Proxy for GTP traffic between multiple SGSNs and GGSNs

 This package is part of osmo-sgsn and provides a proxy for GTP traffic
 between multiple SGSNs and GGSNs.
 .
 The SGSN implements
  - the Gb interface to the BSS's (like the OsmoPCU or an ip.access nanoBTS)
  - the Gp interface with its GTP protocol to one or more Gateway GPRS Support
    Node (GGSN) like OsmoGGSN.
  - the IuPS interface with its RANAP protocol to onre or more RNCs or HNB-GWs
    like OsmoHNBGW
  - the GSUP Interface/Protocol towards OsmoHLR