AS4000 Subscriber Terminal
Installation and Commissioning
GSI 001
605-0000-454
Draft Issue 1.3 Date 8/02/00
Page 2 of 2
WARNING – HAZARDOUS VOLTAGES
On AC installations, hazardous voltages exist. Use caution when verifying or
working with AC power. Remove metal jewellery that could come into contact
with AC power.
On DC sections, short circuiting the low voltage, low impedance circuits can
cause severe arcing that may result in burns or eye damage. Remove rings,
watches etc. to avoid shorting DC circuits.
4.
Overview of ST operation
Traffic channels support either 32, 64, or 128kbit/s services. Each link operates
using a master RW code to provide a 160kbit/s channel. These links are then sub-
divided using 2nd level RW (overlay) codes that allow the construction of 2 x
80kbit/s or 4 x 40kbit/s smaller links. Hence Traffic Channels (TCH) are composed
of either 160kbit/s, 80kbit/s or 40 kbit/s links. The size of the traffic pool is
automatically and dynamically sized so channels may be made available as 32, 64, or
128kbit/s on demand. All STs are continually polled, and receive regular downloads
of a Free List containing available RWs and their channelisation (i.e. 128kbit/s,
64kbit/s or 32kbit/s) on RW14 (the call control channel).
If a phone goes off hook
then it waits for a new free list and takes an available RW selected at random from
the free list. (Note: if unslotted access is set in the ST class the ST will not wait for a
new free list but will acquire based on the last free list it received, this allows for
faster acquisition but increases the chance of collisions). If a channel is not available
at a required rate the next highest rate is selected. When a user’s line goes “off-
hook” and it is invited to acquire an uplink, it takes an RW. If contention occurs due
to another ST trying to acquire an uplink on the same RW, at the same time then
both STs disconnect and attempt to re-acquire.
Net Entry Channels
: The ST acquires a downlink on a Net Entry channel and waits
to be invited to acquire an uplink. RW15 is allocated for this purpose and additional
Net Entry Channels can be used if allocated. After an ST has net entered a demand
assigned ST is told to wait in RW15 where it is updated with free lists. Fixed
assigned STs are allocated a permanent channel
Free List:
The free list allocates the free list at each traffic rate. (160k, 80k, 40k)
The way the list is divided depends on the ST population. The free list dynamically
allocates new free channel when a channel allocated by the existing free list is used.
If for example an allocated 160k channel is used the free list will allocate another
one. This reduces the number of incoming calls that can be accommodated.
