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Minimising data loss during SRNS relocation

IP.com Disclosure Number: IPCOM000004825D
Original Publication Date: 2001-Jun-19
Included in the Prior Art Database: 2001-Jun-19
Document File: 3 page(s) / 32K

Publishing Venue

Motorola

Related People

Peter Legg: AUTHOR

Abstract

This paper addresses data loss during Serving Radio Network System (SRNS) relocation in the UMTS Third Generation cellular telecoms system. Data loss is minimised using the MAC scheduler and flow control between the UTRAN and the core network.

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Minimising data loss during SRNS relocation

by Peter Legg

Abstract

This paper addresses data loss during Serving Radio Network System (SRNS) relocation in the UMTS Third Generation cellular telecoms system. Data loss is minimised using the MAC scheduler and flow control between the UTRAN and the core network.

Introduction

This paper is written within the context of the Third Generation cellular telecommunication system known as UMTS and specified by 3GPP. The system is divided into a radio network (the UTRAN) and a core network; these are linked by the Iu Interface. The Iu connection for an individual mobile lies within the Serving Radio Network System, or SRNS. A Radio Network System RNS comprises one RNC and a number of Node Bs. When the mobile moves, it may need to handover to a cell which lies in a different RNS, termed the drift RNS, or DRNS. On this event, traffic is routed to the Iu via the DRNS and SRNS (Figure 1). In various circumstances, it is beneficial to move the SRNC function of a mobile from one RNC to another. In the example above, the DRNC would become the SRNC for the mobile, and the Iu connection supporting the mobile will move. This procedure is called a SRNS relocation (Figure 1).

Figure 1. SRNS relocation.

Problem(s) To Be Solved

During a UMTS SRNS relocation, data loss is likely on the switch over :

Data in transit over the Iur and 'old' Iu will be discarded or routed to the wrong destination.

Data buffered in the RLC and MAC-d of the 'old' SRNC can no longer be sent on the downlink.

Proposed Solution to the Problem(s)

In this paper, we address the problem of data loss in several ways:

(a) downlink schedulable traffic

Within the UTRAN , we may control the traffic to the mobile using the scheduler (i.e. the MAC and RRC protocols). The method has two steps: I) we schedule data preferentially to those users who are to be affected by SRNS relocation (this may be only one mobile). This burst of traffic helps to clear the MAC-d buffer of data, at the 'old' SRNC. II) After clearing the buffer we then prohibit transmissions to this mobile (using the scheduler), just before and during the relocation. This prevents the generation of Iur traffic which would be lost.

(b) uplink schedulable traffic

In the uplink, we can control the transmissions by the mobile using the TFC control message which limits the transport format combinations which may be used by the mobile on the uplink. Just before relocation, we prevent the mobile from transmitting, thus avoiding data loss on the Iur and Iu. The mobile is considered again by the scheduler once relocation is complete.

(c) all schedulable traffic

Over the Iu interface, we can exploit flow control with the SGSN to prevent data transmission from the SGSN to the 'old' SRNC. This stops the build up of traffic in the MAC-d of the 'old' SRNC (which would be lost) and stops data loss on the old Iu. Note, no flow control is placed on the SRNC to SGSN path to help clear the 'old' SRNC of data.

Note, these methods are on...