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diff --git a/doc/rfc/rfc6058.txt b/doc/rfc/rfc6058.txt new file mode 100644 index 0000000..0a18df3 --- /dev/null +++ b/doc/rfc/rfc6058.txt @@ -0,0 +1,1963 @@ + + + + + + +Internet Engineering Task Force (IETF) M. Liebsch, Ed. +Request for Comments: 6058 NEC +Category: Experimental A. Muhanna +ISSN: 2070-1721 Ericsson + O. Blume + Alcatel-Lucent Bell Labs + March 2011 + + + Transient Binding for Proxy Mobile IPv6 + +Abstract + + This document specifies a mechanism that enhances Proxy Mobile IPv6 + protocol signaling to support the creation of a transient binding + cache entry that is used to optimize the performance of dual radio + handover, as well as single radio handover. This mechanism is + applicable to the mobile node's inter-MAG (Mobility Access Gateway) + handover while using a single interface or different interfaces. The + handover problem space using the Proxy Mobile IPv6 base protocol is + analyzed and the use of transient binding cache entries at the local + mobility anchor is described. The specified extension to the Proxy + Mobile IPv6 protocol ensures optimized forwarding of downlink as well + as uplink packets between mobile nodes and the network infrastructure + and avoids superfluous packet forwarding delay or even packet loss. + +Status of This Memo + + This document is not an Internet Standards Track specification; it is + published for examination, experimental implementation, and + evaluation. + + This document defines an Experimental Protocol for the Internet + community. This document is a product of the Internet Engineering + Task Force (IETF). It represents the consensus of the IETF + community. It has received public review and has been approved for + publication by the Internet Engineering Steering Group (IESG). Not + all documents approved by the IESG are a candidate for any level of + Internet Standard; see Section 2 of RFC 5741. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + http://www.rfc-editor.org/info/rfc6058. + + + + + + + + +Liebsch, et al. Experimental [Page 1] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +Copyright Notice + + Copyright (c) 2011 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents + (http://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. Code Components extracted from this document must + include Simplified BSD License text as described in Section 4.e of + the Trust Legal Provisions and are provided without warranty as + described in the Simplified BSD License. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Liebsch, et al. Experimental [Page 2] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +Table of Contents + + 1. Introduction ....................................................4 + 2. Conventions and Terminology .....................................5 + 2.1. Conventions Used in This Document ..........................5 + 2.2. Terminology and Functional Components ......................5 + 3. Analysis of the Problem Space ...................................6 + 3.1. Handover Using a Single Interface ..........................6 + 3.2. Handover between Interfaces ................................6 + 3.2.1. Issues with Downlink Traffic ........................7 + 3.2.2. Issues with Uplink Traffic ..........................9 + 3.3. Need for a Common Solution ................................10 + 4. Use of Transient Binding Cache Entries .........................11 + 4.1. General Approach ..........................................11 + 4.2. Impact on Binding Management ..............................13 + 4.3. Role of the LMA and nMAG in Transient State Control .......14 + 4.3.1. Control at the nMAG ................................14 + 4.3.2. Control at the LMA .................................15 + 4.4. LMA Forwarding State Diagram ..............................15 + 4.5. MAG Operation .............................................18 + 4.6. LMA Operation .............................................19 + 4.6.1. Initiation of a Transient BCE ......................19 + 4.6.2. Activation of a Transient BCE ......................20 + 4.7. MN Operation ..............................................22 + 4.8. Status Values .............................................22 + 4.9. Protocol Stability ........................................22 + 5. Message Format .................................................24 + 5.1. Transient Binding Option ..................................24 + 6. IANA Considerations ............................................25 + 7. Security Considerations ........................................25 + 8. Protocol Configuration Variables ...............................26 + 9. Contributors ...................................................26 + 10. Acknowledgments ...............................................26 + 11. References ....................................................26 + 11.1. Normative References .....................................26 + 11.2. Informative References ...................................26 + Appendix A. Example Use Cases for Transient BCE ..................28 + A.1. Use Case for Single Radio Handover ........................28 + A.2. Use Case for Dual Radio Handover ..........................30 + Appendix B. Applicability and Use of Static Configuration at + the LMA ..............................................33 + B.1. Early Uplink Traffic from the nMAG ........................33 + B.2. Late Uplink Traffic from the pMAG .........................33 + B.3. Late Switching of Downlink Traffic to nMAG ................34 + + + + + + + +Liebsch, et al. Experimental [Page 3] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +1. Introduction + + The IETF specified Proxy Mobile IPv6 (PMIPv6) [RFC5213] as a protocol + for network-based localized mobility management, which takes basic + operation for registration, tunnel management, and deregistration + into account. In order to eliminate the risk of lost packets, this + document specifies an extension to PMIPv6 that utilizes a new + mobility option in the Proxy Binding Update (PBU) and the Proxy + Binding Acknowledgement (PBA) between the new Mobility Access Gateway + (nMAG) and the Local Mobility Anchor (LMA). + + According to the PMIPv6 base specification, an LMA updates a mobile + node's (MN's) Binding Cache Entry (BCE) and switches the forwarding + tunnel after receiving a Proxy Binding Update (PBU) message from the + mobile node's new MAG (nMAG). At the same time, the LMA disables the + forwarding entry towards the mobile node's previous MAG (pMAG). In + case of an inter-technology handover, the mobile node's handover + target interface must be configured according to the Router + Advertisement being sent by the nMAG. Address configuration as well + as possible access-technology-specific radio bearer setup may delay + the complete set up of the mobile node's new interface before it is + ready to receive or send data packets. In case the LMA performs + operation according to [RFC5213] and forwards packets to the mobile + node's new interface after the reception of the PBU from the nMAG, + some packets may get lost or experience major packet delay. The + transient BCE extension, as specified in this document, increases + handover performance (optimized packet loss and forwarding delay) + experienced by MNs, which have multiple network interfaces + implemented while handing over from one interface to the other. The + transient BCE extension also increases handover performance for + single radio MNs, which build on available radio layer forwarding + mechanisms, hence re-use existing active handover techniques. + + Some implementation-specific solutions, such as static configuration + on the LMA to accept uplink packets from the old MAG in addition to + accepting packets from the new MAG for a short duration during the + handover and buffering at the new MAG, can help to address some of + the issues identified in this document. Please see Appendix B for + more details. A dynamic solution by means of the proposed protocol + operation helps to optimize the performance for a variety of handover + situations and different radio characteristics. + + Additionally, this document specifies an advanced binding cache + management mechanism at the LMA according to well-defined transient + BCE states. This mechanism ensures that forwarding states at LMAs + are inline with the different handover scenarios. During a transient + state, a mobile node's BCE refers to two proxy Care-of-Address + (Proxy-CoA) entries, one from the mobile node's pMAG, another from + + + +Liebsch, et al. Experimental [Page 4] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + its nMAG. MAGs can establish settings of a transient binding on the + LMA by means