MIPSHOP Working Group T. Melia Internet-Draft NEC Expires: December 20, 2006 J. Korhonen TeliaSonera R. Aguiar IT S. Sreemanthula Nokia V. Gupta Intel June 18, 2006 Network initiated handovers problem statement draft-melia-mipshop-niho-ps-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 20, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This is a first document describing the rational about network Melia, et al. Expires December 20, 2006 [Page 1] Internet-Draft Network Initiated Handovers June 2006 support for decision making and execution of handovers. Starting from existing technologies and considering new trends from mobile operators, we draw potential deployment scenarios and derive a set of associated functionalities. These functionalities and associated assumptions are listed in the document. Application areas for network initiated handovers are then illustrated specifying a set of goals and non-goals to be addressed in a future version. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Overview of the problem . . . . . . . . . . . . . . . . . 4 1.2. Definition of Network Initiated Handover . . . . . . . . . 6 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.1. Administrative domain wise considerations . . . . . . . . 10 3.2. Technology wise considerations . . . . . . . . . . . . . . 13 3.3. NIHO Application Areas . . . . . . . . . . . . . . . . . . 13 4. General Requirements . . . . . . . . . . . . . . . . . . . . . 14 4.1. Network assistance with global mobility management . . . . 14 4.2. Network assistance with local mobility management . . . . 15 4.3. Inter-domain handovers . . . . . . . . . . . . . . . . . . 15 5. Framework and Functional Components . . . . . . . . . . . . . 16 6. NIHO with IEEE 802.21 . . . . . . . . . . . . . . . . . . . . 17 6.1. Network Selection . . . . . . . . . . . . . . . . . . . . 18 6.2. Handover Control . . . . . . . . . . . . . . . . . . . . . 20 7. Design considerations . . . . . . . . . . . . . . . . . . . . 22 7.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 22 7.2. Non-goals . . . . . . . . . . . . . . . . . . . . . . . . 23 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 9. Security Considerations . . . . . . . . . . . . . . . . . . . 23 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24 11.1. Normative References . . . . . . . . . . . . . . . . . . . 24 11.2. Informative References . . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26 Intellectual Property and Copyright Statements . . . . . . . . . . 28 Melia, et al. Expires December 20, 2006 [Page 2] Internet-Draft Network Initiated Handovers June 2006 1. Introduction Standards based IP mobility enabling protocols such as Mobile IP [RFC3344] [RFC3775], HIP [RFC4423], MOBIKE [RFC4555] and SCTP with address management support [I-D.ietf-tsvwg-addip-sctp] [mSCTP] are all mobile node centric: the handover related decision making is mostly done in the mobile node only. Public mobile network access is gaining increased diversity, both in terms of the types of access technologies, in terms of the diversity of the offer (with clear separation of roles between access and service providers), and in terms of the size of that offer. This diversity has been compounded by increasing number of multi-access capable terminals equipped with IP technologies, and of operator- provided multi-technology mobile connection software. Overall, this creates a complex environment, where the mobile terminal might not have enough information or even the possibility to make an intelligent handover decision (as is often the case of operator- provided software). In fact, handover decisions and inherent target network selection is not necessarily anymore based on access availability but further depends on policies and commercial roaming arrangements on access network level, access provider level and service provider level. Furthermore, the information required for an intelligent target network selection might change periodically with such a frequency that maintaining all knowledge (and intelligence) in the mobile node might not be viable anymore. Some of this information is only available for network elements. However, none of the mobility protocols above referred have capabilities or procedures to significantly involve network side entities in intelligent handover decision making. A good example of the type of information only available at network entities is radio resource usage. It is expected that radio resource usage optimization will be a task of major relevance in future wireless network environments, with millions of users roaming between access routers across multiple technologies (i.e. 802.11, 802.16, e.g. [draft-cui-mobopts-hcf-wlan-00]). This task can resort to mechanisms and algorithms able to gather measurements and force terminal handovers between cells. The handover can be issued according to predefined mobility patterns, mechanisms for intelligent flow balancing, mechanisms for optimized resource re-allocation, mechanisms for user-traffic performance optimization, or mechanisms for user profiling (e.g. access rights) - all of them ultimately leading to better service to be provided to the users, with additional increased resource usage for the network operator. For these expectations to be realized, network control capabilities are required to instruct specific terminals to perform handovers, either between access points or between different technologies. Melia, et al. Expires December 20, 2006 [Page 3] Internet-Draft Network Initiated Handovers June 2006 Going even further, handovers over administrative domains i.e. inter- domain handovers are not explicitly prohibited with the existing IP mobility enabling protocols, but at the same time these protocols are not designed or optimized for such cases in any way. Also a general network controlled triggering mechanism for a handover from an administrative domain to another does not currently exists. Some initial work in this direction is introduced in [I-D.nakhjiri-aaa- hokey-ps]. The document describes how EAP keying material combined with hierarchical schemes could enhance roaming scenarios. This problem statement document describes various scenarios where handovers could be network initiated, even over administrative domains, presenting some ideas on functional components and protocol operations required to fulfill the above requirements. This, however, will further require a new handover triggering mechanism that originates from entities located in the network side, and is acted upon by entities on the mobile node. These network side entities may also be located in other administrative domains than the one the mobile node is currently visiting. In Section 6 an example is provided on how IEEE 802.21 can implement the required signalling. Finally, this document also discusses and lists a set of goals and non-goals for further work that aims at enabling network initiated and assisted handovers, even over administrative domains. 