Browse Prior Art Database

Cancel Location in a 2G system for a 3G roamer

IP.com Disclosure Number: IPCOM000132039D
Original Publication Date: 2005-Nov-29
Included in the Prior Art Database: 2005-Nov-29
Document File: 4 page(s) / 663K

Publishing Venue

Motorola

Related People

Jheroen P. Dorenbosch: AUTHOR

Abstract

To facilitate roaming of a dual-mode Mobile Station (MS) that is homed in 3G to and from 2G networks, a 2G/3G gateway subscribes to mobility events of the MS. When the MS roams out of the 2G system the gateway is notified of the mobility of the MS. This enables the gateway to generate the required Cancel Location message.

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Cancel Location in a 2G system for a 3G roamer

Jheroen P. Dorenbosch, Motorola, Inc.

Abstract

To facilitate roaming of a dual-mode Mobile Station (MS) that is homed in 3G to and from 2G networks, a 2G/3G gateway subscribes to mobility events of the MS.  When the MS roams out of the 2G system the gateway is notified of the mobility of the MS.  This enables the gateway to generate the required Cancel Location message.

Problem

Operators are planning to provide dual-mode phones that are homed in a 3G system and that can roam into 2G systems.  In the context of this article 2G systems are 2G and 2.5G wireless cellular networks (i.e. GMS, iDEN, and CDMA), while 3G systems refer to 3G and 4G wireless systems such as UTMS, 802.11, 802.16 and 802.20 as well as wired IP networks that support real time IP applications like voice. 

2G and 3G systems use different registration paradigms.  In a 2G system a Mobile Station (MS) can roam between zones controlled by Visitor Location Registers (VLRs).  When a MS moves to a new 2G zone it registers with the new VLR.  As part of the 2G registration procedure,  the new VLR informs the Home Location Register (HLR) of the MS.  The HLR stores the ID of the new VLR as the ‘current VLR’ of the MS.  The HLR will also inform the previous VLR that the MS has left by sending a “Cancel Location” message to the previous VLR.  The previous VLR removes the location information it has for the MS.  This is important because if the previous VLR does not remove this information, subsequent calls through the previous VLR to the MS will not be routed correctly.

When an MS moves between 3G domains, the MS itself will perform the registration, typically using SIP.  As part of the 3G SIP registration the MS’s SIP registrar stores location information for the MS in a Location Service database in the form of a contact.  When the MS moves to a new location, the MS itself is responsible to inform the SIP registrar that  the contact corresponding to the previous location is no longer valid.  (The MS can also let the old contact expire).

To facilitate roaming of a dual-mode MS from 3G to 2G, operators typically use a 2G/3G gateway (Figure 1).  The gateway is a Pseudo-HLR; it is made to look like the MS’s HLR to the 2G system.   That way the gateway will automatically be informed when the dual-mode MS registers in the 2G system.  As part of such a registration procedure, the 2G/3G gateway executes a 3G SIP registration with the MS’s SIP registrar.  The gateway typically specifies a SIP contact for the MS (or adds a path header) that terminates on the gateway itself.  That way calls made from the 3G system to the MS will be routed via the gateway.

Problems occurs when an MS moves out of the 2G system to another 2G or 3G system.  Since the MS does not have a real 2G HLR, there is no mechanism to automatically generate a Cancel Location message to the MS’s previous VLR.  Thus, calls made at the previous 2G...