Ka band satellite network technology: Demonstration of mobile services in multi segment IP networks M. Holzbock 1, A. Jahn 1, F. Grassl 2, J. van Noten 3, M. Pugliese 4, V. Schena 5, S. Dragas 6 1
DLR, Deutsches Zentrum für Luft- und Raumfahrt - German Aerospace Center, Wessling, Germany. {Matthias.Holzbock,
[email protected]}@dlr.de 2 Siemens AG Österreich, Wien, Austria,
[email protected] 3 SmartMove, Leuven, Belgium,
[email protected] 4 Telit Mobile Terminals s.p.a., Roma, Italy,
[email protected] 5 Alenia Aeropazio, Roma, Italy,
[email protected] 6 TTI, Tecnologías de Telecomunicaciones y de la Información, Santander, Spain,
[email protected] Abstract: Future mobile communication, information, and navigation services will impact society in a significant way. With IP becoming more and more dominant in the variety of networking protocols, emerging systems must be capable to provide IP services ubiquitously with high data rates at low cost. In the framework of the IST project SUITED (multi-segment System for broadband Ubiquitous access to InTErnet services and Demonstrator) a demonstration of mobile services in multi-segment IP networks will be performed. Investigations will focus on integrating a Global Mobile Broadband System (GMBS), comprising different, but interoperating, wireless network systems, by means of serving multi-mode mobile or portable user terminals. This paper will address the overall demonstration concept, present each communication system segment, and will devote a section to the satellite terminal developments. Moreover it will provide methods for a seamless handover and IP mobility of the user terminal between and in these segments while quality of service (QoS) is maintained.
SUITED demonstrator system description The SUITED demonstration network will interconnect four different segments, i) the EuroSkyWay (ESW) satellite segment, ii) a GPRS terrestrial segment, iii) a UMTS terrestrial segment and vi) a wireless link (W-Link) segment, with the Internet (Fig. 1). These wireless network systems will be addressed in detail later on.
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Figure 1. SUITED Demonstrator Architecture The proposed demonstrator system architecture will support terminal mobility in these heterogeneous networks. The support shall comprise not only mobility in the same network segment (for instance
inside GRPS by cell update), but also mobility across coverage borders of different segments. A key feature of the system will be a seamless handover between terrestrial wireless segment (GPRS, UMTS and W-LINK) and the satellite segments, that means at least, application sessions shall not be interrupted, and the handover procedure shall not be visible for the user. For example a ftp download will not be interrupted and new login of the user will not be necessary when the terminal moves to a new network segment. However, a user profile will manage by pre-selection of various option, in which way the terminal shall proceed, if a inter-segment handover is necessary. In order to respect user needs this profile will control the handover between the network segments each differing in pricing, data rate, and QoS constraints. The user can for instance accept handover to all available and registered networks. Or, he chooses that he has to confirm a connection to a new segment if e.g. pricing is changing, the data rate or the QoS of the initial connection can not be maintained. Inter-segment handover will be initiated by the user terminal controlled by a mobility manager, based on the availability of segments and the preferences chosen in the user profile. Handover is necessary, if the user is leaving the coverage of the actual segment. If more than one segments are available handover can be advantageous, e.g., if applications with higher data rate or QoS requirements are started or a cheaper segment gets available. The whole mobile terminal (called mobile node) will consist of one or more laptoptype user terminals, an interworking unit (IWU), a navigation unit, and certainly the multiple segment radio modems with baseband part and outdoor units (Fig. 2). These components will be realised partly by new developments (like the IWU or the satellite terminal's outdoor unit) and by modifications on available hardware (e.g. the GPRS terminal).
