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5 Hardware Structure of the AVM ISDN-Controller T1/T1-B
5.1 The ISDN-Controller T1
The AVM ISDN-Controller T1/T1-B—the core of the
full T1 installation—is contained in the 19" housing and
includes all the main components for communication
between ISDN and the host PC. The ISDN-Controller is
connected to the network terminator (NT) and the host
PC. A special high-speed interface is used for the PC
connection.
The ISDN-Controller consists of two functional sub-
systems. One is the ISDN subsystem, which handles
the data transmission to and reception from ISDN and
converts the ISDN data stream into a format that the PC
can process. The other subsystem comprises the
application and control logic.
Data are transferred across the ISDN Primary Rate
Interface using a time-multiplex technique and a pseudo-
ternary modified alternate mark inversion (AMI) coding.
The multiplex time frame is 256 bits long and divided
into 32 slots of eight bits each. Slots 1–15 and 17–31
correspond to the data channels and carry user infor-
mation. D-channel information is transmitted in Slot 16.
In the T1’s ISDN interface, the 30 data channels of the
incoming data stream are handled by a Munich32. An
HSCX is used for the D channel. The ISDN interface is
controlled by the T1’s application and control sub-
system, which consists of a transputer network of at
least three CPUs.
The term “transputer”, a mixture of “transmitter” and
“computer”, refers to a processor that combines pro-
gram execution with fast communication capabilities. A
transputer is a RISC CPU equipped with two or four
special high-speed interfaces called “links”. This CPU
design is ideal for communications applications. The
T1’s CPUs are networked together through their links,
and one link is used for communication with the host
PC.