Global Mobility and QoS Provision for Internet Services: the SUITED Solution

P. Conforto, C. Tocci, G. Losquadro Alenia Spazio

Via G.V. Bona, 85 00156 Rome (Italy)

R.E. Sheriff, P.M.L. Chan Satellite Mobile Group, University of Bradford

Bradford, West Yorkshire, UK

Abstract-The need to extend the Internet services in the new environments characterized by nomadic users, such as travelers on wheels, on water or in the air, is becoming one of the major driving forces for research activity in the telecommunication area Global mobility is more and more required by Internet users willing to access multimedia services regardless of their location. Moreover, the bed Mori quality of the services currently available over the Internet network is now becoming unsatisfactory for several classes of users.

SUITED, a project developed in the framework of Information Societies Technology (IST) program funded by the European Union, intends to provide a solution to the growing needs of Internet users requiring to a m multimedia applications irrespective of the location and with the desired QoS. It aims at Contributing to the definition and deployment of the Global Mobile Broadband System (GMBS) by focusing, in particular, on its land mobile component. The SUITED approach is based on the integration of different kinds of networks - both satellite and mobile terreshial - presenting mutually complementary features in order to create a multi- segment access network for the Intemet

This paper intends to provide an overview of the SUITED/GMBS system The main architectulal features will be described by highlighting how the different network components cooperate to form a global system. The approaches followed in designing the global mobility management and QoS support schemes will be presented along with an example of procedure - Le the inter-segment handover - showing their strict intetaction.

I. INTRODUCTION

Inmasingly, Intemet is becoming a part of our day-to-day life and a standard for Communication and software applications. However, this communication revolution has not yet completely reached the environments for nomadic users, e.g. mvelers on wheels, on water or in the air. The Intemet based mobile service is a revolutionary concept especially so when such an approach is based on high data transmission rates, ubiquitous usage, low cost for service and terminals and rapid system deployment.

SUITED (multi-segment System for broadband Ubiquitous access to InTErnet services and Demonstrator) is an ongoing project developed in the framework of Information Societies Technology (IST) program funded by the European Union. It aims at contributing to the definition and deployment of the Global Mobile Broadband System (GMBS) by focusing, in particular, on its land mobile component. The GMBS is based on an integrated satellitelterrestrial infrastructure where all the network components are fully merged with each other.

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0-7803-7133-X/00/$10.00 0 2000 IEEE

From a user perspective, the GMBS system is perceived as a single network able to support mobile and portable, QoS guaranteed, Intemet services.

The SUITED solution to reach this objective foresees that a multi-segment access network is integrated with the Internet network. This means that a generic user, provided with a suitably designed GMBS Multi-Mode Terminal (GMMT)), should be able to access his preferred Internet services regardless of his location. Moreover, such a user should have, the possibility to receive guarantees about the Quality of Service (QoS) negotiated and agreed with the network on the basis of both its specific contract profile and the network congestion status.

This paper intends to provide an overview of the SUITED/GMBS system. The main architectural features will be described by highlighting how the different network components cooperate to form a global system. The approaches followed in designing the global mobility management and QoS support schemes will be presented along with an example of procedm - i.e. the inter-segment handover - showing theii strict interaction.

11. GMBS SYSTEM AND SERVICE REQUIREMENTS An analysis of a very promising market prediction scenario based

on the provision of mobile broadband communication services for business and consumer, individual and group of users, led to focusing the SUITED activity towards a set of very well identified markt segments: i) land mobile (cars, trucks, trains) and ii) man- portable (briefcase, laptop).

Starting from the identification of the market segments of interest, and with reference to such segments, the set of service requirements of the overall system were characterized in terms of:

the service area: which has to be world-wide ranging fiom the highdensity urban areas up to the rural and open areas.

the tvpe of services: high and medium data rate for both individual (e.g. personal laptop) and collective use (e.g. trains, buses etc.) in portable and mobile scenarios.

Internet service QOS requirements: service performance parametem defined for i) guaranteed client-server, ii) real time and iii) streaming services.

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The system requirements resulting fiom the service requirements above mentioned, foresee that a multi-segment access network whose components present mutually complementary features, shall inter-work with the Internet terrestrial network As a matter of fact, the provision of broadband ubiquitous services can be assured by only envisaging a global service coverage area, which in SIllTED is obtained by exploiting the complementary service coverage capabilities of land mobile and satellite mobile networks. Such networks have also to satisfy the additional requirement of the equivalent service support features, e.g. service rate, QoS support, so as to obtain an homogeneous multi-segment access network This allows a generic user to select the most suitable segment to support the access to Internet, depending of several factors such as environment, kind of services, cost effectiveness etc.. The access segments envisaged in SUITED are listed in the following:

Ka Bmd OBP Based Satellite system: a geostationary broadband satellite segment operating at Ka-band with advanced on board processing capabilities, e.g. fast circuit switching, dynamic bandwidth allocation etc., is provided by the EuroSkyWay (ESW) system. This segment allows a wide range of terminal typologies suited for different service environments (portable and mobile, individual and collective) with proper service rates as summarised in Table 1. The satellite system is characterized by optimized inter- working functions with many terrestrial network (e.g. Intemet) including QoS, security, and service mobility support Moreover its advanced connectivity capabilities enable it to operate as both an access and a core network.