of signaling. An LMA can establish or change the + settings of a transient binding according to events, such as a + timeout, a change of the radio technology due to a handover, or a + completed set up of a radio bearer or configuration of an MN's IP + address. Such an event may also be triggered by other protocols, + e.g., Authentication, Authorization, and Accounting (AAA) messages. + This document specifies advanced binding cache control by means of a + Transient Binding option, which can be used with PMIPv6 signaling to + support transient BCEs. Furthermore, this document specifies + forwarding characteristics according to the current state of a + binding to switch the forwarding tunnel at the LMA from the pMAG to + the nMAG during inter-MAG handover according to the handover + conditions. As a result of transient binding support, handover + performance can considerably be improved to smooth an MN's handover + without introducing major complexity into the system. + +2. Conventions and Terminology + +2.1. Conventions Used in This Document + + 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 [RFC2119]. + +2.2. Terminology and Functional Components + + o IF - Interface. Any network interface, which offers a mobile node + wireless or wired access to the network infrastructure. In case a + mobile node has multiple interfaces implemented, they are numbered + (IF1, IF2, etc.). + + o Transient Binding Cache Entry. A temporary state of the mobile + node Binding Cache Entry that defines the forwarding + characteristics of the mobile node forwarding tunnels to the nMAG + and pMAG. This transient BCE state is created when the Transient + Binding option is included in the PBU and PBA as specified in this + document. The LMA forwards the mobile node traffic according to + current transient BCE characteristics as specified in this + document. The transient BCE state is transparent to the pMAG. + + o Active Binding Cache Entry. A valid mobile node Binding Cache + Entry according to [RFC5213], which is not in transient state. + + + + + + + + +Liebsch, et al. Experimental [Page 5] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +3. Analysis of the Problem Space + + This section summarizes the analysis of the handover problem space + for inter-technology handover as well as intra-technology handover + when using the PMIPv6 protocol as in [RFC5213]. + +3.1. Handover Using a Single Interface + + In some active handover scenarios, it is necessary to prepare the + nMAG as the handover target prior to the completion of the link-layer + handover procedures. Packets sent by the LMA to the nMAG before the + completion of the link-layer handover procedure will be lost unless + they are buffered. + + In some systems, the nMAG will be the recipient of uplink traffic + prior to the completion of the procedure that would result in the + PBU/PBA handshake. These packets cannot be forwarded to the LMA. + + During an intra-technology handover, some of the MN's uplink traffic + may still be in transit through the pMAG. Currently, and as per the + PMIPv6 base protocol [RFC5213], the LMA forwards the MN's uplink + traffic received from a tunnel only as long as the source IP address + of the MN's uplink traffic matches the IP address of the mobile + node's registered Proxy-CoA in the associated BCE. As a result, + packets received at the LMA from the MN's pMAG after the LMA has + already switched the tunnel to point to the nMAG will be dropped. + +3.2. Handover between Interfaces + + In client-based mobility protocols, the handover sequence is fully + controlled by the MN, and the MN updates its binding and associated + routing information at its mobility anchor after IP connectivity has + been established on the new link. On the contrary, PMIPv6 aims to + relieve the MN from the IP mobility signaling, while the mobile node + still controls link configuration during a handover. This introduces + a problem during an MN's handover between interfaces. According to + the PMIPv6 base protocol [RFC5213], the Access Authentication and the + Proxy Binding Update (PBU) are triggered in the access network by the + radio attach procedure, transparently for the MN. In addition, a + delay for the MN's new interface's address configuration is not + considered in the handover procedure. As a consequence, the + immediate update of the MN's BCE after the PBU from the MN's nMAG has + been received at the LMA impacts the performance of the MN's downlink + traffic as well as its uplink traffic. Performance aspects of + downlink as well as uplink traffic during a handover between + interfaces are analyzed in the subsequent subsections. + + + + + +Liebsch, et al. Experimental [Page 6] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +3.2.1. Issues with Downlink Traffic + + Delay of availability of an MN's network interface can be caused by + certain protocol operations that the MN needs to perform to configure + its new interface, and these operations can take time. In order to + complete the address auto-configuration on its new interface, the MN + needs to send a Router Solicitation and awaits a Router + Advertisement. Upon receiving a Router Advertisement from the new + MAG, the MN can complete its address configuration and may perform + Duplicate Address Detection (DAD) [RFC4862] on the new interface. + Only then the MN's new interface is ready to receive packets. + + Address configuration can take more than a second to complete. If + the LMA has already switched the mobile node tunnel to point to the + nMAG and started forwarding data packets for the MN to the nMAG + during this time, these data packets may get delayed or lost because + the MN's new interface is not yet ready to receive data. However, + delaying the PBU, which is sent from the new MAG to the LMA after the + MN's new interface has attached to the network, is not possible, as + the new MAG retrieves configuration data for the MN from the LMA in + the PBA, such as the MN's Home Network Prefixes (HNPs) and the link- + local address to be used at the MAG. + + The aforementioned problem is illustrated in Figure 1, which assumes + that the HNP(s) will be assigned under control of the LMA. Hence, + the HNP option in the PBU, which is sent by the new MAG to the LMA, + is set to ALL_ZERO. An MN has attached to the network with interface + (IF) IF1 and receives data on this interface. When the MN's new + interface IF2 comes up and is detected by the new MAG, the new MAG + sends a PBU and receives a PBA from the LMA. If the LMA decides to + forward data packets for the MN via the new MAG, the new MAG has to + buffer these packets until address configuration of the MN's new + interface has completed and the MN's new interface is ready to + receive packets. While setting up IF2, the MN may not reply to + address resolution signaling [RFC4861], as sent by the new MAG [A]. + If the MAG's buffer overflows or the MN cannot reply to address + resolution signaling for too long, data packets for the MN are + dropped and the MN can experience severe packet losses during an + inter-access handover [B] until IF2 is ready to receive and send data + [C]. + + + + + + + + + + + +Liebsch, et al. Experimental [Page 7] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + +------+ +----+ +----+ +---+ + | MN | |pMAG| |nMAG| |LMA| + +------+ +----+ +----+ +---+ + IF2 IF1 | | | + | | | | | + | |- - - - - - - - - Attach | | + | | |---------------PBU--------------->| + | | |<--------------PBA----------------| + | |--------RtSol------->| | | + | |<-------RtAdv--------| | | + | Addr. | | | + | Conf. | | | + | |<--------------------|==================data============|-- + | | | | | + |- - - - - - - - - - - - - - - - - Attach | + | | | |----------PBU-------->| + | | | |<---------PBA---------| + | | | |<-====data============|-- + [A]?|<-----------NSol---------------------|<-====data============|-- + | | | [B] ?|<-====data============|-- + | | | ?|<-====data============|-- + |-----------RtSol-------------------->|<-====data============|-- + |<----------RtAdv---------------------| : | + Addr. | | | : | + Conf. | | | : | + |<-----------NSol---------------------| : | + |------------NAdv------------------->[C] | + !