 a directory can be local or global in scope. For example, a directory that stores local information might consist of the names, e-mail addresses, and public encryption keys of members of a department or workgroup. A directory that stores global information might store information for an entire company. In this context, the universe of interest is the company. The clients who access information in the directory can be local or global. Local clients may all be located in the same building or on the same LAN. Global clients might be distributed across the conti- nent or PLMN. Transparent Access Transparent access (shown in Figure 10-15) means that the GGSN doesn't participate in user authentication; the GPRS authenticates based on GSM authentication of the user's Subscriber Identity Module (SIM) card only. The GGSN is able to allocate the user a public IP address; this user has to sub- scribe to the ISP for Internet services such as e-mail, news, Web, and SO on. In most cases, the transparent mode is used when the GPRS operator already is an ISP. In this case, the GPRS operator provides basic Internet GTP Tunnel Figure 10-15 Transparent access. DNS/DHCP Server Internet No authentication is done by the GGSN A Public IP @ is allocated via DHCP or internal address pools End-to-end data path via TE Client - IPsec for data security - PPP, PPTP, L2TP for user authentication Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. SGSN-to-GGSN (Gn) and GGSN-to-PDN (Gi) Interface SGSN-to-GGSN (G) and GGSN-to-PDN (G) Interface access. For this reason, the GPRS operator allocates a static or dynamic public address to the mobile station using the DHCP local server. Transparent Mode In case of intranet access, the authentication of this user will be performed at the service provider side. Figure 10-16 shows this in the transparent mode. A tunnel is created from th