General Packt Radio Service (GPH) system: it represents the land mobile system which in the short term will provide bearer services allowing an efficient wireless access to packet data networks [l]. This segment allows both individual and collective mobile terminal typologies (the collective terminal concept being based on grouping together a set of individual terminals) with transmission data rate as summarised in the Table 1. This segment has specific network capabilities to inter-work with temesmd data packet network (e.g. Internet) including QoS, security, and service mobility support

Universal Mobile Telecommunication System (UMiT$: it represents the land mobile system, which in the long term will

provide kn-er services allowing an efficient wireless access to packet data network. The W S is considered the target solution for the GMBS temstrial component aiming at complemenmgheplacing the GPRS system. This segment allows a wide range of terminal typologies suited for different service environments (portable and mobile, individual and collective) with appropriate service rates as summarised in Table 1.

Wireless AM (WW) system: this component provides a short range connectivity to prolong the satellite link in shadowed environmerits such as indoor, outdoor near-building areas, where the satellite avidability is poor or not available at all. This segment allows mobile terminal typology with transmission data rate as summarized in the Table 1. This segment has no specific network capabilities a part access to a satellite termination node, e.g. Satellite Fixed Earth Station (FES).

The Internet network considered in the SUITED system is assumed tci be formed by Internet Autonomous Systems operated by a federation of Internet Service Providers (ISP). The term federation refers to a set of ISPs which have defined peer Service Level Agreements (SLA) to provide end-to-end QoS support allowing the provision of QoS sensitive Internet services to a common subscriber population.

The federation concept is based upon an agreement among the service providers. To satisfy the SUITED service requirements a migration path has been defined from the currently adopted SLA. This is based only on requirements in terms of bandwidth and availability categorized on a per user class, to a more complete scheme which includes QoS guarantee, e.g. transfer delay, packet loss and jitter, on either a service classes basis following the Differentiated Services model or the more advanced per flow bases in accordance with the Integrated Service model. The SLA applies to both ISP vs. Consumer interface and ISP-ISP interface, provided that both ISP belong to the federation. The full compatibility with the existing Internet infrastructure shall be maintained.

TABLE I GMBS SEGMENTS' USER TERMINAL DATA RA" COMPARISON

11/5.5/ 2 /1 Mbps

UMTS Individual Zoo0 Kbps 384 / 5 12** Kbps 144/384** Kbps 2000 Kbps

Collective N x 2000 Kbps* N x 384 /512** Kbps* N x 144/384** Kbps* N x 2000 Kbps* W-LAN Individual 11 /53 2 /1 Mbps N/A N/A***

* Collective terminal will be achieved by grouping N individual terminals. ** Planned; *** The current utilisation of the W-LAN is limited to low speed application, e.g. parking area.

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111. GMBS SYSTEM ARCHIT!XTURE

Fig. 1 schematically depicts the SUITED/GMBS system architecture. The figure shows a multi-segment access network connected to the Federated Internet network whose main features are described below.

A unique GPRS/UMTS core network characterized by a unique Home Location Register (HLR) is envisaged. The Gateway GPRS Support Node (GGSN) is physically linked to the edge router of an Internet edge sub-network towards which the IP packets traffic directed to a GMBS user exploiting the GPRSAJMTS segment is addressed.

The broadband satellite segment provided by the ESW system, is characterized by multiple points of attachment to the Internet network, each one represented by a Fixed Earth Station (FES). An appropriate Satellite Interface Unit (SIU) placed between a FES and an edge sub-network router, allows interworking between the IP protocol and the ESW specific protocols. The Satellite Network Operation Center (NOC) represents a centralized entity, which is in charge of executing synchronization, registration, authentication and connection admission control procedures. Moreover the NOC is also in charge of selecting, according to appropriate algorithms, the most suitable FES to support data traffic.

The W-LAN has to be considered as a backup access of a mobile user to the satellite segment. It aims at prolonging the satellite link in environments such as low range outdoor and indoor, where satellite link availability is very poor or not present at all. This is the reason why in Fig. 1, the W-LAN Base Station (BS) is .connected to the satellite FES and not directly to an Internet edge router (ER).

The Federated Znternet architecture is the current Internet architecture enhanced with ad hoc capabilities for the provision of end-to-end QoS support, and IP mobility. Such capabilities, in addition to those ones related to the support of IP security, have been spread among different portions of the Federated Internet in accordance to the sDecific role that each portion covers

Internet allows to interconnect a mobile IP user either with another mobile user or with a fixed IP user via QoS aware connectivity and transport services. IPv6, along with Mobile IP protocol, is assumed to be supported by the different domains composing the Federated Internet even though full compatibility with IPv4 is guaranteed.

