DVR Buying Guide
The main function of a digital video recorder (DVR) is to record 1 or more channels of video to an internal hard drive disk. This information can later be played back directly from the disk via the DVR. The amount of video the DVR will be able to store at any 1 time is determined by many factors such as:
• Hard drive size
• Recording frame rate
• Recording quality
• Recording compression
• Recording resolution
• Continuous, scheduled or motion detection recording
DVR’s have many options to enable users to get the most recording time out of their DVR. Recording quality and frame rates can be reduced giving a reduced image quality but longer record time or units can be set to record only on a schedule or only record when something moves in front of one of the cameras. Most DVR’s also allow alarm activation equipment such as passive infra-red detectors or door contacts to be attached and trigger recording.
The hard drive is where all recorded footage is stored and played back from. Very simply, the higher the capacity of the hard drive, the more recorded footage can potentially be stored on it. Hard drive sizes range from 80Gb to 2Tb (2000Gb).
A DVR will accept one of two types of hard drive depending on when the DVR was made and who the manufacturer is:
IDE – An older interface which is currently being phased out by the industry, IDE hard drives have been in use for some time. Some DVR manufacturers have not updated their hardware in line with the hard drive industry and still make use of these drives. The maximum capacity of a single IDE hard drive is 750Gb.
SATA – These drives are a new generation of hard drive. SATA hard drives allow faster data transmission and are more fault tolerant meaning that data loss is less likely. These drives also have a higher maximum capacity of up to 2Tb (2000Gb) as of April 2009. More and more DVR manufacturers are moving over to SATA drives.
IDE hard drives cannot be used in SATA DVR’s but an adapter is available to allow SATA drives to be used in IDE machines.
In addition to this, there are different hard drives for different purposes. In most cases, standard PC hard drives are installed into DVR’s. While these hard drives are fit for purpose, they have been designed to be read from 50% of the time and written to 50% of the time (the usual ratio for PC usage).
Obviously, DVR’s are writing to the hard drives most of the time so with this in mind, hard drive manufacturers have designed ranges of drives that are specifically designed for the security industry. These hard drives have been made to be written to 90% of the time and read from 10% of the time. The Seagate SV35 hard drive is an example of these security specific units.
Recording frame rate
In order to show a realistic moving image, 25 individual images with slight movement should be shown in sequence per second. Much like with a cartoon where an animator will draw a sequence of images then flick through them to give the illusion of movement.
DVR’s work in the same way although instead of a single movie being shown at a time, multiple movies are shown at a time depending on how many cameras are on the system.
In order to show a realistic illusion of movement, a single camera system must be set to 25 frames per second (FPS). If 2 cameras are on the system, the overall frame rate will need to be 50FPS to give the illusion of movement. If 16 cameras are on the system, the overall frame rate would have to be 400FPS (16 cameras x 25FPS per camera = 400FPS overall) and so on.
The method of recording this way is known as real time recording and has its advantages and drawbacks:
If we have a 16 camera system and we say that a single high quality image is 26Kb (1024Kb are in a Mb and 1024Mb are in a Gb), 400 of these 26Kb images would need to be recorded in just 1 second to give a real time playback from that second. 400 images at 26Kb would take up around 10Mb in 1 second. In 1 hour, the unit would have used up nearly 36Gb and would easily use up an entire 500Gb hard drive in under 14 hours.
In order to avoid this excessive use of disk space, DVR’s have the ability to reduce the frame rate (the number of images which are recorded per second). Reducing the frame rate can allow much less hard drive space to be used but does become noticeable when less than 10 frames are recorded per second per camera.
As less images are being recorded per second, the moving image becomes more jerky as more movement goes by before another image is stored.
DVR’s have the ability to reduce the quality of the recorded image. Most DVR’s have quality levels ranging from low to normal to high quality. The higher the quality of the image, the more space it will require on the hard drive meaning that a shorter period of time will be recorded onto the drive.
The way the DVR’s reduce the picture quality is basically by recording less pixels on the individual pictures. Every picture is made up form tiny dots called pixels, the more pixels there are on the picture, the smaller they are and more detail can be captured. In a low quality image, larger pixels are used and there are less of them. As there are fewer pixels, the size of the recorded image is smaller.