1.1. Overview of the problem Current standard mobility protocols provide Internet connectivity to mobile nodes roaming from one access router to another. To reduce handover latency, extensions to mobility protocols are available (e.g. [RFC4068], [RFC4140]). Although some of the approaches support network initiation of the handover procedure, none of them takes into consideration the existence of a backend combining mobility, resource management and roaming scenarios. In this document we present a list of requirements according to which this characteristic is not adequate, and the protocols need to be extended with handover initiation by the network. In [I-D.mohan-nflm-proto] a network based fast handoff based mechanism is proposed. The scenario considers a mobility anchor point controlling several access routers. On behalf of the mobile node the serving access routers updates routes and binding caches allowing the traffic to be routed to the new location. The trigger comes from the mobile node. There has been work started in the last months to split local mobility from global mobility. Local mobility in the access network mainly optimizes control signaling by reducing the need to update the home/visited network about user mobility. Local mobility can be Melia, et al. Expires December 20, 2006 [Page 4] Internet-Draft Network Initiated Handovers June 2006 handled independently of the global mobility. As an example, in [I-D.ietf-netlmm-nohost-ps] a list of requirements is given in order to identify desired functionalities. In the proposed document mobile devices are able to move across an access network by reducing to the minimum the complexity in the terminal itself. Therefore the network is requested to handle user mobility by means of appropriate schemes. In this last proposal the trigger for host route update executed by the network (which is actually an handover execution) is originating in the terminal. By means of layer two mechanisms (e.g. link up or link down in IEEE 802.11) or layer three mechanisms (e.g. Neighbor discovery) the terminal is detected on the new link and the route to the host updated for packet delivery. Thus, the whole network intervention is simply the support of route update. The real trigger/decision comes, once again, from the terminal. Following the split between global mobility domain and local mobility domain, [3GPP.23.882] provides additional scenarios where the network controlled and initiated handovers are also considered. The key point is that is the initiator of the handover procedure is mainly the serving radio access network, in contrast to the above explained methods. More short term deployable solutions have also been proposed. In [draft-cui-mobopts-hcf-wlan-00] a WLAN scenario is presented and extensions to Mobile IPv6 messages are introduced to support an handover control function for handover decision. [I-D.melia-mobopts- niho-fmip] proposes a fast mobile IP based approach where both mobile terminal and network initiated handovers are possible. Network initiated handovers are combined with advanced admission control mechanisms and potential race conditions are solved by appropriate protocol operations. Additional ways of providing information to the network enabling handover decisions are presented in [I-D.korhonen-mobopts-link- characteristics-ps]. Methods are provided to enable Mobile IPv6 and Mobile IPv4 capable nodes to exchange link information with the HA and any CN. However, to generalize the approach, the link characteristics exchange should happen during the handover process, since the Binding Update handshake conclude the handover process, when (bicasted) packets are already routed to the new Care-of Address (nCoA). For instance, specialized traffic shapers could be installed in the ARs to adapt a selected MT-CN flow to the specific underlying wireless/wire line access technology. Or (re)INVITE messages could be issued, in 3GPP multimedia communications. In the above mentioned examples we note an increasing involvement of the network in the mobility management problem. The aim of this Melia, et al. Expires December 20, 2006 [Page 5] Internet-Draft Network Initiated Handovers June 2006 document is to identify common lines to existing solutions and to derive the set of functionalities required to perform this kind of handovers. 1.2. Definition of Network Initiated Handover As mentioned above, available solutions rely on the existence of triggers generated in the mobile terminal and conveyed to respective network components which then will take adequate actions. However, recently we have been assisting to new different trends [3GPP.23.882] where the serving radio access network issue handover preparation/ execution by means of different events gathered at different levels (e.g. radio conditions, QoS requirements). We therefore are required to define use cases in which the network takes active decisions without requiring the terminal to perform expensive operations. In this document by network initiated handover we identify the action taken in the network to initiate the handover based on: o Link events originated in the mobile node. In this case the terminal sends link events to the network. The event might be generated because of radio variations, powering on of new network