GTP(GPRS Tunnelling Protocol) 协议

1. GTP v1 for user plan. 3GPP TS 29.281. used in:
      LTE-S1 (between eNodeB and SGW), control plan is S1AP
      LTE-S5 (between SGW and PGW), control plan is GTPv2-C
      LTE-X2 (between eNodeBs), control plan is X2AP

2. GTPv2-C for control plan. 3GPP TS 29.274. used in:
      LTE-S5
      LTE-S8

3. GTP (GTP-C and GTP-U) 3GPP TS 29.060. used in
      Gn (between GSNs within a PLMN)
      Gp (between GSNs in different PLMNs)
      Iu (between SGSN and UTRAN),  GTP-U only. The control plan is RANAP

4. GTP based charging protocol GTP'. 3GPP TS 32.295