fferences, we have already learned that the EPS network architecture is very different, and the EPS procedures are sometimes quite different. However, in the EPS user plane we can see clearly the GPRS pedigree in the EPS architecture - although the interface names are different, the user-plane protocol architecture seems exactly the same in 3G-GPRS. On the other hand, when we look more closely the following differences become apparent. PDCP is a new version in EPS [36]. The PDCP's responsibility in EPS includes transmission of the user packets over the radio interface, header compression, user traffic ciphering and integrity protection, and delivery of the packets in sequence and without duplicates. Hence, in EPS the PDCP's functionality has increased quite bit from the 3G version of PDCP. In addition, the PDCP is terminated in the EPS architecture in the eNodeB. GTP is responsible for transporting users' packets over the EPS network. This is the same GTP that is also used in the GPRS architectures. 2.3.3 GPRS Tunneling Protocol Versions Although we promised not to dwell too deeply on the protocols themselves, it is good to understand a little about GTP. GTP is used in both control and user planes in all of the 3GPP architectures. Therefore, it is an important building block in the 3GPP system. Currently, three versions of GTP exist: GTP version 0 was the first version of GTP. It is now deprecated, and not used in modern systems. Deploying IPv6 in 3GPP Networks GTP-U GTP-U UDP/IP UDP/IP LTE-Uu S5/S8 eNodeB Figure 2.17 EPS control plane protocols in PMIP architecture variant. GTP version 1 is used in GPRS in both control and in user planes, and in EPS in user plane. GTP version 2 is used in EPS in the control plane. 3GPP has defined fallback from version 2 to version 1 in nodes that support the fallback. However, fallback to version 0 is not supported, and version 0 is compatible neither with version 1 nor version 2. 2.3.4 PMIP Based EPS Architecture As we briefly mentioned earlier, there are two different variant