IETF Next Steps in Signaling S. Lee, Ed. Internet-Draft Samsung AIT Expires: August 21, 2005 S. Jeong HUFS H. Tschofenig Siemens AG X. Fu Univ. of Goettingen J. Manner Univ. of Helsinki February 20, 2005 Applicability Statement of NSIS Protocols in Mobile Environments draft-ietf-nsis-applicability-mobility-signaling-01.txt Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. 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 August 21, 2005. Copyright Notice Copyright (C) The Internet Society (2005). All Rights Reserved. Abstract The mobility of an IP-based node affects routing paths, and as a result, can have a significant effect on the protocol operation and Lee, et al. Expires August 21, 2005 [Page 1] Internet-Draft NSIS Signaling in Mobility February 2005 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 . . . . . . . . . . . . . . . . 9 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 . . . . 11 4. Basic Operations for Mobility Support . . . . . . . . . . . . 12 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 . . . . . . . . . . . 17 4.3 Path update . . . . . . . . . . . . . . . . . . . . . . . 18 4.3.1 State setup and update . . . . . . . . . . . . . . . . 19 4.3.2 State teardown . . . . . . . . . . . . . . . . . . . . 21 5. Applicability Statement . . . . . . . . . . . . . . . . . . . 21 5.1 Support for macro mobility-based scenarios . . . . . . . . 22 5.1.1 Implications to Mobile IP-related scenarios . . . . . 22 5.1.1.1 Mobile IPv4-specific issues . . . . . . . . . . . 24 5.1.1.2 Mobile IPv6-specific issues . . . . . . . . . . . 26 5.2 Multihoming scenarios . . . . . . . . . . . . . . . . . . 28 5.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . 28 5.2.2 Examples of NTLP/NSLP support for mobility . . . . . . 28 5.3 QoS performance considerations in mobility scenarios . . . 29 5.4 Support for Ping-Pong type handover . . . . . . . . . . . 31 5.5 Peer failure scenarios . . . . . . . . . . . . . . . . . . 32 6. Security Considerations . . . . . . . . . . . . . . . . . . . 33 6.1 MN as data sender . . . . . . . . . . . . . . . . . . . . 34 6.1.1 MN is authorizing entity . . . . . . . . . . . . . . . 34 6.1.2 CN is authorizing entity . . . . . . . . . . . . . . . 36 6.1.2.1 CN asks MN to trigger action (on behalf of the CN) . . . . . . . . . . . . . . . . . . . . . . . 36 6.1.2.2 CN uses installed state to route message backwards . . . . . . . . . . . . . . . . . . . . 37 6.1.2.3 MN and CN are authorized . . . . . . . . . . . . . 39 6.1.3 CN as data sender . . . . . . . . . . . . . . . . . . 39 6.1.3.1 CN is authorizing entity . . . . . . . . . . . . . 39 6.1.3.2 MN is authorizing entity . . . . . . . . . . . . . 40 6.1.4 Multi-homing Scenarios . . . . . . . . . . . . . . . . 40 Lee, et al. Expires August 21, 2005 [Page 2] Internet-Draft NSIS Signaling in Mobility February 2005 6.1.4.1 MN as data sender . . . . . . . . . . . . . . . . 41 6.1.4.2 CN as data sender . . . . . . . . . . . . . . . . 41 6.1.5 Proxy Scenario . . . . . . . . . . . . . . . . . . . . 42 6.1.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . 43 7. Change History . . . . . . . . . . . . . . . . . . . . . . . . 44 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 45 8.1 Normative References . . . . . . . . . . . . . . . . . . . . 45 8.2 Informative References . . . . . . . . . . . . . . . . . . . 45 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 46 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 47 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 47 A. Generic Route Changes . . . . . . . . . . . . . . . . . . . . 47 Intellectual Property and Copyright Statements . . . . . . . . 49 Lee, et al. Expires August 21, 2005 [Page 3] Internet-Draft NSIS Signaling in Mobility February 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. Normal IP mobility (i.e., macro-mobility) also involves the change of mobile node 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. The goals of this draft are to present the effects of mobility on the NSIS Transport Layer Protocol (NTLP) and on the NSIS Signaling Layer Protocols (NSLP). The NTLP is an application independent protocol to transport service-related information between nodes in a network, and each specific service has its own NSLP protocol. This draft also discusses how the NSIS protocols should work in various mobility scenarios. 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, the following terms are used. (1) Downstream The direction from a data sender towards the destination. (2) Upstream The direction from a data destination towards the sender. (3) Crossover Node (CRN) Lee, et al. Expires August 21, 2005 [Page 4] Internet-Draft NSIS Signaling in Mobility February 2005 A Crossover Node is a node that for a given function is a merging point of two or more separate sets of state information. The CRN may not necessarily be a physical route splitting point. There can be different types of logical (but not necessarily physical) CRNs according to the signaling states, flow directions, mobility management types, and generic routing (not caused by mobility): From the perspective of NSIS states (i.e., NSLP and NTLP states), the types of CRN are basically classified as follows. NSLP CRN, from the NSLP's point of view, is a signaling application-aware node in the network where the corresponding signaling flows begin to merge or split after route changes or mobility. The NSLP CRN may be different according to the types of NSLP. NTLP CRN, from the NTLP's point of view, is a network node where more than one NTLP states begin to merge or split after route changes or mobility. NSIS CRN is an NTLP CRN and/or an NSLP CRN. Note that although the types of CRN differ according to the state information, the CRN required for