|<------------------------------------|======data============|-- + | | | | | + | | | | | + + Figure 1: Issue with dual radio handover + + Another risk for a delay in forwarding data packets from a new MAG to + the MN's IF2 can be some latency in setting up a particular access + technology's radio bearer or access-specific security associations + after the new MAG received the MN's HNP(s) from the LMA via the PBA + signaling message. + + In case an access network needs the MN's IP address or HNP to set up + a radio bearer between an MN's IF2 and the network infrastructure, + the access network might have to wait until the nMAG has received the + associated information from the LMA in the Proxy Binding + Acknowledgment. Delay in forwarding packets from the nMAG to the + MN's IF2 depends now on the latency in setting up the radio bearer. + + + + + + +Liebsch, et al. Experimental [Page 8] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + A similar problem can occur in the case in which the setup of a + required security association between the MN's IF2 and the network + takes time and such a setup can be performed only after the MN's IP + address or HNP is available on the nMAG. + + Both scenarios, as depicted above, can be found in [TS23.402], where + the protocol sequence during a handover between different accesses + considers a PMIPv6 handshake between the nMAG and the LMA to retrieve + the MN's HNP(s) before access-specific operations can be completed. + +3.2.2. Issues with Uplink Traffic + + In the case of an inter-technology handover between two interfaces, + the MN may be able to maintain connectivity on IF1 while it is + completing address configuration on IF2. Such a handover mechanism + is called "make-before-break" and can avoid uplink packet loss in + client-based Mobile IP. However, in a PMIPv6 domain, the attachment + of the MN on IF2 will cause the nMAG to send a PBU to the LMA, which + will cause the LMA to update the BCE for this mobility session of the + MN. According to Section 5.3.5 of the PMIPv6 base specification + [RFC5213], the LMA may drop all subsequent packets being forwarded by + the MN's pMAG due to the updated BCE, which refers now to the nMAG as + a "Proxy-CoA". + + A further issue for uplink packets arises from differences in the + time of travel between the nMAG and LMA in comparison with the time + of travel between the pMAG and LMA. Even if the MN stops sending + packets on IF1 before the PBU is sent (i.e., before it attaches IF2 + to nMAG), uplink packets from pMAG may arrive at the LMA after the + LMA has received the PBU from nMAG. Such a situation can, in + particular, occur when the MN's previous link has a high delay (e.g., + a Global System for Mobile Communications (GSM) link) and is slow + compared to the handover target link. This characteristic is + illustrated in Figure 2. + + + + + + + + + + + + + + + + + +Liebsch, et al. Experimental [Page 9] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + +------+ +----+ +---+ + | MN | |nMAG| |LMA| + +------+ +----+ +---+ + IF2 IF1 | | + | |\ | |BCE exists + | | \ | | for pMAG + |- -|- - - - \- - - - Attach | + | | s\ |---------PBU----------->|BCE update + | | l\ |<--------PBA------------| for nMAG + | | o\ | + | | | w\ | + | | | l\ | + | | | i\ | + | | | n \ |packet dropped + | | | k --->| as BCE has only + | | | | entry for nMAG + | | | | + | | | | + + Figure 2: Uplink traffic issue with slow links + +3.3. Need for a Common Solution + + To reduce the risk of packet loss, some settings on an MN could be + chosen appropriately to speed up the process of network interface + configuration. Also, tuning some network parameters, such as + increasing the buffer capacity on MAG components, could improve the + handover performance. However, some network characteristics, such as + access link delay or bearer setup latency, cannot be easily fine + tuned to suit a particular handover scenario. Thus, a common + solution that dynamically controls and enhances this handover + complexity using a simple extension to the PMIPv6 base protocol is + preferred. + + This document specifies transient BCEs as an extension to the PMIPv6 + protocol. Set up and configuration of a transient BCE can be + performed by means of extended PMIPv6 signaling messages between the + MAG and the LMA component using a new Transient Binding mobility + option. The transient BCE mechanism supports three clearly + distinguished sequences of transient states to suit various handover + scenarios and to improve handover performance for both inter- and + intra-technology handover. As a result of using transient BCEs, + excessive packet buffering at the nMAG during the MN's handover + process is not necessary and packet losses and major jitter can be + avoided. + + + + + + +Liebsch, et al. Experimental [Page 10] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +4. Use of Transient Binding Cache Entries + +4.1. General Approach + + The use of transient BCE during an MN's handover (HO) enables greater + control on the forwarding of uplink (Ul) and downlink (Dl) traffic to + harmonize handover performance characteristics with the capabilities + of the handover source and target access networks. Updating of an + MN's BCE at an LMA is split into different phases before and after + the radio setup and IP configuration being associated with the MN's + handover from a pMAG to an nMAG. + + The use of a transient BCE during an MN's handover splits into an + initiation phase and a phase turning the transient BCE into an active + BCE. Figure 3 illustrates the procedure to enter and leave a + transient BCE during an MN's handover. As a result of the MN's + attachment at the nMAG, the first PBU from the MN's nMAG can turn the + MN's BCE at the LMA and the nMAG into transient state by including a + Transient Binding option (Section 5.1). The LMA enters the nMAG as a + further forwarding entry to the MN's BCE without deleting the + existing forwarding entry and marks the BCE state as 'transient'. + Alternatively, in case the nMAG does not include a Transient Binding + option, the LMA can make the decision to use a transient BCE during + an MN's handover and notify the nMAG about this decision by adding a + Transient Binding option in the PBA. After receiving the PBA, the + nMAG enters the MN's data, such as the assigned HNP(s), into its + Binding Update List (BUL) and marks the MN's binding with the LMA as + 'transient', which serves as an indication to the nMAG that the + transient BCE needs to be turned into an active BCE. + + During the transient state, the LMA accepts uplink packets from both + MAGs, the pMAG and the nMAG, for forwarding. To benefit from the + still available downlink path from pMAG to MN, the LMA forwards + downlink packets towards the pMAG until the transient BCE is turned + into an active BCE. Such a downlink forwarding characteristic is + denoted as "late path switch" (L). During a dual radio handover, an + MN can receive downlink packets via its previous interface; during a + single radio handover, the late path switch supports re-using + available forwarding mechanisms in the radio access network. + Appendix A describes both use cases. + + Decisions about the classification of an MN's BCE as transient during + a handover can be made either by the nMAG or the LMA. Detailed + mechanisms showing how an nMAG or an LMA finds out to use a transient + BCE procedure are out of scope of this document. + + + + + + +Liebsch, et al. Experimental [Page 11] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + A transient BCE can be turned into an active BCE by different means, + such as a timeout at the LMA, a PBU from the nMAG, which has no + Transient Binding option included, or a deregistration PBU from the + pMAG. As soon as the MN's BCE has been initiated to turn into an + active BCE, the LMA switches the forwarding path for downlink packets + from the pMAG to the nMAG. + + +-----+ +----+ +----+ +-----+ + | MN | |pMAG| |nMAG| | LMA | + +-----+ +----+ +----+ +-----+ + | | | |[pMAG serves + | | | | MN as + | | | | Proxy-CoA] + | | | | + |<-----------------|===============data tunnel=====|--->data + | | | | + [Handoff | | | + Start] | | | + | | | | + e|-----------------------[MN Attach] | + x| | | | + e| | |---PBU(transient)--->|[Add nMAG to + c| | | | MN's BCE, + u| | |<--PBA(transient)----| enter trans- + t| | | | ient state] + i| | | | + o|<-----Dl+Ul-------|===============data tunnel=====|--->data + n|--------Ul------------------|=====data tunnel=====|--->data + | | | | + [Handoff/ | | | + Configuration | | | + Completed] | [HO Complete] | + | | |--------PBU--------->|[Activate + | | | | MN's BCE, + | | |<-------PBA ---------| update for- + | | | | warding path + | | | | to nMAG] + | | | | + |<---------------------------|=====data tunnel=====|--->data + | | | | + + Figure 3: General mechanism and forwarding characteristics during + handover with transient BCE + + This specification considers an optional state when turning the + transient BCE into an active BCE of a transient BCE with a late path + switch, which keeps the pMAG for some more time as the forwarding + + + + +Liebsch, et al. Experimental [Page 12] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + entry in the transient BCE, solely to ensure