devices or new service requirements. In all cases the measurement action is required to be performed also in critical conditions. For instance speed dynamic effects on terminal mobility have to be taken into account as well as variable round trip time. Positioning of the decision function is a critical issue. o Events generated in the network for e.g. resource management reasons. It should be noted that the Mobile Operator can initiate an handover procedure also based on location and current services. Multihoming scenarios can also be considered as part of the overall optimization problem. The action described is similar to exiting behavior of current GSM/3G systems. Measurements are requested by the network and performed by the mobile terminal. The results of these measurements, combined with current QoS conditions and other user profile requirements, could result in the execution of an handover. Measurements are a key issue, for instance, in indoor wireless LANs environments, affected also by different user mobility patterns. 1.3. Terminology In this document, several words are used to signify the requirements of the specification. These words are often capitalized. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", Melia, et al. Expires December 20, 2006 [Page 6] Internet-Draft Network Initiated Handovers June 2006 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. This document frequently uses the following terms: NAP Network Access Provider. A network operator that provides direct IP packet forwarding to and from the end host. MRMH Mobility and Roaming Manager, usually located at home network. The Roaming Manager part is aware of administrative relationships between the home network, various ISPs and possibly with various NAPs as well. MRMV Mobility and Roaming Manager located at visited network. MRMV is generally a local representative of MRMH in the visited network. MSP Mobility Service provider. A service provider that provides IP mobility services. In order to obtain such service, the mobile node must be authenticated and prove authorization to obtain the service. NIHO Network initiated and assisted handover. AN Access Network composed of several access routers. Identified as well as local mobility domain. IS Information services provide an information query mechanism for mobile or network nodes to obtain information about specific networks and their capabilities, as explained in IEEE 802.21. The information service plays a critical role in the network selection at the mobile node or in the network. Melia, et al. Expires December 20, 2006 [Page 7] Internet-Draft Network Initiated Handovers June 2006 ES Event service is a protocol exchange mechanism between network nodes to inform of recently happened or impending change in link or network status information, as explained in IEEE 802.21. The event notification can originate either from a mobile node or a node in the network. Receipt and processing of an event belonging to the ES may generate a reaction in the receiving node (e.g. trigger IP layer mobility). CS Command service is a protocol exchange mechanism between network nodes to instruct the recipient network nodes to execute a specific function, as explained in IEEE 802.21. Execution of a command service at the mobile node or a node in the network may result in loss of current link connectivity and/or change in the network point of attachment. Receipt and processing of a command belonging to the CS generates an expected response in the receiving node (e.g. create a new link layer connection, disconnect a link layer connection, etc). MIHF Media independent handover function (MIHF)is a shim layer in the mobility management protocol stack of the mobile nodes or network element that provide media independent or inter-technology mobility, specifically handovers (e.g. as defined in IEEE 802.21). MIHF can implement one or more of IS, ES and CS. MM A mobility management entity (MM) implements network selection and handover decision algorithms and utilizes mobility signaling protocols and other protocols that aid in mobility functions. MM functionality should utilize MIHF. 2. Assumptions This document has some few fundamental assumptions concerning the general networking environment and network initiated handovers. The rest of the document makes use of the following assumptions: Melia, et al. Expires December 20, 2006 [Page 8] Internet-Draft Network Initiated Handovers June 2006 o Reusing existing security mechanisms -- The mobile node should reuse the existing security associations it created while establishing the initial access to the network and its mobility service provider (MSP). Applicable scenarios are identified in [I-D.nakhjiri-aaa-hokey-ps]. o All mobile nodes within the scope of this document are expected to support at least one (potentially modified) existing or future IP mobility enabling protocol. However, if a MN does not support network initiated handover functionality, the network might refuse to give service to that MN. o All mobile nodes, correspondent nodes and mobility management nodes are not expected to understand or support network initiated and assisted handovers. When either peer lacks support for network initiated and assisted handover triggering and signaling the peer supporting these features must fall back to the base IP mobility protocol mechanisms. o The network initiated handover concept relies on the presence of a centralized functional entity. This entity controls the network side and implement the intelligence to select nodes and targets access routers. It is not in the scope of this document to specify the policies that will be implemented. o To provide adequate scalable support, distributed functions are required to support the above functional entity. This gives more flexibility to the overall architecture and protocol operation. o It is envisioned the presence of multi wireless access, such as 802.11, 802.16, UMTS, forming an heterogeneous composition of macro and micro cells. The network support SHOULD leverage user mobility focusing on vertical handovers. Hence, the terminal does not need to apply filtering