he PLMN provides the address during PDP context activation in the case of external PDN address allocation, then it is the responsibility of the GGSN and PDN to allocate and release the dynamic PDP address by means of protocols such as DHCP or RADIUS. If the DHCP is used, the GGSN provides the function of a DHCP client. If RADIUS is used, the GGSN provides the function of a RADIUS (remote authentication dial-in user server) client. If the MS negotiates a PDP address with the PDN after PDP context activation in the case of external PDN address allocation, it is the responsibility of the MS and the PDN to allocate and release the PDP address by means of protocols such as the DHCP. Only static PDP addressing is applicable in the network-requested PDP context activation case. Encapsulation The packet domain PLMN backbone network encapsulates a PDP PDU with a GPRS tunneling protocol header, and inserts this GTP PDU in a UDP PDU that again is inserted in an IP PDU. The IP and GTP PDU headers contain the GSN addresses and tunnel end point identifier necessary to uniquely address a GSN PDP context. Between a 2G SGSN and an MS, the SGSN or MS PDP context is uniquely addressed with a temporary logical link identity and a network layer service access point identifier pair. TLLI (temporary logical link identifier) is derived from the PTMSI. NSAPI is assigned when the MS initiates the PDP context activation function. 4.8.3 Interface of the GPRS with the 2G GSM Network In a 2G network the Gb interface connects the GPRS with the GSM. It is between the BSC and the SGSN. It may consist of E1 PCMs with a data rate of 2 Mbps, i.e. 32 timeslots of 64 kbps each. Out of these, 30 timeslots may be used for traffic (user data) and 2 for signalling. The Gb interface allows many users to be multiplexed over the same physical resource. When a user needs to send or receive data, the timeslots are allocated temporarily and are reallocated after completion of the activity. In this way, the Gb interface is more efficient than the A interface, w