The obvious drawback to reducing the image quality setting on a DVR is that details on the playback are less distinguishable. This wouldn’t be so much of a problem if the camera is focussed on an object which is quite close but can cause problems when the camera is focussed on a wide area.
In short, the lower the quality of a recorded image, the less disk space it will use.
Uncompressed video footage would be unusable in the CCTV industry as it takes up much too much hard drive space. For this reason, DVRs digitally compress the recorded image in order to squeeze down the size of recorded footage as much as possible.
Throughout the history of digital video recording, many compression techniques have been used each with their various drawbacks and advantages. At the moment, there are two main types of compression:
• JPEG compression
• MPEG compression
JPEG compression usually offers better image quality but uses more hard drive space whereas MPEG compression give slightly less detailed images but uses less hard drive space.
JPEG compression works by recording a complete picture of everything that the camera sees every time the frame rate determines (25 a second for real time on a single camera). So if the camera is looking at the front of building with a car in front, it will record a single image including the building, the car, the pavement and anything else which happens to be in the frame.
MPEG compression saves hard drive space by taking an initial image of an entire scene and overlaying anything that moves on top of that original picture. So if the camera is looking at the same building with a car parked outside, it will not record a new picture of anything that isn’t moving. Once a person walks in front of the camera, it will record that person then overlay them on top of the original picture.
As technology has progressed, so has the way each compression technique records. This has lead to there being further compression techniques based on the original two. It is these offshoots of the original compression techniques that most DVR’s use today.
Offshoots of JPEG compression include:
An older compression technique, M-JPEG is still used in many low end DVR’s. The fact that M-JPEG has been around for some time means that it is not particularly technologically advanced and uses quite a lot of hard drive space.
This compression method is an updated version of JPEG compression and offers really good, clear picture quality. Whilst it uses more disk space than MPEG type DVR’s, it does not use as much as
M-JPEG DVR’s and is still preferred on installations where picture quality is more important than hard drive usage.
Offshoots of MPEG compression include:
Introduced in the 1990’s, MPEG-4 compression enables hard drive space to be maximised by only recording a new image of moving objects. MPEG-4 is used in a wide range of DVR’s both mid range and high end.
This is basically an updated version of MPEG-4 compression but allows a great deal more disk space to be used while keeping picture quality almost identical to MPEG-4. H.264 is a relatively new compression technique in the security industry but more and more DVR manufacturers are moving towards it due to the phenomenal saving in hard drive space.
The recording resolution of a DVR determines the maximum number of pixels that can be used on recorded footage. As mentioned earlier, the fewer pixels that are used, the smaller the image and the more can be recorded onto a hard drive. Many different resolutions can be employed on a DVR but the two most commonly used resolutions are:
• 352 pixels wide x 288 pixels high (also known as CIF)
• 704 pixels wide x 576 pixels high (also known as D1)
Recording resolution works in conjunction with recording quality to determine the end result in image quality.
Continuous, scheduled or motion detection recording
In order to further save hard drive space and reduce the amount of data which needs to be stored, most DVR’s have a motion detection (and/or alarm activation recording) and a schedule setup.
Motion detection recording:
Most DVR’s have the facility of video motion detection (VMD). VMD is an intelligent feature of the DVR whereby it calculates parameters such as colour temperature and brightness and monitors them for change. When an object moves in front of the camera, it will invariably change these parameters and this is what triggers recording.
Most DVR’s with VMD have the option to change the sensitivity of motion detection. If the sensitivity is set to its highest setting, practically the smallest movement will trigger recording. If the sensitivity is set to its lowest setting, it would take a larger object moving into frame to trigger recording. This is useful as the unit could be set to ignore small object such as dogs or cats but trigger recording when a larger object such as a person or a car come into frame.
Once the VMD has been triggered, it will record for a pre-determined time limit (set up by the installation engineer) and then stop recording. If however, at the end of the time limit, something is still moving in front of the camera, recording will continue.