QoS-NSLP operation is the NSLP CRN which has the corresponding signaling application information for the path update. There are some differences between route changes and mobility in forming the CRN according to the direction of signaling flows followed by data flows In the mobility scenarios, there are two different types of merging point in the network according to the direction of signaling flows followed by data flows as shown in Figure 2 of Section 4.1, where we assume that the MN is a data sender. Upstream CRN (UCRN), after a handover, is the node closest to the data sender from which the state information towards the data sender begins to diverge. Downstream CRN (DCRN), after a handover, is the node closest to the data sender from which the state information towards the data receiver begins to converge. In this case, the DCRN and the UCRN may be different due to the asymmetric characteristics of routing although the CN is the same. Lee, et al. Expires August 21, 2005 [Page 5] Internet-Draft NSIS Signaling in Mobility February 2005 In 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, which is referred to as a divergence-convergence pair: Upstream CRN, after a route changes, is the node at which the state information towards the data sender begins to diverge, or to converge. As a result, a (divergent-convergent) UCRN pair will be formed. Downstream CRN, after a route changes, is the node at which the state information towards the data receiver begins to diverge, or to converge. As a result, a (divergent-convergent) DCRN pair will be formed. From the mobility management point of view, mobility CRN is the node where the old and new paths (physically) merge. Note that in general, the mobility CRN may be different from the NSLP CRN or NTLP CRN. Routing CRN is the node where the old and new paths (rather physically) merge using normal routing. Depending on the location of nodes, the routing CRN may not be equal to the NSLP CRN or NTLP CRN. (4) Path Update and Local Repair 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. This is used to improve mobility handling 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). 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, the update of NSIS state on the common path is not required due to no change of flow identifiers, which makes the NSIS signaling the localized. Especially, in mobility Lee, et al. Expires August 21, 2005 [Page 6] Internet-Draft NSIS Signaling in Mobility February 2005 scenarios, if the NSIS signaling interacts with localized mobility management 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. The various protocols that seek to support the mobility of end hosts may use some techniques to reach their goals. 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 entail the change of routes for data packets sent to or from the MN and may lead to the change of host IP addresses. (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, for example, those due to failure, adding or removal of nodes/links. (3) Explicit routes Signaling protocols usually expect the data traffic to follow the same path as the signaling traffic, but the data traffic sometimes traverses the path different from the path of signaling traffic due to the adaptation of routing protocol according to varying network conditions such as load balancing, load sharing and mobility. For example, Mobile IP adds the possibility to use the routing headers to define explicit routes, which diverts the traffic from an expected path, too. (4) IP-in-IP encapsulation Lee, et al. Expires August 21, 2005 [Page 7] Internet-Draft NSIS Signaling in Mobility February 2005 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 harms any attempt to identify and filter. Moreover, encapsulation may lead to changes in the routing paths, since the sender and destination IP addresses differ from the values in the original user data packet. The same considerations apply if the signaling packets are encapsulated, too. (5) Ping-pong type handover Signaling protocols should remove states quickly along the old path to mitigate 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 causes 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 may not be equal, the upstream and downstream CRNs may not be equal, either. Therefore, the Path Update needs to be handled independently for upstream and downstream flows, including the discovery of upstream and downstream CRNs. (7) State identification problem A mobility event may cause the address of flow endpoints to change, and thus it is desirable that the signaling application state is independent of the underlying flows to keep the state from being re-installed completely. Therefore, the session and flow identifiers need to be created independently, and this makes it possible to correlate the session identifier with the signaling application which may generate different flows. (8) Double reservation problem Since the state on the old path (and the common path) still 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 and common paths can be torn down by the timeout of soft state, the refresh timer value may be quite long (e.g., 30s as a default value in RSVP). This problem results in the waste of resources and call blocking. (9) End-to-end signaling problem Lee, et al. Expires August 21, 2005 [Page 8] Internet-Draft NSIS Signaling in Mobility February 2005 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) AA Issues The Path Update procedure may be initiated by the MN, the CN, or even nodes within the network (e.g., MAP/GPA in HMIP). This Path Update on behalf of the MN raises authentication and authorization issues. 3.2 Mobility-Related Issues with NSIS Protocols Considering the issues identified in Section 3.1, this section mainly discusses the concerns that arise for the NSIS protocols. 