criteria to select a target network (which could be an expensive operation in heterogeneous environments). Solutions similar to the 3GPP interface between the Home Subscriber Server (HSS) and any application server, for downloading of filtering criteria at registration time, could be applied here - being the HSS a AAA backend, and the application server the MRMV/MRMH. o Performing network initiated handover has the main implication that the network has first to assess the terminal view of the network. Signal level evaluation is a important matter when considering user mobility. This is typically very well handled with terminal initiated handovers and automatic evaluation of signal level. Different methods apply to different technologies. Melia, et al. Expires December 20, 2006 [Page 9] Internet-Draft Network Initiated Handovers June 2006 o Neighborhood discovery relates to the above assumption when neighborhood scanning is requested from the network. It is expected these functions to be available on the terminal side. 3. Scenarios This section describes few usage scenarios where the network initiated and assisted handover could be justified and deployed. Also we list here initial requirements for the general network initiated and assisted handover functionality. 3.1. Administrative domain wise considerations Figure 1 and Figure 2 introduce two different possible scenarios. In the first case one single administrative scenario is described. The Mobile Operator (MO) owns both the ISPs and the NAPs. It provides as well mobility services. This is the simplest case where security restrictions are less relevant. The MO has therefore full control. Figure 2 illustrates another example architecture, where the signaling and triggering relationship between home network domain, ISP domain, NAP domain and the mobile node domain are shown. Each of previously mentioned technical domains may belong to a different administrative domain. Melia, et al. Expires December 20, 2006 [Page 10] Internet-Draft Network Initiated Handovers June 2006 .--. <-++ Mobile Operator _( `. |S Home Network ( MRMH ) |i ( ` . ) ) |n `--(___.-' |g ^ |l NIHO / triggers signaling |e / | .--. V |a _( `. |d ( ISP ) |m ( ` . ) ) |i `--(___.-' |n ^ ^ |i / NIHO \ triggers signaling |s / \ |t V V |r .--. .--. |a _( `. _( `. |t ( NAP ) ( NAP ) |i ( ` . ) ) ( ` . ) ) |v `--(___.-' `--(___.-' |e | | | ) |d V ) ) NIHO trigger & signaling |o ____ ) ) ) |m |____|_Y |a /_____/ |i |n <--+ Figure 1: An overall architecture for network initiated and assisted handover. Single Administrative domain Melia, et al. Expires December 20, 2006 [Page 11] Internet-Draft Network Initiated Handovers June 2006 .--. <-+ _( `. | Home Network ( MRMH ) | ( ` . ) ) | `--(___.-' | D ^ ^ | o NIHO / triggers \ signaling | m / \ | a .--. V V .--. | i _( `. NIHO triggers _( `. | n <--- ( ISP A ) <---------------> ( ISP B ) ---> | ( ` . ) ) signaling ( ` . ) ) | `--(___.-' `--(___.-' | 1 ^ ^ ^ ^ ^ | / NIHO \ \ triggers / \ signaling | / \ \ / \ <-+ V V \ V V | D .--. .--. \ .--. .--. | o _( `. _( `. V _( `. _( `. | m ( NAP A ) ( NAP A ) ( NAP B ) ( NAP C ) | a ( ` . ) ) ( ` . ) ) ( ` . ) ) ( ` . ) ) | i `--(___.-' `--(___.-' `--(___.-' `--(___.-' | n | 2 | ) <-+ V ) ) NIHO trigger & signaling | D ____ ) ) ) | o |____|_Y | m /_____/ | 3 <-+ Figure 2: An overall architecture for network initiated and assisted handovers over multiple administrative domains The architecture in Figure 2 has been divided into three different domains. Domain 1 represents the home network or the services provider that owns and manages user's subscription. It eventually contains Internet Service Providers (ISPs) as well. Domain 2 contains Network Access Providers (NAPs). A NAP provides access services for one or more Home Networks. Domain 3 is the mobile node and may also represent the end user. The end user does not need to have any relationship with NAPs or ISPs in order the gain access to the services accessible through the home network. Along these lines [I-D.nakhjiri-aaa-hokey-ps] proposes a distributed Melia, et al. Expires December 20, 2006 [Page 12] Internet-Draft Network Initiated Handovers June 2006 system interacting with a AAA backend. The introduced key Holder element acting as a AAA client for the AAA server COULD -- in this scenario -- be implemented at the boundaries of each single cloud, belonging either to a NAP or to an ISP. SAs presented in the document can be mapped to the mechanisms depicted in Figure 2. 3.2. Technology wise considerations In the previous section we provided an high level view of network relationships between the different entities involved. Figure 1 and Figure 2 describes a general network view without describing which technologies are supported and where optimizations take place. It is clear MO will have different environment deployments. In the following we give some examples on how technologies can be mapped to NAP implementing several Access Networks and creating potentially complex overlapping of macro and micro cells scenarios. +=====================================+ = UMTS MACROCELL = = = = = = +--------------------------+ = = | 802.16 CELL | = = | | = = | 802.11 | = = | oo xx @@ | = = | o o x x @ @ | = = | o ox x@ @ | = = | o xo @x @ | = = | o ox x@ @ | = = | o o x x @ @ | = = | oo xx @@ | = = +--------------------------+ = = = +=====================================+ Figure 3: An example of overlapping Micro and Micro cells These cells can be actually owned by the same or by different NAPs. In any case, the MRMH will collect information about all these cells (as visible from the terminal) across the different domains. 