Considering the mechanisms for the QoS control currently envisaged [2] in packet data networks (i.e. IntServ and DiffServ schemes) and with reference with the approach adopted in SUITED which will be described in the following sections, the overall system obtained by connecting the multi- segment access network to the Federated Internet can be seen as composed by two different portions:

an edge portion: adopting the Integrated Service model and consisting of the wireless segments and the edge terrestrial subnetworks.

a core portion: adopting a Differentiated Service model enhanced with a measurement-based admission control mechanism (explicitly devised in the framework of SUITED). This portion consists of one or more terrestrial subnetworks, and optionally of a satellite segment (in this case the IntServ approach applies).

The inter-operation between IntServ and enhanced- DiffServ mechanism takes place within suitably devised Gateways placed at the boundaries between the edge and the core portions of the Internet network. This hybrid Intserv/Diffserv solution devised in the SUITED system is particularly attractive since it i) solves scalability problems (DiffServ in the core portion), ii) allows to easily cope with the future evolutions of the Internet network (towards completely DiffServ or IntServ solutions) and iii) allows to set a fully IntServ compatible end-toend path in the case that only the edge portion is involved. Moreover, dynamically configurabie SLAs among ISP’s Autonomous Systems to cope with transient overload conditions have been defined. These SLA’s are controlled by Bandwidth Brokers which interact with the IP QoS support entities of each Autonomous System.

I BR=Border Router: BSS=Base Station System: CN=Correrpondent Node; CR=Core Router; ER-Edge Router; FES=Fixed Earth Station; GGSN= Gateway GPRS Support Node: GTW=Gateway; LR=Loaf Router; NOC=Network Operation Center; SGSN- Serving GPRS Support Node: SHA=Secondary Home Agent: URAN=Universal Radio Access Network:

Fig. 1. GMBS System Architecture

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In the multi-network scenario characterizing the SUITED/GMBS system, the coordination of the mechanisms envisaged for the management of the usedterminal mobility and end-to-end QoS support is realized by means of functionality located in both the terminal and suitably selected network nodes. In this context, the Terminal Inter- Working Unit (T-IWU), i.e. the terminal component grouping the SUITED specific functional entities at terminal side, plays a key role since it performs specific tasks for the management of inter-segment mobility and QoS provision on the multi-segment access network. Toward this end, the functional entities (FE) composing the different modules of the T-IWU interact with peer functional entities located in different network nodes. In particular:

the FE’s in the T-IWU Wireless Adaptation Layer (WAL) module interact with the WAL FE’s located in appropriately selected access segment nodes such as ESW FES and UMTS/GPRS GGSN. The WAL layer is inserted between the IP layer and the upper layer of the underlying wireless networks to offer a uniform interface to the Internet protocols

. requesting connectivity services to any of the SUITED wireless segments.

the FE’s in the T-IWU Enhanced Mobile IP (MIP) module interact with the FE’s located in the Secondary Home Agent (SHA) representing a new mobility agent supporting, at network side, the service which allows QoS IP connectivity to be transparent to mobility issues. The SHA is just a software module that is fully integrated with resource management and mobility support modules, and runs in suitably selected routers. Adopting an evolutionary approach for the deployment of the SHA’s, a first phase could be characterized by their integration in Border Routers (BR), while subsequent phase could envisage a hierarchical structure with SHA’s progressively added in routers closer to the edge of the network.

the FE’s in the T-IWU Registration and Authentication module interact with the FE’s in the GMBS Service Node representing a centralized entity which in addition to registration and authentication of a GMBS user, performs specific tasks for i) the GMBS user location management (e.g. it stores the access segment selected by each GMBS user at a given time) and for ii) the resource management (e.g. it triggers a satellite resource release during a terrestrial- satellite handover).

the FE’s in the T-IWU Inter-Segment Mobility Management modules interact with the FE’s in the GMBS Service Node, which should be able to access data about the congestion status of the access segment, to elaborate them and to provide to the T-IWU information useful for an efficient management of inter-segment mobility.

Finally it is worth stressing that, even though not depicted in Fig. 1, the SUITED/GMBS system envisages the use of a LEO (Low Earth Orbit) satellite component to complement the absence of the GEO (Geostationary Orbit) satellite service area of the ESW segment in the polar zones. In such an hybrid constellation architecture the LEO component collects traffic at very high data rate (in the order of 100 Mbit/s). Such a traffic is then delivered through an Inter Orbit Link

(IOL) to t k GEO component, which, in turn, delivers it to the terrestriitl networks through its FES’s.

117. GMBS MULTI-MODE TERMINAL Broadband satellite, GPRS/UMTS and W-LAN access

segments complement each other in order to allow a generic user to acwss QoS guaranteed Internet services regardless of his current location. Such a user will be provided with a GMBS Muhi-Mode Terminal (GMMT) where the satellite component is complemented by a wireless terrestrial one which is lepresented, in the first phase of the GMBS deployment, by the GPRS, while in the further evolution of the system, by the UMTS. It is also envisaged that the GMMT be provided with a W-LAN card allowing satellite intra-segment handover for low range outdoor / indoor coverage miming at prolonging the satellite connectivity in shadowed areas. Depending on several factors including coverage features, economic considerations, type of services etc., the most suitable access segment to support the IP packet transfer will be automatically or manually selected.