Alarm activated recording
Some DVR’s have inputs that will allow alarm equipment such as PIR’s or door contact be connected. Typically, there is 1 alarm input per camera channel. These alarm activations can trigger recording. Many people use alarm activated recording when they find that the sensitivity setup on VMD is not comprehensive enough and they get too many false motion detection events. Providing the correct detection equipment is used and set up properly, alarm activation recording is the most accurate type of recording trigger.
An example of when alarm activation recording would be used is if a camera is facing a glass door and the customer wants to record anyone who walks through the door. As the sun moves and is obscured by clouds or as people walk past outside, motion detection would be activated unnecessarily. If the installer was to attach a door contact to the door and then wire it to the alarm input on the DVR, the recording could be triggered by the door contact whenever someone walks through the door but not by any external influences.
As with VMD, once the alarm input has been triggered, it will record for a pre-determined time limit (set up by the installation engineer) and then stop recording. If however, at the end of the time limit, the alarm device is still being triggered, recording will continue.
Some DVR’s ha a recording schedule; users can set the DVR to record between certain times on certain days. This would be useful in an office where people are going to be in the premises from 9AM to 5PM Monday to Friday but no one will be there between 5PM and 9AM or at weekends. The DVR could be set to not record at all during office hours but to start recording from when everyone has left.
More advanced DVR’s have the ability to record in different modes at different times of the day so for example, a DVR could be recording continuously throughout the day and flick over to motion detection recording at night time.
Some DVR’s can perform a multitude of tasks such as record and playback at once, other DVR’s have to stop recording before they can play back. The different record modes are listed below:
Simplex – Just record, user has to stop recording to playback
Duplex – Unit can continue recording whilst playing back
Triplex – Unit can continue recording whilst playing back and being remotely logged into
Quadraplex – Unit can record, playback, remote view and view the menu
Pentaplex – Unit can record, playback, remote view, menu view and backup incidents
Video inputs & outputs:
Most DVR’s use the industry standard BNC connection for video inputs and outputs; this BNC connection is also used on most cameras.
Video inputs are where the cameras connect into the DVR. DVR’s tend to have 4, 8, 16 or 32 video inputs. Some manufacturers build their DVR’s with a different amount of BNC inputs such as 6 or 9. If a customer needs the system to record over 32 cameras, it is usually best to look into IP (network) cameras.
Video outputs are where the camera signal is sent out from the DVR. There are two types of video outputs:
• Monitor outputs
• Loop through outputs
Monitor outputs have two types; main monitor outputs which can display all cameras on a screen either in a multiplexed (split screen) way or in a sequential (one camera after the other) way. Monitors connected to the main output also allow the user to view the DVR menu and other OSD icons. The spot (or call) monitor output generally just sequences between each camera without any OSD icons or the ability to enter the menu. Usually, users cannot control which camera is to be viewed on the spot monitor.
Video loop throughs allow the video signal of a single camera to be outputted from the DVR to be displayed on another monitor on its own or to be individually recorded on another DVR. Not all DVR’s have video loop through outputs but those that do will generally have one for each camera.
An example of when a video loop through would be useful is when a store has 8 cameras, 4 in the front of the shop and 4 in the store room. All 8 cameras are connected to a DVR and a monitor in the office. The owners want to display the 4 front cameras on a monitor in the shop but not display the store room cameras in the shop. The 4 shop front cameras could be looped out of the DVR into a 4 channel switcher or quad unit then connected to the monitor in the shop front. This system would record all 8 cameras and display them all on a monitor in the back but also display the 4 shop front cameras on a monitor in the store.
Audio recording and 2 way audio
DVR’s in the mid to high end of the market tend to have audio inputs as well as video inputs. These audio inputs allow the connection of a microphone which relates to a certain video channel and allows audio to be recorded and played back via an external speaker.
The amount of audio inputs varies from DVR to DVR; some have only 1 input while some have 1 input for each channel.
The connection for an audio input or output is normally a female RCA connector but can also be a BNC connector as with the video connections.
On a few DVR’s that are currently on the market, a 2 way audio option is available and allows users to not only listen in to their premises but to also talk back. This is achieved over a network connection; a user connects to their premises over the internet and is able to listen in via their PC speakers. Using a standard PC microphone they can then speak directly into site. A separate speaker connected into an audio output will then enunciate the user’s voice.
