Section: 13.2 PDN Interworking Model of GGSN for DHCP
Content: A DHCP relay agent shall be located in the GGSN used for interworking with the IP network as illustrated in the following figure 16b. Figure 16b: The protocol stacks for the Gi IP reference point for DHCP The DHCP relay agent relays the requests received from the DHCP client to the DHCP server(s), and the replies received from the server(s) to the corresponding client. The DHCP relay agent allows for the replies from DHCP servers to be delivered to the correct terminal, as the logical connection from the MT terminates in the GGSN, and consequently only the GGSN holds enough information to locate the DHCP client. How the DHCP relay agent identifies the MT based on the DHCP messages is out of the scope of 3GPP standardisation. DHCP provides mechanisms for user authentication and integrity protection, but does not offer any message confidentiality, therefore additional mechanisms (e.g. Ipsec tunnel) may be provided if the link towards the external network is not secure. However this is out of the scope of the present document. Apart from the particulars mentioned above, this model is basically the same as the one for interworking with IP networks described elsewhere in the present document. Using DHCP corresponds to the transparent access case as the GGSN does not take part in the functions of authentication, authorisation, address allocation, etc.