Fig. 2 shows the internal structure of the GMMT where the GPRS and UMTS mobile terminals (MT) have to be considered as alternative solutions for the wireless terrestrial component and where the W-LAN component is omitted just for simplicity. Table I1 lists the main blocks composing the GMMT, de:scribing the functionality they are in charge of. GMMT’s have been devised for both individual and collective use. As a matter of fact, three different typologies have been envisaged:

car version terminal (mobile): with not protuberant antenna to itvoid disturbance to the aesthetic of the car.

large vehicle version terminaI(mobi1e): to be mounted on collective means of transportation like trains, buses, tracks etc..

briefcase version terminal (portable): specifically conceived for easy transportation and fast activation of the service.

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Fig. 2. GMBS Multi-Mode Terminal Internal Structure

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A. T m i d Inter- Working Unit

The T-IWU, hosting SUITED specific entities, is involved in all the inter-segment mobility procedures defined in SUITED and it co-operates with the access segment specific mechanisms for the provision of QoS over the GMBS multi- segment access network.

The devised mobility management scheme foresees that the correct execution of SUITED specific inter-segment mobility procedures - such as segment selection, segment re-selection and inter-segment handover - is strictly related to the execution of specific Mobile IP related tasks. The T-IWU is in charge of co-ordinating these activities in order to support the global mobility of the GMMT, which roams across the different access segments used to access a MIP based Federated Internet architecture.

At the same time, the T-IWU is also responsible for the execution of specific tasks necessary for the end-to-end QoS support. The Wireless Adaptation Layer (WAL) entities, implemented in the T-IWU, are in charge of taking care of these tasks. The WAL is a transparent layer placed between the underlying network layers and the IP layer, both at the terminal and at the network side, to provide usedusers with the same QoS regardless of the access segment supporting the communication. In order to reach this objective, WAL layer entities are in charge of executing QoS related functions which complements the mechanisms for the support of QoS envisaged in each access segment. Modules in WAL are designed to handle call admission control, congestion control, classification, scheduling etc.. These modules, depending on the underlying network, are selectively enabled/disabled.

In Fig.3 the T-IWU functional block diagram is depicted. Each block represents a software module grouping similar functionality executed inside the T-IWU. The interactions among modules are shown. Details about these interactions can be found in the next sections. Six different modules are envisaged:

WAL module: it is in charge of performing functions aiming at complementing the access segment specific mechanisms in the provision of QoS. Specific actions are executed by the WAL entities over the IP flow such as: i) WAL QoS Classes Switching, ii) Traffic Shaping, iii) Traffic Policing iv) Scheduling. Communication of WAL entities at the terminal (in the T-IWU) and at the network side takes place by means of WAL signalling packets carried over the air interface within IP packets.

RSVP (Resource Reservation Protocol) Intermediate Entity module: it is the wireless segment RSVP entity which participates in the SUITED end-to-end RSVP signalling process. It is in charge of both interceptinglreconstructing RSVP messages in order to extract RSVP parameters and generating RSVP (Path and Resv) messages to avoid interruption to the end-to-end semantic of the RSVP protocol.

Enhanced Mobile IP module: it implements Mobile IP protocol functionality with enhanced capability to support QoS aware handover procedures. Functional entities in this module are in charge of assigning IP address to the TE’s connected to the T-IWU, of managing local binding table and to perform MIP registration procedures towards the Internet network.

Registration Handler module: it is in charge of retrieving from the segment specific terminals information about the segment availability and of executing, by interacting with the TE and with the GMBS Service Node (at network side), procedures for the GMBS user registration and authentication.

Location Handler module: it executes the procedures needed to locate users-terminals and to establish IP connectivity. In particular this module is in charge of performing the segment selectiodre-selection procedures and to trigger segment specific terminal for the establishment of wireless connectivity.

TABLE I1 GMMT CONSTITUTING BLOCK FUNCTIONALITY

It is a standard equipment (e.g. a PC, a laptop, etc. ) implementing Mobile IP protocol. In the vehicular version of the GMMT

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Fig. 3. T-IWU Functional Block Diagram

Handover Handler module: it is in charge of executing the different phases of the inter-segment handover procedure - i.e. handover information gathering, handover decision; handover execution.

What is worthwhile stressing is that the correct execution of these procedures requires a strict interaction among the different modules composing the T-IWU. Such interactions take place by means of suitably devised commands aiming at triggering internal routines and at passing the necessary parameters. In Fig. 3 these commands are schematically indicated by arrows linking the different modules. Bold arrows represent instead the IP packet flows.

The interworking between T-IWU and the segment specific mobile terminals (SS-MT) - i.e. the broadband satellite terminal, the wireless terrestrial (GPRS or UMTS) terminal and the W-LAN terminal - is performed through two service access points (SAP): one S A P for data transfer and one SAP to exchange commands which trigger segment specific procedures.