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. In this situation, is it necessary to define a Mobile IP-specific API in NSIS? 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? Lee, et al. Expires August 21, 2005 [Page 9] Internet-Draft NSIS Signaling in Mobility February 2005 (2) Localized Path Update NSIS protocols need to make the Path Update localized to enhance and performance parameters such as signaling setup delay, resource utilization, and in this case, a few issues on the interaction between the micro-mobility management protocols and NTLP protocols 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 the old AR is the last node on the old signaling path due to the MNí¯s handover, its QoS-NSLP may trigger an error message to indicate that QoS-NSLP messages cannot be forwarded any further. This error message may mistakenly cause the removal of the state on the obsolete path, which is called the í«invalid NR problemí¯ [12]. (2) Priority of signaling messages Some messages of QoS-NSLP need to be used to check the availability of resources in a new access network to ensure that the moving MN gets the required QoS. for example, the Query message can be used for that purpose. In this case, should a high priority be given to the signaling message to expedite the process? (3) Optimal refresh timer value for mobile environments In 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 environment (e.g., access network, or core network). (4) Athorization-related issues with teardown 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 QoS-NSLP state may delete the state. (5) Peering agreement issue Lee, et al. Expires August 21, 2005 [Page 10] Internet-Draft NSIS Signaling in Mobility February 2005 In the inter-domain handover scenarios, how is the peering agreement established for aggregate reservation and authorization to support individual sessions? (6) 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 [6]. With regard to mobility, a few issues need to be considered: (1) Update of firewall rules and NAT bindings When an IP address changes, firewall rules and/or NAT bindings become invalid, which effectively prevents the end host from sending or receiving data packets. 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. In this case, the QoS-NSLP might 'only' temporarily experience a weaker QoS if the installed flow identifier is not up-to-date. (2) Re-use of NAT/FW-NSLP's old state Although NSIS states can be released by applying the soft-state principle, mobility can leave states (such as firewall pinholes) in place for some time. Since the NAT/FW-NSLP aims to install pinholes (and NAT bindings), it is possible to re-use this installed state once a mobile node roams to a new location. Deleting state along the old path helps 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 usage of non-cryptography-based IP address filters. Therefore, the teardown of the NAT/FW-NSLP state in mobility scenarios needs to be considered in the fashion different from that of QoS-NSLP state. 3.2.4 Common problems related to both NTLP and NSLP Lee, et al. Expires August 21, 2005 [Page 11] Internet-Draft NSIS Signaling in Mobility February 2005 (1) CRN discovery-related issues Which layer should be responsible for the CRN discovery, NTLP (GIMPS) or NSLP (QoS-NSLP)? Although the QoS-NSLP can detect the change of signaling path and discover the CRN by keeping track of SII, the CRN discovery at the NTLP layer may be preferred to at the QoS-NSLP. However, is there any advantage if NSLP discovers the CRN? (2) CRN discovery and Path Update on the IP-tunneling path Considering interworking with IP-tunneling, NTLP needs to consider how to perform CRN discovery and Path Update on the IP-tunneling path. For example, whether the GIMPS peer discovery can be used for the CRN discovery on the tunnel should be discussed further. Additionally, after route optimization, when to remove the tunneling segment on the signaling path and/or how to tear down the state via interworking with the IP-tunneling operation should also be discussed. (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, 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 A host that is an initiator or responder of signaling messages may be multi-homed in mobile environments. NSIS signaling protocols should use such multi-homed interfaces to perform load-balancing and load-sharing, or to support seamless mobility. However, which NxLP functionality is required in various multihoming scenarios (e.g., load balancing, bi-casting, etc.) is an open question. An overall coordination for interworking between the NSIS protocol and multihoming capability needs to be discussed further. 4. Basic Operations for Mobility Support In this section, we mainly discuss the basic operations of NSIS signaling protocols needed after route changes caused by mobility. The basic operations include how to discover an appropriate CRN and Lee, et al. Expires August 21, 2005 [Page 12] Internet-Draft NSIS Signaling in Mobility February 2005 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 address 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. 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 the mobility may be considered similar to the generic route changes, the main difference is that the Message Routing Information (MRI: e.g., flow identifier) may not change after the route changes while the 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 identify the session of any signaling application [4]. The route change brings on the change of signaling topology, and this causes differences between the types of route changes (e.g., the generic route changes or mobility) (see Appendix). The mobility generally creates a common path, an old path, and a new path, and the old and new paths converge or diverge depending on the direction of each signaling flow as shown in Figure 1. 