3.3. NIHO Application Areas We foresee three possible application areas that are listed and briefly described in the following section. Each application area uses the NIHO triggering and signaling as part of their tasks. Melia, et al. Expires December 20, 2006 [Page 13] Internet-Draft Network Initiated Handovers June 2006 o Application for Mobility Reasons In this context user mobility is handled from the network side assisted by the mobile terminal. This particular application requires network capabilities to request measurements and evaluate technologies specific link conditions. The approach can be considered similar to what current mobile networks do. The most challenging aspect is the freshness of the reported information. Particular scenarios, such as WLAN, could impose stringent requirements. o Application for Resource Optimization Reasons As mentioned before, network optimization is a delicate issue when resources are scarce, especially in the wireless access network. Standards that able to support natively quality of services capabilities are becoming mature to be sold on the market (802.11e). A cross layer design is therefore required to convey link layer specific information to decision points located in the access network. These decision points can combine standard admission control mechanisms with advanced NIHO functionalities, resulting in a new dimension of mobility management (i.e. more terminals can be granted with network access). o Application for inter-domain handover Handovers that cause the mobile to cross administrative domain borders involve inter-domain signaling. One example of this kind of scenario is when the mobile node moves between different NAPs under the same ISP or when even the ISP changes as a result of the movement. In both of these scenarios the NIHO signaling could be used to prepare the new target domain (either ISP and/or NAP) for the arriving mobile node. Especially if the handover was initiated from the network side, the handover initiating network could help distributing all security, policies, billing and service related material cross administrative domains before the mobile node arrives. 4. General Requirements 4.1. Network assistance with global mobility management This aspect is particularly important for inter-domain handovers. The network will provide information required for speeding the handover. This information is related with two types of data: i) Melia, et al. Expires December 20, 2006 [Page 14] Internet-Draft Network Initiated Handovers June 2006 operator related data, such as billing information, policies, etc..; ii) terminal related data, such as security associations. 4.2. Network assistance with local mobility management This aspect is particularly important for resource optimization and intra-domain handovers. The network will provide information to lead (or impose) the mobile terminal to associate to specific access points. 4.3. Inter-domain handovers Inter-domain handovers and inter-domain handover preparations require entities involved in the triggering and signaling to have security relationships in place between them. For example the MRMH located at the home network (service provider) must have a security relationship between all ISPs the end user can use for accessing services. Also ISPs must have security relationship between all NAPs the end user can use for accessing services. However, NAPs do no necessarily need to have any relationship with the actual service provider. And going even further the end user does not need to have any relationship between NAPs and ISPs, only with the service provider. It is service provider's duty to grant access to services via any NAP and ISP the service provider has a direct or indirect pre-setup relationship. In addition to obvious security and AAA related challenges between the service operator, ISPs and NAPs, the general when and why to trigger a handover towards the mobile node is not a trivial task. The service provider's home network needs to have rather exact and up to date knowledge of the mobile node's current topological location and surrounding network conditions before it should trigger a handover on the mobile node due same policy decision at the home network. Example of such policy decisions is when a mobile node roams (after a handover) to a target network the home network does not want the end user to use for the active service set the end user has requested. As a consequence the home network MRMH triggers a new handover suggestion towards the mobile node indicating a more feasible target network (based on the information the mobile node has previously signaled to the home network MRMH). Another home network policy decision could be distributing roaming end users in visited networks based on some distribution criteria. Such criteria could, for example, be directing voice users to ISP A network, where as data service users to ISP B network. A simpler rationale can be simply redirecting the user to the mobile network whose charges are lower at that time. The IEEE 802.21 Information service, for instance, could help in this process. The whole policy mechanism in the home network MRMH is a complex Melia, et al. Expires December 20, 2006 [Page 15] Internet-Draft Network Initiated Handovers June 2006 issue and out of scope of this document. However, the home network MRMH needs information of its end users from dedicated NAP and ISP entities. These information aggregating entities are discussed in more detail in Section 5. 5. Framework and Functional Components In the previous sections the need to implement decision points in the network as well as measurements and aggregation functions has been justified. We can draw on the previous considerations to derive a framework view. o Policy Decision Point This could be on the MRMH or MRML depending on the case. In the IEEE 802.21 draft event and command services for network initiated handovers are associated with the Point of Services (PoS). In [3GPP.23.882]the access nnetwork takes decision about initiating the handover. Generalizing the approach we call this functional entity Policy Decision Point. It is envisioned to place the PDP at the edge of a localized mobility domain or in the home network. In case of a ISP or NAP the PDP needs to have in place a SA with the home domain of the mobile user as specified in [I-D.nakhjiri- aaa-hokey-ps]. The PDP can trigger/enforce a horizontal or vertical handover, depending on the user device. It is also envisioned the possibility to detect multihomed devices as part of the resource management process. o Policy Enforcement Point Enforcement points participating to