V. MOBILITY MANAGEMENT SCHEME

The GMBS system is obtained by integrating a multi- segment access network - consisting of several satellite/terrestrial components - with the Internet network. The overall SUITED mobility management scheme has been designed by taking into account that every GMBS segment is characterized by a suitably defined architecture and way of working. The methodological approach followed in SUITED is that the modifications to the system components should be as minimal as possible but at the same time guaranteeing an efficient co-operation among segments. The final objective is that, from a user perspective, the GMBS system is perceived as a single network able to provide “anywhere” and “anytime” Internet services with a guaranteed QoS.

In order to support global mobility, a suitable GMBS Mobility Management (MM) scheme has been devised. Considering the main architectural features of the system, the GMBS MM scheme has resulted from the harmonization of the three following levels of mobility management:

IP Mo4bility Management: based on the Mobile IP protocol implemented in the Internet network. Mobile IPv6 has been considered as baseline even though full compatibility with Mobile IPv4 is also taken into account; 0 Inter-Segment Mobility Management: devised in order to allow the GMBS user to move from one access segment to another.

Intra-Segment Mobility Management: completely handled by the entities of the access segment serving at a certain time the GMMT, as long as GMMT remains within its radio coverage.

It is worth highlighting that the class of intra-segment mobility management consists of all the procedures already designed in each access segment (i.e. ESW and GPRS/UM’TS). No modifications are envisaged for such “segment specific” procedures apart form two cases represented by: i) the intra-segment handover for low range outdoor/indoor coverage explicitly devised in the framework of the SUI.TED project to exploit the W-LAN segment as prolongation of the satellite connection in shadowedindoor areas where the satellite link is poor or not available at all; ii) the smart routing, executed at satellite connection set-up in order to select the most suitable FES; even if this procedure is considered as belonging to the mobility management scheme, it allows a meaningful improvement of the end-to-end QoS since the adopted criterion is based on the reduction of terrestrial path between the edge router connected to the FES and the correspondent node involved in the application.

A generic GMBS user provided with a GMMT is able to connect to each one of the multi-segment access network components. The GMMT can be seen, from the Internet point of view, as a mobile node 181. A node can change its point of attachment from one link to another, while still being reachable via its home address. In order to access the Internet network, the mobile node represented by the GMMT can select one of the access components which, according to the results of an appropriate algorithm, is “the most suitable one”. Since the different components of the GMBS multi- segment access network connect to edge routers belonging to Internet domains which, in the general case, are not coincident, the point of access to Internet will depend on the access network chosen to support the packet transmission. The GMMT, or to be more precise the T-IWU, will be assigned a different care of address (CoA) depending on the selected segment and a change in the access segment (inter- segment mobility) implies a change of CoA (IP mobility). At the same time, as long as the GMMT remains in the same access segment, no change in the CoA is required and the mobility is completely managed by the access segment specific entities (intra-segment mobility). To better clarify the aspect related to the CoA assignment one can consider the case of collective terminal where several TE’s - each one corresponding to a GMBS user - are connected to the same, through a I A N to the T-IWU. Each TE is assigned by the T- IWU a care of address - i.e. the COAE - having a local validity and used for the routing within the LAN internal to the GMMT. Then the T-IWU, depending on the selected access segment, receives from the SHA (controlling the Internet edge router the access segment is linked to) a

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different care of address - i.e. the COAT.^^ - used for routing purposes within the Federated Internet network.

The GMBS mobility management scheme is based on the execution of procedures belonging to three different classes: i) GMBS Generic procedures ii) GMBS Location Management procedures and iii) GMBS Handover Management procedures.

A . Generic GMBS Procedures

This class is composed by the set of Registration and Authentication procedures. Such procedures take place at two different levels:

GMBS (De-) Registration and Authentication procedure: each segment specific terminal executes a segment specific registration procedure (i.e. ESW Terminal Registration and GPRSAJMTS Attach) towards the corresponding access network. This procedure is executed both at the GMMT switching-on and when, assuming the GMMT operative, a new access segment becomes available after a period of unavailability. The successful completion of the procedure requires the existence of suitable access network radio coverage and resource availability conditions.

GMBS User (De-) Registration and Authentication procedure: it is executed, when the TE (with the GMBS Smart card inserted) is connected to the T-IWU. This procedure is executed with an exchange of messages among FE’S contained in the GMBS Smart card, in the T-IWU and in the GMBS Service Node acting as an authentication server. B. GMBS Location Mrmagement Procedura

GMBS Location Management consists of all procedures needed to locate users and terminals. Five different procedures are envisaged:

GMBS Location Update procedure: it has the twofold objective of keeping track of both the availability of each access segment (resulting from successfully/unsuccessfully completion of GMBS Registration and Authentication) and the result, for each GMBS user, of Segment Selection procedure (see next bullet) which is nested within the Location Update procedure. Such a result is stored both in the T-IWU and in the GMBS Service Node acting as a sort of home location register for GMBS users.

