (specific firewall configuration on surveillance computer and router).
During remote work, the user can change setup parameters of images from individual cameras and zones of motion detection.
Internet browser limits control features in comparison to client software (the firmware for the product), but allows to share images with users that only have typical software.
Video transmission with dynamic IP.
Many DVR cards allow video transmission via the Internet. There is no problem if we have fixed IP - we have access through standard Internet browser, e.g. IE or through additional client software.
Many ISPs do not ensure fixed IP, but there are available two simple solutions. The hardware solution is to run router with DDNS support (the devices which have this feature are e.g. Access Point with xDSL router and 4p switch TP-Link TL-WR542G N2950) and using Internet service, e.g. http://www.no-ip.org.
The software solution is used when we already have a router and we can't change or don't want to change it (e.g. provided by ISP ADSL modem/router, usually with USB interface). It is possible to install client software on one of the computers connected to LAN. The software will update the entry in DDNS service every time when IP address changes. Such a client application is available e.g. on http://www.no-ip.org.
Control of speed dome cameras
The connection is realized by RS485/RS232 converter, and the control process is performed using mouse pointer directly on the screen with the image from the camera. ADACS has implemented protocols allowing control of cameras of the following manufacturers: Videotec, Dynacolor, Samsung, Panasonic, Pelco, Vortex, Sensormatic, Kalatel, GANG SZ, Lilin, YAAN, YOKO.
Sound transmission.
Sound playback is also available in the moment of intruding a zone. Many other cards also enable direct sound transmission.
Caution: If the computer, with which we want to connect from outside (via Internet), is a part of LAN network and is behind a router (usually computers in LAN are seen as having common single IP address), in the router/server acting as firewall we have to redirect traffic of the following ports: 20900, 20910 and 21060.
Important feature of these cards is that they can be combined, so we can extend our system with additional inputs. We can install in one computer 1, 2, 3 or 4 cards.
Standalone DVRs.
New technical features, also related to network work, should rather be found in DVR cards than in standalone DVRs. It is mainly for the reason of longer designing and implementation process.
However, in the case of fulfilling all requirements, the standalone DVRs should be preferred, for their stability of work and easy and intuitive operation.
There is a large group of recorders designed for network operation. During selection of a recorder we should draw our attention to features allowing to backup the video onto external device/carrier and possibility of playback on regular PC.
Color Digital Video Recorder MTC-9004-M (4-IN, USB)
CCTV Digital Video Recorder: AVC777 (16 channels)
Description of digital recorders available in DIPOL offer.