Timeslot Assignment on the Abis Interface

This describes the principles and algorithm of timeslot assignment on the Abis interface.

NOTE:

Physical 16 kbit/s multiplexing refers to the permanent assignment of a 16 kbit/s timeslot to a channel. The channel exclusively uses this 16 kbit/s timeslot.
Statistical multiplexing means that n channels use one 64 kbit/s timeslot. Each channel uses the 64 kbit/s bandwidth in a different time slice, that is, Time Division Multiplexing (TDM). In statistical multiplexing mode, more than one channel is multiplexed onto one 64 kbit/s bandwidth.
DML : Dynamic Maintenance Link. During the loading of the BTS software, the software is loaded on the OML/EML, besides, the transmission resources allocated to the RSL or TCHs are dynamically pre-empted to establish the extended loading links to load the software simultaneously. In this way, the software loading is accelerated. After the software is successfully loaded, the extended links are released and the pre-empted transmission resources are reallocated to the TCHs or RSL. Then, the allocation of transmission resources on the Abis interface is restored.

Principles of Timeslot Assignment on the Abis Interface

The principles of timeslot assignment on the Abis interface are as follows:

The n:1 statistical multiplexing and physical 16 kbit/s multiplexing cannot coexist on one link.
The OMLs, RSLs, ESLs, idle timeslots, monitoring timeslots, and TCHs are assigned based on sub-timeslots.
In physical 16 kbit/s multiplexing mode, any of the OMLs, RSLs, idle timeslots, monitoring timeslots, and TCHs can coexist on one 64 kbit/s timeslot.
When using the n:1 64 kbit/s statistical multiplexing mode, adhere to the following principles:
- The timeslots of different BTSs cannot be multiplexed onto one 64 kbit/s timeslot.
- Traffic channels and signaling channels cannot be multiplexed onto one 64 kbit/s timeslot.
- One 64 kbit/s timeslot must be used even if one signaling channel or traffic channel is configured.
- Monitoring timeslots cannot share the same 64 kbit/s timeslot with other timeslots, except for the semipermanent connection.
- In different E1s of cascaded BTSs, all the objects multiplexed onto one 64 kbit/s timeslot must stay in the same 64 kbit/s timeslot and the relative positions of their corresponding sub-timeslot numbers must remain the same.
- The timeslots of different device groups in one BTS cannot be transmitted on the 64 kbit/s bandwidth of the same E1.
- Idle timeslots and the timeslots on TRXs cannot use the same 64 kbit/s bandwidth with the semipermanent connection.
- The number of OMLs for the GEIUB/GOIUB cannot exceed 384.
- The number of RSLs for the GEIUB/GOIUB cannot exceed 384.
- The number of OMLs for one GEHUB/GFGUB/GOGUB cannot exceed 384.
- The number of RSLs for one GEHUB/GFGUB/GOGUB cannot exceed 384.
When BTSs, cells, TRXs, idle timeslots, or monitoring timeslots are added, timeslots on the Abis interface must be assigned. The resources on the Abis interface should be assigned to the following objects: OMLs, RSLs, traffic channels, idle timeslots, and monitoring timeslots.

Algorithm of Timeslot Assignment on the Abis Interface

The algorithm of timeslot assignment on the Abis interface is as follows:

Each E1 port of the BTS manages sub-timeslots 0-255. Sub-timeslots 0-7 are used for synchronization. They cannot be assigned to any object.
The OML must be assigned timeslot 31 on port 0 or port 1 of the local BTS. In n:1 statistical multiplexing mode, the OML must be assigned to sub-timeslot 0 of timeslot 31; in physical 16 kbit/s multiplexing mode, the OML must be assigned to sub-timeslot 3 of timeslot 31.
Except for the incoming E1 timeslot, the E1 port directly connected to the BSC is selected preferentially during the timeslot assignment of the upper-level BTS.
Monitoring timeslots and idle timeslots can be assigned only on the ports of the main cabinets in the main cabinet groups.
Lower-level BTSs can be established only on the ports of the main cabinets in the main cabinet groups.
Before the OML between the BTS and the BSC is established, the BTS scans different timeslots and tries to establish the OML to the BSC. The number of BTS cascades is limited to reduce the link setup time.