IETF Next Steps in Signaling S. Lee, Ed. Internet-Draft Samsung AIT Expires: January 19, 2006 S. Jeong HUFS H. Tschofenig Siemens AG X. Fu Univ. of Goettingen J. Manner Univ. of Helsinki July 18, 2005 Applicability Statement of NSIS Protocols in Mobile Environments draft-ietf-nsis-applicability-mobility-signaling-02.txt 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 January 19, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract The mobility of an IP-based node affects routing paths, and as a Lee, et al. Expires January 19, 2006 [Page 1] Internet-Draft NSIS Signaling in Mobility July 2005 result, can have a significant effect on the protocol operation and state management. This draft discusses the effects mobility can cause to the NSIS protocols, and how the protocols operate in different scenarios, and together with mobility management protocols. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Requirements Notation and Terminology . . . . . . . . . . . . 4 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 7 3.1 General problems . . . . . . . . . . . . . . . . . . . . . 7 3.2 Mobility-Related Issues with NSIS Protocols . . . . . . . 9 3.2.1 NTLP-Specific Problems . . . . . . . . . . . . . . . . 10 3.2.2 QoS-NSLP-Specific Problems . . . . . . . . . . . . . . 10 3.2.3 NAT/FW NSLP-Specific Problems . . . . . . . . . . . . 11 3.2.4 Common problems related to both NTLP and NSLP . . . . 12 4. Basic Operations for Mobility Support . . . . . . . . . . . . 13 4.1 Route changes caused by mobility . . . . . . . . . . . . . 13 4.2 CRN discovery . . . . . . . . . . . . . . . . . . . . . . 15 4.2.1 Possible approaches for CRN discovery . . . . . . . . 15 4.2.2 The identifiers for CRN discovery . . . . . . . . . . 16 4.2.3 The procedures of CRN discovery . . . . . . . . . . . 18 4.3 Path update . . . . . . . . . . . . . . . . . . . . . . . 19 4.3.1 State setup and update . . . . . . . . . . . . . . . . 20 4.3.2 State teardown . . . . . . . . . . . . . . . . . . . . 22 5. Applicability Statement . . . . . . . . . . . . . . . . . . . 23 5.1 Support for macro mobility-based scenarios . . . . . . . . 23 5.1.1 Implications to Mobile IP-related scenarios . . . . . 24 5.1.1.1 Mobile IPv4-specific issues . . . . . . . . . . . 25 5.1.1.2 Mobile IPv6-specific issues . . . . . . . . . . . 27 5.2 NSIS operations in multihomed mobile environments . . . . 29 5.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . 29 5.2.2 Examples of NTLP/NSLP operations . . . . . . . . . . . 30 5.3 QoS performance considerations in mobility scenarios . . . 31 5.4 Support for Ping-Pong type handover . . . . . . . . . . . 33 5.5 Peer failure scenarios . . . . . . . . . . . . . . . . . . 34 6. Security Considerations . . . . . . . . . . . . . . . . . . . 36 6.1 MN as data sender . . . . . . . . . . . . . . . . . . . . 36 6.1.1 MN is authorizing entity . . . . . . . . . . . . . . . 36 6.1.2 CN is authorizing entity . . . . . . . . . . . . . . . 39 6.1.2.1 CN asks MN to trigger action (on behalf of the CN) . . . . . . . . . . . . . . . . . . . . . . . 39 6.1.2.2 CN uses installed state to route message backwards . . . . . . . . . . . . . . . . . . . . 40 6.1.2.3 MN and CN are authorized . . . . . . . . . . . . . 41 6.1.3 CN as data sender . . . . . . . . . . . . . . . . . . 41 6.1.3.1 CN is authorizing entity . . . . . . . . . . . . . 42 6.1.3.2 MN is authorizing entity . . . . . . . . . . . . . 43 Lee, et al. Expires January 19, 2006 [Page 2] Internet-Draft NSIS Signaling in Mobility July 2005 6.1.4 Multi-homing Scenarios . . . . . . . . . . . . . . . . 43 6.1.4.1 MN as data sender . . . . . . . . . . . . . . . . 43 6.1.4.2 CN as data sender . . . . . . . . . . . . . . . . 44 6.1.5 Proxy Scenario . . . . . . . . . . . . . . . . . . . . 45 6.1.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . 45 7. Change History . . . . . . . . . . . . . . . . . . . . . . . . 46 7.1 Changes from -00 version . . . . . . . . . . . . . . . . . 46 7.2 Changes from -01 version . . . . . . . . . . . . . . . . . 47 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 48 8.1 Normative References . . . . . . . . . . . . . . . . . . . 48 8.2 Informative References . . . . . . . . . . . . . . . . . . 48 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 49 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 51 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 51 A. Generic Route Changes . . . . . . . . . . . . . . . . . . . . 51 Intellectual Property and Copyright Statements . . . . . . . . 53 Lee, et al. Expires January 19, 2006 [Page 3] Internet-Draft NSIS Signaling in Mobility July 2005 1. Introduction The mobility of IP-based nodes incurs route changes, usually at the edge of the network. Route changes may also be caused by reasons other than mobility, such as routing protocol adaptation in response to varying network conditions (load sharing, load balancing, etc), or host multi-homing. Macro mobility also involves the change of the mobile node's IP addresses. Since IP addresses are usually part of flow identifiers, the change of IP addresses implies the change of flow identifiers. Local mobility usually does not cause the change of the global IP addresses, but affects the routing paths within the local access network [3]. In multi-homed mobile networks, mobile nodes (MNs) can have an access to multiple interfaces and obtains multiple addresses (e.g, CoAs and HoAs). It enables the MN to choose most appropriate interface or address according to application (or flow) types or network conditions in homogeneous/heterogeneous environments. The Multihoming helps alleviate various problems caused by wirless bottleneck and mobility events, scarce resources and frequent handovers for examples. NSIS protocol suit consists of two layers: NSIS Transport Layer Protocol (NTLP) and the NSIS Signaling Layer Protocol (NSLP). The NTLP is an application independent protocol which transports service- related information between nodes in a network, and each specific service has its own NSLP protocol (e.g., QoS-NSLP, NAT/FW-NSLP, etc.). The goals of this draft are to present the effects of mobility on the NTLP/NSLPs and to provide guides on how such NSIS protocols should work in various mobility scenarios including multihoming. Most of all, this draft mainly discusses the operations of the NSIS protocols in very basic mobility scenarios (e.g., macro mobility management protocols such as Mobile IPv4 and Mobile IPv6), including support for multi-homing. More complex scenarios and issues on interworking with various mobility-related protocols, such as Seamoby and local mobility management protocols, are left for future work. 2. Requirements Notation and Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [1]. The terminology in this draft is based on [2] and [3]. In addition, Lee, et al. Expires January 19, 2006 [Page 4] Internet-Draft NSIS Signaling in Mobility July 2005 the following terms are used. Note that in this draft, a generic route change casued by regular IP routing is referred to as a 'route change', and especially, the route change caused by mobility is referred to as 'mobility' like [4]. (1) Downstream The direction from a data sender towards the data receiver. (2) Upstream The direction from a data receiver towards the data sender. (3) Crossover Node (CRN) A Crossover Node is a node that for a given function is a merging point of two or more paths along which states are installed. The CRN may not necessarily be a physical route splitting point. There exist different types of logical (but not necessarily physical) CRNs depending on the signaling states, flow directions, mobility management types, and the routing infrastructure: From the perspective of NSIS state (i.e., NSLP and NTLP state), the types of CRN can be classified as follows. NSLP CRN: a signaling application-aware node in the network where the corresponding signaling flows begin to merge or split after a route change or mobility. If multiple signalling application sessions refer to the same data flow, the NSLP CRN after a route change may be different for each NSLP involved NTLP CRN: an NTLP-aware network node where multiple NTLP state begin to merge or split after a route change or mobility. NSIS CRN: A node is called an NSIS CRN if it an NSLP or an NTLP CRN. The types of CRN can be further classified according to their location in the network, with respect to the path from data sender to data receiver, as follows. In the mobility scenarios, there are two different types of merging points in the network according to the direction of signaling flows followed by data flows as shown in Figure 1 of Section 4.1, where we assume that the MN is the data sender. Lee, et al. Expires January 19, 2006 [Page 5] Internet-Draft NSIS Signaling in Mobility July 2005 Upstream CRN (UCRN): the node closest to the data sender from which the state information in the direction from data receiver to data sender begins to diverge after a handover. Downstream CRN (DCRN): the node closest to the data sender from which the state information in the direction from the data sender to the data receiver begins to converge after a handover. In general, the DCRN and the UCRN may be different due to the asymmetric characteristics of routing although the data receiver is the same. In case of the route changes, the path change of signaling flows results in forming a chain of two CRNs regardless of the direction of signaling flows followed by data flows as shown in Figure 14 of Appendix A. The CRN chain is referred to as a divergence-convergence pair: Divergent-convergent UCRN pair: a chain of the nodes at which the state information towards the data sender begins to diverge and to converge after a route changes. Divergent-convergent DCRN pair: a chain of the nodes at which the state information towards the data receiver begins to diverge and to converge after a route changes. Routing CRN is the node where the old and new paths (rather physically) merge using regular IP routing. For example, the merging points caused by mobility management protocols are a kind of Routing CRN. Depending on the location of nodes, the routing CRN may not be equal to the NSLP CRN or NTLP CRN. (4) Path Update Path Update is the procedure for the re-establishment of NSIS state on the new path, the teardown of NSIS state on the old path, and the update of NSIS state on the common path due to the mobility. The Path Update procedure is used to address mobility for the affected flows. Upstream Path Update: Path Update for the upstream signaling flow which is initiated by an upstream signaling initiator. If the MN is a data sender, the Path Update is initiated by an NI on the common path (e.g., a CN, an HA, or an MAP). Lee, et al. Expires January 19, 2006 [Page 6] Internet-Draft NSIS Signaling in Mobility July 2005 Downstream Path Update: Path Update for the downstream signaling flow which is triggered by a downstream signaling initiator. If the MN is a data sender, the Path Update is triggered by an NI on the new path (e.g., an MN, a mobility agent, or an AR). In case of route changes except for mobility, the update of NSIS state on the common path is not required because the flow identifiers do not change, which limits the scope of the required NSIS signaling . Especially, in mobility scenarios, if the NSIS signaling interacts with local mobility management (LMM) protocols (e.g., HMIPv6), the Path Update can be localized within the access network. (5) Dead Peer Discovery (DPD) The procedure for finding a dead NSIS peer due to a link/node failure or due to an MN moving away. 3. Problem Statement IP mobility in its simplest form only includes route changes. This section identifies problems caused by mobility, which may have a significant impact on the operations of NSIS protocols. 