User Manual

Dimensioning rules
Nortel Networks Confidential
5–4
PE/DCL/DD/0063
411–9001–063
Standard 12.07/EN September 2000
GSM/BSS V12
5.1.1.2 AGCH + PCH common channel
The channel payload is largely induced by “paging” messages used for locating the
MS with a view to setting up a call. The remaining load is taken up by resource
allocation messages issued by the AGCH for location updating purposes, paging
responses and calls emitted by MS onto the fixed network.
The rule is to systematically reserve at least one access grant channel (AGCH).
By dimensioning paging channels a single common channel is occupied even when
the needs of high capacity base station, wide location area and paging repeat
message have to be covered .
5.1.2 Abis Interface dimensioning
Time slots at 64 kbit/s are needed to convey user traffic along the TCH between the
BSC and BTS. Each cell must continuously transmit the BCCH frequency.
The traffic channel supports user traffic and signaling channels used for traffic
management functions and operation/maintenance purposes. TCH channels are
concentrated on radio sites and conveyed onto the Abis interface. Different
configurations are possible on Abis interface. Each of them, is shown on
Figure 5–1.
5.1.2.1 Drop and insert techniques
Two types of connections allow drop and insert technique: chain connection and
loop connection.
Chain connection
The same external PCM link enables the connections between BSC and several Base
Transceiver Station (BTS) equipments.
Each BTS uses a set of 64 kbit/s time slots.
Loop connection
For a chain connection, if one link between two BTSs fails, all the BTSs will be lost.
However, to correct this disadvantage, the last BTS in the chain is looped back to
the BSC using a PCM link. It is then possible to reconfigure the BTS units.
This drop and insert capability does not require any additional or specific
equipment, or any specific software. When a BTS is being configured, the 64 kbit/s
time slots are reserved for its usage. All other time slots stay in the “dropped”
position.
The drop and insert techniques obey to the following rules: