User Manual

Demand Assignment
System Overview GSI 002
605-0000-450
Draft Issue 1.3dr Date 8/02/00
Page 3 of 16
The Central Terminal (CT) comprises at least one rack with a RF Combiner Shelf and
associated Modem Shelf(s). A CT rack will provide two modem shelves and an RF
Combiner Shelf. An Expansion Rack provides for two further modem shelves. All four
modem shelves utilise the RF Combiner Shelf in the CT Rack to provide the radio
interface. It will typically be remote in a location chosen for best radio coverage with all
control, signalling and traffic backhauled to an operator's central office using point-to-
point microwave equipment. The CT provides the functionality to terminate the
network digital interface and connect to multiple STs simultaneously via the AS4000
DA CDMA radio interface.
The Access Concentrator (AC) is located at the operator's central office or local
exchange, it's purpose to consolidate traffic from multiple CT modem shelves and
present traffic and signalling interfaces in unconcentrated and concentrated form to the
network switching equipment. A fully equipped AC shelf will support up to 64 E1
connections to the switch. The AC may also consolidate management communications
back to the management system.
The AS8100 Sitespan Management System interfaces to the AC and dependent CTs
either directly or via a communications network. Sitespan supports system
configuration and provisioning functions, alarm reporting, performance monitoring and
allows tests to be invoked.
1.1. AC Switch Interface
The AC interfaces to the Network Switching Equipment via multiple E1 2Mb/s ports.
Each E1 port carries traffic and may also carry signalling information. The architecture
supports the following 'standard' signalling protocol types;
i. CAS; Unconcentrated , 30 x 64 kb/s speech channels, ABCD Channel Associated
Signalling embedded within timeslot 16.
ii. V5.1; Unconcentrated, 30 x 64 kb/s speech channels, at least one message based
signalling channel, embedded within timeslot 16.
iii. V5.2; Concentrated, 30 x 64 kb/s speech channels per E1, at least one message
based signalling channel per group of E1s up to a maximum of 16 x E1.
1.2. The DA Radio Interface
The DA radio interface incorporates the signal coding and protocols to support the
flexible allocation of radio bandwidth among a large number of STs. The DA radio
interface uses the application of overlay codes and time division multiplexing (TDM) to
increase channelisation, and DA protocols that manage link access and RF channel
switching.
Effective utilisation of RF bandwidth requires that user data rates be efficiently matched
to available bandwidth. The DA system supports access rates of 32 kbit/s, 64 kbit/s,
128 kbit/s and 144 kbit/s depending on the type of ST deployed and the configured data
rate. Overlay codes extend the CDMA spreading codes employed in AS4000 to allow