3.1 General problems The general problems caused by mobility are as follows. (1) Change of route and possibly change of the MN IP address Topology changes might lead to path changes for data packets sent to or from the MN and may lead to an IP address change of the MN. (2) Latency of route changes The change of route and IP addresses in mobile environments is typically much faster and more frequent than traditional route changes caused by node or link failure. (3) Explicit routes Path-coupled signaling protocols usually expect the data traffic to follow the same path as the signaling , but the data traffic sometimes traverses a path different from the path of signaling traffic due to the adaptation of routing tables to varying network Lee, et al. Expires January 19, 2006 [Page 7] Internet-Draft NSIS Signaling in Mobility July 2005 conditions and to techniques such as load balancing, load sharing and mobility. For example, Mobile IP may use the routing headers to define explicit routes, which diverts the traffic from an expected path. (4) IP-in-IP encapsulation Mobility protocols may use IP-in-IP encapsulation on the segment of the end-to-end path for routing traffic from the CN to the MN, and vice versa. Encapsulation makes any attempt to identify and filter data traffic belonging to, for example, a QoS reservation. Moreover, encapsulation of data traffic may lead to changes in the routing paths since the source and the destination IP addresses of the inner header differ from those of the outer header. If the signaling packets are encapsulated it might be necessary to perform a separate signaling exchange for the tunneled region. (5) Ping-pong type handover Signaling protocols should remove state quickly along the old path to limit the waste of resources. However, in a ping-pong type handover, the MN returns to the previous AR after staying with the new AR only for a short while, so the prompt removal of state along the old path would cause the state to be re-established soon again, and therefore it adds overhead. (6) Upstream Path Update vs. Downstream Path Update Since the upstream and downstream paths are likely not to be the same, the upstream and downstream CRNs may not coincide, either. Therefore, the Path Update needs to be handled independently for the upstream and the downstream, including the discovery of upstream and downstream CRNs. (7) State identification problem A mobility event typically causes the addresses of corresponding flow endpoints to change, and thus it is desirable that the signaling application state is independent of the underlying flows to avoid the state being re-installed completely. Therefore, the identifiers for the session and the flow must not be dependent on each other. This makes it possible to associate the session identifier with the signaling application and with different data flows. (8) Double reservation problem Since the state on the old path (and the common path) still Lee, et al. Expires January 19, 2006 [Page 8] Internet-Draft NSIS Signaling in Mobility July 2005 remains as it is after re-establishing the state along the new path due to mobility (or route changes), the double reservation problem occurs. Although the state on the old path will be deleted automatically based on the soft state timeout, the refresh timer value may be quite long (e.g., 30s as a default value in RSVP). This problem might result in the waste of resources and lead to failure of other reservations (due to lack of resources). Note, however, that the degree of impact depends on the frequency of path changes and also on the chosen refresh interval. (9) End-to-end signaling problem The mobility may change the flow identifier, and the change of flow identifier requires state update along the entire path to reflect the physical location of the MN, resulting in the end-to- end signaling. This also incurs a long state setup delay and increased signaling overhead, which affects overall performance of signaling protocols. The long state setup delay may ultimately give rise to the service blackout or degradation of multimedia services in mobile environments. (10) Identification of the crossover node When a handover at the edge of network has happened, in the typical case, only a part of the end-to-end path used by the data packets changes. In this situation, the CRN plays a central role in managing the establishment of the new signaling application state, and removing any useless state. (11) Key exchange When a handover happens, nodes on the new path must be able to verify the signaling messages of the MN, and vice versa. For example, if signaling messages are encrypted on a hop-by-hop basis, the new access router should be able to continue the message encryption and decryption with the incoming MN. (12) Authorization Issues The Path Update procedure may be initiated by the MN, the CN, or even nodes within the network (e.g., MAP in HMIP). This Path Update on behalf of the MN raises authorization issues about the entity that is allowed to make these state modifications. 3.2 Mobility-Related Issues with NSIS Protocols Considering the issues identified in Section 3.1, this section discusses the concerns that arise for the NSIS protocols. Lee, et al. Expires January 19, 2006 [Page 9] Internet-Draft NSIS Signaling in Mobility July 2005 3.2.1 NTLP-Specific Problems (1) Interfaces between Mobile IP and NSIS protocols To continue to support the existing NSIS state for a session, the NTLP protocol should be immediately involved in the CRN discovery and Path Update after a mobility event (e.g., handover) happens. Therefore, is might be necessary to develop a Mobile IP-specific API or reuse/extend existing APIs from Mobile IP (if applicable) in NSIS to learn quickly about mobility events at the NTLP and at the NSLP layer. Should a common triggering mechanism between routing and NSIS processes be defined to monitor the operations of other mobility protocols and trigger a relevant event accordingly? (2) Localized Path Update The Path Update needs to be localized to improve the performance metrics, such as signaling setup delay, resource utilization.Afew issues on the interaction between the micro mobility management protocols and the NSIS protocol suite arise. For example, when interacting with HMIP, how is the Path Update performed with scoped signaling messages within the access network under the control of MAP? 3.2.2 QoS-NSLP-Specific Problems (1) Invalid NR problem If MN is receiver, it might be determined as the last QNE (QNR) on the signaling path [5]. If MN, however, moves into a new network attachment point, the old AR can not forward QoS-NSLP messages any futher to the MN (QNR). In this case, the old AR's QoS-NSLP may trigger an error message to indicate that the last node fails or is truncated. This error message forwarded to QNI may mistakenly cause the removal of the state on the existing paths. It is called the 'invalid NR problem' [12]. This situation would not be desirable. (2) Optimal refresh timer value for mobile environments IIn the situation where handover occurs frequently, the maintenance of signaling state on the old path for a long time is not necessary. The QoS-NSLP needs to choose appropriate refresh intervals depending on the network environments (e.g., access network, or core network) or access technologies (e.g., 3G, IEEE 802.16, WLAN, etc.). (3) Athorization-related issues with teardown Lee, et al. Expires January 19, 2006 [Page 10] Internet-Draft NSIS Signaling in Mobility July 2005 When tearing down the obsolete state after CRN discovery, can the teardown message be sent toward the opposite direction to the state initiating node? This leads to an authorization problem because a node which does not initiate signaling for establishing the NSLP state may delete the state. Please note that this authorization problem heavily depends on the design of the NSLP. (4) Peering agreement issue In the inter-domain handover scenarios, how is the peering agreement established for aggregate reservation and authorization to support individual sessions? (5) Dead peer discovery A dead peer can occur either because a link or a network node failed, or because the MN moved away without informing QoS-NSLP (it is recommended to link mobility and NSIS signaling such that this does not happen). How can dead peers be detected in a fast and efficient manner? 3.2.3 NAT/FW NSLP-Specific Problems The NAT/FW-NSLP establishes and maintains firewall pinholes and NAT bindings at NAT/FW-NSLP nodes along the data path [10]. With regard to mobility, a few issues need to be considered: (1) Update of firewall rules and NAT bindings When an IP address changes by mobility, firewall rules and/or NAT bindings become invalid because the established flow identifer refers to a non-existent flow, which effectively blocks the end host's traffic. For example, without updating the firewall pinhole by an NSIS-aware data sender (located behind a firewall), data packets with a new source IP address are most likely dropped at the firewall. if a data receiver (located behind a NAT) changes its IP address, incoming packets are rewritten at the NAT and forwarded to the wrong IP address. The impact of a out-dated flow identifier is more servere in the NAT/FW case than in QoS case. In the latter case, the impact is only that the flow experiences best-effort treatment for a limited period of time (until the flow identifier is updated again. [sung- hyuck]Here, do we need to add why the impact in the NAT/FW is more severe although some detailed description exists above? (2) Re-use of NAT/FW-NSLP's old state AAlthough NSIS state can be released by applying the soft state Lee, et al. Expires January 19, 2006 [Page 11] Internet-Draft NSIS Signaling in Mobility July 2005 Principle after a mobility event, states (such as firewall pinholes) can be left in place for some time. Since the NAT/ FW-NSLP aims to install pinholes (and NAT bindings), it is still possible to re-use this installed state although a mobile node roams to a new location. This means that another host can send data through a firewall without any prior NSIS NAT/FW signaling because of the previous state which is not yet expired. This might be a problem since an unauthorized end host might be able to inject packets through the firewall for a limited period of time. Deleting state along the old path might help to limit this problem. However, this problem exists anyway due to the capability of IP spoofing as identified in [7], and the main problem is the missing data origin authentication (i.e., missing cryptographic protection of data traffic). 3.2.4 Common problems related to both NTLP and NSLP (1) CRN discovery-related issues Which layer should be responsible for the CRN discovery, NTLP (GIMPS) or NSLP (QoS-NSLP or NAT/FW-NSLP)? Although the QoS-NSLP, for example, can detect the change of signaling path and discover the CRN by keeping track of SII, the CRN discovery at the NTLP layer may also be preferred to at the QoS-NSLP. Concerning CRN discovery, the pros and cons of two mechanisms on CRN discovery dependent on NSIS layers (i.e., either NTLP or NSLP) need to be identified. (2) CRN discovery and Path Update on the IP-tunneling path Mobile IP uses tunneling mechanisms to forward data packets among end hosts. Traversing over the tunnel, NSIS signaling messages are transparent on the tunneling path due to the change of flow's addresses. In case of interworking with IP-tunneling of Mobile IP, CRNs can be discovered on the tunneling path. It enables NSIS protocols to perform Path Update procedure over the IP-tunnel. In this case, GIMPS needs to cope with the change of Message Routing Information (MRI) for the CRN discovery on the tunnel. Also, NSLP signaling needs to determine when to remove the tunneling segment on the signaling path and/or how to tear down he state via interworking with the IP-tunneling operation. (3) Issues on API between NTLP and NSLP In mobile environments, mobility-related information for Path Update can be exchanged through the API specified in [2]. Based on the information, the involved NSLP can initiate Path Update by sending necessary signaling messages through the API. However, Lee, et al. Expires January 19, 2006 [Page 12] Internet-Draft NSIS Signaling in Mobility July 2005 what information should be sent from GIMPS to an NSLP to inform of the route changes needs to be discussed further. The details on the API can be an implementation issue. (4) Multihoming-related issues An NSIS-aware node (e.g., Mobile Node (MN)) may be multihomed. NSIS signaling can be used in such multihomed environments. In this case, which NxLP functionality is needed in various multihoming scenarios (e.g., bandwidth increase, load balancing, bi-casting, resilience, etc.) is an open question. An overall coordination for interworking between the NSIS protocol suite and multihoming capability needs to be discussed further. 