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Three types of user terminals are foreseen for the demonstration: a car terminal, a big vehicle terminal (for train, aeroplane, bus) Mobile Terminal and a transportable re-locatable terminal. They will be connected to the SUITED Figure 2. SUITED Mobile Node Lay-Out network by the IWU that provides a local area network (LAN). In a mobile car scenario, different types of user terminals may be thought of which have to be connected to the Internet and to the onboard facilities. For a driver supporting terminal, more traffic information or guidance-oriented services must be implemented in the front with a - during drive - easy-to-use interface mode. Infotainment internet terminals for car passengers may be located for access from the back- and co- drivers seat. The LAN will be connected via the different radio segments to the IP backbone. Each segment acts as an independent entity with one (or more) gateways to other networks. The gateways can be realised by one (or more) edge routers connected to the IP backbone. Services will be provided from an application server anywhere located in the IP network. WWW browsing, ftp, email, MP3 audio multicast, video streaming, video conferencing, voice over IP, and location services are suggested for demonstration. A navigation unit will be implemented and enhance the mobile node in various ways. Support of the navigation unit to different OSI layers is advantageous. Position and attitude determination will be used for steering the satellite terminal high-gain antenna towards the satellite. Position data will help in the network layers to facilitate the inter-segment handover procedures. Finally the communication system services will be enhanced by position knowledge. During the demonstration a Java-based IP
service will guide the driver to the next park and ride parking lot and support other location based information. The segment specific entities and functionality is described in the following section for each segment separately. The forth part of the mobile node, the multiple segment radio modems with baseband part and outdoor units will be detailed partly with the corresponding segment.
Segment descriptions Satellite The satellite segment in the SUITED Demonstrator system represents the satellite network access. The proposed satellite architecture is based on a switching technology payload (OBP-SW), being the heritage of the ASSET Project Demonstrator, a previous E.C. project. The radio environment of the satellite network is based on ITALSAT satellite working in national global coverage. It guaranties a Ka-band link and a large bandwidth capability. The ESW layer 2 (logical link control) and layer 3 (call control and resource management) functionality will be implemented in the baseband modems of the Sat terminal and the Gateway Station. To emulate the switching/regenerative capabilities of ESW payload the OBP-SW will be modified and used in a laboratory environment. The satellite terminal is one of the new developments in the demonstrator context, particularly the satellite antenna technology. The satellite terminal comprises the RF front-end, the antenna and the mechanical sub-system. It will take use of a high gain antenna with a beamwidth of some degrees. In order to establish a communication link, these antenna require a precise aiming towards the satellite regardless of the vehicle position. The antenna will realise a mechanical azimuth and electronic elevation agility of the beam. An appropriate pointing, acquisition and tracking process to steer the antenna exactly towards the satellite direction will be developed, taking the channel characteristic at high frequencies, the vehicle dynamics and the need of an easy to implement realisation into account. One of the most important parts of the terminal are the antenna arrays, which consist of separate active arrays for reception at 19 GHz and transmission at 29 GHz. These arrays will be inclined with respect to the horizontal plane in order to avoid large scan losses and panel over-sizing. In relation to the radiating elements printed antenna are chosen because are the cheapest and more suitable for fabrication. The linear polarisation requirement of the ITALSAT being used for the SUITED demonstration is key to determine the kind of radiating elements to be used, and that is the reason why a dipole element has been chosen. Elementary sub arrays which need series-fed antenna arrays is the most appropriate option. GPRS The General Packet Radio Service (GPRS) is the packet oriented bearer service in GSM. It provides efficient wide area wireless access to external Packet Data Networks (PDN). The system was designed for low bit rates and bursty data. GPRS is generic with respect to the protocol used by the external PDN (the Packet Data Protocol, PDP), however for the SUITED demonstrator, the GPRS segment will be connected to an IP backbone, thus the only relevant network layer protocol will be the Internet Protocol. The GPRS segment of the SUITED demonstrator will consist of a standard GPRS system, comprised of a Mobile Termination (MT), a Base Transceiver Station (BTS), a Base Station Controller (BSC), a Serving GPRS Support Node (SGSN), a Gateway GPRS Support Node (GGSN) and a Home Location Register (HLR) containing the necessary subscriber data. At the mobile side, the system is accessed at the R - reference point. The GPRS MT interfaces with the interworking unit (IWU) of the multi-mode mobile node in order to perform several tasks: (a) The MT reports radio measurements to provide the necessary information regarding radio coverage. (b) The MT transfers and receives control information regarding the registration, session handling and the relevant procedures for inter-segment roaming and handover. (c) The MT relays any user data from and to the IWU.