forwarding of delayed + uplink packets from the pMAG. This optional activation state has a + lifetime associated, and termination does not need any signaling. + + Whether or not to enter this optional activation state is decided by + the LMA. The LMA may take information about the access technology + associated with the MN's pMAG and nMAG from the MN's BCE to decide if + using the activation state is beneficial, e.g., since a slow link is + associated with the pMAG and uplink packets from the pMAG may arrive + delayed at the LMA. + + The Transient Binding option allows configuration of the transient + BCE late path switch and signaling of associated settings. Signaling + of the Transient Binding option and the LMA's decision whether or not + to use an optional activation state defines the sequence through the + clearly defined transient BCE states, as illustrated and described in + Section 4.4. Section 4.2 describes the required extension to an + LMA's binding cache to support transient BCE operation. Section 4.3 + provides a concise overview about the possible roles of the nMAG and + the LMA to control a transient BCE handover sequence. Details about + the Transient Binding option and its use are described in Sections + 4.5 and 4.6. + +4.2. Impact on Binding Management + + The use of a transient BCE requires temporary maintenance of two + forwarding entries in the MN's BCE at the LMA, one referring to the + MN's pMAG and the other referring to its nMAG. Forwarding entries + are represented according to [RFC5213] and comprise the interface + identifier of the associated tunnel interface towards each MAG, as + well as the associated access technology information. + + Each forwarding entry is assigned a forwarding rule to admit and + control forwarding of uplink and downlink traffic to and from the + associated MAG. Hence, according to this specification, a forwarding + entry can have either a rule that allows only forwarding of uplink + traffic from the associated MAG, or a rule that allows bidirectional + forwarding from and to the associated MAG. At any time, only one of + the two forwarding entries can have a bi-directional forwarding rule. + The interface identifier and access technology type info can be taken + from the PBU received at the LMA and linked to each forwarding entry + accordingly. + + MAGs should maintain the status of an MN's binding and the lifetime + associated with a transient BCE at the LMA in their binding update + list. This is particularly important if the new MAG needs to + explicitly turn a binding into an active BCE after the associated + MN's new interface has proven to be ready to handle IP traffic. + + + +Liebsch, et al. Experimental [Page 13] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +4.3. Role of the LMA and nMAG in Transient State Control + + This section provides an overview about the nMAG's and the LMA's + possibility to control a transient BCE. Please refer to the Protocol + Operations sections for a detailed protocol description (Sections 4.5 + and 4.6). + +4.3.1. Control at the nMAG + + Initiate a late path switch - Since the nMAG needs to have knowledge + about the nature of a handover to set the Handoff Indicator (HI) + option in the PBU and whether or not the handover implies a change + in the used radio interface or technology, the nMAG is a suitable + entity to make the decision to delay the downlink path switch in a + controlled manner by means of a transient BCE. The nMAG can make + the decision to initiate a transient BCE handover for an MN only + when it knows that the MN supports a delayed downlink path switch + (Section 4.7) according to this specification. It may know this + due to a number of factors. For instance, during dual radio + handover, most cellular networks have controlled handovers where + the network knows that the host is moving from one attachment to + another. In this situation, the link-layer mechanism can inform + the mobility functions that this is indeed a movement, not a new + attachment and that the MN has sufficient control on its + interfaces to support a transient BCE handover. Where no support + from the link layer exists and no such indication can be provided + to the nMAG by the network, the nMAG MUST assume that the host is + incapable of this mode of operation and employ standard behavior + as specified in [RFC5213]. In other words, the nMAG initiates a + regular [RFC5213] handover. + + The nMAG is also a suitable entity to estimate a maximum delay + until the new connection can be used, as it knows about its + locally connected radio network characteristics. Hence, the nMAG + can set the maximum lifetime to delimit the transient BCE + softstate at the LMA. The LMA may still override the proposed + lifetime and notify the nMAG about the new lifetime in the + Transient Binding option included in the PBA. + + Activation of a transient BCE to perform a downlink path switch - + During a transient BCE handover, the nMAG may get an indication + that the MN's radio link can be used and the MN has completed the + setup of the IP address to send and receive data packets via the + new link. In this case, the nMAG can initiate turning a transient + BCE into an active BCE before the expiration of the associated + maximum transient BCE lifetime. To do that, the nMAG sends a PBU + message without the Transient Binding option to the LMA. This + results in a downlink path switch to the nMAG. + + + +Liebsch, et al. Experimental [Page 14] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +4.3.2. Control at the LMA + + Initiate a late path switch - If the LMA has received a PBU without + a Transient Binding option included, the LMA can take a decision + to use a transient BCE to optimize the handover performance. The + LMA indicates its selected settings for the late path switch (L) + and the associated maximum lifetime in the Transient Binding + option, which is included in the PBA and sent to the nMAG. + + Decision to use an optional activation state - The LMA is a suitable + entity to decide about the use of an optional activation state, as + the LMA has the knowledge about the MN's previous and new access + technology. Hence, the LMA can make this decision to use an + activation state to temporarily keep alive the forwarding of + uplink packets from both MAGs, the pMAG, and the nMAG, even though + the downlink path has been switched to the nMAG already. One + reason to enter such an activation state may be a slow link + between the pMAG and the LMA as described in Section 3.2.2. + +4.4. LMA Forwarding State Diagram + + The current specification of transient BCEs covers three clearly + defined transient BCE states at the LMA, which can be used during an + MN's handover. Each state implies a dedicated characteristic + regarding forwarding entries, in which forwarding rules for uplink + traffic are maintained separately from downlink traffic. This + section explains how the forwarding state sequentially changes during + the optimized handoff. To suit different handover scenarios, + different sequences through the forwarding states can be entered. + Figure 4 depicts the possible cases, their sequence of forwarding + states, and the triggers for the transitions. Two example use cases + are described in detail in Appendix A to illustrate which sequence + through the forwarding states suits a particular handover. + + According to this specification, each BCE has a state associated, + which can be either 'Active' or any of the specified transient states + 'Transient-L', 'Transient-LA', or 'Transient-A'. In the case that a + BCE is in 'Active' state, the information in a BCE and associated + forwarding conforms to [RFC5213]. + + Any of the transient states imply that the transient BCE has two + forwarding entries, which are denoted as pMAG and nMAG in the + forwarding state diagram. The diagram includes information about the + forwarding rule along with each forwarding entry. This rule + indicates whether a forwarding entry is meant to perform forwarding + only for Uplink (Ul) traffic or to perform bi-directional forwarding + for Uplink (Ul) and Downlink (Dl) traffic. + + + + +Liebsch, et al. Experimental [Page 15] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + State transitions can be triggered as a result of processing a + received PBU or by a local timeout event on the LMA. In the + forwarding state chart below, the presence of a Transient Binding + option in a PBU is indicated by 'Topt' as an argument to a PBU or + PBA, respectively. As a further argument to a PBU message, the + source of the message is indicated, which can be either the MN's nMAG + or pMAG. A PBA is always sent by the LMA and addressed to the + originator of the associated PBU. + + A