4. Basic Operations for Mobility Support In this section, the basic protocol interaction of the NSIS protocol suite needed after mobility related route changes is discussed. The basic operations include how to discover an appropriate CRN and how to perform the Path Update according to the direction of data flows. The procedures for CRN discovery (explained in Section 4.2.3) can be applied in the same way for both the generic route changes and mobility. However, the Path Update for mobility is different from that for the generic route changes as explained in Section 2. 4.1 Route changes caused by mobility The route change caused by mobility occurs due to the change of the network attachment point of an MN. It causes divergence (or convergence) between the old path where the NSIS state has already been installed and the new path where data forwarding will actually happen. Although mobility may be considered similar to generic route changes, the main difference is that the Message Routing Information (MRI: e.g., flow identifier) may not change after generic route changes while mobility may cause the change of MRI by having a new network attachment point. Since the session should remain the same after any mobility event, the MRI should not be used to determine the session of any signaling application [4]. The route change brings on the change of signaling topology different from the mobility. That is, the route change results in forming a loop of signaling path that the old path and the new path meet both starting point and end point of the route change (i.e., divergence- converence pair) (see Appendix). However, as shown in Figure 1, the Lee, et al. Expires January 19, 2006 [Page 13] Internet-Draft NSIS Signaling in Mobility July 2005 mobility generally causes signaling path to either converge or diverge depending on the direction of each signaling flow. Old path +--+ +-----+ original |MN|------> |OAR | ----------V | | |NSLP1| address +--+ +-----+ V common path | K +-----+ +-----+ +--+ | | |---|NSLP1|--->|CN| | |NSLP2| |NSLP2| | | v New path +-----+ +-----+ +--+ +--+ +-----+ ^ M N New CoA |MN|------> |NAR |-----------^ >>>>>>>>>>>> | | |NSLP1| ^ +--+ +-----+ ^ L ^ >>>>>>>(Binding process)>>>>>>>>>>>>^ ====(downstream signaling followed by data flows) ======> (a) The topology for downstream NSIS signaling flow due to mobility Old path +--+ +-----+ original |MN|<------ |OAR | ---------^ address | | |NSLP1| ^ +--+ +-----+ ^ common path | C +-----+ +-----+ +--+ | | |<---|NSLP1|---|CN| | |NSLP2| |NSLP2| | | v New path +-----+ +-----+ +--+ +--+ +-----+ V B A New CoA |MN|<------ |NAR |----------V >>>>>>>>>>>> | | |NSLP1| ^ +--+ +-----+ ^ D ^ >>>>>>>(Binding process)>>>>>>>>>>>>^ <=====(upstream signaling followed by data flows) ===== (b) The topology for upstream NSIS signaling flow due to mobility Figure 1: The topology for NSIS signaling caused by mobility. These topological changes caused by mobility make the NSIS state Lee, et al. Expires January 19, 2006 [Page 14] Internet-Draft NSIS Signaling in Mobility July 2005 established on the old path useless and thus it should be removed (in the end). In addition, NSIS state should be established newly along the new path and be updated along the common path. Re-establishment of NSIS signaling should be localized when route changes (including mobility) occur to minimize the impact on the service and to scalability. This localized signaling procedure is referred to as PathUpdate (refer to the terminology section). In mobile environments, for example, the NSLP/NTLP needs to limit the scope of signaling information only to the affected section of the signaling path because the path in the wireless access network usually changes only partially. One of the most appropriate nodes to perform the Path Update is the CRN where the old and new session paths meet. The CRN should be logical merging point, physical merging point. In the end, CRN discovery can be a crucial element to alleviate the double reservation and end-to-end signaling problems identified in Section 3.1. The NTLP (of a node experiencing a topological change) should detect the route change through the various mechanisms described in [4] at the transport level and notify the relevant NSLP(s). For example, the NSLP should initiate NSIS state re-establishment (i.e., QoS re- establishment) along the new path and the update or removal of the existing state at the signaling application level. 4.2 CRN discovery 4.2.1 Possible approaches for CRN discovery The approaches for CRN discovery can be divided into two classes depending on which layer is responsible for the CRN discovery (addressed in Section 3.2.2), and whether or not the discovery is coupled with the transport of signaling application messages. From the NSIS protocol stack point of view, the CRN can be discovered at either NTLP or NSLP layer. For the CRN discovery at the NSLP layer, the information contained in NSLP signaling messages sent from the NSIS initiator (NI) can be used. For example, the QoS-NSLP of an NSIS node can determine whether or not the node is a CRN by comparing the Source Identification Information (SII) contained in the incoming signaling message to the one stored previously in the node. That is, when a RESERVE message with an existing SESSION ID and different SII is received, the QNE knows its upstream peer has changed and realized it is implicitly the CRN [5]. It is also possible to discover the CRN at the NTLP layer since NTLP Lee, et al. Expires January 19, 2006 [Page 15] Internet-Draft NSIS Signaling in Mobility July 2005 is responsible for detecting the path change of data (or signaling) flow (and the route changes may easily be detected at the NTLP level rather than at the NSLP). The CRN discovery at the NTLP level can be considered as a partial process of the peer discovery (e.g. using GIMPS query-response message [2]). In general, the GIMPS messages have message routing state information such as flow/session/signaling application identifiers, so the signaling application can be identified at the NTLP level. In the connection mode of NTLP, when NTLP establishes a messaging association between two adjacent peers, two NTLP peers exchange message routing state information through GIMPS query and response messages. In procedure of the messaging association, CRN is implicitly discovered by comparing MRI contained in the coming signaling to the one stored previously in the node. Therefore, although the CRN can be discovered at the NTLP level, the discovered CRN could be actually an NSLP-aware node which has an involved signaling application. The CRN discovery at the NTLP layer is only one part of peer discovery procedure, and it does not require any explicit process for CRN discovery itself except for GIMPS notification on the information ('CRN-is-discovered to NSLP') to NSLP over API. The NTLP level approach results in decreasing complexity of overall NSIS protocol processing. If a route change is directly detected by NSLP, the CRN discovery at the NSLP layer is considered as a way to report the rerouting. However, this NSLP-level approach requires additional messages at corresponding NSLPs and thus results in adding complexity of overall NSIS protocol processing. There can also be two different approaches for the CRN discovery depending on whether or not the discovery is coupled with a signaling message: coupled approach and uncoupled approach. In the coupled approach, the signaling to install the NSIS state along the new path or update the state along the common path is performed simultaneously with the CRN discovery. In the uncoupled approach, the signaling for the Path Update is performed after the CRN discovery is completed. These two approaches may differ in terms of security. Generally, the coupled approach would be preferred to the uncoupled approach to reduce the delay for state update. Note that the CRN discovery and Path Update described in this draft are based on the coupled approach. 4.2.2 The identifiers for CRN discovery There are some basic identifiers which can be used for the CRN discovery at the NTLP level: session identifier (SID), flow identifier (MRI), and signaling application identifier (NSLP_ID) related to message routing state [2], and NSLP branch identifier (NSLP_Br_ID) which identifies an NSIS signaling branch. Lee, et al. Expires January 19, 2006 [Page 16] Internet-Draft NSIS Signaling in Mobility July 2005 The SID in GIMPS messages is used to identify the involved session because it remains the same while the MRI may change. The MRI is used to specify the relationship between the address information and the state (e.g., QoS-NSLP state) re-establishment. In other words, the change of MRI indicates a topological change to the CRN and therefore it represents that the state along the common path should be updated and the refresh reduction mechanism needs to be used on the common path if any. The NSLP_ID is used to refer to the corresponding NSLP at the NTLP level, and it helps to discover an appropriate NSLP CRN using the GIMPS peer discovery message. As a virtual branch identifier, the NSLP_Br_ID is a pointer which identifies peer nodes in GIMPS messaging association, and it can be used to establish or delete messaging associations between NSIS peers. It can also be used as an identifier to determine the CRN at the NTLP layer. The NSLP_Br_ID may include the location information of NSIS peer nodes with the corresponding NSLP ID obtained by the procedure of GIMPS message association. For instance, as shown in Figures 1 (b) and 2 (a), for the upstream flow case, node A has messaging association with node C for NSLP 1 on the old path. In this case, the NSLP_Br_ID for node C at the node A is set to 1-D-#1: 1, D, and #1 indicate an NSLP_ID-flow, a direction of node (Downstream or Upstream), and a value of the branch counter, respectively. After a handover, NSLP 1 of node A requires a messaging association for sending its messages towards node D. In this case, NSIS entity A creates another NSLP_Br_ID for NSLP 1 toward node D and increases the counter of NSLP_Br_ID to locally distinguish each virtual interface identifier between adjacent NSLP peers: the [NSLP_Br_ID for the node D at the node A is 1-D-#2;. Note that the NSLP_Br_ID can be included in the NSIS message, but it can also be considered as an implementation issue. This identifier would be more useful when the physical merging point of the old path and the new path is not an NSLP CRN as shown in Figure 1. Note that GIMPS message routing state table [2] including the NSLP_Br_ID can also be created as Figure 2. Optionally, the Mobility identifier as an object form can also be used to inform of the handover of an MN or a route change [12] and therefore to expedite the CRN discovery. The Mobility object is defined in the NTLP (e.g., in GIMPS payload) [8] or NSLP messages to notify of any mobility event explicitly, and it contains various mobility-related fields such as mobility_event _counter (MEC) and handover_init (HI) fields. For example, the