Segment Selection procedure: the T-IWU selects, for each GMBS user connected (general case of collective terminal), the “most suitable” access segment to support the connection to the Internet network. The selection is based on several parameters such as: i) link availability of a segment, ii) signal strength (e.g. RSSI passed to the T-IWU by the segment specific terminals), iii) GMBS user profile (e.g. user preferences) etc..

Segment Reselection procedure: the same algorithm used for Segment Selection is adopted. The only difference is that Segment Reselection is executed when the GMMT is on stand-by mode and a new segment that was previously not available becomes available, or when a new segment has to be chosen due to a change in radio link parameters, economic considerations or user preferences.

GMBS Session Establishment procedure: it establishes IP connectivity from a TE of the GMMT to the IP backbone using the segment resulting from the Segment (Re-) Selection procedure (e.g. connection set-up in the satellite system and PDP context activation in the GPRS and UMTS segments). GMBS Session Establishment is triggered in two different phases: i) during the registration or location management to obtain a CoA for the T-IWU [3] and to register it in the appropriate Internet network nodes (in this case a default best effort QoS is required for the connection) and ii) when an application is started in the TE the and an IP connection is needed to support the associated data traffic (in this case QoS guarantees are required for the connection and managed as described in the next section).

GMBS Session Release procedure: it is executed to cancel IP connectivity to the Internet network. The user can terminate a session at any time and when this procedure is initiated, all current operation would be cancelled. It can also be invoked when there has been no IP traffic for a defined time. Resources of the access segments are released by executing specific procedures while resources in the Internet portion are released due to the lack of refresh messages.

C. GMBS Handover Management GMBS Handover Management class is composed by the

Inter-Segment Handover (ISHO) procedure. It is executed in order to change access segment during an active IP session. Intra-Segment handover (i.e. the change of radio channel within the same access segment) is instead completely handled by the entities of the access segment serving at a certain time the GMMT, as long as GMMT remains within its radio coverage and no modification to the segment specific procedure is necessary.

One of the main requirements to be satisfied is that the QoS perceived by the user should not suffer significant degradations due to the change of access segment. Actually the possibility to successfully terminate an Inter-Segment Handover without QoS degradation is strictly related to several conditions: i) the current link does not have to experience an abrupt drop, ii) there should be enough available resources on the new path (consisting of a wireless and a fixed portion), iii) the overall procedure should be fast etc.. Due to the fact that these conditions are not always respected, two different kinds of ISHO can be executed:

forced handover: taking place when a sudden drop of the link layer QoS (e.g. the radio link is lost due to fading or interference) occurs. In this case the IP QoS temporary degrades until a new end-to-end QoS procedure is executed.

QoS Aware Handover: executed when “old” and ‘hew” access segments are simultaneously available for a while. The handover procedure consists of two phases: a “test and reservation” phase and then the actual handover. It allows to seamlessly switch the point of attachment to the Internet, without any drop in the IP QoS. This ISHO can be executed for both i) QoS related issues (when a new access segment more suitable for the QoS needs - e.g. in terms of bandwidth - of the user becomes available) and for ii) mobility related issues (when the GMBS terminal detects that is moving away from the current coverage area of a certain access segment

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and is entering in the coverage area of a new one - without loosing the old link).

Table I11 summarizes the main features of the approach selected in SUITED for the Inter-Segment Handover execution in terms of handover controlling, connection establishment and connection transference schemes.

VI. END-TO-END QoS SUPPORT

One of the most challenging objectives of the SUITED GMBS system is to support Internet QoS sensitive services providing the users with end-to-end QoS guarantees. When an application is started in the TE, a GMBS Session Establishment (see previous section) is triggered in order to “set-up’’ an IP connection in charge of supporting the associated data traffic. According to the main characteristics of the SUITED system architecture, in the most general case this connection involves different network portions: i) an edge portion which in turn is composed by a wireless part supported by the access segment and a fixed part supported by the edge terrestrial subnetworks and ii) a core portion involving the Internet core network.

The successful completion of a GMBS Session Establishment procedure with a guaranteed QoS requires that each subsystem involved in the support of the IP connection has enough resources. An “hybrid” approach has been developed in the framework of SUITED in order to firstly test resource availability and then to perform resource allocation in such an heterogeneous scenario. The following section is devoted to the description of such an approach.

A. Overall Approach

In the last years, work performed in the framework of Internet Engineering Task Force (IETF) standardization body to provide the Internet with QoS support capability, led to two distinct approaches: i) the Integrated Services (IntServ) model with the relevant Resource Reservation Protocol (RSVP) [4] [SI, and ii) the Dzflerentiated Services (Diflerv) model [6].

more terrestrial subnetworks, is characterized by a DiffServ model (optionally a satellite segment can be included in the core portion; in this case the IntServ approach applies). Considering that the IntServ architecture and the DiffServ architecture can be seen as complementary technologies in the pursuit of IP end-to-end QoS, the solution adopted in the SUITED system is based on the so-called hybrid IntServ- DiJServ approach. The rationale is to exploit on one side the possibility for the hosts to request quantifiable resources along end-to-end data paths, possibly provided by the IntServ architecture, and on the other side the scalability properties provided by the DiffServ architecture.