the signalling, and contributing to the scalable approach, are necessary. PEP are mainly access routers terminating different kind of transport protocols (e.g. ICMPv6 over the last hop and SCTP between network components). o Measurements Functions Measurements functions are critical components considering the overall procedure, being collectively distributed between the access routers and the mobile terminals. As mentioned before, the network, prior to any action, needs to assess the terminal view (i.e. link signal quality) of the access network. Currently none of the available protocols can support such feature. Options could be specified, though scalability and security have to be Melia, et al. Expires December 20, 2006 [Page 16] Internet-Draft Network Initiated Handovers June 2006 deeply studied. It is well understood measurements are requested from the network to the mobile terminal. o Aggregators Components To increase the overall scalability of the procedure aggregation points could be installed in different places in the access networks. Aggregated reports to PDP about QoS conditions, service availability, network load help in the decision process contributing to build an overall picture of the access network conditions. reports could be periodic or event based. In either cases information of several hundreds of mobile terminals could be carried. Generally, the PDP acts upon events and combines required actions with user profiles. Depending on billing rates, user preferences action A instead of action B can be issued. The transfer and definition of such profiles is not in scope of this document. 6. NIHO with IEEE 802.21 IS, ES and CS as defined in IEEE 802.21 WG can be used as enablers for network initiated and assisted handover scenarios between different access technologies. The discussion of such scenarios in IP networks can easily raise a long list of questions regarding the feasibility of e.g. sending information in real-time between the mobile node and the MM, and of sending commands between the MM and the mobile node. The issue considered in these cases is typically the delay that can be introduced by the transport and that may make the overall handover delay quite considerable. This document does not discuss these specific issues, and does not argue in favor or against such issues. However, in order to identify some of the scenarios of applicability for IS, ES and CS for network-controlled handover, we need to consider the following classification of handovers. There are two main reasons to perform a handover: 1. degradation of current link/connection quality: the quality of the link is degrading and it is necessary to perform a handover to avoid losing the current connection; 2. "opportunistic" handover: due to a set of events and based on specific policies, it is preferable to move the communication to another link. In order to support inter-technology network-controlled handovers the first case, the delay between the moment the handover decision is made and the moment the command to perform the handover is received Melia, et al. Expires December 20, 2006 [Page 17] Internet-Draft Network Initiated Handovers June 2006 by the mobile node needs to be considered carefully. However, for "opportunistic" handover the impact of such delay is less significant, since the mobile node is not having any degradation over the current link, and the handover will be performed because the network has policies indicating that it is preferable to move to the new link. One motivation for performing opportunistic network-controlled handover is load sharing, in scenarios where a network exercises tight control of various wireless link technologies to distribute the load of communications according to network policies. The network may perform a network-controlled handover decision in at least two steps. 1. Network selection, and 2. Handover control. The two steps are described in the following sections 6.1. Network Selection Network selection is a process of selecting a favorable network for a mobile node to transfer or handover the ongoing services to the selected network. The selected network may be a different link technology from the previous one. It may also be possible that the mobile node, after handover, may not experience exactly the same level of QoS as the current link due to this network selection. But, in general, it may result in some user benefit in one way or another e.g. cost savings, higher bandwidth etc. MM in the network may have access to subscriber profile, contracts, and device capabilities to make use of the network selection algorithms for a certain subscriber or mobile node. Figure 4 shows a simple network selection procedure with the help of the mobile node. This example call flow diagram employs remote event services and information services. Remote command services are not used in this particular example, however, they can also be useful in the network selection mechanisms under certain scenarios. E.g. depending on user geographical location, the network may command the mobile node to perform a scan for a specific 802.11 network and report the results that can be used in the network selection process. In the scenario shown, the mobile node initially performs a registration or attachment to the network on any link, e.g. 3GPP network. The MM and the mobile node are able to discover each other in the same or following step. MM may then register for specific Melia, et al. Expires December 20, 2006 [Page 18] Internet-Draft Network Initiated Handovers June 2006 remote event services, e.g. ES-link-detect by sending a registration request and filter information for both 802.16 and 802.11 networks. The mobile node accepts the request with a positive reply. From time to time, the mobile node may receive broadcast information from 802.11 and 802.16 networks. In this scenario, the 802.16 broadcast is received and a link-detect is sent by the 802.16 MAC layer to the MIHF. The MIHF translates this to an ES-link-detect message to the MIHF implementing ES in the network (collocated in the MM) with the basic network information received in the broadcast. The