DVR’s can display a single camera on screen or a combination of multiple cameras on screen at any 1 time (a multiplexed image). Most DVR’s also have the ability to sequence through the connected cameras 1 at a time.
Some DVR’s can also display picture in picture (or PIP) whereby 1 camera will take up the whole screen and a smaller second camera will be will be overlaid on top of the first camera.
Usually, these different display modes can be used in live view or playback.
Covert camera function
Some DVR’s have a feature for a covert camera. This feature allows a camera not to be displayed on the live view screen but still recorded and displayed in playback. This feature is very useful if a customer has a covert camera such as a camera built into a smoke detector housing as it does not give away the position of such cameras.
On screen display (OSD)
The on screen display (or OSD) is a series of icons that act as a quick reference for users. Typical OSD icons include:
• HDD usage
• Frame rate
• Record mode
• Motion / alarm activation
• Network connection status
• Camera title
• Date & time
Some OSD aspects such as camera title can be changed by the user. As default, the camera titles are the same as the channel number but can usually be changed to any alpha-numeric.
On some DVR’s the OSD icons can be switched on or off individually.
Upon a motion or alarm activation, some DVR’s have a feature which brings up the camera which has seen an event for a short period of time to allow users to see what has triggered the event. After the defined period of time, the display will revert to whatever it was set to before the activation.
Camera picture setup
Most DVR’s include a feature in the menu to tweak the camera picture as displayed on screen. Users are able to change parameters such as colour, brightness, hue and contrast. The flexibility of the camera picture set up varies from DVR to DVR.
Usually, lower end DVR’s only allow the camera picture to be altered globally (i.e. all cameras are changed based on the picture settings) whereas mid range and high end DVR’s will have picture set up individually per camera.
DVR menu system
All DVR’s have an interface for adjusting settings and setting up various aspects of the system; this is known as the menu system.
The menu system can be text based or graphical and is usually password protected. It is from here that most aspects of the system set up are completed.
Factory default option
Most DVR’s have a factory default function which allows the unit to be reset to the same settings it had when it was first switched on thus removing all altered settings.
Audio alerts are a common feature on many DVR’s. There are a variety of different audio alerts for different events. Most DVR’s have an audio alert for video loss (i.e. if a camera loses power or becomes disconnected from the DVR for any reason).
Other audio alerts include:
• Motion activation
• Alarm activation
• Key press
• Incorrect password
Three types of remote control are available for DVR’s:
• Wireless remote control (Works on infra-red in the same way as a standard TV remote control)
• Wired remote control (A duplicate of the front panel of the DVR, usually wired in CAT5 or RS-232)
• Remote connection remote control (A method of controlling the DVR using a PC over a LAN or WAN)
Relay outputs are linked into the alarm inputs and are used to trigger external devices upon alarm activation. This feature could be used to switch on a light or unlock a door upon alarm activation (providing the correct additional equipment is used).
Footage is usually played back 1 of 2 ways:
• Time & date search
• Event search
When performing a time & date search, the user needs to know roughly when the incident took place so that they can enter that time and view the footage
An event search is a list of all events that have taken place on the DVR, usually accompanied by the time and date of the event. Events include motion detection, alarm activation, video loss and power loss. Depending on the DVR, many other events could also be used. To play back using the event search, users will simply navigate to an event and press the enter or play button to begin playing back.
Some DVR’s will also have other methods of playback but the two listed above are the most common.
Once the unit is playing back, users can fast forward and rewind (usually up to 32x normal speed), pause and move frame by frame. Most DVR’s have a 2x digital zoom in playback mode which will enlarge the picture but reduce the quality.
On some DVR’s, the backup process is also initiated once playback has started.
Back up incidents
There are various methods of backing up incidents from a DVR so that it can be played back on other media. These include:
Allows backup to a recordable 700Mb CD-R to be played back on a PC. CD’s cannot generally store much data and only usually have enough space for 5-10 minutes of footage depending on image quality and frame rate.