The SlJITED hybrid IntServ-DiffServ approach, conceptually shown in Fig. 4, foresees that all the wireless segments, acting as access networks, provide QoS assurances by adopting the IntServ solution, while as far as the terrestrial Internet network (Federated ISPs network) is concerned, it is envisaged that some subnetworks adopt the IntServ approach and others the DiffServ solution. More precisely, the subnetworks at the edge of the Federated ISPs network implement the RSVP signaling protocol by means of which strict QoS guarantees can be provided, whereas in the core of the Federated ISPs network, the scalable DiffServ model is adopted.

Moreover, as the DiffServ approach provides distinguished and “predictable” service levels (“better than best effort” traffk) but does not provide strict end-to-end QoS assurances, in the core portion of the Federated ISPs network, in order to improve the user-perceived QoS performance, an innovative solution, called Gauge&Gate Reservation with Independent Probing (GRIP) [7], is implemented. This solution foresees that each router supports a Per Hop Behaviour (PHB) defined in terms of service priority between two classes of packets: i) the active packets, which correspond to the information packets, with higher service priority and ii) the probing packets, with lower service priority, which, generated within the Gazewqs (see Fig. I), are delivered in order to determine if the considered

As already stated in the previous sections, the SUITED/GMBS system architecture is composed of two main parts: i) an edge portion consisting of wireless segments and edge terrestrial subnetworks where an IntServ model is adopted and ii) a core portion which, consisting of one or

connection can be admitted to the network while maintaining the QoS OF the already admitted connections and of the new one. If the assumption that all the traffic entering the network is regulated by Dual Leaky Buckets (DLB) is made,’ the GRIP technique allows to provide hard guarantees to the admitted connections; so that QoS performances are improved with respect to a simple DiffServ network.

TABLE 111

Handover Criteria

Handover Controlling Scheme

Connection Establishment Scheme

Connection Transference Scheme

- Approach

Mobile Controlled Handover

-

Fonvard Handover

Signalling Diversity

INTER-SEGMENT HANOVER FEATURES

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Federated BPs Fig. 4: SUITED hybrid IntServ-DiffServ approach for IP QoS

support

It is important to note that other Internet network topologies, envisaging either an extension of the DiffServ core portion to the entire Internet or a full IntServ architecture, represent only particular cases which do not prevent the utilization of the above mentioned approach. The reference topology shown in Fig. 4 is the most general case which allows to define an Internet architecture suitable to evolve towards all the predictable QoS architectural solutions.

Moreover, the proposed Internet topology, by means of the edge subnetworks implementing the RSVP protocol, provides the opportunity to set a fully IntServ-compatible end-to-end communication path (e.g. from a Mobile Node to a Wired Host) by-passing the Federated ISPs core network. A typical scenario where a fully IntServ-compatible end-to-end communication path can be set is represented by the Ka band OBP-based satellite segment acting as access network to the terrestrial Internet network and implementing smart routing functionality. For example in the case of mobile originated communications between a GMMT (i.e. mobile node) and a wired host, when the satellite segment is selected as supporting network, smart routing functionality will allow to select the FES directly connected to the edge router of the edge subnetwork to which the wired host is connected to so that the terrestrial path is minimized and it takes place only within the edge subnetwork implementing the RSVP protocol.

B.

The establishment of an IP connectivity with end-to-end QoS guarantees, between one of the E ' s in the GMMT and a wired host' requires that an RSVP session is activated for each direction of communication (i.e. TE towards wired host and wired host towards TE).

The followed approach foresees that, in the deployment of an RSVP session, both the wireless segments and the DiffServ core portion of the Federated ISPs network play the role of "network elements" in the IntServ framework and are used as components of an overall end-to-end IntServ QoS solution. To be more precise, the access portion comprised between the terminal and network WAL layers, as well as the core portion comprised between two Gateways are seen, from the RSVP protocol perspective, as simple RSVP-capable routers. This implies that WAL and Gateway entities

QoS-related SUITED Architecture and Protocols

' Similar considerations can be extended to the case where the connection is between two TE's in two different GMMT's.

participate to the RSVP session execution by updating the Adpec parameters in the RSVP Path message in order to take into account the features of the network portion they take care of, and by evaluating if in the same portion the resource required by the RSVP Resv message are available. Anyway, it is worth stressing that all the RSVP messages exchanged

. between the TE and the wired host during a RSVP session 'evolve transparently on the core portion of the Federated ISPs network where, as the RSVP is designed to operate correctly through non-RSVP cloud, the non-RSVP capable routers do not affect these messages.

