GPRS for GSM upgrade strategies using network redundancy

Abstract

The Serving GPRS Support Node (SGSN) is the most fundamental node in GPRS. Ericsson produces and manages an increasing number of SGSN nodes in the world. SGSN nodes require upgrades on software and hardware regularly, forcing restarts, which gives service interrupts for subscribers. This report presents four different upgrade strategies intended to avoid or minimize service interrupts, while being cost-efficient: Hot standby, Subscriber based PCU routing, RA based PCU routing, and Redundant links solutions. The RA based PCU routing is considered the best, because it provides a smooth transfer of subscribers from one SGSN to another on a routing area basis, but not under all circumstances. It employs the Inter SGSN Routing Area Update (ISRAU) procedure to transfer subscribers. The routing mechanism is based on existing technology, namely Point- To-Point BVC connections bound to different Network Service Entities (NSEs) leading to different SGSN nodes from each cell through the Packet Control Unit (PCU).