At the core network side, the GGSN is connected to the IP backbone of the demonstrator at the Gi reference point; from the IP backbone point of view the GGSN appears as a standard IP router. It is assumed that the GGSN used for the demonstrations supports IPv4 only, thus IPv6 packets need to be tunnelled through the GPRS segment by means of encapsulation in IPv4 packets. Several steps are necessary to establish IP connectivity between the mobile node and the IP backbone: (1) The MT needs to perform a registration procedure that generates a database entry at the SGSN consisting of subscriber data (transferred from the HLR) and of location information of the MT. (2) A data session is set-up by the activation of a PDP context. During this procedure the GGSN allocates a PDP address (i.e. an IP address) to the MT. This public IP address is one of the GGSN's address space. (3) During the session IP packets are tunnelled from the MT to the GGSN by GPRS specific means, then routed to the destination in the IP backbone by standard IP routing means, downstream traffic is handled vice versa. UMTS The UMTS Segment: UMTS network is made of two independent parts linked with a standard Iu interface. These parts are the “UMTS Terrestrial Radio Access Network (UTRAN)”, composed of a Node B and a Radio Network Controller (RNC) , and the “UMTS Core Network (UMTS CN)” (see Fig.3). The Node B is functionally equivalent to the GSM BTS and it is Node B RNC the infrastructure entity responsible for radio transmission / reception in TE Iub Core Node B Iur one or more cells. The Radio Network Controller supports Node B signalling and data transmission RNC over the following terrestrial Uu Iub Iu interfaces: Iub to Node B, Iur Node B between RNCs, Iu to the Core Figure 3. A Simplified Function View of UMTS System Network. These interfaces are standardised by 3GPP [3GPP]. Current UMTS CN configuration (i.e. Release 99 is conceived as an evolutionary step from the GSM / GPRS network; the overall UMTS CN infrastructure can be splitted in two domains: a CircuitSwitched (CS-) domain where network elements, as MSC and GMSC, allow CN to support CSservices, and a Packet-Switched (PS-) domain where network elements, as SGSN and GGSN, allow CN to support PS-services. UMTS Segment Implementation in SUITED Demonstration: The SUITED demonstration will involve only the PS-domain of UMTS CN. The implementation of the SUITED Terminal UMTS segment in SUITED demonstration can be foreseen as depicted in Fig.4. IPTA is the IP/UMTS Inter-Segment IWU R99 I Terminal Adapter implemenUMTS Segment n ting the UMTS Uu interface t e SW Protocol Stack and the UTRAN SGSN GGSN r UMTS segment specific part IP TE UMTS MT IP TA n IP TE of the inter-segment mobility e t management protocol. In the IWU/UMTS (R) Uu Iu demonstration, the IPTA can be an ad-hoc equipped Figure 4. The Foreseeable Functional Architecture of the UMTS Personal Computer. A design Segment in SUITED Demonstration choice (see Fig. 5a) can be to implement separated Uu L2 functionality (SW part of Uu) from Uu L1 functionality (HW/RF part of Uu). In this case signalling and data transmission primitives will be exchanged through an embedded
interface between IPTA and UMTS MT. The UMTS MT implements the UMTS modem functionality. The Integration Module provides all the SW facilities (e.g. mapping functions, packets segmentation and re-assembly) in order to transparently support IP-based services over UMTS segment. Another choice (see Fig. 5b) can be the implementation of all Uu interface functionality in the UMTS MT . The UTRAN network and the Core network will be provided by the available UMTS Service Provider at the time of SUITED demonstration trials.
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Fig. 5a – A Design Choice for the UMTS IPTA in Fig. 5b – A Design Choice for the UMTS IPTA in SUITED Demonstration SUITED Demonstration W-Link The wireless link covers those areas where satellite, GPRS and UMTS are unusable or where the WLink is the cheaper solution. A typical example could be an underground parking lot or a tunnel. For the demonstrator an off-the-shelf Wireless LAN (IEEE 802.11) will be utilised. For the target system a solution optimised for roadside automotive access will be developed. Wireless LAN adaptation to the IWU will be performed by an extension to the handover procedure. Based on radio link measurements the availability of W-LAN access will be monitored and handover initiated. A responsible server will assign the actual IP address for the terminal in this segment.
