IP Subnet Mobility over General Packet Radio Service Mika Mizutani Christian Bonnet Hitachi Systems Development Laboratory Institut EURECOM 292 Yoshida-cho, Totsuka-ku 2229, route des Cretes BP 193 Yokohama 244-0817 Japan 06904 Sophia Antipolis Tel: (+81) 45 860 3078, Tel: (+33) 4 93 00 26 26 Fax: (+81) 45 860 1675 Fax: (+33) 4 93 00 26 27 [email protected] [email protected] Abstract: The growth of the mobile network system of which the cellular systems like Global System Mobile Communications (GSM) and Personal Digital Cellular (PDC) are representative and the IP network attracts worldwide attention. The IP network access through the mobile data network system is required strongly to use the useful IP services anytime and anywhere. Therefore on the mobile data network system such like General Packet Radio Service (GPRS), there has been the necessity for realizing the mobility over IP level. This paper focuses to combine the proprietary mobility management of GPRS and Mobile IP. In our proposal the mobile terminal only treats the GPRS mobility management and doesn’t recognize the location of IP level. The GPRS core network manages the movement between IP subnets using the information of the GPRS mobility management. One of the advantages is no additional control message on the radio I/F necessitated by the IP mobility. Keywords: GPRS, Mobile IP, Mobile data network 1. Introduction data network system is required and anticipated. As the infrastructures of the data service on the Currently, gathering information from the current mobile network system that provides the Internet and selecting the useful and necessary circuit-switched service has the following limitation. information are getting to pervade [1]. And there are First, the transmission speed of Short message various services to realize it, for example the access Services (SMS), that transmits short data messages of the e-mail server and the web server on the each up to 160 alphanumeric characters long, cannot Internet and the Intranet, the access of the private reach 1 Kbps and the data service over the circuit- database on the Intranet, the information delivery switched service cannot reach 10 kbps. Secondly, service using the push technology and the electronic the circuit-switched service isn’t suitable for IP commerce such as banking service and reservation traffic that has a characteristic of the burst traffic. In service. As the result, the IP packet traffic is this service, the radio resource remains being increasing remarkably, and it is forecasted that IP assigned while there is no IP traffic. And the same packet traffic is going to be over 160 Gbps in the bandwidth is allocated for the upstream and the year of 2001 [2]. So the next generation IP network downstream even if the subscriber downloads the should become to consist of the network which is much information from the Web server. So the advanced from the heterogeneous network such as circuit-switched service can’t use the radio resource the telephone network and the mobile network in effectively when IP packet traffic is transmitted. addition to the growth of the IP network itself. And thirdly, the cost that is in proportion to the time of occupying the radio resource is a problem to show On the other hand the mobile network system a tendency to be getting higher. such as the cellular systems that is called GSM or PDC is paid attention to as the telephone network. To solve these problems, the new infrastructures Because the mobile subscribers are increasing appear. Using the current radio resource efficiently, rapidly, too, and the access with the fixed IP network the High-speed circuit switched data (HSCSD) and over the mobile network system is very attractive in GPRS that provides the packet-switched services order to take advantage of get the above-mentioned have been standardized by European service anytime and anywhere [3]. So the mobile Telecommunications Standards Institute (ETSI), and they are expected to be launched in the year of 2000 section 2.2 and section 2.3 describe the Attaching [4]. The 3rd generation mobile network systems that procedure and PDP activation procedure, and the are called as International Mobile location management procedures as the represent of Telecommunications–2000 (IMT-2000) and GPRS mobility management procedures [4][10][11]. Universal Mobile Telecommunication System (UMTS) are standardized by International Telecommunication Union (ITU) and ETSI [5][6][7]. 