mobility_event_counter (MEC) field in the mobility object can be used to detect the latest handover event to avoid any confusion about where to send the confirmation message in cae of Ping-pong type handover. Therefore, Lee, et al. Expires January 19, 2006 [Page 17] Internet-Draft NSIS Signaling in Mobility July 2005 the Mobility identifier is useful to discover the most appropriate CRN. +------------------+-------+-------+--------+------------+-------+ | Message Routing |Session| NSLP |Upstream| Downstream | NSLP | | Information | ID | ID | Peer | Peer |Br. ID | +------------------+-------+-------+--------+------------+-------+ | Method = Path | 0xABCD| NSLP1 | | Pointer to | 1-D-#1| |Coupled; Flow ID =| | | | A-C | | | {IP-#X, IP-#V, | | | | Pointer to | 1-D-#2| | protocol, ports} | | | | A-D | | | | | | Z | | 1-U-#1| | Method = Path | | | | | | |Coupled; Flow ID =| 0x1234| NSLP2 | | B | 2-D-#1| | {IP-#X, IP-#V, | | | | | | | protocol, ports} | | | Z | | 2-U-#1| +------------------+-------+-------+--------+------------+-------+ (a) Routing state table at node A (NSLP CRN) +------------------+-------+-------+----------+----------+-------+ | Message Routing |Session| NSLP |Upstream |Downstream| NSLP | | Information | ID | ID | Peer | Peer |Br. ID | +------------------+-------+-------+----------+----------+-------+ | Method = Path | 0xABCD| NSLP1 |Pointer to| | 1-U-#1| |Coupled; Flow ID =| | | K-N | | | | {IP-#X, IP-#V, | | |Pointer to| | 1-U-#2| | protocol, ports} | | | L-N | | | | | | | | O | 1-D-#1| | Method = Path | | | | | | |Coupled; Flow ID =| 0x1234| NSLP2 | | Pointer | 2-D-#1| | {IP-#X, IP-#V, | | | | to N-R | | | protocol, ports} | | | M | | 2-U-#1| +------------------+-------+-------+----------+----------+-------+ (b) Routing state table at node N (NSLP CRN) Figure.2 Routing state table and NSLP branch ID 4.2.3 The procedures of CRN discovery When a mobility event occurs, the CRN can be recognized by comparing the previously stored identifiers with the identifiers included in the incoming NSIS peer discovery message initiated by an NI (e.g., an MN or a CN). For example, if an NTLP message is routed to an NSIS peer node, the following information (shown in Figure 2 (a) and (b)) Lee, et al. Expires January 19, 2006 [Page 18] Internet-Draft NSIS Signaling in Mobility July 2005 should be checked to determine if the current node is CRN: - Whether or not the same NSLP_ID exists - Whether or not the corresponding CRN has already been discovered - Whether or not the same SID and MRI exist - Whether or not the NSLP_Br_ID has been changed: for example, as shown in Figure 2 (a), for NSLP 1 it has been changed to 1-D-#2 from 1-D-#1 at the node A. - Optionally, the Mobility identifier can be examined, if any. For example, the MEC field of the Mobility object can be used to find out which message has been sent due to the latest handover. The CRN discovery can be further divided into the UCRN discovery and DCRN discovery depending on which node is a signaling initiator (by upstream or downstream), or whether the MN is the data sender or receiver: - If the MN is a data sender and undergoes a handover, the MN begins to transmit signaling messages toward a CN in the downstream direction. If an NSLP-aware node recognizes that the session paths logically converge at that node, then the node determines that it is the DCRN; the procedure for CRN discovery corresponds to the creation of the routing table of node N as shown in Figure 2 (b). - When an MN (as a sender) undergoes handover, the UCRN can be discovered for the upstream flow. The UCRN should be the node (closest to the MN) where the signaling flow begins to logically diverge: it corresponds to the creation of the routing table of node A as shown in Figure 2 (a). Since the UCRN is determined according as depending on whether the outgoing logical interfaces diverge or not, the UCRN discovery is more complex than the DCRN discovery and needs to be discussed further. 4.3 Path update The CRN discovery procedures are different depending on the direction of signaling flows in mobility scenarios, and therefore the procedures for Path Update also are different according to the direction of the signaling flow. The Path Update can be divided into upstream Path Update and downstream Path Update. For both types of Path Update, the NSIS protocol suite may need to interact with various mobility signaling protocols, if any (during or after handover) to obtain performance gains (e.g., through fast Lee, et al. Expires January 19, 2006 [Page 19] Internet-Draft NSIS Signaling in Mobility July 2005 establishment of the NSIS state on the new path). For this purpose, NSIS may also need to monitor the movement of the MN through several methods [4]. In this section, we assume that an MN is the data sender. 4.3.1 State setup and update Before initiating the Path Update, the MN or the CN need to have its session ownership by the procedures for authentication and authorization. The MN or the CN may also check the availability of resources on the new path. In case of QoS-NSLP, the Query message can be used to find the availability of resources in the new access network. If the resources along the new path are not sufficient, it may be needed to keep the state established previously using multihomed interfaces while blocking incoming new requests (see Section 5.2). In this situation, providing NSIS signaling for the Path Update over local requests for the resources will be helpful for seamless service. The admission control for the Path Update should prefer to admit an exisiting NSIS state. In the downstream Path Update, if resources are available, the MN initiates the NSIS signaling for state setup toward a CN along the new path and the implicit DCRN discovery is performed by this type of signaling as described in Section 4.2.3. When the DCRN is discovered, it sends a response message towards the MN to notify of the NSLP state installed (e.g., QoS-NSLP state) or installs the NSLP state as a response to the initiated NSLP signaling (e.g., as in RSVP). In case of QoS-NSLP, the sender-initiated approach leads to faster setup than the receiver-initiated approach as in RSVP as shown in Figure 3. And afterwared, the DCRN sends a refresh message towards the signaling destination to update the MRI on the common path and also sends a teardown message towards the old AR to delete the NSIS state (if possible). In the case of upstream Path Update, the CN (or a HA/ a GFA/MAP) sends a refresh message toward the MN to perform Path Update. UCRN is discovered implicitly by the CN-initiated signaling along the common path as described in Section 4.2.3 . In this case, the CN should be informed of the mobility event using an NSIS signaling message sent by the MN or monitoring the mobility signaling procedure (e.g., detecting a change in its binding entry (see Section 5.1)). After the UCRN is determined, it may send a refresh message to the MN along the new path while establishing the messaging association between the newly found peers. Afterwards, the UCRN may send a teardown message towards the old AR to delete the NSIS state (if possible). Lee, et al. Expires January 19, 2006 [Page 20] Internet-Draft NSIS Signaling in Mobility July 2005 NI (MN) NF NF NR (CN) | RESERVE | | | +--------->| RESERVE | | | +--------->| RESERVE | | | +--------->| | | | | | | | RESPONSE | | | RESPONSE |<---------+ | RESPONSE |<---------+ | |<---------+ | | | | | | (a) Sender Initiated Reservation NI (MN) NF NF NR (CN) | QUERY | | | +--------->| QUERY | | | +--------->| QUERY | | | +--------->| | | | | | | | RESERVE | | | RESERVE |<---------+ | RESERVE |<---------+ | |<---------+ | | | | | | | RESPONSE | | | +--------->| RESPONSE | | | +--------->| RESPONSE | | | +--------->| (b) Receiver Initiated Reservation Figure.3 Sender- vs. Receiver-initiated reservation The state update on the common path to reflect the changed MRI brings issues on the end-to-end signaling addressed in Section 3.1. Although the state update does not give rise to re-processing of AAA and admission control, it may lead to the increased signaling overhead and latency. One of the goals of the Path Update is to avoid the double reservation (in QoS signaling) on the common path as described in Section 3.1. The double reservation problem on the common path can be solved by establishing a signaling association using a unique SID and by updating packet classifier/flow identifier. In this case, the NSLP state should be shared for flows with different flow identifiers. Lee, et al. Expires January 19, 2006 [Page 21] Internet-Draft NSIS Signaling in Mobility July 2005 4.3.2 State teardown After establishment of the NSIS state along the new path, the state on the obsolete path needs to be quickly removed by the Path Update mechanism to prevent the waste of resources due to double reservation (and resource allocation problem by call blocking) and to reduce the cost of using resources in the access network as identified in Section 3.1. Although the release of the existing state on the old path can be accomplished by the timeout of soft state, the refresh timer value may be quite long to reduce the overhead of signaling messages. Especially, in mobility scenarios, the maintenance of the NSIS state on the old path for a long time is not necessary. Therefore, the transmission of a teardown message is useful to quickly delete the old state. Note that, however, it is not necessary for GIMPS state to be explicitly removed because of the inexpensiveness of the state maintenance at the GIMPS layer [2]. The CRN is an appropriate point to initiate the teardown toward the old AR after establishment of the state along the new path. The release of the state on the obsolete path can be accomplished by comparing the NSLP_Br_IDs and through reverse routing using SII. This can prevent the teardown message from being forwarded toward along the common path. It may not be desirable to allow the teardown message to be sent toward the opposite direction to the state initiating node. This is because it leads to an authorization problem because a node which does not initiate signaling for establishing the NSIS state can delete the already established state. One simple way to avoid the authorization problem is to disallow the transmission of the teardown message in the reverse direction [7]. The immediate removal of state along the old path may not be always appropriate for some mobility situations addressed in Section 3. For instance, in the ping-pong type of fast handover, it increases signaling overhead, and thus when to delete the state along the obsolete path needs to be discussed further (see Section 5.4). Another example is the 'invalid NR' problem. If the old AR is the last node on the signaling path due to handover, its NSLP may trigger an error message to indicate that NSLP messages cannot be forwarded any further. This error message can immediately remove the state on the old path, which should not be deleted before re-establishing the state along the new path (make-before-break handover). More details are given in Section 5.5. 