Implementation approach of IWU functionality for the demonstrator In the SUITED demonstrator system the IWU will be the entity to manage handover, mobility and QoS maintaining of the mobile node. In particular the IWU (i) will provide a local LAN to the user terminals; thus, router functions will be located in a protocol stack; (ii) will access the radio networks; thus, the radio modems must be interfaced and call/session set-up protocol stacks must be implemented; (iii) will allow handover with a handover manager; (iv) will perform QoS functions; and (v) will enable the support for inter-segment user mobility. The IWU functionality will be mainly based on routing function where the route table is permanently updated with segment-specific IP addresses connected to the network interfaces via several radio modems with a call set-up layer for each segment. This allows that single nodes but also LANs consisting of several user terminals are connected to GMBS services. The IWU will also be responsible to initiate and control the inter-segment handover. It must be stressed that the terminalinitiated handover is only for the inter-segment handover. For the intra-segment handover of the subnetworks, the handover is not visible to the IP layer, and handover is only performed by the wireless radio access protocols of each segment. This approach of terminal-initiated handover bears several advantages with respect to networkinitiated handover : - the availability of all segments is known to the IWU by means of receive power feedback (for instance from beacon measurements) - the user should have the control over the segments to be chosen since this choice impacts the cost of the connection - signalling overhead as involved in network-initiated handover schemes is avoided. - route optimisation can be performed at the IWU since only few routes must be maintained in the routing table
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Segment specific information on QoS aspect (route congestion, delay, etc.) can be obtained by polling a segment-specific network entity.
Mobility of the SUITED user comprises not only mobility inside one network segment but also mobility between different network segments. Appropriate mobility functions must assure that communication is possible along the user path. For the demonstration we envisage full support of mobility in the available segments. That is, in each segment there can be a forced connection set-up (from user side) as well as roaming (from network side) in covered areas of the respective segments. Furthermore, automated seamless handover procedures will be provided in cases where a user leaves the coverage area of an segment and another segment is available. Seamless IP handover among segments faces several problems. The fact that the IP source address is visible to upper application layers, and is checked by applications, shows the necessity to maintain the same IP address during a handover. If the mobile terminal is attached to a new segment, it receives a new address from the serving node (for instance the GGSN in GPRS). If a new IP source address is detected by the application, the session is usually stopped (for instance, during a telnet session the user has to login again with user name and password, change directory etc. ...). To avoid this annoying procedure, the handover has to be seamless. This can be achieved by the use of mobile IP of IPv6 [Sol98]. Here, the first point-of-contact is a home agent that informs IP packets being addressed to the mobile node about the mobile node's actual care-of-address. The packets are now forwarded to the mobile node at remote side. The mobile node receives the care-of-address from routers called correspondent node. The Ipv6 source addresses remain permanent (home agent addresses) and are globally routable. That means that on-going application sessions are not interrupted and the handover is invisible to the user. The IWU has to perform this function for the attached terminals by DHCP (dynamic host configuration protocol) stateless autoconfiguration. The route addresses of the IWU for each segment are obtained at call set-up for each segment every time a new segment is entered. For example, in the GPRS segment the IP address of the IWU GPRS port is obtained dynamically from the GGSN. The choice of Ipv6 has several other advantages like, a huge address space, the function of the corresponding agent can be performed by the IWU, the IWU can update its routing tables by Neighbour Discovery and many more [Sol98]. Of course the GMBS terminal must be compliant with existing IPv4 core networks and servers. For this reason, smooth migration will be provided by use of Dual Stack Routers with Ipv4 and Ipv6 protocol stacks. In this way, Ipv6 services can be transported through tunnelling over Ipv4 networks. Also Ipv4 servers can be accessed. QoS support in the Suited demonstrator is based on a novel distributed protocol called GRIP (Gauge&Gate Realistic Internet Protocol) [BFR00]. The Suited implementation of this QoS support is described in more detail in [BBH+00].
References [BFR00] [BBH+00] [SOL98] [3GPP]
N. Blefari-Melazzi, M. Femminella, G. Reali: “Dynamic Bandwidth Allocation in a CircuitSwitched Satellite Network: Provision of Deterministic and Statistical QoS guarantees”, IEEE INFOCOM 2000, Tel-Aviv, Israel, March 2000. G. Bianchi, N. Blefari-Melazzi, M. Holzbock, A. Jahn: QoS and Mobility Support in a MultiSegment IP Infrastructure", IST Mobile Communications Summit, this proceedings, 2000 J. D. Solomon: “Mobile IP”, Prentice Hall, Upper Saddle River (NJ), 1998. 3GPP; TS 25.301, TS 25.410, TS 25.420, TS 25.430, TS 25.321, TS 25.322, TS 25.331