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 Lee, et al. Expires August 21, 2005 [Page 13] Internet-Draft NSIS Signaling in Mobility February 2005 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 established on the old path useless and therefore it should be removed (in the end). In addition, the existing NSIS state should also be re-established along the new path and to be updated along the common path. NSIS signaling should be localized when route changes (including mobility) occur to minimize the impact on the seamless service and to improve signaling scalability, This localized signaling procedure is referred to as Path Update (see the Terminology section). In mobile environments, 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 logically. Therefore, the CRN discovery can be a crucial element to alleviate the double reservation and end-to-end signaling problems identified in Section 3.1. Lee, et al. Expires August 21, 2005 [Page 14] Internet-Draft NSIS Signaling in Mobility February 2005 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 trigger the necessary operation of the relevant NSLP. 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 according as which layer is responsible for the CRN discovery (addressed in Section 3.2.2), and whether 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 NSLP of an NSIS node can determine whether 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. It is also possible to discover the CRN at the NTLP layer since NTLP is responsible for detecting the path change of data (or signaling) flow (the route changes may easily be detected at the NTLP level rather than at the NSLP). The CRN discovery can be considered as an extension to the peer discovery at the NTLP level (e.g., using GIMPS query-response [2]). In general, the GIMPS message has 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. 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. There can also be two different approaches for the CRN discovery according as whether the discovery is coupled with signaling message or not: 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 have some effect on security aspect. Lee, et al. Expires August 21, 2005 [Page 15] Internet-Draft NSIS Signaling in Mobility February 2005 Generally, the coupled approach would be preferred to the uncoupled approach to reduce the delay for signaling setup. 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. The SID in the GIMPS message is used to easily identify the involved session because it remains the same while the MRI may (or may not) change due to handover. 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. The NSLP_ID is used to refer to the corresponding NSLP at the GIMPS 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 can be used to establish or delete NSIS associations between NSIS peers. It can also be used as an identifier to determine the CRN at the GIMPS 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 Figure 2, for the downstream case, NSLP1 of node A requires a messaging association for sending its messages towards node D after a route changes. In this case, NSIS entity A creates an 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 corresponding NSLP_Br_ID is 1-D-#2; 1, D, and #2 indicate an NSLP_ID-flow, a flow direction (Downstream or Upstream), and a value of the branch counter, respectively. 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 2 (a). Lee, et al. Expires August 21, 2005 [Page 16] Internet-Draft NSIS Signaling in Mobility February 2005 +------------------+-------+-------+--------+------------+-------+ | 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 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. 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. Therefore, the Mobility identifier is useful to discover the most appropriate CRN. 4.2.3 The procedures of CRN discovery When a mobility event occurs, the CRN can be recognized by comparing Lee, et al. Expires August 21, 2005 [Page 17] Internet-Draft NSIS Signaling in Mobility February 2005 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)) should be checked to determine if the current node is CRN: - Whether the same NSLP_ID exists - Whether the corresponding CRN has already been discovered - Whether the same SID and MRI exist - Whether the NSLP_Br_ID has been changed: for example, as shown in Figure 3 (a), for NSLP 1 it has been changed to 1-D-#2 from 1-D-#1. - 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 according as which node is a signaling initiator (by upstream or downstream), or whether the MN is a data sender: - 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, and 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 whether the outgoing path diverges or not, the UCRN discovery is more complex than the DCRN discovery. 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 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 may need to interact with various Lee, et al. Expires August 21, 2005 [Page 18] Internet-Draft NSIS Signaling in Mobility February 2005 mobility signaling protocols, if any (during or posterior handover) to obtain performance gains (e.g., through fast re-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 a data sender. 4.3.1 State setup and update Before initiating the Path Update, the MN or CN needs to have its session ownership by the procedures for authentication and authorization and to 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. It may be desirable to provide the Query message with a higher priority than other signaling messages. 