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Saving of stable PDP contexts in case of Hardware or Software failure Disclosure Number: IPCOM000012287D
Original Publication Date: 2003-May-25
Included in the Prior Art Database: 2003-May-25

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In order to enable data transfer to/from the mobile station in UMTS, a so-called PDP context is established in SGSN and in the GGSN. A PDP context in the SGSN comprises all the information required to transport data packets from the Iu-interface to the Gn-interface and vice versa. Likewise, in the GGSN, a PDP context comprises all the information required to transport data packets between the Gn-interface and the Gi-interface. The data flow between the mobile station and the internet service provider is shown in the figure 1. The data packets are transported over the Iu- and Gn-interface via so-called GPRS tunnels. The protocol responsible for these GPRS-tunnels is the GTP (GPRS tunneling protocol). Both the SGSN and the GGSN contain a processor where the GTP-functionality resides (in the following, this will be referred as the GTP Module - GTM). For reliability reasons, there are several GTMs working in some kind or redundancy. Since 1+1 redundancy is usually too expensive, the GTMs will normally work in load sharing. In the following situations, the PDP contexts handled by a given GTM can no longer be served: 1) Hardware (HW)/Software (SW) failure of the GTM 2) Software-Update/Software-Upgrade of the GTM The IP-address of the GTM is visible to the outside world (at the Iu- and Gn-interface), therefore without further measures, the work of the GTM cannot simply be overtaken by another GTM. Hence, the sessions related to the PDP contexts on this GTM are lost. If the above mentioned situations occur frequently, then this loss of sessions has a very bad effect on the overall session drop rate, which is an important aspect of the reliability of an SGSN or GGSN.