Allows backup to a recordable 4.7Gb DVD-R to be played back on a PC. DVD’s can hold more footage than CD’s. Once data is written to a DVD, it will not be able to be played on a standard DVD player in most cases, only on a PC
USB sticks are widely available, fairly cheap and are available in sizes of up to 32Gb. As with CD’s and DVD’s, footage can only be played back on a PC. It is also worth noting that although USB sticks are available up to 32Gb, some DVR’s may have a limit on the size of sticks they can accept.
SD card backup
SD card backup is much the same as USB backup except for the different format of the memory card. Only a few DVR’s feature SD card ports as most favour USB.
External hard drive
High end DVR’s sometimes feature an external hard drive backup facility. External hard drives can be up to 2Tb in size and can backup much more data than CD’s or memory sticks. The drawback of the external hard drive backup is that it can take a long time to perform.
Disk mirroring is more of a way to prevent data corruption than a backup method. An external disk is connected to the DVR (as well as the internal hard drive). All data that is written to the internal drive is also written to the external drive. This method is usually used on systems where evidence is critical and cannot be lost due to a hard drive failure.
A network backup is performed over a Local Area Network or a Wide Area Network (the internet). This can be useful when a backup is needed off site or when the DVR features no other means of backing up footage.
On the very rare occasion that a DVR does not have any of the above backup methods, a VHS backup can be taken. This works by connecting a standard VCR to a monitor output on the DVR, playing back the footage on the DVR and recording it onto a tape on the VCR. In addition, some Police forces still prefer backups in VHS form for evidential purposes.
Most DVR’s will feature 1 or 2 of these backup methods; it is very unlikely that a DVR will feature all of them. The most common backup interfaces are USB backup and CD/DVD backup.
In most cases (except for VHS backup) the footage will need to be played back on a PC. Some DVR’s write the viewing software to the backup device so that minimal software installation is required, some DVR’s will need a separate application (usually supplied free with the DVR) to be installed on the PC and some DVR’s will write the backup in a format which can be played back in a standard media player (i.e. Windows Media Player).
On most occasions, once a backup has been made, it can be made to play on any PC by saving the file as a different format via the viewer software.
PTZ camera inputs
Most DVR’s now feature inputs for not only video connection of PTZ cameras but also for telemetry control. On most DVR’s this is in the form of RS-485 communication (twisted pair cable) although some DVR’s can also communicate in RS-422 (a slightly different communication method to RS-485 which also uses twisted pair) as well as Coaxitron (telemetry up the same coaxial cable as video).
Most PTZ dome cameras communicate via RS-485.
To connect the PTZ camera to the DVR, there are 2 RS-485 inputs (1 is positive and 1 is negative). As many PTZ cameras as required can be connected (limited by the amount of video channels as are on the DVR).
PTZ cameras are given a numerical ID (starting at 001 and going up to 255) which is how the DVR will know which camera to send signals to and therefore move. On some DVR’s, the video channel number must relate to the PTZ ID (i.e. the camera on channel 1 must have the ID 001 and the camera on channel 5 must have the ID 005) whereas on other DVR’s, a specific dome ID can be allocated to any channel (i.e. the camera on channel 3 could have the ID 015).
The DVR also needs to be able to communicate with the camera by using the same protocol. A protocol is like the language the PTZ camera speaks. Different manufactures of PTZ cameras will often program it to communicate in their own protocol so that it is fully compatible with their own range of accessories. To this end, most DVR’s are supplied with a multitude of protocols to enable them to communicate fluently with the speed domes.
It should be noted, however, that most PTZ camera manufacturers add on an industry standard protocol to their cameras called Pelco-D. This protocol is also on most DVR’s making virtually all speed domes compatible with all DVR’s.
Other options should also be synchronised between the DVR and the PTZ camera. The other option that is usually on DVR’s is the Baud rate which is the speed at which data is transferred between the DVR and the PTZ camera. This should always be the same on the PTZ camera and the DVR. In short, whatever options are set in the PTZ camera should be reflected in the DVR.
A single speed dome can also be connected to a separate control keyboard as well as the DVR allowing users to control the unit from multiple locations. To do this, the telemetry cable can either be split before it gets to the DVR or run off to the keyboard or daisy chained out of it (where the appropriate outputs exist).
Once a PTZ camera is connected to a DVR and users are successfully able to move the camera from the front panel of the DVR, it should also be controllable via the Local Area Network or over the internet.