5. Applicability Statement Lee, et al. Expires January 19, 2006 [Page 22] Internet-Draft NSIS Signaling in Mobility July 2005 5.1 Support for macro mobility-based scenarios This section considers how NSIS protocols should interact with the basic macro mobility protocols such as Mobile IPv4 [12] and Mobile IPv6 [11]. Basically, the following scenarios need to be considered. (1) A flow associated with an MN, either sent or received by the MN, desires to continually get signaling services even after a Mobile IP handover . In this case, NSIS needs to be able to signal for such flows upon the MN's movement to provide seamless service (e.g. seamless QoS). The signaling procedures will create a new NSIS branch in the changed direction of flow by using the CRN discovery and Path Update. (2) Either the sender or the receiver of a flow can initialize NSIS signaling, and a node within the network may also initiate NSIS signaling for the given session to handle route changes caused by Mobile IP-based routing, or to support seamless handover if necessary. (3) Data traffic, in either direction between an MN and a CN, can be routed directly using a routing header, or indirectly by IP-in-IP encapsulation (or a combination of both approaches) on different segments of the data path depending on the operation of the mobility protocol (e.g., Mobile IPv4, Mobile IPv6, LMM, reverse tunneling, etc.) In this case, NSIS signaling needs to be triggered immediately. initiated via a mobility routing interface (e.g., mobility API) between the NSIS protocol and the Mobile IP or by the query routing tables. (4) Mobile IP protocol uses IP-tunneling mechanism to forward data traffics among end hosts. This IP-tunneling mechanism makes it difficult for nodes on the tunneling path to intercept or deal with NSIS signaling messages (which require special treatments at NSIS-aware nodes) because of change of message routing information. Therefore, to perform end-to-end signaling, NSIS needs to interact with such IP-tunneling mechanisms. (5) An MN undergoes either intra-domain (within an access network domain) handover or inter-domain (from an access network domain to another) handover. In case of the inter-domain handover, topology information exchange, authorization and accounting issues may be more complicated. In such various handover scenarios, the interaction between NSIS signaling and some local mobility management protocols (e.g., HMIP, FMIP, etc..) may give rise to significant performance gains (see Section 5.3). (6) With Mobile IPv6, an MN can support multiple CoAs simultaneously, Lee, et al. Expires January 19, 2006 [Page 23] Internet-Draft NSIS Signaling in Mobility July 2005 if it is connected to multiple access networks simultaneously (even if it is connected to one access network). Although only one primary CoA will be used for routing traffic from the CN to the MN, this multi-homing feature potentially can be used to enhance the NSIS signaling performance (see Section 5.2). 5.1.1 Implications to Mobile IP-related scenarios As the NSIS WG concentrates on path-coupled signaling, one imposed requirement here is that the NSIS protocols are to be associated with route changes to support route optimization between the CN & the MN, and the IP-in-IP encapsulation from the HA to the MN. This interaction needs to be notified to all NSLPs (by the API between GIMPS and NSLP) for the CRN discovery and the Path Update. Therefore, either NTLP or NSLP needs to have an interface with the Mobile IP to react to the mobility event . In other words, an NSIS implementation needs to be developed to react on mobility events based on the endpoint notification depending on which behaviour of a mobility protocol has taken place (e.g., the timer of Mobile IP expires). An ideal interface between the NSIS signaling and the Mobile IP should make it possible for NSIS signaling to immediately react to the mobility event whenever Mobile IP changes its related characteristics in any place for the flows. In general, it is appropriate that NTLP is involved in the interaction with Mobile IP rather than NSLP because NTLP is responsible for routing NSIS messages. Therefore, it is reasonable to assume NTLP should be able to notify NSLP for the necessity of state update over API between NTLP and NSLP when the mobility events are detected. The following issues also arise concerning the API between the NSIS protocol and the Mobile IP. - Which information should be used to detect the movement? After an MN moves to a new network attachment point, the new reachability information is transferred from the MN to its HA as the last procedure of handover. It indicates that the NTLP may need to interact with a binding process (e.g., a registration request in Mobile IPv4 and Binding Update in Mobile IPv6) to detect the IP address change and refer to the tunneling-related information. Provided that the NTLP detects the mobility using the information regarding binding process, faster state establishment and removal can be performed. However, in the fast or ping-pong type handover, it may result in significant signaling overhead and some possible errors (see Section 5.4). - How and what information can the NSLP expect from NTLP, or Lee, et al. Expires January 19, 2006 [Page 24] Internet-Draft NSIS Signaling in Mobility July 2005 directly from the routing interface after a mobility event happens? - How is the mobility binding update interval coordinated with the NSIS signaling interval? Since the binding update or the registration request occurs periodically even for the MN with the same point of attachment, the movement detection based on the binding process may cause the NTLP/NSLP to initiate the CRN discovery and the Path Update inappropriately. To avoid the problem, the change of CoA should be checked carefully. Although this issue is closely related to implementation, it should be considered to obtain any performance gains in signaling. An overall coordination/synchronization for the interworking between the NSIS and the Mobile IP needs to be discussed further. 5.1.1.1 Mobile IPv4-specific issues With Mobile IPv4, the data flows are forwarded based on the triangular routing, and an MN retains a new CoA from the FA (or an external method such as DHCP) in the visited access network [5]. When the MN acts as a sender, the downstream data flows sent from the MN are directly transferred to the CN not necessarily through the HA or indirectly through the HA using the reverse routing. On the other hand, upstream data flows sent from the CN are routed through the IP tunneling between the HA and the FA (or the HA and the MN in case of the Co-located CoA). With this approach, routing is dependent on the HA, and therefore the NSIS protocols needs to interact with the IP tunneling procedure of Mobile IP for signaling. Note that in QoS-NSLP, if Mobile IPv4 protocol uses triangular routing mechanism, the receiver-initated approach is not suited to establish the QoS states over the Mobile IPv4 because the path of Query messages directly sent from an MN to a CN is not identical with that of RESPONSE messages forwarded via HA from the CN to the MN. Therefore, in this case, the Mobile IP should use the reverse tunneling mechanism and the Query messages need to be forwarded over reverse tunneling from FA to HA. On the other hand, since in the sender-initiated approach, RESERVE messgees travel in the same direction as data flow without any QUERY message to establish the desired QoS states, this approach can be used for both triangular routing and reverse tunneling mechanisms. The Figures 5 (a) to (e) show the NSIS signaling flows depending on the direction of data flows and the routing methods. Lee, et al. Expires January 19, 2006 [Page 25] Internet-Draft NSIS Signaling in Mobility July 2005 MN FA (or FL) CN | | | | IPv4-based Standard IP routing | |------------ |------------------------------>| | | | (a) MIPv4: MN-->CN, no reverse tunnel MN FA HA CN | IPv4 (normal) | | | |--------------->| IPv4(tunnel) | | | |--------------->| IPv4 (normal) | | | |-------------->| (b) MIPv4: MN-->CN, the reverse tunnel with FA CoA MN (FL) HA CN | | | | | IPv4(tunnel) | | |------------------------------->|IPv4 (normal) | | | |-------------->| (c) MIPv4: MN-->CN, the reverse tunnel with Co-located CoA CN HA FA MN |IPv4 (normal) | | | |-------------->| | | | | MIPv4 (tunnel) | | | |---------------->| IPv4 (normal)| | | |------------->| (d) MIPv4: CN-->MN, Foreign agent Care-of-address CN HA (FL) MN |IPv4(normal ) | | | |-------------->| | | | | MIPv4 (tunnel) | | | |------------------------------->| | | | | (e) MIPv4: CN-->MN with Co-located Care-of-address Figure 5. Implications for signaling under different Mobile IPv4 scenarios When an MN (as a sender) arrives at a new FA and the corresponding binding process for the FA CoA is completed, Lee, et al. Expires January 19, 2006 [Page 26] Internet-Draft NSIS Signaling in Mobility July 2005 - For the downstream signaling flow, the MN needs to perform the CRN discovery (DCRN) and the (downstream) Path Update toward the CN (as described in Section 4) to establish the NSIS state along the new path between the MN and the CN as shown in Figure 4 (a). If the reverse tunnel is used and the state along the tunneling path does not exist, the NSIS state should be established along the tunneling path from the FA to the HA as shown in Figure 4 (b). In this case, a DCRN may be discovered on the tunneling path and the new flow identifier for the state update on the tunnel may need to be created. That is, signaling flows over the tunnel are considered as separated flows and thus the tunnel endpoints can initiate a new signaling session for the flow over the tunnel. - For the upstream signaling flow, the CN may initiate the NSIS signaling to update the existing state between the CN and the HA, and in this case NSIS signaling should interact with the IP tunneling operation to update the state along the tunneling segment from the HA to the FA as shown in Figure 4 (d). During this operation, a UCRN may be discovered on the tunneling path, and the new flow identifier for the state update on the tunnel may need to be created. When the MN (as a sender) arrives at a new foreign link (FL) and the corresponding binding process for the co-located CoA is completed, - For the downstream signaling flow, the NSIS signaling for the DCRN discovery and the Path Update is the same as the case for FA CoA above except for the use of the reverse tunnel path from the MN to the HA as shown in Figure 4 (C). That is, in this case, one of tunnel end points is to be the MN, not the FA. - For the upstream signaling flow, the NSIS signaling for the UCRN discovery and the Path Update is also the same as the case for FA CoA above except for the end point of tunneling path from the HA to the MN as shown in Figure 4 (e). Note that the DCRN and UCRN may be identified at the same node on the tunneling path. For example, NSIS CRN may be usually the HA if the HA and the FA are NSIS-aware but the NSIS signlaing over the tunneling path is not coped with. Therefore, the CRN discovery will be affected depending on the type of interaction between NSIS signaling and IP tunneling. The FA and the HA should be NSIS-aware to do the Path Update along the appropriate path. The effect that the IP tunneling has on the CRN discovery and the Path Update should be discussed further. 