https://www.cisco.com/c/en/us/td/docs/wireless/asr_5000/21-19_6-13/SGSN-Admin/21-19-sgsn-admin/21-17-SGSN-Admin_chapter_010.html
SGSN Administration Guide, StarOS Release 21.19 - Serving GPRS Support Node (SGSN) Overview [Cisco...
Serving GPRS Support Node (SGSN) Overview
serving gprs support node