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 6.2). In this situation, providing NSIS signaling for the Path Update with a high priority over local requests for the resources will be helpful for seamless service. In the downstream Path Update, if resources are available, the MN initiates the NSIS signaling for state re-setup toward a CN along the new path, and the DCRN discovery is implicitly performed by this type of signaling as described in Section 4.2.3. When the DCRN is discovered, it sends a response message toward 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 then, the DCRN sends a refresh message toward the signaling destination to update the changed MRI on the common path and also sends a teardown message toward 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 6.1)). After the UCRN is determined, it may send a refresh message to the MN along the new path while establishing the NSIS association between the newly found peers. Afterward, the UCRN may send a teardown message toward the old AR to delete the NSIS state (if possible). The state update on the common path to reflect the changed MRI brings Lee, et al. Expires August 21, 2005 [Page 19] Internet-Draft NSIS Signaling in Mobility February 2005 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 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. 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 Lee, et al. Expires August 21, 2005 [Page 20] Internet-Draft NSIS Signaling in Mobility February 2005 4.3.2 State teardown After re-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 and the maintenance of the NSIS state on the old path 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 the GIMPS 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 re-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 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. 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 í«invalid NRí¯ 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). The more details are discussed further in Section 5.5. 5. Applicability Statement Lee, et al. Expires August 21, 2005 [Page 21] Internet-Draft NSIS Signaling in Mobility February 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 and Mobile IPv6. 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 through 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. In this case, it is essential to require the NI to be authorized to initialize NSIS signaling. (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 immediately be initiated via a mobility routing interface (e.g., mobility API) between the NSIS protocol and the Mobile IP. (4) 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 mobility management protocols (e.g., HMIP, FMIP, etc..) may give rise to significant performance gains (see Section 5.3). (5) With Mobile IPv6, an MN can support multiple CoAs at a time, 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 Lee, et al. Expires August 21, 2005 [Page 22] Internet-Draft NSIS Signaling in Mobility February 2005 As NSIS is 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, 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 based on the endpoint notification regarding 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 the Mobile IP rather than NSLP because NTLP is responsible for detecting the mobility and routing NSIS messages. Therefore, it is reasonable to assume NTLP should be able to notify NSLP for the necessity of state update when the mobility is detected. Here are also some issues which 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 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 Lee, et al. Expires August 21, 2005 [Page 23] Internet-Draft NSIS Signaling in Mobility February 2005 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. The Figures 5 (a) to (e) show the NSIS signaling flows depending on the direction of data flows and the routing methods . 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 Lee, et al. Expires August 21, 2005 [Page 24] Internet-Draft NSIS Signaling in Mobility February 2005 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, - 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. - 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 and the corresponding binding process for the co-located CoA is completed, - For the downstream signaling flow, the NSIS signaling for the DCRN Lee, et al. Expires August 21, 2005 [Page 25] Internet-Draft NSIS Signaling in Mobility February 2005 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). - 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 and the NSIS state along the tunneling path is not established. 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 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. 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 may initiate NSIS signaling for the DCRN discovery and the (downstream) Path Update to establish the state along the new path between the MN and the CN or the tunneling path from the MN to the HA if the reverse tunnel is used, as shown in Figures 5 (a) and (b), respectively. - 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). However, if the route optimization is used between the CN and the MN, for the upstream flow, CN needs to newly initiate 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 bidirectional Lee, et al. Expires August 21, 2005 [Page 26] Internet-Draft NSIS Signaling in Mobility February 2005 state establishment may be required. In this case, the obsolete path of the existing tunneling segments needs to be removed after re-establishment of NSIS state along the optimized 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. Although the routing based on Mobile IPv4 with the co-located CoA is similar to the case of Mobile IPv6, one of the differences is the method to acquire the CoA. The Mobile IPv6 is able to acquire the CoA from the corresponding access router or external method through the stateless autoconfiguration or the stateful autoconfiguration (e.g., DHCPv6), respectively while the Mobile IPv4 obtains the CoA through from FA or using an external method such as DHCP. This difference may have some effects on the creation of flow identifier and make NSIS signaling performed differently. It is still an open issue and needs to be discussed further in the later version of this draft. 