User`s manual

EAGLE - ANNEX A.2. ISDN NATIONAL-1 communications guide (USA) 54
A.2. ISDN NATIONAL-1 communications guide (USA)
1.- Notes about the ISDN and the peculiarities of the different types of ISDN
1.1.- Generalities about the ISDN
The ISDN (Integrated Services Digital Network) is a telephone connection system that permits
the establishment of fully digital end-to-end communications.
There are two types of ISDN links, depending on the number of 64 Kbps channels: Basic links
(BRI – Basic Rate Interface) and Primary links (PRI – Primary Rate Interface).
Basic links allow the simultaneous establishment of two connections or data channels, each
with a capacity of 64Kbps.
Primary links allow 23 - 64 Kbps channels to be established in the USA, and 31 - 64Kbps
channels in Europe.
To access ISDN services, you must subscribe to an ISDN phone line and connect equipment to
it, such as an audio codec, that has an ISDN Terminal Adapter device to perform the tasks of
establishing and maintaining connections through digital ISDN phone lines.
The Eagle has an ISDN Terminal Adapter for Basic links (BRI), which gives it a communications
capacity of two independent 64 Kbps data channels. Eagle allows these channels to be grouped
into a single 128 Kbps channel, doubling the bandwidth and the communications cost.
1.2.- Types of connection to Basic ISDN Links
We can find two types of physical connection to the ISDN: connection to a type U interface, and
connection to a type S/T interface.
The U interface connects the telephone exchange with the subscriber. It has two wires; the
same as in conventional analog telephony, and only allows a point-to-point connection (a single
device connected to the interface).
The S/T interface is obtained from the U interface, passing it through a Network Terminator
(NT1) located at the subscriber’s premises. It has four wires and allows a multipoint connection
of up to 7 devices.
In the USA, phone companies do not supply the NT1, so the user is the one who must install it if
he wants it. The most common situation is for there to be no NT1, and therefore access is
through a U interface.
In summary, in the USA, access via a U interface is most common, unless the subscriber has
asked the phone company to install an NT1 or has installed it himself (the NT1 is usually a box
attached to the wall, with a power supply, and some kind of light indicator, to which the two-wire
external line enters and which has RJ-45 jacks).
The Eagle’s universal TA (terminal adapter) allows both types of connections, and thus has two
ISDN connectors, one marked ETSI (RJ-45, 8 pins) for the S/T interface connection, and the
other marked ANSI (RJ-11, 6 pins) for the type U interface connection. The type of connection
used must be configured in the unit’s setup.
1.3.- Protocol
Although the ISDN is supposed to be a standard, differences can be found between the
protocols used by different countries.
In the USA, there are several protocols that are incompatible with each other; fortunately,
however, there is one protocol that is fairly standardized (called National-1), which is usually
available at all exchanges.