MM requests for more information about the network via the IS query to another MIHF implementing IS to check the suitability of the detected network due to roaming agreements. The MM decides that this particular 802.16 network is not a favorable network and takes no action. The mobile node also takes no action and does not report the detection of same network more than once. At a later time, the mobile node may receive beacon information from 802.11 AP and the MAC layer in the mobile node reports the to the MIHF along with the SSID information. The MIHF provides this information to the MM in the network. The MM may perform an IS query based on the SSID information and determines that this SSID belongs to a favorable network. The network selection process, thereby, is completed. Melia, et al. Expires December 20, 2006 [Page 19] Internet-Draft Network Initiated Handovers June 2006 Mobile Node |----------------------| +--------+ +-------+ +-------+ +------+ +------+ +------+ |MIHF(ES)| | Link | | MM | | IS | |802.16| |802.11| | | | Layers| | | | | | | | | +--------+ +-------+ +-------+ +------+ +------+ +------+ | | | | | | +------------------------------+ | | | | Discovery & Registration| | | | +------------------------------+ | | | | 1.ES-reg-req | | | | |<========================| | | | | 2.ES-reg-resp | | | | |========================>| | | | ~ ~ ~ ~ ~ | |3.DL-burst| | | | | 4.link-detect|<--------------------------------| | |<-------------| | | | | | 5.ES-link-detect | | | | |========================>|6.IS-query| | | | | |--------->| | | | | +-------------+ | | | | | |not favorable| | | | | | +-------------+ | | | ~ ~ ~ ~ ~ ~ | |7.Beacon | | | | |8.link-detect |<-------------------------------------------| |<-------------| | | | | | 9.ES-link-detect | | | | |========================>|10.IS-query | | | | |--------->| | | | | +-----------+ | | | | | | favorable | | | | | | +-----------+ | | | | | | | | | +--------+ +-------+ +-------+ +------+ +------+ +------+ |----------------------| Legend: ===== ES over current link Figure 4: Network Selection in Network 6.2. Handover Control Handover control procedure follows a network selection process as explained in the previous section. The following scenario in Figure 5 shows a network-controlled handover procedure with fast MIP handover signaling [RFC4068]. Here, the MM in the network utilizes MIHF implementing CS and generates a link switch command with CS- Melia, et al. Expires December 20, 2006 [Page 20] Internet-Draft Network Initiated Handovers June 2006 switch-req to the mobile node. The parameters in the message may include that a make-before-break mechanism is to be performed along with the target link information e.g. 802.11 network as shown from the network selection procedure earlier. The MIHF indicates the Mobile IP function of the impending link switch along with new link information. The Mobile IP functionality, If necessary, i.e., it does not have a valid Access Router Tuple-Info [RFC4068], it sends a Proxy Router Solicitation (PrRtrSol) with the new link information (e.g. MAC address of AP) and the Proxy Router Advertisement (PrRtrAdv) provides the relevant L3 information for the mobile node to use on the new link. The MIHF in the mobile node executes the command by sending an "associate" request to the 802.11 MAC which will perform all necessary L2 association and authentication procedures for the new link. For completeness, steps 3 and 4 in Figure 5 can take place in parallel to steps 3 and 4. A link-up indication is sent to the interested parties including Mobile IP functionality. Mobile IP sends a Fast Binding Update (FBU) to the old FA over the old link so that old FA could switch (tunnel) the packets to the new FA. The mobile node now is able to receive packets from new FA that are tunneled from old FA. At a later time, the mobile node performs an Mobile IP update procedure to update the binding in the HA and reroute the tunnels directly from HA to the new FA in the new network corresponding to the 802.11 link. Once the traffic uses the new link, the MIHF releases the old link by sending a request to that MAC layer, here the 3GPP radio link. A CS-switch- resp is sent back to the MM upon completion of the command. The following signaling flow shows how the network controlled handoff can work with fast MIP handover signaling [RFC4068]. It shows a make-before-break mechanism, so that the mobile node sends the FBU on the old link after the setup of the new link to minimize the latency due to L2 association and authentication procedures. For completeness, steps 3 and 4 in Figure 5 can take place in parallel to steps 2 and 3. Melia, et al. Expires December 20, 2006 [Page 21] Internet-Draft Network Initiated Handovers June 2006 Mobile Node |--------------------------| +----+ +-----+ +-------+ +----+ +------+ +----+ +----+ |MIP | |MIHF | | Link | | MM | |802.11| | AR | | HA | | | |(CS) | | Layers| | | | | | | | | +----+ +-----+ +-------+ +----+ +------+ +----+ +----+ | | | | | | | | | | +-----------+ | | | | | | | Network | | | | | | | | Selection | | | | | | | +-----------+ | | | | | 1.CS-switch-req | | | | 2.switch-ind|<====================| | | | |<-------| 3. PrRtrSol | | | | |=================================================>| | | | 4. PrRtrAdv | | | |<=================================================| | | |3.associate| | | | | | |---------->| 4.L2 Association | | | 5.link-up | |<---------------->| | | |<--------| | | | | | | | 6. FBU | | | | |=================================================>| | +----------------------------------------------------------------+ | Mobile IP update procedure over new link | +----------------------------------------------------------------+ | 7.release | | | | | | |---------->| | | | | | | 8.CS-switch-resp | | | | | |>>>>>>>>>>>>>>>>>>>>| | | | | | | | | | | +----+ +-----+ +-----+ +-----+ +----+ +------+ +---+ |------------------------------| Legend: ===== over current link, >>>>over new link Figure 5: Network-Controlled Handover Procedure 7. Design considerations 7.1. Goals This section lists the general goals for the network initiated and assisted handovers framework design. The network initiated and assisted handover framework solution MUST fulfill all the goals listed below: Melia, et al. Expires December 20, 2006 [Page 22] Internet-Draft Network Initiated Handovers June 2006 G1 Independent of the IP mobility management mechanism -- The network initiated and assisted handover triggering mechanism must be independent of any particular IP mobility management protocol. However, there might be mappings/implementations of the triggering mechanism to a specific IP mobility protocol such as Mobile IP. G2 Work over administrative domains e.g. in inter-domain handover cases or when a multi-homed host is attached to multiple ISPs. G3 Provide similar degree of security as existing with the current security protocols. 