Specifications

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KNOW-HOW: Video Webservers
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S21
Video Webservers
The classic video surveillance applies own cable networks for the trans-
mission of video signals. That is where the English term CCTV (closed
circuit television) comes from. This means, that there is a considerable
financial expense for larger systems or in spacious buildings. If the sys-
tem is to be extended, long cabling distances have to be newly led. At
the same time, very efficient networks are partly installed with optical
cables nowadays, so that very wide range are available. Therefore, it
is likely that these networks are also used for the transmission of video
pictures. Here, it is not the point to use the leads or wires as it is the
case at the 2-wire transmission. The point is rather to administer the
video data in such a way, that these can be transmitted as data pack-
ages in the network and can be received and displayed by the con-
nected computers.
Video webservers are available in various designs: as stand-alone
units or as an additional feature to be installed in DVRs or in cameras
(network cameras).
Transmitting side
The video webserver is the actual heart, because the cameras are con-
nected to this video webserver. The signals are internally coded and
are made available for the transmission via TCP/IP. Depending on the
version, the webservers feature inputs and outputs, by which additional
functions can be carried out. Alarm inputs can be connected in such a
way, that alarm messages can be transmitted e.g. via e-mail or SMS;
or switching operations can be started by it if alarm outputs are avail-
able.
The units are of course protected against misuse by several pass-
word levels.
Network connection
Depending on the network and power capability of the video web-
server, picture transmission rates of up to 25 pictures per second are
possible. The units support the standard 10BaseT with 10Mbits or with
10/100Mbits, depending on the type of unit. The units are assigned
with a fixed IP address and the corresponding sub network mask.
ISDN, DSL, and Internet
A router is required to access units which are connected to the network
via ISDN, DSL, or the Internet. It is impossible to recommend a certain
router, because the routers are available in large quantities and the
models are changing very quickly. Nevertheless, you should pay at-
tention to the following features: NAT, DDNS, Dial-in (at ISDN), Firewall,
built-in modem.
Additionally, valid admission for accessing the Internet is required.
If there is no access to the Internet with a fixed IP address, a DDNS
service is necessary. These DDNS services are offered in the Internet,
sometimes free of charge.
Receiving side
A computer which has access to the telephone network, network (LAN),
or direct access to the video webserver is always needed on the re-
ceiving side.
The video webserver is operated via an Internet browser or via sup-
plied client software.
What is required to connect a webserver to a network?
Crossover cable
This is a network cable which is especially configured and only used if
a video server is connected directly to a computer, e.g. if a laptop is to
be connected directly to a digital recorder which is suitable for net-
work applications. As opposed to the patch cable the transmitting leads
and receiving leads are crossed over in the crossover cable.
Patch cable
This is the ”standard” network cable. It is used each time a webserver
is to be connected to a network socket, a hub, switch, or router.
IP address
Each unit within a network has its own IP address which can be com-
pared to an individual telephone number. This is the only way to di-
rectly address individual units.
The IP address is only to be allocated once within one network.
Sub net mask
All units which should have access to the webserver, must use the same
sub net mask. A typical sub net mask looks like this:
255.255.255.000
Gateway
This is usually the IP address of a router by which the webserver is con-
nected to the Internet.
In most cases, routers occupy the first address in a network segment,
e.g. 192.168.001.001
Webserver vs. client software
Units with a network connection can be divided roughly into two
groups. The first group has an integrated webserver function and can
be addressed via a browser just like an Internet site.
The advantage of this is that no software has to be installed on the
inquiry computer.
The second group is addressed via so-called client software which is
specific to the unit. This software is supplied with the unit. The client
software is not subject to the restrictions of a browser and thus offers
a lot more featuers. The software has to be installed on each computer.
Some units use both methods.
Port release
Ports can be compard with admission doors in a network. The access
to features of the network and the connected units is invisibly con-
trolled via these ports. Those have to be released for this access,
i.e. enabled for use. This is done via the network administrator. There
are usually no restrictions within the network. This is different if an ac-
cess from the outside via the Internet is to be feasible. In this case, only
the ports which are required for e-mails and Internet services are re-
leased; all the others are locked. However, some of the video
servers require special releases. If these are not made, an access
within the network is generally possible. Due to the missing port re-
lease, it might only be possible to see e.g. the home page via the
Internet
but not a video transmission.
Only the required ports are released towards the Internet in order to
obtain the greatest level of safety against worms and computer viruses.