handover with transient BCE is either triggered when the nMAG sends + a PBU with a Transient Binding option or when the LMA decides to + answer a normal PBU with a PBA after including a Transient Binding + option. Figure 4 illustrates the possible transitions between an + active BCE and a transient BCE from the LMA's point of view. It also + shows the direct transition between two active BCE states during an + MN's handover according to [RFC5213], bypassing any transient states. + + The diagram refers to two timeout events. TIMEOUT_1 is set according + to the Lifetime value in a Transient Binding option (see Section 5 + for the format of the Transient Binding option), whereas TIMEOUT_2 is + set to ACTIVATIONDELAY (see Section 8 for the default value). + + The first sequence of a transient BCE handover is followed when the + LMA decides not to use the optional activation state and is going + through Transient-L state, in which the LMA continues forwarding + downlink packets to the pMAG, whereas uplink packets are accepted and + forwarded from both, the pMAG and the nMAG. On reception of a PBU + without a Transient Binding option from the nMAG, a TIMEOUT_1 event, + or the reception of a deregistration PBU from the pMAG, the + forwarding entry of the pMAG is removed from the MN's BCE, and the + BCE state changes to active. + + If the LMA decides to use the activation state, the second sequence + is used. In this case, the BCE state turns into Transient-LA. + Forwarding characteristics in the Transient-LA state are the same as + for the Transient-L state, but the Transient-LA state follows a + Transient-A state when the LMA receives a PBU from the nMAG without a + Transient Binding option included or a TIMEOUT_1 event occurs. In + the Transient-A state, the LMA performs a downlink forwarding path + switch from the pMAG to the nMAG, whereas uplink packets are still + accepted and forwarded from both, the pMAG and the nMAG. The + Transient-A state is terminated by a TIMEOUT_2 event, the forwarding + entry of the pMAG is removed from the MN's BCE, and the BCE state + turns to active. If the LMA receives a deregistration PBU from the + pMAG while the associated MN's BCE is in Transient-LA state, the + uplink forwarding rule of the pMAG is no longer valid and the + transition through Transient-A state is skipped. In such a case, the + BCE turns into active state immediately. + + + +Liebsch, et al. Experimental [Page 16] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + +----------------+ Before + PBU(nMAG) & PBA(LMA) | Active | Handover + +-----------------------| | -------- + | | pMAG [Dl,Ul] | . + | *----------------* . + | | . + | | V + | PBU(nMAG, Topt) | PBU(nMAG) & PBA(LMA, Topt) . + | | . + | | . + | V Handover + | __________ Procedure + | / LMA \ . + | _________ / selects \ _________ . + | No| \ activation / |Yes . + | | \_state_?__/ | . + | | | V + | V V . + | +--------------+ +--------------+ . + | | Transient-L | | Transient-LA | . + | | | | | . + | | pMAG [Dl,Ul] | +-------| pMAG [Dl,Ul] | . + | | nMAG [Ul] | | | nMAG [Ul] | . + | +--------------+ | +--------------+ . + | | | | + | | PBU(pMAG, | PBU(nMAG) | TIMEOUT_1 + | | lifetime=0)| | . + | | | V . + | | | +--------------+ . + | | | | Transient-A | . + | PBU(nMAG) | TIMEOUT_1 | | | . + | | | | nMAG [Dl,Ul] | . + | |PBU(pMAG, | | pMAG [Ul] | . + | | lifetime=0) | +--------------+ . + | | | | + | | | PBU(pMAG, | TIMEOUT_2 + | | | lifetime=0)| . + | | | | V + | | | | ------- + | | | | Handover + | | | V Complete + | | | +--------------+ + | | +------->| Active | + | +-------------------------->| | + +----------------------------------------->| nMAG [Dl,Ul] | + +--------------+ + + Figure 4: Possible transient forwarding states during a handover + + + +Liebsch, et al. Experimental [Page 17] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +4.5. MAG Operation + + In case of a handover, the MN's nMAG may decide to control the MN's + handover at the LMA to perform a late path switch according to the + transient BCE procedure. In such a case, the nMAG includes the + Transient Binding option in the PBU and sets the L-flag to 1 to + indicate a late path switch. Furthermore, the nMAG MUST set the + Lifetime field of the Transient Binding option to a value larger than + 0 to propose a maximum lifetime of the transient BCE and to delimit + the delay of switching the downlink path to the nMAG. The chosen + lifetime value for the Transient Binding option SHOULD be smaller + than the chosen lifetime value for the PBU registration. Other + fields and options of the PBU are used according to [RFC5213]. + + In case the nMAG does not include a Transient Binding option but the + LMA decides to perform a handover according to the transient BCE + procedure, the nMAG may receive a Transient Binding option along with + the PBA from the LMA as a result of the PBU it sent to the LMA. + + In case the nMAG receives a PBA with a Transient Binding option + having the L-flag set to 1, it SHOULD link the information about the + transient BCE sequence and the associated transient BCE lifetime with + the MN's entry in the BUL. Since the L-flag of the Transient Binding + option is set to 1 to indicate a late path switch, the nMAG MAY turn + an MN's transient BCE into an active BCE before the expiration of the + transient BCE lifetime (TIMEOUT_1), e.g., when the MN's nMAG detects + or gets informed that address configuration and radio bearer setup + has been completed. To initiate turning a transient BCE into an + active BCE, the nMAG sends a PBU to the LMA without including the + Transient Binding option. All fields of the PBU are set according to + the procedure for the binding lifetime extension described in Section + 5.3.3 of [RFC5213]. In case the lifetime of a transient BCE expires + or the LMA approves turning a transient BCE into an active BCE as a + result of a PBU sent by the nMAG, the nMAG MUST delete all + information associated with the transient BCE from the MN's BUL + entry. + + In case the nMAG includes a Transient Binding option into the PBU, + only one instance of the Transient Binding option per PBU is allowed. + + A MAG, which serves the MN current Proxy-CoA while the LMA already + has an active or transient binding for the MN pointing to this MAG, + SHALL NOT include a Transient Binding option in any subsequent PBU to + create or update a transient BCE for the MN's current registration + with this MAG. + + + + + + +Liebsch, et al. Experimental [Page 18] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +4.6. LMA Operation + +4.6.1. Initiation of a Transient BCE + + In case the LMA receives a handover PBU from an MN's nMAG that does + not include a Transient Binding option and the associated MN's BCE is + active and not in transient state, the LMA MAY take the decision to + use a transient BCE and inform the nMAG about the transient BCE + characteristics by including a Transient Binding option in the PBA. + In such a case, the LMA should know about the nMAG's capability to + support the Transient Binding option. The configuration of the MN's + transient BCE is performed according to the description in this + section and the selected transient state. Otherwise, the LMA + processes the PBU according to the PMIPv6 protocol [RFC5213] and + performs a normal update of the MN's BCE. + + In case the PBU from the nMAG has a Transient Binding option + included, the LMA must enter the sequence of transient BCE states + according to its decision whether or not to use an optional + activation state. In case the LMA decides not to use an activation + state, it configures the MN's transient BCE and the forwarding rules + according to Transient-L state. As a result, the LMA performs a late + path switch and forwards downlink packets for the MN towards the MN's + pMAG, whereas uplink packets being forwarded from both Proxy-CoAs, + the MN's pMAG, as well as from its nMAG, will be routed by the LMA. + + In case the PBU from the nMAG has a Transient Binding option included + and the LMA decides to use an optional activation state, the LMA + configures the MN's transient BCE and the forwarding rules according + to Transient-LA state. As a result, the LMA performs a late path + switch and forwards downlink packets for the MN towards the MN's + pMAG, whereas uplink packets being forwarded from both Proxy-CoAs, + the MN's pMAG, as well as from its nMAG, will be routed by the LMA. + In addition, the LMA marks the transient BCE to enter a temporary + activation phase in Transient-A state after the LMA received an + indication to turn a transient BCE into an active BCE. + + The LMA sets the lifetime of the transient BCE according to the + lifetime indicated by the nMAG in the Transient Binding option's + lifetime field or may decide to reduce the lifetime according to its + policy. If the lifetime value in the Transient Binding option + exceeds the lifetime value associated with the PBU message, the LMA + MUST reduce the lifetime of the transient BCE to a value smaller than + the registration lifetime value in the PBU message. In the case of a + successful transient BCE registration, the LMA sends a PBA with a + Transient Binding option back to the nMAG. The L-flag of the + + + + + +Liebsch, et al. Experimental [Page 19] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + Transient Binding option MUST be set to 1 in this version of the + specification. The lifetime field is set to the value finally chosen + by the LMA. + + In any case where the LMA finds the L-flag of the received Transient + Binding option set to 1, but the lifetime field of the Transient + Binding option is set to 0, the LMA MUST ignore the Transient Binding + option and process the PBU according to [RFC5213]. After the PBU has + been processed successfully, the LMA sends back a PBA with the status + field set to PBU_ACCEPTED_TB_IGNORED_SETTINGSMISMATCH. + + In case the LMA receives a Transient Binding option with the L-flag + set to 0, this version of the specification mandates the LMA to + ignore the Transient Binding option and process the PBU according to + [RFC5213]. After the PBU has been processed successfully, the LMA + sends back a PBA with the status field set to + PBU_ACCEPTED_TB_IGNORED_SETTINGSMISMATCH. + + In case the LMA receives a PBU with a Transient Binding option + included from a MAG that serves already as Proxy-CoA to the + associated MN in an active or transient BCE, the LMA MUST ignore the + Transient Binding option and process the PBU according to [RFC5213]. + After the PBU has been processed successfully, the LMA sends back a + PBA with the status field set to + PBU_ACCEPTED_TB_IGNORED_SETTINGSMISMATCH. In case the MN's BCE was + in transient state before receiving such PBU from the MAG, the LMA + SHALL interpret this PBU as indication to turn a transient BCE into + an active BCE and proceed with leaving the Transient-L or + Transient-LA state, respectively. + + In any case where the LMA includes a Transient Binding option in the + PBA, only one instance of the Transient Binding option per PBA is + allowed. + +4.6.2. Activation of a Transient BCE + + When the LMA receives a PBU from the MN's nMAG that has no Transient + Binding option included but the MN's BCE is in a transient state or + the LMA receives a local event trigger due to expiration of the MN's + transient BCE, the LMA should check whether the forwarding rules for + the associated MN are set to route the MN's downlink traffic to the + MN's pMAG. If the forwarding entry for downlink packets refers to + the MN's pMAG, the LMA must update the forwarding information to + forward downlink packets towards the MN's nMAG. After the forwarding + path has been switched, the LMA must update the MN's BCE accordingly. + + + + + + +Liebsch, et al. Experimental [Page 20] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + If the transient BCE indicates that the LMA must consider an + activation state Transient-A after leaving a transient BCE has been + initiated, the LMA must keep both forwarding entries for the pMAG and + the nMAG for uplink packets and perform forwarding of packets it + receives from both Proxy-CoAs. If no activation phase is indicated, + the LMA sets the state of the MN's BCE to active and deletes any + forwarding entry referring to the MN's pMAG. The LMA must delete any + scheduled timeout event for the MN that is associated with a + transient BCE. + + When the LMA receives a deregistration PBU from the MN's pMAG, which + has the registration lifetime set to 0 and the MN's BCE is in + transient state, the LMA must update the forwarding rules for the MN + and switch the downlink traffic path from the pMAG to the nMAG. + Furthermore, the LMA sets the state of the MN's BCE to active and + removes any forwarding entry towards the pMAG from the MN's BCE, + irrespective of whether or not the transient BCE was configured to + enter an activation state of Transient-A. + + When the LMA receives a local event trigger due to the expiration of + a timer that has been set to ACTIVATIONDELAY and scheduled to + terminate the activation state of an MN's transient BCE, the LMA sets + the state of the MN's BCE to active and removes any forwarding entry + towards the pMAG from the MN's BCE. + + When the LMA receives a PBU for binding lifetime extension from the + MN's pMAG while the MN's BCE is in transient state, the LMA must + approve the lifetime extension to pMAG according to [RFC5213] and + proceed with the transient BCE handover towards nMAG according to + this specification. + + When the LMA receives a PBU from pMAG or a (n+1)MAG, which indicates + a handover, e.g., according to the indications specified in + [RFC5213], while the MN's BCE is in any of the specified transient + states, the LMA MUST terminate the transient state and perform a + handover to pMAG or (n+1)MAG, respectively, according to [RFC5213]. + After the PBU has been processed successfully, the LMA sends back a + PBA to the MAG that sent the PBU. If the PBU included a Transient + Binding option, the LMA must ignore the Transient Binding option and + set the status code of the PBA to + PBU_ACCEPTED_TB_IGNORED_SETTINGSMISMATCH. + + + + + + + + + + +Liebsch, et al. Experimental [Page 21] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +4.7. MN Operation + + For a single radio handover, this specification does not require any + additional functionality on the mobile node, when compared to + [RFC5213]. + + During dual radio handover, the MN benefits most from the transient + BCE extension to PMIPv6 when it is able to keep communication on the + previous interface while it is setting up its handover target + interface with the configuration context that has been received as a + result of the new interface's attachment to the nMAG. Various + techniques enable support for such an operation, e.g., the use of a + virtual interface on top of physical radio interfaces [NETEXT] or + implementation-specific extensions to the MN's protocol stack. + Details about how to enable such make-before-break support on the MN + are out of scope of this document. + +4.8. Status Values + + This section specifies the following PBA status value (6) for + transient binding cache entry support. This status value is smaller + than 128 and has been added to the set of status values specified in + [RFC5213]. + + PBU_ACCEPTED_TB_IGNORED_SETTINGSMISMATCH: 6 + + The LMA has processed and accepted the PBU, but the attached + Transient Binding option has been ignored. + +4.9. Protocol Stability + + The specification and use of transient BCEs ensures that correct + PMIPv6 operation according to [RFC5213] will not be broken in any + case. Such cases include loss of signaling information and + incompatibility between an nMAG and an LMA in case one or the other + side does not support the transient BCE option. The following list + summarizes such cases and describes how the PMIPv6 protocol operation + resolves incompatibility or loss of a signaling message. + + LMA does not support transient BCEs: In case the nMAG sends a PBU + with a Transient Binding option included to an LMA but the LMA + does not support transient BCEs, the LMA ignores the unknown + option [RFC3775] and processes the PBU according to [RFC5213]. + Since the nMAG receives a PBA that has no Transient Binding option + included, it does not set any transient binding information in the + MN's BUL entry and operates according to [RFC5213]. + + + + + +Liebsch, et al. Experimental [Page 22] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + nMAG does not support transient BCEs: In case the LMA makes the + decision to perform a handover according to any of the specified + transient BCE sequences and includes a Transient Binding option in + the PBA, the receiving nMAG ignores the unknown option [RFC3775] + and processes the PBA according to [RFC5213]. As the LMA does not + get any further indication or feedback about the incompatibility + at the nMAG, the LMA enters the selected transient state, which + will be terminated at the latest time after (TIMEOUT_1 + + ACTIVATIONDELAY) seconds. During this period, the nMAG performs + according to the PMIPv6 specification [RFC5213], whereas the LMA + will accept all uplink packets for the MN, from the pMAG, as well + as from the nMAG according to the transient BCE specification. It + is transparent to the nMAG if the LMA forwards downlink packets to + the pMAG during the transient BCE phase; thus, no protocol + conflict occurs due to the different