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 Lee, et al. Expires August 21, 2005 [Page 27] Internet-Draft NSIS Signaling in Mobility February 2005 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 Multihoming scenarios 5.2.1 Overview A host that is an initiator or responder of signaling messages may be not only mobile but also multi-homed. When considering current activities in the Multi6 and HIP WGs, multi-homed hosts and scenarios may be common in the future IPv6-based Internet. Such scenarios may include load balancing where multiple connections to different providers are used simultaneously. In this case, the multi-homed MN may use different paths that converge at some CRN. If load balancing is active, the paths are used at the same time, but if multi-homing is used for resilience only, the active path changes during fail-over. The term "seamless mobility" is often referred to mean that the MN is able to keep an ongoing session seamlessly (without experiencing perceivable service interruption or performance penalty) during and after moving from one access network to another. Measures to achieve seamless mobility include soft handover and anticipated handover. The former requires the MN to keep the old path, while data is received over the new path. This approach is possible if the MN is multi-homed. Other possible scenarios may include bi-casting, bandwidth increase, etc. 5.2.2 Examples of NTLP/NSLP support for mobility The NTLP uses an endpoint address (e.g., CoA) to install message routing state. In multi-homed MN scenarios, there are multiple CoAs for the MN, and therefore an appropriate CoA should be selected to establish the NSIS state between the MN and the CN. If the multi-homed MN has multiple network interfaces, each network interface may use a unique CoA. To find a feasible signaling path, multiple NSIS messages (e.g., multiple QUERY messages of the Lee, et al. Expires August 21, 2005 [Page 28] Internet-Draft NSIS Signaling in Mobility February 2005 QoS-NSLP) can be sent from the MN to the HA or CN (in case of route optimization), 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 new CoA introduced in Mobile causes the change of message routing state, both new and old addresses are valid during a certain period of time, and the new data path may co-exist with the old one. It is theoretically possible to perform an NSIS state update on the new path during this period, 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 can be mitigated if the MN is multi-homed. For load balancing purposes, NSIS may need to install the NSIS state along 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. In this way, multiple paths can be set up for load balancing between the same endpoints. A more detailed analysis of the NTLP/NSLP functionality in different multi-homed scenarios (e.g., including load balancing, bi-casting, etc.) will be presented in the later version of this 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 be changed and the exiting protocols which do not support NSIS signaling in dynamic environment may cause the problems addressed in Section 3.1. In particular, QoS performance in terms of resources utilization and signaling latency needs to be examined so that how NSIS protocols should interact with mobility protocols is correctly analyzed. From the perspective of resource utilization, the double reservation problem can be alleviated by the CRN discovery and the Path Update. However, how to manage the resource utilization in NSIS signaling should be taken into account; in this regard, the adjustment of refresh interval should be considered as addressed in Section 3.2. Lee, et al. Expires August 21, 2005 [Page 29] Internet-Draft NSIS Signaling in Mobility February 2005 The NSIS protocol suite normally uses a soft-state approach based on the peer-to-peer refresh to manage state in NEs. At the GIMPS layer, the state is maintained through the exchange of GIMPS query/ response messages between adjacent peers [2]. The peer relationship is maintained using a timer which indicates how long the association between the peers can be considered valid. In other words, if the timer has not been refreshed until it expires (e.g., in 30 seconds as a default value), the peer relationship is removed. The management of state (i.e., routing state and messaging association) can be controlled in this way. In case of QoS-NSLP, states are set up and maintained using the peer-to-peer refresh messages. The peer-to-peer based refresh allows the QoS-NSLP to appropriately select the refresh interval by considering the current network environment. For example, the refresh timer value is set to a smaller value in the mobile/wireless (access) network than that in the core (wired) network as in [7]. Especially, in the situation where handover happens very frequently, the adjustment of the refresh interval reduces the waste of resources. However, unlike the QoS-NSLP, the refresh timer of NTLP state does not need to be adjusted in the network since 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, the 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 [8]. 