ELSA MicroLink ISDN PCI User Manual page 50

44 ISDN Connections
What's more, it is usual for three subscriber numbers to be assigned to your connection.
If you need additional subscriber numbers, just apply to your telecommunications provi-
der.
The advantages:
You can assign specific numbers to the individual devices. For example, separate
numbers can be assigned to each telephone and the fax machine, as well as to the
PC with the ELSA MicroLink ISDN PCI (subject to the availability of free numbers).
Two tasks can now be performed simultaneously: For example, it's possible to
speak to two different parties at the same time, or to use the telephone and fax at
the same time. You can also surf the Internet without tying up the telephone.
A number of things are also considerably faster using ISDN. Your phone calls won't
be any shorter, but the call establishment is quicker. You have a clear advantage
when it comes to data applications, as the transfer rates of the ELSA MicroLink
ISDN PCI cannot be reached with an analog modem. If 64,000 bps aren't enough,
you can bundle the ISDN channels to double your transfer rate. This will, however,
incur double the call costs and you will, for example, no longer be reachable by tele-
phone.
What Is the Difference Between DSS1 and 1TR6 (Germany only)?
The various terminal devices in the ISDN network must agree on a common "language"
before they can understand one another. This is standardized for some services, such as
telephony, and does not require any further attention. The situation is different for data
applications, however: When two devices (e.g. ELSA MicroLink ISDN PCI ) exchange data
using a B channel, the language that they use for their interaction is established in a 'pro-
tocol'. PPP (Point-to-Point Protocol), which is generally used in the Internet, and X.75 are
examples for such protocols.
However, there is also the control channel (D channel) in addition to the basic channels
(B channels). This channel also has a protocol which regulates the transfer of control
information between the exchange and the terminal device. The 1TR6 protocol was used
in Germany in the early years of ISDN. More recent connections operate almost exclusi-
vely with the newer Euro-ISDN (DSS1) protocol. It is not necessary for the two commu-
nicating terminal units to use the same D-channel protocol. Data from connections using
DSS1 will make their way to 1TR6 connections and vice versa.
DSS1 and 1TR6 connections use different designations for the numbers of the terminal
devices.
DSS1 connections provide at least three different Multiple Subscriber Numbers
(MSNs) which can be assigned to the individual devices.
1TR6 connections offer ten terminal selection digits (EAZs, from the German Endge-
räteauswahlziffern) which can be assigned to terminal devices.
ELSA MicroLink ISDN PCI