2.1 GPRS Architecture In the meantime the IP community recognized GPRS provides the packet-switched service to the need for mobility handling between IP subnets as transfer the burst traffic in an efficient manner. portable computers become more and more popular. GPRS introduces two network nodes in the GSM This effort resulted in Mobile IP specifications and core network. The Serving GPRS Support Node Ipv6 [8][9]. At present the users have to chose (SGSN), which is at the same hierarchical level as between two different solutions in order to combine the MSC, keeps track of the individual MTs ’ location IP network access and mobility: the GPRS world and performs security functions and access control. where the user’s terminal address belongs to the The SGSN is connected to the base station system address space of a GPRS operator or an Internet, and (BSS). The Gateway GPRS Support Node (GGSN) the IP world where the terminal address belongs to provides the interworking with external packet the address space of its home network. network like the IP network or X.25 network. And This paper looks at the integration of IP the GGSN is connected with the SGSNs via IP-based GPRS backbone network. The HLR is enhanced mobility based on Mobile IP and GPRS. In this with GPRS subscription data that includes the packet framework the user’s terminal retains its home address while roaming under the coverage of a network address like the IP address. Fig. 2.1.1 shows the GPRS architecture. wireless GPRS network. The proposed solution does not impose additional signaling traffic on the radio interface between the terminal and the fixed infrastructure. It has an impact on the GPRS GSM environment equipment that should handle the functions of the (Circuit-switched service) Mobile IP protocol. This leads to architecture the MSC PSTN / ISDN GPRS network not only by defining Routing Areas (RA) but also by grouping the RAs into IP subnets. HLR The expected benefit of this approach is a transparent BS MT way to communicate between a roaming terminal IP network BS and other correspondent terminals. SGSN IP based GPRS GGSN backbone network Section 2 shows GPRS architecture and the X.25 network mobility management procedure. Section 3 SGSN GPRS GGSN describes the way to combine the mobility between (Packet-switched service) IP subnets (IP subnet mobility) with the peculiar PSTN: Public switched telephone network ISDN: Integrated services digital network mobility management defined in the GPRS. And section 4 shows the impact of the proposed Fig. 2.1.1 GPRS Architecture architecture on the performance of the system. 2. Outline of GPRS 2.2 GPRS attaching procedure and PDP The purpose of GPRS is to efficiently activation procedure accommodate burst data sources. Another important goal of the technology is to make it possible for Before the MT starts transmitting packets, it has GSM operators to share physical resources between to initiate the GPRS attaching procedure and the packet data services and other GSM services. It Packet Data Protocol (PDP) activation procedure. In means that the GPRS shares the GSM frequency the GPRS attaching procedure (Fig. 2.2.1), the MT bands with telephone and circuit-switched service, shall provide its identity. After receiving “Attach and makes use of many properties of the physical Request” with Packet Temporary Mobile Subscriber layer of the original GSM system such as the time- Identity (P-TMSI) or International Mobile Subscriber division multiple access (TDMA) frame structure, Identity (IMSI) from the MT, the SGSN identifies modulation technique and structure of GSM time the MT and then the authentication procedure and the slots. equipment checking procedure are initiated between the MT and the HLR via the SGSN. As the result, Section 2.1 shows the GPRS architecture, and the SGSN gets the GPRS subscription data that includes the PDP contexts and then creates the SGSN address instead of the GGSN address. mobility management (MM) contexts. The MM Contexts consist of the GPRS subscription data including the IMSI and the information of the 2.3 Location Management Procedure authentication and the ciphering, and the mobility information like the identifications of the area and When the packet is received for a MT, the the cell where the MT exists. The PDP contexts packet has to be routed to the cell in which the MT is consist of the information of the packet data protocol located. In the circuit-switched service, the mobile like the IP address of the MT and the attaching network system is split up into a number of location GGSN that are registered in HLR beforehand. areas that consist of a number of cells. In this way the core network can keep a registration of the MM Contexts current location area of each MT, and therefore it PDP Contexts Subscription data will only need to call the mobile within that area. In MT New- Old- HLR the packet-switched service of GPRS, the registration SGSN SGSN (a) Attach area is called as the routing area (RA), and this RA is Request defined to be smaller than the location area. Because (b) IMS I resolution the radio resource is only assigned while packet is (c) Authentication transferred, so the frequency of paging per the MT (d) Equipment has a tendency to be increasing in comparison with checking the circuit-switched service.