5.1.1.2 Mobile IPv6-specific issues Lee, et al. Expires January 19, 2006 [Page 27] Internet-Draft NSIS Signaling in Mobility July 2005 Unlike Mobile IPv4, with Mobile IPv6, the FA is not required in the data path and the route optimization process between the MN and CN can be used to avoid the triangular routing in the Mobile IPv4 scenario as shown in Figure 5 [9]. If the use of route optimization is not mandatory, data flow routing and NSIS signaling procedures (including the CRN discovery and the Path Update) will be similar to the case of using the Mobile IPv4 with co-located CoA described in Section 5.1.1.1. In Mobile IPv6-based scenarios, the non-existence of FA depicts the endpoint of IP-tunneling is extended to the MN. If the MN is sender and route optimization is optional, it should initiate both tunnel signaling session and end-to-end signaling session by using reverse tunneling, and HA as another tunnel endpoint needs to react on the tunnel signaling messages and forward the end-to-end NSIS signaling messages to the CN. However, if the route optimization in Mobile IPv6 is used as mandatory, NSIS signaling is not necessary to interact with IP-tunneling any more. It also means that NSIS signaling should not be initiated simultaneously with Binding Update messages. When an MN (as a sender) arrives at a new AR and the binding process is successfully completed, - For the downstream signaling flow, the MN initiates NSIS signaling for the DCRN discovery and the (downstream) Path Update to establish the state along the new optimized path between the MN and the CN as shown in Figrue 5 (a). The MN initiates tunnel NSIS signaling for DCRN discovery and te path Update over the tunneling path from the MN to the HA if the reverse tunnel is used, as shown in Figures 5 (b). In this case, CRN discovery over tunnel can be performed as the same approach described in Section 4.2. - For the upstream signaling flow, the CN may also update the state along the common path toward the HA through the Path Update, and afterward the NSIS state along the tunneling segment from the HA to the MN may be updated via the interaction with IP tunneling operation as shown in Figure 5 (d). In this case, the HA needs to create a new NSIS tunnel signaling toward the MN as the tunnel endpoint. The obsolete path of the existing tunneling segments needs to be removed when re-establishment of NSIS state along the new tunneling path. When to remove the tunneling segment and/or how to tear it down through the interworking with the IP-tunneling operation is still an open issue.However, if the route optimization is used between the CN and the MN, for the upstream flow, CN needs to newly initiate end-to-end NSIS signaling to discover an appropriate UCRN and do the Path Update along a new path between the CN and the MN as shown in Figure 5 (c): the Lee, et al. Expires January 19, 2006 [Page 28] Internet-Draft NSIS Signaling in Mobility July 2005 bidirectional state establishment may be required between the CN and the MN. MN CN | | |IPv6+HomeAdressOpt | |--------------------------------------------->| | | (a) MIPv6: MN-->CN, no reverse tunnel MN HA CN |IPv6(tunnel) | | |------------->| IPv6(normal) | | |------------------------------>| | | (b) MIPv6: MN-->CN, with reverse tunnel CN MN | | | MIPv6(RH Type 2) | |--------------------------------------------->| | | (c) MIPv6: CN-->MN, route optimization CN HA MN |IPv6(normal) | | |------------->| | | | MIPv6(tunnel) | | |------------------------------>| (d) MIPv6: CN-->MN, no route optimization Figure 6. Implications for signaling under different Mobile IPv6 scenarios 5.2 NSIS operations in multihomed mobile environments 5.2.1 Overview Multihoming refers to a situation where an end node has several parallel communication paths to use. An end node (e.g., an MN in mobile environments) may have multiple homogeneous/heterogeneous interfaces. Multiple interfaces can be used in order to increase bandwidth availability or to select the most appropriate interface according to the type of flow or choices of the user [17]. Lee, et al. Expires January 19, 2006 [Page 29] Internet-Draft NSIS Signaling in Mobility July 2005 Basically, each network interface has different performance, bandwidth, access range, and reliability. Users may want to select the most appropriate set of network interface(s) depending on the network environment, particularly in wireless networks which are less reliable than wired networks. Users may also want to select the most appropriate interface based on certain criteria or to combine a set of interfaces to get sufficient bandwidth [17]. In multihomed environments, multiple addresses can be allocated to either a single interface or multiple interfaces to provide ubiquitous and fault-tolerant access to the Internet. Other benefits of having multiple interfaces include load balancing, bi-casting, load sharing, and etc. 5.2.2 Examples of NTLP/NSLP operations NSIS signaling can be used in various multihoming scenarios described above. This section briefly describes NSIS operations and applicability in multihomed Mobile IP-based environments. The NTLP uses an endpoint address (e.g., CoA of the MN) to install message routing state. As stated above, there can be multiple CoAs for the multihomed MN, and therefore an appropriate CoA (active) should be selected to establish the NSIS state between the MN and the CN. Each network interface may be associated with a CoA. To find a feasible CoA for the signaling path, multiple NSIS messages (e.g., multiple QUERY messages of the QoS-NSLP) can be sent from the MN to the HA or CN (in case of route optimization), and the HA or CN may decide which one to choose based on some criteria (e.g., resource availability, delay, etc.). According to the decision, the HA or CN should send a signaling message (e.g., RESERVE) to the MN with the selected CoA for further action. In the situation where the newly introduced CoA causes the change of message routing state, both new and old addresses may be valid for a certain amount of time, and the new data path may co-exist with the old one. It is theoretically possible to perform an NSIS state re- establishment on the new path during this time interval. In this case, however, the signaling endpoints need to be careful, so that the correct routing information will be delivered for setting up a new message routing state or updating the existing message routing state on the correct path segment. In addition, performing such actions should not cause any NSLP service interruption, protocol misbehaviors, or security holes. When there is a need for inter-domain handover, an additional delay may be caused to perform authentication and authorization compared to the intra-domain handover, but the latency penalty of NSIS signaling Lee, et al. Expires January 19, 2006 [Page 30] Internet-Draft NSIS Signaling in Mobility July 2005 can be mitigated if the MN is multihomed. For load balancing purposes, NSIS can install the NSIS state along the multiple paths. In this case, multiple NSIS messages (e.g., multiple QUERY messages in case of QoS-NSLP) can be sent to the remote endpoint to establish NSIS state. As a result, multiple paths can be set up for load balancing between the same endpoints. When the MN has multiple CoAs, those CoAs may be sent to the HA together with the binding update message for immediate state re- establishment. When to send the CoAs during the binding update procedure should be optimized for reducing state setup delay. IPv6 has no clearly defined mechanism for detecting the availability or loss of media except through the ability or inability to receive router advertisements within a stipulated period [18]. An efficient way to detect media loss should be provided so that the redirection between interfaces can be performed quickly to support seamless services. The result of media detection can be used to trigger necessary NSIS operations. A more detailed analysis of the NTLP/NSLP operations in various multihoming scenarios will be presented in the later version of this draft or in a separate draft. 5.3 QoS performance considerations in mobility scenarios The routing characteristics of Mobile IP described in Section 5.1 cause the session path to frequently be changed and thus the NSIS signaling in such dynamic environments may cause the various problems mentioned in Section 3.1. In QoS-NSLP, critical issues which make QoS performance being degraded should be resolved to guarantee services for that data flow. In this section, particularly, QoS performance in terms of resource utilization and signaling latency is discussed to give some guidelines on how NSIS protocols should interact with mobility management protocols. As an example of resource utilization, the double reservation problem can be alleviated by usage of a unique session identifier and the Path Update procedure including CRN discovery. However, management of the resource utilization in overall NSIS signaling processing point of view should be taken into account; in this regard, the adjustment of refresh interval is one of crucial elements which decide performance metrics of resource utilization as mentioned in Section 3.2. This issue needs to be discussed further in the case of the soft state approach to release the obsolete state in mobility scenarios is preferred to any explicit tear-down approach. Lee, et al. Expires January 19, 2006 [Page 31] Internet-Draft NSIS Signaling in Mobility July 2005 The NSIS protocol suite normally uses a soft-state approach based on the peer-to-peer refresh to manage state in NEs. The peer-to-peer based refresh allows the NSIS to appropriately select the refresh interval by considering the current network environment. For example, the refresh timer value in networks with scarce resources (e.g., mobile/wireless (access) networks ) may set for a long time to decrease the overhead of signaling messages. If any explicit teardown messages for state removal are not used, in the situation where handover happens very frequently, the dynamic adjustment of the refresh interval can reduce the waste of resources. In this case, the refresh timer value needs to be set to a smaller value in the mobile/wireless networks than that in the core (wired) network as in [5]. To create dynamic refresh intervals, a general mechanism to be able to choose an optimal refresh timer value according to various mobile environments needs to be considered. However, this approach requires refresh interval traits dependent on specific network environments. When an MN, for example, roams from WLAN to UMTS or WIMAX (or WiBro) networks, the refresh interval in the UMTS or WIMAX(or WiBro) networks need to be set up differently from the WLAN networks. This advanced approach to automatically decide refresh intervals is further study. Note that unlike the QoS-NSLP, the refresh timer of NTLP state does not need to be adjusted in the network since signaling application as resource reservation is not involve directly. Furthermore, the NTLP state along the obsolete path does not need to be explicitly removed before the expiration of refresh timer. In mobile wireless networks, QoS-NSLP (rather than the NTLP) is able to set the refresh timer value depending on the handover type (e.g., make-before-break or break-before-make) or the reservation style (e.g., pre-establishment or re-establishment) to optimize the resources utilization. For example, in the make-before-break handover, an appropriate refresh time interval can be notified using the reserved field of REFRESH object. If the refresh timer value is set to a little higher value than the estimated handover latency, the MN can be provided with seamless QoS service using the pre-reserved resources without the waste of resources [6]. After the state setup on the new path, QNEs on the signaling path may send a refresh message to the neighboring peer node before the refresh timer expires to update only the state previously installed along the path, or update the changed MRI along the common path . In this case, the overhead required to perform refresh can be reduced, in a way similar to the refresh reduction in RSVP [16]. Once a RESPONSE message which indicates the successful installation of a reservation has been received, subsequent RESERVE messages for refresh can simply refer to the existing reservation, rather than Lee, et al. Expires January 19, 2006 [Page 32] Internet-Draft NSIS Signaling in Mobility July 2005 including the complete reservation specification. For example, in case of QoS-NSLP, only the SID and the SII with no QSPEC are sent to just refresh the state (e.g., reservation) previously installed. The changed flow ID together with those IDs is only sent to update it along the common path. Especially, transmission of the reduced number of refresh messages over wireless channels, access networks, or core networks results in the efficient utilization of resources. As mentioned in Section 3.1, unlike the generic route changes, in mobility scenarios, the end-to-end signaling problem by the Path Update gives rise to the degradation of network performance such as increased signaling overhead, service blackout, and so on. To reduce signaling latency in the Mobile IP-based scenarios, the NSIS protocol suite needs to interwork with localized mobility management (LMM). If the GIMPS/NSLP( QoS-NSLP or NAT/FW-NSLP) protocols interacts with Hierarchical Mobile IPv6 and the CRN is discovered between an MN and MAP, the Path Update can be localized by address mapping. However, how the Path Update is performed with scoped signaling messages within the access network under the MAP is for further study. In the inter-domain handover, a possible way to mitigate the latency penalty is to use the multi-homed MN. It is also possible to allow the NSIS protocols to interact with mobility protocols such as Seamoby protocols (e.g., CARD [RFC4066] and CXTP [RFC4067]) and FMIP. Another scenario is to use peering agreement which allows aggregation authorization to be performed for aggregate reservation on an inter- domain link without authorizing each individual session. How these approaches can be used in NSIS signaling is for further study. 