Most DVR’s on the market today have the ability to connect into a TCP/IP (computer) network giving the user the ability to log in and view or take control of their CCTV system from a remote location or a PC on site.
Methods of connection:
A Local Area Network connection is a connection to a DVR from a PC which is on the same network and usually on the same site.
A Wide Area Network connection is a connection over the internet from a remote location. These connections require the bandwidth of a broadband internet connection
LAN connection overview:
Each piece of networkable equipment on a LAN will need its own specific IPV4 address. An IPV4 address is a sequence of numbers separated into 4 parts by dots. A typical IP address may look like this:
On most networks, the first 3 sets of numbers must be the same on all networkable equipment (clients) but the last set of numbers will differ. This is what makes all equipment on the network unique.
By use of the IP address, clients can communicate with each other and transfer data. In the context of CCTV, the DVR would have its own IP address and this is what users would enter into the remote connection program logon screen.
There are two types of IP address:
Static IP address
This address is defined by the user and does not change
Dynamic IP address
This address is generated automatically and can change at specified intervals or when the client is rebooted
Usually, a DVR would be given a static IP address so that the address does not change and users can have a specified address to log in to.
Some DVR’s do have the facility to get their IP address automatically from a DHCP server. A DHCP server is a piece of network equipment that automatically detects all clients on the network and gives them an IP address automatically from a specified range.
IP addresses issued by a DHCP server have a lease time. Once this lease time has expired, the client will release its IP address and get a new one (usually, though not always, the same address). In addition, if the client is rebooted, it will release its address and get a new one which could be different from the original.
This is the reason that it is better to issue a static IP address to a DVR.
However, the DHCP function can be used to find out all of the necessary IP details that will need to be programmed into the DVR. In this case, the user can put the DVR in DHCP mode, write down the details then put the DVR in static mode and enter them in manually. This guarantees that the IP information entered into the DVR is correct and, as it has been set to static, means that the details will not change when the unit is rebooted.
A LAN with a single PC and a DVR
The PC can be connected straight into the DVR by use of a crossed network patch lead. As can be seen, the DVR and PC are in the same IP address range but the last of the 4 groups of numbers differs slightly between the two units.
A LAN with 2 or more PC’s and a DVR connected through a switch:
In this instance, 2 computers are on the network as well as the DVR. Obviously, the DVR and the computers only have 1 port to connect to the network each and so can’t be connected directly together. This is where a network switch comes in. The network switch allows the connection of multiple clients at the same time.
With the above connection, both PC’s would be able to view the DVR once they have entered the correct details.
WAN connection overview:
Every internet connection is supplied with an IP address much in the same way as a LAN client. On some internet connections this IP address is fixed and does not change at all. These internet IP addresses are known as Static.
On other internet connections, the IP address changes from time to time. These internet IP addresses are known as Dynamic.
Both types of internet connection allow users to log in from a remote location. Internet connections with static IP addresses are generally easier to log in to and are more reliable simply due to the fact that there is a constant address to log in to.
Internet connections with a dynamic address require a little more set up than connections with static addresses. Due to the fact that the IP changes, there is no constant address for remote users to log in to so a third party must provide a DDNS service which acts as a static IP address for a connection with a dynamic IP address.
The function of Dynamic Domain Name Server (DDNS) is to provide a user's Internet connection that has a dynamic IP address with a well known hostname resolvable by network applications through standard DNS queries.
Basically, DDNS gives an internet connection a name that does not change like a dynamic IP address does. This allows users to log in to their CCTV system using just the name of the internet connection rather than an IP address as they would if they had a static IP address.
In order to set up DDNS, the user would have to register an account with a DDNS provider. The most well known DDNS provider is www.dyndns.com but others do exist.
Some DVR manufacturers offer their own DDNS service rather than using a 3rd party DDNS server. These services are usually free and tend to be more reliable as they are specifically made for the DVR.
Clients on the Local Area Network which need to have access to the internet must have a specified gateway. The gateway is so named as it is where all clients on the LAN must pass through in order to get on to the internet. It is the client’s gateway to the internet.
