Specifications

Security 2009
KNOW-HOW: Remote Access
S18
KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW
This is a commonly asked question. The answer to this question could
basically be: yes.
Made possible by the DSL-based Internet connections which are
available nowadays. In order to allow access, a few requirements have
to be met beforehand which are described below. The access via a
DSL connection is described only, because sole telephone connections,
e.g. analog or ISDN are irrelevant nowadays and are thus not con-
sidered in this case. The following information does not only apply to
DVRs, but also to all units with built-in webservers, e.g. video web-
server, network cameras.
Note: Such access should only be set up if the DSL connection on the
side DVR is combined with a flatrate. A rate calculated by time would
cause very high costs, because the connection has to be set up for con-
tinuous operation.
One address for each unit
This principle applies to both an internal LAN and the Internet. Each
unit which is connected to the network requires a unique IP address by
which the unit can be contacted. This can easily be realised with an in-
ternal network. It might be a little harder with an Internet connection.
The illustration 1 shows this in a simplified way.
The DVR is connected to the network on the side Local where is has a
fixed IP address. This is usually in the range: 192.168.001.xxx. In this
case, the last digit of all connected unit is different.
Another PC is also connected to a router on the side Remote. From this
PC, the pictures of the DVR are to be called up. The routers allow a con-
nection to the Internet. For this purpose, the access data for an
ISP (Internet Service Provider) are stored on these routers, e.g. a stand-
ard DSL connection. The routers receive their IP addresses from the
provider.
The IP address is important for the next steps done on the local side,
i.e. the side with the DVR.
Static IP address
The static IP address is given once and is not changed again. With
most providers, an IP address has to be applied for additionally and
usually paid for.
Dynamic IP address
Now it is going to be tricky. Even within the Internet, the IP address is
only to be given once at the same time. Thus, the routers will receive
an IP address from the ISP when logging in. The providers use a little
trick, because there are insufficient free IP adresses available in the In-
ternet for every PC. Because it can be assumed, that not all users are
in the Internet at the same time, the IP addresses of one provider are
given out temporarily. This is usually done in two different ways. Either,
one user interrupts the Internet connection, or in order to answer our
question, the second way is the crucial one. To prevent a continuous
operation, the provider automatically disconnects the unit from the
Internet once, usually every 24 hours. Afterwards, the router can re-
connect without delay, but it will receive a new IP address.
Is it Possible to Access the
Digital Recorder via the Internet?
graphic 1