5.4 Support for Ping-Pong type handover NSIS signaling needs to consider the interaction with ping-pong type handover as addressed in Section 3.1 because it has a significant effect on when to initiate signaling for state setup or for state release. With the sender-initiated approach, if an MN (as a sender) undergoes a handover into a new AR, the NTLP interacts with the binding process of Mobile IP to initiate state setup. However, if the MN moves to other ARs or the previous AR again in a short while, signaling using the interaction with the binding process may result in considerable signaling overhead and some possible errors. Immediate teardown of state on the old path may also bring on the similar result. Some identifiers defined in [5] [6] may be useful for this situation. An NE (e.g. QNE) can determine if it is a merging point (i.e. an NSLP CRN) of the old and new paths, and then it can perform an involved state setup on the new path and state teardown on the old path . However, if the QNE receives an NSIS message (e.g., RESERVE) Lee, et al. Expires January 19, 2006 [Page 33] Internet-Draft NSIS Signaling in Mobility July 2005 with a special flag (e.g. NO_REPLACE flag) set but with the different SII, state teardown on the old path should not happen. This may apply to a ping-pong type handover where the MN wishes to keep state to its old attachment point in case it moves back there. For interaction with the ping-pong type handover, NSIS should determine when to set the NO_REPLACE flag depending on when and where the MN handovers. It requires NSIS to monitor or react on the mobility events over possible API. It is stil an open issue and needs to be discussed further. The Reservation Sequence Number (RSN) may be useful in detecting duplicate messages in the mobile environment. For example, it is possible for the MN to move to the second NAR soon after being attached to the 1st NAR. The CRN may receive the RESERVE messages (with different RSN) twice when the RESERVE message from the 1st NAR arrives later than the RESERVE message from the 2nd NAR. In this case, the CRN should determine which RESERVE message is the latest one via the RSN. The Mobility object described in Section 4.2.2 can be defined in the NTLP (e.g., in GIMPS payload) or NSLP messages to notify of any mobility event explicitly, and it may contain various mobility- related fields, e.g., mobility_event_counter (MEC). The MEC field can inform the CRN of which incoming massage is the latest and so it is useful to detect the latest handover event for avoiding any confusion about where to send a confirmation message and to handle the ping-pong type of movement. 5.5 Peer failure scenarios A dead peer can occur either because a link or a network node failed, or because the MN moved away without informing NSLP/NTLP (it is recommended to link mobility- and NSIS signaling such that this does not happen). Dead peers of interest in mobility scenarios include CRN, MN, AR (or FA), and HA. In general, it is possible that only NSIS functions (i.e., NTLP/NSLP) of the node may fail, or the that the node itself fails completely. In this regard, the following issues arise. - An MN may either fail or move (or just operate normally). When it fails, it becomes a dead peer. If it moves and changes its IP address without notifying NSLP/NTLP, it also becomes a dead peer. The failure or movement of an MN may cause the 'invalid NR' problem [8] where the NR is the MN mentioned in Section 3.2. If the MN moves, care should be taken to prevent the teardown of NSIS state on the old path before the NSIS state is re-established on the new path . In this case, an error message (or refresh Lee, et al. Expires January 19, 2006 [Page 34] Internet-Draft NSIS Signaling in Mobility July 2005 timeout) should not be generated (or happen) to avoid any teardown on the old path and common path. The problem can be solved by using hanover_init (HI) field of the Mobility object described in Section 5.4. The HI field can explicitly inform AR (or CRN) that a handover is now initiated, and thus the AR does not initiate any error messages (or refresh timeout) when it does not receive responses to refresh messages from the MN [6]. In this case, AR's possible approach may be a proxy for the MN (the last node) and it may be able to send RESPONSE messages in response to REFRESH (or RESERVE) messages from a upstream node. AR may also forward the error message including the HI field toward CN to prevent the NI from removing the NSIS state. However, it is sill an open issue whether the hint information such as the HI field through NSIS signaling messages needs to be forwarded. - The failure of a (potential) NSIS CRN may result in incomplete state re-establishment on the new path and incomplete teardown on the old path after handover. In this case, a new CRN should be re-discovered immediately by the CRN discovery procedure described in Section 4.2.3. - The failure of an AR may make the interactions with Seamoby protocols (such as CARD and CXTP) impossible. In this case, the neighboring peer closest to the dead AR may need to interact with such protocols. A more detailed analysis of interactions with Seamoby protocols is left for future work. - In Mobile IP-based scenarios, the failures of NSIS functions at a FA and a HA may result in incomplete interaction with IP- tunneling. In this case, recovery for NSIS functions needs to immediately be performed. Also, a more detailed analysis of interactions with IP-tunneling is left for future work. In any case, dead peers should be discovered fast to minimize service interruption. The procedures for dead peer discovery (DPD) should be the same no matter why a peer is dead, because an NE discovering a dead peer cannot judge the specific reason. The procedures for DPD should be handled by the NTLP. In fact, the DPD can be considered as an extension to the GIMPS peer discovery. A peer discovery message can be periodically transmitted to the neighboring peer (e.g., responding node in [2]), and the responding node can send a response message. To determine if the peer is alive, the use of a timer may be helpful. For example, the response message may need to be received by the sender (e.g., querying node in [2]) before the timer expires. Otherwise, the responding node can be considered dead. Lee, et al. Expires January 19, 2006 [Page 35] Internet-Draft NSIS Signaling in Mobility July 2005 6. Security Considerations This section describes authorization issues for mobility scenarios in NSIS. It tries to raise additional questions beyond those discussed in [7]. For the discussion of various authorization problems we assume that initial authorization is strongly coupled to authorization handling in subsequent message interactions. Making this assumption has some implication to the signaling message behavior. It is certainly possible that the entities who request the initial reservation or a firewall pinhole and those who subsequently cause modifications are not the same entities. NSIS NSLPs define a flexible authorization scheme. As argued in [8] it is necessary to consider cases where the sender, the receiver or both are authorizing a reservation. For NAT and Firewall signaling it is necessary that, the sender and the receiver, authorize the creation of a NAT binding and the creation of a firewall pinhole and the reason is described in [8]. Subsequently, we will consider the case where the mobile node acts as a data sender followed by a discussion of the CN as a data sender. 6.1 MN as data sender This section refers to Figure 1 where the MN acts as a data sender which moves from one point of attachment to another. This description starts with an initial signaling exchange triggered by the MN. The user (or another entity associated the initial setup) provides the credentials for setup as part of the NSLP authorization procedure (e.g., QoS reservation). 6.1.1 MN is authorizing entity This scenario considers the initial flow setup executed by the MN whereby the MN provides authorization for the initial flow setup. The initial setup might be used to create state for subsequent authorization actions by the MN. It is obvious that the authorization for the NSLP application (e.g., QoS NSLP) has to be provided. Depending on the underlying authorization model it might be either peer-to-peer or end-to-middle. This authorization decision can possibly be treated independently of the authorization issues discussed in this section. The following questions seem to be interesting: Lee, et al. Expires January 19, 2006 [Page 36] Internet-Draft NSIS Signaling in Mobility July 2005 - Should the MN indicate that it is the authorizing entity for subsequent actions to all entities along the path? - What information should be used for this purpose? - Who should add this information? Should the visited network of the MN add something to the signaling message during the initial flow setup? - How do other entities along the path learn this information? MN CN ------>----->------>------>------>------>------> + ACTION (MN is authz) | | <-----<-----<------<------<------<------<------- | Flow ACK | Setup | | ===============================================> + Traffic Figure 6: MN authorized initial reservation Next, the case for a mobile node authorizing the DCRN is considered. This communication is illustrated in Figure 7. The movement of the mobile node after the initial flow setup requires authorization. Various session ownership authorization issues are illustrated in [7]. MN DCRN CN + E.g. ------>----->------>------>------>------>------> | Movement ACTION | with state | creation at <-----<-----<------<------<------<------<------- + new path ACK Figure 7: MN authorizes DCRN The following questions are of interest: - Why should the DCRN execute something on behalf of the MN? (i.e., Lee, et al. Expires January 19, 2006 [Page 37] Internet-Draft NSIS Signaling in Mobility July 2005 why should it trust the MN and what information can the DCRN use for verification? [the trust is not the other way round: the MN trusts the DCRN?]) As an example, the DCRN might delete state along the old segment. - Should the DCRN alone be able to start signaling (the DCRN might be a dedicated node in some mobility protocols (e.g., MAP)) since it is the node which has more information than other nodes based on the mobility signaling protocols? - How should other nodes between the MN and the DCRN and the nodes between the DCRN and the CN know that the DCRN is now acting on behalf of the MN? The case of a corresponding node triggering an action is discussed in the paragraph below. Figure 8 shows the exchange graphically. In this scenario the CN wants to, for example, tear-down a reservation. MN DCRN CN <~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + TRIGGER | E.g. | Tear | Down ------>----->------>------>------>------>------> | ACTION | | <-----<-----<------<------<------<------<------- + ACK Figure 8: CN triggers action The following questions arise: - Why should the MN trust the trigger? Why should the intermediate nodes trust it? - Is it possible to specify the security properties of the trigger message in more detail? Is this an NSIS signaling message? - The discussions about an indicator which entity to charge for the reservation might be relevant (see [8]). - Should the CN restrict the actions of the MN (e.g., delete, update, create action of established state information)? On the Lee, et al. Expires January 19, 2006 [Page 38] Internet-Draft NSIS Signaling in Mobility July 2005 shared segment it might, for example, be possible to restrict the allowed action to a flow identifier update. 