7.2. Non-goals This section lists issues that are considered as strictly out of scope of this problem statement and requirements document. o Designing a new security framework in order to enable network initiated and assisted handover triggering. o Initial bootstrapping problem -- The mechanism to gain the initial access to some network is out of scope of. 8. IANA Considerations This document does not define any new name spaces to be managed by IANA. This document does not either reserve any new numbers or names under any existing name space managed by IANA. 9. Security Considerations At the time of writing this document, the threats to network initiated and assisted IP handovers in general, and signaling and triggering between the mobile node and corresponding network entities are not widely understood, particularly in the inter-domain handover case when the signaling and triggering takes place across administrative domains. Part of the experimental task in preparing network initiated and assisted handovers (even across administrative domains) for eventual standards track will be to better characterize threats to network initiated and assisted handovers, inter-domain triggering and signaling, and design specific mechanisms to counter them. Work along these lines already started. [I-D.nakhjiri-aaa-hokey-ps] presents initial ideas how the problems described in this document could be solved. Melia, et al. Expires December 20, 2006 [Page 23] Internet-Draft Network Initiated Handovers June 2006 10. Acknowledgments The authors would like to thank Rajeev Koodli for his valuable comments and suggestions. 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 11.2. Informative References [RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August 2002. [RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol (HIP) Architecture", RFC 4423, May 2006. [RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)", RFC 4555, June 2006. [I-D.ietf-mobike-design] Kivinen, T. and H. Tschofenig, "Design of the MOBIKE Protocol", draft-ietf-mobike-design-03 (work in progress), July 2005. [I-D.ietf-tsvwg-addip-sctp] Stewart, R., "Stream Control Transmission Protocol (SCTP) Dynamic Address Reconfiguration", draft-ietf-tsvwg-addip-sctp-12 (work in progress), June 2005. [mSCTP] Xing, W., Karl, H., and A. Wolisz, "M-SCTP: Design and prototypical implementation of an end-to-end mobility concept", October 2002. [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. [draft-cui-mobopts-hcf-wlan-00] Cui, Y., "Handover Control Function Based Handover for Mobile IPv6", draft-cui-mobopts-hcf-wlan-00 (work in progress), July 2005. [draft-daniel-mip-link-characteristic-02] Melia, et al. Expires December 20, 2006 [Page 24] Internet-Draft Network Initiated Handovers June 2006 Park, S., "Link Characteristics Information for Mobile IP", draft-daniel-mip-link-characteristic-02 (work in progress), June 2005. [3GPP.23.882] 3GPP, "3GPP system architecture evolution (SAE): Report on technical options and conclusions", 3GPP TR 23.882 0.10.1, February 2006. [I-D.nakhjiri-aaa-hokey-ps] Nakhjiri, M., "AAA based Keying for Wireless Handovers: Problem Statement", draft-nakhjiri-aaa-hokey-ps-01 (work in progress), January 2006. [I-D.vidya-mipshop-handover-keys-aaa] Narayanan, V., "Handover Keys Using AAA", draft-vidya-mipshop-handover-keys-aaa-01 (work in progress), October 2005. [I-D.ietf-netlmm-nohost-ps] Kempf, J., "Problem Statement for IP Local Mobility", draft-ietf-netlmm-nohost-ps-00 (work in progress), February 2006. [I-D.mohan-nflm-proto] Parthasarathy, M., "Network-based Fast Handovers for Local Mobility (NFLM)", draft-mohan-nflm-proto-00 (work in progress), October 2005. [RFC4140] Soliman, H., Castelluccia, C., El Malki, K., and L. Bellier, "Hierarchical Mobile IPv6 Mobility Management (HMIPv6)", RFC 4140, August 2005. [RFC4068] Koodli, R., "Fast Handovers for Mobile IPv6", RFC 4068, July 2005. [I-D.melia-mobopts-niho-fmip] Melia, T., "Network initiated handover in fast mobile IPv6", draft-melia-mobopts-niho-fmip-01 (work in progress), July 2005. [I-D.korhonen-mobopts-link-characteristics-ps] Korhonen, J., "Link Characteristic Information for IP Mobility Problem Statement", draft-korhonen-mobopts-link-characteristics-ps-00 (work in progress), October 2005. Melia, et al. Expires December 20, 2006 [Page 25] Internet-Draft Network Initiated Handovers June 2006 Authors' Addresses Telemaco Melia NEC Europe Network Laboratories Kufuerstenanlage 36 Heidelberg 69115 Germany Phone: +49 6221 90511 42 Email: telemaco.melia@netlab.nec.de Jouni Korhonen TeliaSonera Corporation. P.O.Box 970 FIN-00051 Sonera FINLAND Phone: +358 40 534 4455 Email: jouni.korhonen@teliasonera.com Rui L.A. Aguiar Instituto de Telecomunicacoes Universidade de Aveiro Aveiro 3810 Portugal Phone: +351 234 377900 Email: ruilaa@det.ua.pt Srinivas Sreemanthula Nokia 6000 Connection Dr. Irving, Texas 75039 USA Phone: +1 972 894 4356 Email: Srinivas.Sreemanthula@nokia.com Melia, et al. Expires December 20, 2006 [Page 26] Internet-Draft Network Initiated Handovers June 2006 Vivek Gupta Intel Corporation 2111, NE 25 Avenue Hillsboro, OR 97124 USA Phone: +1 503 712 1754 Email: vivek.g.gupta@intel.com Melia, et al. Expires December 20, 2006 [Page 27] Internet-Draft Network Initiated Handovers June 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Melia, et al. Expires December 20, 2006 [Page 28]