An Introduction to the Ericsson Transport Network Architecture ...

88
Fig. 8
Protection Switch Unit structure
The triplication of the Switch structure includes
the TCUs
ESU is used for synchronisation of the
AXD with external 2 MHz synchronisation
signals. ESU compares the frequency of
the incoming 2 MHz signal with the divided
signal from AXD's internal clock. The
result of this comparison is sent to the Central
Processor (CP) for control of the clock
modules. The generation of the 2 MHz timing
information is also performed by the
ESU. Frequency division logic is performed
in a Field Programmable Gate
Array (FPGA), and one ASIC is used for
SNI-3 communication.
CTU is used for connection of the CP to
the AXD. The CP is connected via Ethernet,
and control information is converted
to the internal Basic Control Protocol
(BCP) embedded in SNI interfaces. One
ASIC is used for SNI-3 communication.
TAU 34, TAU 16x2, ESU and CTU are located
in the same magazine. In this magazine
there are three TCUs used by the
SNI-3 Devices for communication to/from
the Switching Network. Devices can be
mixed arbitrarily, except for the CTUs,
which have two specific slots. This flexibility
permits efficient utilisation of available
space when the exchange layout is made.
Conclusions
The AXD 4/1 system presented is a system
with great flexibility and a functional
distribution that makes it useful in a wide
variety of network applications. High availability,
thanks to the use of triplicated HW,
as well as an open architecture have been
key concepts in the system design.
The system handles accesses ranging
from 1.5 Mbit/s up to 155 Mbit/s, PDH (both
NAS and CEPT) as well as SDH. Switching
can be performed at all levels from
576 kbit/s (9x64 kbit/s) to 155 Mbit/s in
steps of 576 kbit/s including all standardised
signal levels.
References
1 CCITT Rec. G.703
2 CCITT Rec. G 707-709
3 Andersson, JO.: Digital Cross-Connect
Systems - a System Family for the Transport
Network. Ericsson Review 67
(1990):2, pp. 72-83.
4 Breuer, H-J. and Hellstrom, B.: Synchronous
Transport Networks. Ericsson Review
67(1990):2, pp. 60-71.
ERICSSON REVIEW No. 3. 1992