In most cases, this gateway will be a network device known as a router. A router is a device which processes all inbound and outbound information between the LAN and the WAN and points all LAN clients through the gateway.
For any client (including a DVR) to have access to the internet, it must have a correctly specified gateway. This gateway is identified by its LAN IP address and in most cases will be the same IP address as the router (though more complicated networks may have a separate gateway).
Most routers will have a DHCP server built in allowing network clients to find their own local IP details. In the case of a DVR, the DHCP server will provide local IP address and gateway details. (Refer to the DHCP section of Local Area Networking for more details).
The router may or may not also have a modem built into it. A modem is a communications device which communicates with the Internet Service Provider (ISP) who will allow the internet connection.
Most ADSL (internet connections based on a BT phone line) routers have a modem built in to them. In this case, clients connect into the router and the router connects into the phone line through a device called a microfilter (which converts the standard phone line to a broadband line).
DSL (or cable) connections provided by NTL / Virgin Media usually require a separate modem and router. In this case, the clients plug into the router, the router plugs into the modem and the modem is connected to the fibre optic line.
A firewall is a feature which stops the flow of unwanted traffic into a network from outside connections (hackers, etc). In order to allow remote users to view the CCTV system, a hole must be made in this firewall in a specific place to allow users through to the DVR only (and not the rest of the clients on the network). This is called port forwarding.
Users specify a port to use in the DVR menu which is usually 80, 8000 or 50000 but can be anything in between. Whatever port is setup on the DVR, that same port needs to be forwarded in the router. It is basically a meeting place in the firewall where internet connections are allowed through.
A WAN connection using a DDNS server
Compression techniques in network transmission
Network compression works much in the same way as recording compression in that there are various different ways of compressing the footage each with their specific advantages and drawbacks.
Compression methods in order of network transmission speed (fastest first):
The compression method along with the speed of the internet connections at both the remote end and on site determine how the frame rate on the remote computer screen.
If a user is logging in on a LAN, chances are that the frame rate will be real time as the speed at which data can be transferred on a LAN is rather quick. If, however, users are logging in over the internet, a slow connection can greatly reduce the frame rate of the footage.
The speed and amount of any data transfer over LAN or WAN is decided by the available bandwidth. This is basically how much space is available to fit data down.
Imagine a pipe which water needs to get through. On a LAN, the pipe is very wide so more water can get through it in a shorter amount of time. On a WAN connection, the pipe is much thinner so it will take the same amount of water longer to get through. This is the same with data transfer rates and bandwidth.
LAN connections have more bandwidth due to the way they are cabled and the fact that there are only a few people (the people on premises) using them. WAN connections tend to be slower again due to the way that they are wired but also due to the fact that hundreds of people / companies are sharing the bandwidth so there is much more data to transfer.
ISP’s can provide more bandwidth and ensure that less people are sharing a set amount of bandwidth but they do charge a higher monthly fee for this service.
Upload and download speeds
Internet connections have a maximum upload speed and download speed which are both determined by the contract with the ISP (usually, the more you pay, the faster the speed).
The upload speed is how quickly you can upload (or send) data to the internet while the download speed is how quickly you can download (or receive) data from the internet. Generally, the download speed is much faster than the upload speed as most internet users receive much more data from the internet than send it.
A decent upload speed (at least 512kb) is required on the same premises of the DVR as it is uploading a lot of data due to the fact that it is sending all of the DVR footage.
A decent download speed (at least 2Mb) is required at the remote site in order to receive all the data and display the image.
In most cases, these speeds will not give a real time frame rate. Higher speeds are available; the customer should contact their ISP if they require a faster frame rate.
Expanded online functionality:
PTZ camera control
On most DVR’s which are networkable and have the ability to control PTZ cameras, the PTZ can be controlled over a LAN or WAN by use of the controls on the PC remote connection software.
Some DVR’s will allow a backup to be taken from footage on the hard drive over a LAN or WAN. In some cases this is done by playing back the footage and saving it as it plays back whereas in other cases, there is a dedicated backup program which does not require playback on the machine.
Remote DVR configuration
Some DVR’s are able to be fully configured (except for network setup) from a remote location.
If you have any further questions or if you have spotted something we've missed in this guide, please let us know so we can add it for future users.