Such an approach allows to overcome the criticality associated with the proposed scenario where heterogeneous systems adopting both Integrated and Differentiated Service models, coexist. Such criticality are represented by: i) the IntServ operation over DiffServ network along with the relevant service mapping and ii) the mapping between the InServIRSVP requests and the underlying capabilities of the SUITED wireless segments.

The first issue is solved within the Gateways which, placed at the interface between the DiffServ region and the IntServ region of the Federated ISP network, are in charge of executing, at the reception of an RSVP Resv message, the mapping of an IntServ/RSVP request into a DiffServ GRIP class and then activating the GRIP Distributed Admission Control mechanism which aims at evaluating if adequate network resources are actually available to support the requested QoS.

A solution to the latter issues is instead represented by the introduction of the WAL layer at both the terminal and network side. The WAL entities, at the reception of the RSVP Resv message, intercepted and reconstructed by the RSVP Intermediate Entity module2, executes the mapping of RSVP parameters onto access segment specific parameters and triggers the access segment connection admission control mechanism to verify that available resources exist and, in such a case, to reserve them.

VII. INTER-SEGMENT HANDOVER

In this section, the QoS Aware ISHO procedure is shortly described. Details about the procedure are not provided due to length constraints of the present work. Such a description has just to be considered as an example of how the mechanisms envisaged in the context of mobility management and QoS support described above are implemented in the practical case of a procedure execution.

As depicted in Fig. 5 , referring to the case of terrestrial- satellite handover (but the same considerations apply also for the opposite direction), the ISHO consists of three main phases. During the first two phases - i.e. handover initiation and handover decision - the T-IWU retrieves appropriate information from both the segment specific terminals (e.g. radio link conditions, access segment congestion status etc.) and the TE (e.g. user profile related information). Moreover the final decision about the need to trigger an ISHO procedure is made.

' The WAL is characterised by the same intemal structure at both the terminal and network side.

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Fig. 5: Inter-Segment Handover (Terrestrial to Satellite) Procedure

During the handover execution phase the change of the access segment supporting the data traffic is executed. Initially a satellite connection set-up procedure with a default “best effort” QoS is triggered in order to assign to the T-IWU the new CoA (i.e. COAT-m) corresponding to the new point of attachment to the Internet network. Then, over this satellite connection, information concerning the SHA serving the new domain are provided to the T-IWU by the edge router the satellite FES is connected to. By comparing this information with the information related to the old access segment, the T- IWU decides if the QoS aware can go on and, in the affirmative case, it activates the RSVP sessions. These sessions are executed to both i) verify if along the new path enough resources are present so that the same QoS provided by the old access segment can keep on being guaranteed and ii) to reserve these resources.

Fig. 6 depicts how this takes place. In particular it is shown the way the different portions of the system interact, according to the hybrid IntServDiffServ approach, to provide an end-to-end QoS. Flow diagrams are self-explanatory. What is worth pointing out is the role of SHA and of T-IWU which are in charge of executing, depending on the direction of RSVP session, the duplication or the worst case selection of RSVP messages (details can be found in [3]). The handover execution phase terminates with the registration of the new COAT-^ in the SHA and with the release of old segment resources.

VIII. CONCLUSIONS In this paper an overview of the GMBS system developed

in the framework of SUITED project has been provided. The system architecture has been described highlighting the main innovative solutions at both network and terminal level. The introduction of these new functionalities has resulted from the approaches adopted in the design of a global mobility

management and QoS support schemes. The Inter-Segment Hanover procedure has been described as exemplifying case of application of such schemes.

I , . , Fig. 6: RSVP Session Execution

ACKNOWLEDGMENT

This work has been partially funded by the European Union in the IST Program under the SUITED project. The authors wish to thank the members of the SUITED Consortium for their contribution.

REFERENCES [ 11 3GPP 23.06Ov3.3.0, Release 1999. [2] X.Xiao, L.M.Ni: “Internet QoS: a big picture”, ZEEE

Network, MachiApril 1999, pag.8-18.

[3] A. De Carolis, “QoS-Aware Handover for Mobile 1P: Secondary Home Agent”, Internet Draft (dra9- decarolis-qoshandover-vl00. at), November 2000.

[4] R. Braden, L Zhang, S. Berson, S . Herzog, S . Jamin, ‘‘Resource Re SerVation Protocol (RSVP) - Version 1 Functional Specification”, RFC2205, September 1997.

[5] J: Wroclawsky, “The use of RSVP with IETF Integrated Services”, RFC2210, September 1997.

[6] K. Nichols, V. Jacobson, L. Zhang, “ A two-bit Differentiated Services Architecture for the Internet”, RFC 2683, July 1999.

[7] G. Bianchi, N. Blefari-Melazzi, M. Femminella, “A Migration Path to provide End-to-End QoS over Stateless Networks by Means of a Probing-driven Admission Control”, Internet Draft ( d r d - bianchi-blefari-end-to-end-QoS-OO.txt), December 2000

[8] D. B. Johnson and C. Perkins; “Mobilility Support in IPv6”; Internet Draft, draft-ietf-mobileip-ipv6-12.txt, 27 April 2000, Work in Progress.

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