states on the nMAG and the + LMA. + + Loss of Transient Binding option: As the Transient Binding option is + included in the PBU and PBA, recovery from signaling packet loss + is according to the PMIPv6 protocol operation and associated + re-transmission mechanisms [RFC5213]. + + Missing PBU to turn a transient BCE into an active BCE: According to + this specification, a lifetime for TIMEOUT_1 is signaled in the + Transient Binding option, and turning a transient BCE into an + active BCE is initiated at the latest time after the timer + TIMEOUT_1 has elapsed. In case PBU signaling is lost or the nMAG + fails to initiate turning a transient BCE into an active BCE, the + transient state of the MN's BCE will be terminated after + expiration of the set lifetime, i.e., stable operation of the + PMIPv6 protocol [RFC5213] has reliably recovered. + + Lost connection with pMAG during late path switch: In case an MN + loses connectivity to its pMAG during a transient BCE phase with + late path switch and the nMAG fails to initiate turning a + transient BCE into an active BCE to perform the path switch to the + nMAG, in a worst-case scenario, downlink packets are lost until + the chosen TIMEOUT_1 expires. After TIMEOUT_1 seconds, the + protocol operation has been recovered successfully. However, this + case is very unlikely for two reasons: If the connectivity to the + pMAG is lost, the pMAG will send a deregistration PBU for the MN + to the LMA, which results in turning the transient BCE into an + active BCE and in a path switch. Furthermore, the nMAG will + initiate turning the transient BCE into an active BCE as soon as + the setup of the data link between the MN and the nMAG has been + completed (Section 4.4). Note that this case, in particular, + affects downlink packets, whereas uplink packets can be sent + + + + +Liebsch, et al. Experimental [Page 23] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + through the new connection after a broken link to the pMAG has + been detected. + + Binding lifetime extension from pMAG while MN's BCE is transient: As + the binding lifetime of the pMAG and the nMAG is not correlated, + pMAG may send a PBU for binding lifetime extension to the MN's LMA + while the MN's BCE is in transient state. In such a case, the LMA + will approve the binding lifetime extension to pMAG according to + [RFC5213] and proceed with the transient BCE handover towards nMAG + according to this specification. + + The specification of the transient BCE extension maintains stable + operation of PMIPv6 in case the MN performs very frequent handover, + e.g., movement while the MN's handover between the pMAG and the nMAG + is still in progress. Such corner cases are summarized in the + following list. + + Handover to (n+1)MAG during transient BCE: In case the MN's BCE is + transient due to a handover from the pMAG to nMAG and during the + transient BCE, the MN performs a further handover to a MAG that is + different from pMAG and nMAG, say to (n+1)MAG, the LMA terminates + the transient BCE and performs a handover to (n+1)MAG according to + [RFC5213]. + + Handover back to pMAG during transient BCE (ping pong): In case the + MN's BCE is transient due to a handover from the pMAG to nMAG and + the MN moves back from nMAG to pMAG during the transient BCE, the + LMA terminates the transient BCE and performs a handover to pMAG + according to [RFC5213]. + +5. Message Format + +5.1. Transient Binding Option + + This section describes the format of the Transient Binding option, + which can be included in a Proxy Binding Update message and a Proxy + Binding Acknowledge message. The use of this Mobility Header option + is optional. + + The Transient Binding option can be included in a PBU message, which + is sent by an MN's nMAG as a result of a handover. In such a case, + the nMAG controls the transient BCE on the LMA. Alternatively, the + LMA may attach the Transient Binding option in a PBA for two reasons. + Either it replies to a received PBU with an attached Transient + Binding option to approve or correct the transient BCE lifetime, or + it notifies the nMAG about its decision to enter a transient BCE + without having received a Transient Binding option from the nMAG in + the associated PBU beforehand. + + + +Liebsch, et al. Experimental [Page 24] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + The Transient Binding option has no alignment requirement. Its + format is as follows: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Type | Length | Reserved |L| Lifetime | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Type: Identifies the Transient Binding option (43). + + Length: 8-bit unsigned integer indicating the length of the option in + octets, excluding the Type and the Length fields. This field MUST be + set to 2. + + L-Flag: Indicates that the LMA applies late path switch according to + the transient BCE state. If the L-flag is set to 1, the LMA + continues to forward downlink packets towards the pMAG. Different + setting of the L-Flag may be for future use. + + Lifetime: Maximum lifetime of a Transient-L state in multiple of 100 + ms. + +6. IANA Considerations + + This specification adds a new Mobility Header option, the Transient + Binding option. The Transient Binding option is described in + Section 5.1. The Type value (43) for this option has been registered + in the Mobility Options registry, the numbering space allocated for + the other mobility options, as defined in [RFC3775]. + + This specification also adds one status code value to the Proxy + Binding Acknowledge message, the + PBU_ACCEPTED_TB_IGNORED_SETTINGSMISMATCH status code (6). The + PBU_ACCEPTED_TB_IGNORED_SETTINGSMISMATCH status code is described in + Section 4.8. Its value has been assigned from the Status Codes sub- + registry as defined in [RFC3775] and has a value smaller than 128. + +7. Security Considerations + + Signaling between MAGs and LMAs as well as information carried by PBU + and PBA messages is protected and authenticated according to the + mechanisms described in [RFC5213]. No new security considerations + are introduced in addition to those in [RFC5213]. Thus, the security + considerations described throughout [RFC5213] apply here as well. + + + + + + +Liebsch, et al. Experimental [Page 25] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + In case the MAGs or LMAs make use of a further protocol interface to + an external component, such as for support of transient BCE control, + the associated protocol must be protected and information must be + authenticated. + +8. Protocol Configuration Variables + + LMA values: + + o 'ACTIVATIONDELAY': This value is set by default to 2000 ms and can + be administratively adjusted. + +9. Contributors + + Many thanks to Jun Awano, Suresh Krishnan, Long Le, Kent Leung, + Basavaraj Patil, and Rolf Sigle for contributing to this document. + +10. Acknowledgments + + The authors would like to thank Telemaco Melia, Vijay Devarapalli, + Rajeev Koodli, Ryuji Wakikawa, and Pierrick Seite for their valuable + comments to improve this specification. + +11. References + +11.1. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support + in IPv6", RFC 3775, June 2004. + + [RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, + K., and B. Patil, "Proxy Mobile IPv6", RFC 5213, + August 2008. + +11.2. Informative References + + [NETEXT] Melia, T., Ed. and S. Gundavelli, Ed., "Logical Interface + Support for multi-mode IP Hosts", Work in Progress, + October 2010. + + [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, + "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, + September 2007. + + + + + +Liebsch, et al. Experimental [Page 26] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless + Address Autoconfiguration", RFC 4862, September 2007. + + [TS23.401] "General Packet Radio Service (GPRS) enhancements for + Evolved Universal Terrestrial Radio Access Network + (E-UTRAN) access", <http://www.3gpp.org>. + + [TS23.402] "Architecture enhancements for non-3GPP accesses (Release + 9)", <http://www.3gpp.org>. