Circuit Switched Data (CSD) Support
The BSC doesn't have to do much to support CSD:
- parse the bearer service details from the 48.008 A signaling side (ASSIGNMENT CMD)
- encode the bearer service details to the 48.058 Abis RSL signaling side (RSL CHAN ACT)
- instruct the MGW to use RTP payload-type 120 as "CLEARMODE/8000"