Interfaces in GSM

Interfaces
in GSM

 

BSS subsystem consist of :-

 

1. A Interface
2. Ater Interface
3. Abis Interface
4. Um Interface

 

 

A Interfaces
:-

 

At MSC uses
PCM30(8000 samples/second) or E1 links to carry the data to and from transcoder. Suppose 4-E1 links
between MSC – Transcoder.

 

1 E1 = 32ch

4 E1=128ch

 

Each channel is of 64kbps.

128*64 = 8.192Mbps

but out of 128 channel only 120 is used (8 for signalling i.e 2 from each E1 link)

so there are 120 channel available for Traffic.

Ater interface :-

as shown above Ater interface consist of 32 channel.

but remember CH0 & CH16 is not converted into 16 kbps i.e it is transparent.

so total of 120 sub channel (30*4) each of 16Kbps.

Abis interface & Um interface:-

2 channel from Abis interface are mapped to 8 timeslot of TDMA Frame.

here in fig it is mapped at full rate of 16kbps but its depends on vendor equipment configuration.one can also use 32kbps or 64kbps. i.e Abis interface is proprietory.

So,maximum 15 TRX = 15 ARFCN = 15*8 timeslots =120 user calls can be handled by 1 BTS with 1 E1.

but if all the channels are used for voice then there wouldn’t be any channel for signaling.so, signaling information is carried over in specific Abis timeslots of 64kbps each,or in 16kbps sub timeslots to atleast 1 TRX per cell.