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. 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 flow ID along the common path . The overhead required to perform refresh can be reduced, in a way similar to the refresh reduction in RSVP [9]. 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 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 Lee, et al. Expires August 21, 2005 [Page 30] Internet-Draft NSIS Signaling in Mobility February 2005 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. 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 and CTP) 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 to 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, 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) 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 Lee, et al. Expires August 21, 2005 [Page 31] Internet-Draft NSIS Signaling in Mobility February 2005 point in case it moves back there. 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 ESERVE 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, and AR. In general, it is possible that only NSIS functions (i.e., NTLP/NSLP) of the node may fail, or the physical hardware. In this regard, the following issues arise. - An MN may either fail or move. 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 addressed 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 should not be generated/sent to avoid any teardown on the old 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 that a handover is now initiated, and thus the invalid NR problem can be resolved [12]. It may be possible that the MN is not the NR, but a router in the access network (possibly the AR) is proxying for the MN instead. Lee, et al. Expires August 21, 2005 [Page 32] Internet-Draft NSIS Signaling in Mobility February 2005 - 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 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 CT) 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 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. 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. Subsequently, we will consider the case where the mobile node acts as Lee, et al. Expires August 21, 2005 [Page 33] Internet-Draft NSIS Signaling in Mobility February 2005 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 flow setup triggered by the MN which is also authorized by the MN. 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 independent of the authorization issues discussed in this section. The following questions seem to be interesting: - 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 Lee, et al. Expires August 21, 2005 [Page 34] Internet-Draft NSIS Signaling in Mobility February 2005 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., why should it trust the MN and what information can the DCRN use for verification?) 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 designed 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. Lee, et al. Expires August 21, 2005 [Page 35] Internet-Draft NSIS Signaling in Mobility February 2005 | Tear | Down ------>----->------>------>------>------>------> | ACTION | | <-----<-----<------<------<------<------<------- + ACK Figure 8: CN triggers action The following questions arise: - Why should the MN trust the trigger? - 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)? On the 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 | | Lee, et al. Expires August 21, 2005 [Page 36] Internet-Draft NSIS Signaling in Mobility February 2005 ------>----->------>------>------>------>------> | 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) 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 As a second variant 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) ] | Lee, et al. Expires August 21, 2005 [Page 37] Internet-Draft NSIS Signaling in Mobility February 2005 | ------<-----<------<------<------<------<------< | 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 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 Lee, et al. Expires August 21, 2005 [Page 38] Internet-Draft NSIS Signaling in Mobility February 2005 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 include authorization information. 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 strawman 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. 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)| | +-----------------+ | +-----------------+ | <------<------<--------+ | +-----------------+ | Lee, et al. Expires August 21, 2005 [Page 39] Internet-Draft NSIS Signaling in Mobility February 2005 | 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 (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 the 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 sessions are tight together with the same session identifier. 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 is stored. Lee, et al. Expires August 21, 2005 [Page 40] Internet-Draft NSIS Signaling in Mobility February 2005 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. 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 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. Mobility handling might be smoother since it is possible that only one interface experiences an IP address change with all the previously discussed implications. 6.1.4.2 CN as data sender This section shows the multi-homing scenario with the CN as a data Lee, et al. Expires August 21, 2005 [Page 41] Internet-Draft NSIS Signaling in Mobility February 2005 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 August 21, 2005 [Page 48] Internet-Draft NSIS Signaling in Mobility February 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. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Lee, et al. Expires August 21, 2005 [Page 49]