6.1.2 CN is authorizing entity This scenario is similar to the CN triggering in Section 6.1.1. Two slightly different protocol variations will be considered. Authorizing some actions in the reverse data flow direction is more difficult as it can easily be seen in Figure 9. 6.1.2.1 CN asks MN to trigger action (on behalf of the CN) In Figure 9 the CN authorizes the MN to start signaling after, for example, a movement. After receiving the trigger message (and some authorization information) the mobile node starts signaling along the new segment and automatically discovers the DCRN. The message travels along the shared segment to the CN and updates the flow identifier (if necessary). The MN might additionally allow the DCRN to delete the reservation along the old segment. MN DCRN CN <~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + TRIGGER | | ------>----->------>------>------>------>------> | ACTION (CN is authz; MN on behalf of CN) | +-----------------+ +-----------------+ | | Action: | | Action: | | | 'create' along)| | 'update' along)| | | new segment) | | shared segment)| | Action +-----------------+ +-----------------+ | <------<------<------- | +-----------------+ | | Action: | | | 'delete' along)| | | old segment) | | +-----------------+ | <-----<-----<------<------<------<------<------- | ACK | | | ===============================================> | Traffic + Figure 9: CN asks MN to trigger an action (on behalf of the CN) Lee, et al. Expires January 19, 2006 [Page 39] Internet-Draft NSIS Signaling in Mobility July 2005 The following questions need to be considered: - How should the "delegation" mechanism work such that intermediate nodes believe the MN that it is acting on behalf of the CN? - Is it possible to carry this information with the trigger message from the CN and the MN? 6.1.2.2 CN uses installed state to route message backwards The CN uses NSIS installed state to route a signaling message backwards along the path. In some rare cases the DCRN node might be known already. In this case it is possible to stop the update process along the shared segment and to possibly mark installed state along the old segment for deletion. When the MN receives the message it again has to install state along the new segment towards the DCRN. The mobile node might also trigger the deletion of resources along the old segment together with this state creation (pessimistic delete). An optimistic delete operation is certainly more error prone. MN DCNR CN [ ~~~~~~~~~~~~ TRIGGER (e.g., MIP) ~~~~~~~~~~~~~~> ] + ------<-----<------<------<------<------<------< | ACTION (CN is authz) | +--------------------+ +-----------------+ | | Action:optimistic | | Action: | | | 'delete' along | | 'update' along)| | | old segment) | | shared segment)| | +--------------------+ +-----------------+ | >------>------>----------->------>------>------- | +-----------------+ ACK | | Action: | | Action | 'create' along)| | | new segment) | | +-----------------+ | <------<------<------- | +-------------------+ | | Action:pessimistic| | | 'delete' along) | | | old segment) | | +-------------------+ | =================Traffic==========================> + Figure 10: CN uses installed state to route message backwards Lee, et al. Expires January 19, 2006 [Page 40] Internet-Draft NSIS Signaling in Mobility July 2005 Figure 10 raises a few questions: The security properties of the trigger message need to be evaluated. It is not always possible to route signaling message backwards from the CN to the MN: - state at the new path might not be established (hence the signaling message cannot travel backwards) - the signaling message might not reach the MN via the old segment. In the multi-homing case where the mobile node can be reached via more than one path it is possible to execute this exchange. The same might be true for some local repair cases. The messages triggered by the MN (namely create state along the new segment and the pessimistic 'delete along the old segment) still need to be executed on behalf of the CN. Compared to the first variant there might be some room for optimization since the first message was transmitted by the CN. 6.1.2.3 MN and CN are authorized If we argue that the authorization at the NSLP layer is somehow tight to the authorization for certain protocol actions then we also have to consider the case where the MN and the CN have to contribute to the authorization decision. This situation appears, for example, in the NAT/Firewall signaling case but also in the area of QoS reservation where both parties might need to share the cost of a reservation. If both end hosts are authorized then some signaling message exchanges are less difficult since the trigger message does not need to delegate the authorization decision. Some problems, however, do not disappear such as the session ownership problem and additional problems might be caused by certain solution approaches. Since this section does not discuss solutions the reader is referred to the [7] draft which lists a few proposals for addressing the session ownership problem. 6.1.3 CN as data sender In this section we consider the scenarios where the CN acts as a data sender. Figure 1 shows the topology and the participating entities. Lee, et al. Expires January 19, 2006 [Page 41] Internet-Draft NSIS Signaling in Mobility July 2005 6.1.3.1 CN is authorizing entity This scenario is similar to the one described in Section 6.1.1. No additional problems arise with a scenario where the CN is both data sender and also the authorizing entity. In Figure 8 the CN authorizes the UCNR to delete the old segment and to establish a new reservation along the new segment. Furthermore, at the shared segment only an update of the flow identifier might be necessary. MN UCRN CN + E.g. <-----<-----<------<------<------<------<------- | Create ACTION | new +-----------------+ | +-----------------+ | State | Action: | | | Action: | | | 'create' along)| | | 'update' along)| | | new segment) | | | shared segment)| | +-----------------+ | +-----------------+ | <------<------<--------+ | +-----------------+ | | Action: | | | 'delete' along)| | | old segment) | | +-----------------+ | | >----->----->------>------>------>------>------> | ACK (along new path) | | <=================== Traffic==================== + Figure 11: CN as data sender is authorized Since the mobile node first detects the route changes. A trigger to the CN allows the CN to quickly react on the route changes. There are three variants: - The MN sends a trigger to the CN and the CN starts signaling as shown in Figure 11. - The MN routes the message back along the reverse path using the previously established state along the old route. This mechanism only works if the MN is able to send messages along the old path. As a generic mechanism this is not suggested. - An intermediate node act on its own. This might be possible that the UCRN is an entity which participates in the mobility signaling Lee, et al. Expires January 19, 2006 [Page 42] Internet-Draft NSIS Signaling in Mobility July 2005 (e.g., Mobility Anchor Point (MAP)) exchange. Depending on the message exchange it needs to be studied whether the signaling message provides sufficient authorization to trigger the NSIS exchange. 6.1.3.2 MN is authorizing entity In this scenario we consider the case where the CN is the data sender but the MN authorizes actions. The considerations are similar to those elaborated in Section 6.1.3 where the MN is the data sender but the CN is the authorizing entity. 6.1.4 Multi-homing Scenarios Multi-homing scenarios have the property that more than one path belongs to a signaling session. In Figure 12 the MN uses two interfaces to route NSIS message towards the CN. The two individual flows are tight together by using the same session identifier and then associate it with the two flow identifiers. The MN needs to indicate that both reservations need to be kept alive (and the DCRN should not delete a reservation). At the shared segment only a single reservation might be stored (if desired). From an authorization point of view the session ownership issues is applicable since the DCRN needs to merge the two reservations into a single one along the shared segment. 6.1.4.1 MN as data sender This section shows the multi-homing scenario with the MN as a data sender. If the MN is the authorizing entity then the session ownership problem needs to be solved. Without solving this type of authorization problem it is possible for an adversary to "join" the reservation at the shared segment. Furthermore, it is an open issue whether reservation merging is allowed only for cases where one flow identifier is used at different interfaces or even with different flow identifiers. If the CN is the authorizing entity then, again, some message needs to be sent from the CN to the MN to trigger the exchange or to route the request backwards along the established path. The MN is reachable via the two paths. Lee, et al. Expires January 19, 2006 [Page 43] Internet-Draft NSIS Signaling in Mobility July 2005 segment 2 +---+ ^>>>>>>>>>>>>>>>| AR|>>>>>>>>>>>>>V ^ +---+ V +----+ +----+ +--+ | MN | |DCRN|>>>>>>>>>>|CN| |UCRN| | |>>>>>>>>>>| | +----+ +----+ +--+ v +---+ ^ shared v>>>>>>>>>>>>>>>| AR|>>>>>>>>>>>>>^ segment +---+ segment 1 =======================Traffic===============================> Figure 12: Multi-homed MN as data sender 6.1.4.2 CN as data sender This section shows the multi-homing scenario with the CN as a data sender. The scenario is simpler (for the CN authorizing case) than the one described in Section 6.1 since the signaling message along the shared segment travels the previously established path. It shows some similarities with a route change scenario. At the mobile node itself the two paths merge which again leads to a session ownership problem. How should the MN know whether a signaling message with the same session identifier hitting a different interface belongs to the indicated session authorized by the CN? segment 2 +---+ v<<<<<<<<<<<<<<<| AR|<<<<<<<<<<<<<^ v +---+ ^ +----+ +----+ +--+ | MN | |UCRN|<<<<<<<<<<|CN| |DCRN| | |<<<<<<<<<<| | +----+ +----+ +--+ ^ +---+ v shared ^<<<<<<<<<<<<<<<| AR|<<<<<<<<<<<<|NE | ... |NE | ------V common path ^ +---+ +---+ V common path +--+ +----+ +----+ +--+ |S |-----> |DCRN| |DCRN| -------> |R | | | | | | | | | +--+ +----+ New path +----+ +--+ V +---+ +---+ ^ V --->|NE | ... |NAR| ------^ +---+ +---+ =======(downstream signaling followed by data flows) ======> (a) The topology for downstream NSIS signaling flow after route changes Old path +---+ +---+ v <---|NE | ... |NE | ----- ^ common path v +---+ +---+ ^ common path +--+ +----+ +----+ +--+ |S |<----- |UCRN| |UCRN| <------- |R | | | | | | | | | +--+ +----+ New path +----+ +--+ ^ +---+ +---+ v ^ <---|NE | ... |NAR| ----- v +---+ +---+ <=====(upstream signaling followed by data flows) ====== (b) The topology for upstream NSIS signaling flow after route changes Figure.14 The topology for NSIS signaling in case of the route changes Lee, et al. Expires January 19, 2006 [Page 52] Internet-Draft NSIS Signaling in Mobility July 2005 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 (2005). 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. Lee, et al. Expires January 19, 2006 [Page 53]