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Liebsch, et al. Experimental [Page 27] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +Appendix A. Example Use Cases for Transient BCE + +A.1. Use Case for Single Radio Handover + + In some systems, such as the 3GPP Evolved Packet Core, PMIPv6 is + supported for providing network-based mobility between the Serving + Gateway (i.e., MAG) and the Packet Data Network Gateway (i.e., LMA) + and handover mechanisms are implemented in the access network to + optimize handover for single radio mobile nodes [TS23.401]. + + In such a system, a well structured inter-MAG handover procedure has + been developed and effectively used. In order to switch the data + tunnel path between the LMA and the pMAG in a systematic way that + reduces packet loss and delay, this inter-MAG handover sets up the + uplink data path from the mobile node through the nMAG and to the LMA + first. As soon as the uplink data path is set up, the mobile node is + able to forward uplink data packets through the nMAG to the LMA. + + Since the downlink data path between the LMA and the nMAG is not set + up at the same time as the uplink data path, the LMA must continue to + forward downlink data packets to the pMAG. Additionally, this system + utilizes a layer 2 forwarding mechanism from the previous Access + Network (pAN) to the new Access Network (nAN), which enables the + delivery of the downlink data packets to the mobile node location + while being attached to the nMAG. + + In order for the LMA to be able to forward the mobile node uplink + data packets to the Internet, the transient BCE mechanism is used at + the nMAG to send a PBU with the Transient Binding option to allow the + LMA to create a transient BCE for the mobile node with uplink + forwarding capabilities while maintaining uplink and downlink + forwarding capabilities for the Proxy-CoA that is hosted at the pMAG. + + During the lifetime of the transient BCE, the LMA continues to accept + uplink traffic from both previous and new MAG while forwarding + downlink traffic to the pMAG only. While the MN is able to receive + downlink traffic via the pMAG, the mechanism used in the pMAG's + access network to forward downlink traffic to the current location of + the mobile node in the nMAG's access network during an intra- + technology handover is out of scope of this description. + + When the nMAG receives an indication that the inter-MAG handover + process has completed, the nMAG sends another PBU without including a + Transient Binding option to update the mobile node's transient BCE to + a regular PMIPv6 BCE with bi-directional capabilities. This + mechanism is used by the LMA as an indication to switch the tunnel to + point to the nMAG, which results in a smoother handover for the MN. + + + + +Liebsch, et al. Experimental [Page 28] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + An example of using a transient BCE for intra-technology handover is + illustrated in Figure 5. When the nMAG receives the indication that + the MN is moving from the pMAG's access network to the nMAG's area, + the nMAG sends a PBU on behalf of the MN to the MN's LMA. In this + PBU, the nMAG includes the MN-ID, the HNP, and the interface ID as + per PMIPv6 base protocol [RFC5213]. + + Furthermore, the nMAG indicates an intra-technology handover by means + of the HI option and includes the Transient Binding option to + indicate to the LMA that this registration should result in a + transient BCE with a late downlink path switch. The nMAG sets the + value of the transient BCE lifetime to a value that is dependent on + the deployment and operator specific [D]. + + After the nMAG receives an indication that the MN has completed the + handover process and the data path is ready to move the tunnel + completely from the pMAG to the nMAG, the nMAG SHOULD send a PBU to + allow the LMA to turn the MN's transient BCE into a regular BCE and + to switch the data path completely to be delivered through the new + Proxy-CoA. In this case, the nMAG sends a PBU with the MN-ID, + Interface ID, and HNP and at the same time indicates an intra- + technology handover by means of the HI option. In this PBU, the nMAG + MUST NOT include the Transient Binding option, as shown in Figure 5 + [E]. + + In the event that the nMAG receives downlink traffic destined to the + MN from the LMA after sending a PBU with the Transient Binding option + included, the nMAG MUST deliver the downlink traffic to the MN. In + this case, the nMAG SHOULD send a PBU to ensure that the transient + BCE has been turned into an active BCE. + + + + + + + + + + + + + + + + + + + + + +Liebsch, et al. Experimental [Page 29] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + +-----+ +----+ +----+ +-----+ + | MN | |pMAG| |nMAG| | LMA | + +-----+ +----+ +----+ +-----+ + | | | bi-directional | + | |<<<<<<<<======================>>>>>>>>|<--> + | | | | + | | | | + [Handoff Event] | | | + | [MN HO Event] | | + | | [HO Event Acquire] | + | | | | + [LL Attach to | | | + nMAG] | |-----PBU(transient)----->| + | | | [D] + | | |<-----PBA(transient)-----| + | | | | + | | bi-directional | + | |<--->|<<<<<<<<======================>>>>>>>>|<--> + | pAN | | | + | |----------->| | | + | | nAN | | + |<------------------| |uplink only | + |------------------>|---->|>>>>>>===========>>>>>>>>|---> + | | | | + | | [HO Complete] | + | | |----------PBU----------->| + | | | [E] + | | |<---------PBA -----------| + | |` | | + | | |<<<<<<<<=========>>>>>>>>|<--> + | | | | + + Figure 5: Transient BCE support for an intra-technology handover + +A.2. Use Case for Dual Radio Handover + + During an inter-technology handover, the LMA shall, on the one hand, + be able to accept uplink packets of the MN as soon as the MN has + finalized address configuration at the new IF2 and may start using + the new interface for data traffic, i.e., the PBU for the uplink + shall be done before the radio setup procedure is finalized. But, to + allow the MN to keep sending its data traffic on IF1 during the + handover, uplink packets with the previously existing binding on IF1 + shall still be accepted by the LMA until the MN detaches from pMAG + with IF1 and the pMAG has deregistered the MN's attachment at the LMA + by means of sending a PBU with lifetime 0. This is of particular + importance as sending the registration PBU from the nMAG is + transparent to the mobile node, i.e., the MN does not know when the + + + +Liebsch, et al. Experimental [Page 30] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + PBU has been sent. On the other hand, switching the downlink path + from the pMAG to the nMAG shall be performed at the LMA only after + completion of the IP configuration at the MN's IF2 and after a + complete setup of the access link between the MN and the nMAG. How + long this takes depends on some interface-specific settings on the MN + as well as on the duration of the target system's radio layer + protocols, which is transparent to the LMA but may be known to MAGs. + + Similar to the use case for single radio handover, a transient BCE + can be utilized for MNs with dual radio capability. Such MNs are + still able to send and receive data on the previous interface during + the address configuration on the new interface. Forwarding between + the nMAG and pMAG is not required, but the case in which the LMA + immediately starts forwarding downlink data packets to the nMAG has + to be avoided. This is enabled by a PBU that has the Transient + Binding option included, so that it is not necessary that MN and LMA + synchronize the point in time for switching interfaces and turning a + transient BCE into an active BCE. + + When the handover is finalized, the nMAG sends a second PBU without + including the Transient Binding option and the LMA turns the MN's BCE + into an active BCE. This PBU may overtake packets-on-the-fly from MN + to LMA via pMAG (e.g., if the previous interface was of type GSM or + Universal Mobile Telecommunications System (UMTS) with up to 150 + milliseconds of uplink delay). The LMA has to drop all these packets + from the pMAG due to the characteristics of the MN's active BCE. + This can be avoided by entering another transient BCE state + (Transient-A) during the activation phase and is characteristic for + this use case. Whether or not to enter a Transient-A state is + decided by the LMA. + + The use of a transient BCE for an inter-technology handover is + exemplarily illustrated in Figure 6. The MN attaches to the PMIPv6 + network with IF1 according to the procedure described in [RFC5213]. + The MN starts receiving data packets on IF1. When the MN activates + IF2 to prepare an inter-technology handover, the nMAG receives an + attach indication and sends the PBU to the LMA to update the MN's + point of attachment and to retrieve configuration information for the + MN (e.g., HNP). The LMA is able to identify an inter-technology + handover by means of processing the HI option coming along with the + PBU sent by the nMAG. As in this example, the nMAG includes the + Transient Binding option in the PBU to control the transient BCE at + the LMA, the LMA updates the MN's BCE according to the transient BCE + specification described in this document and marks the state of the + BCE as 'transient' [F]. + + + + + + +Liebsch, et al. Experimental [Page 31] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + As a result of the transient BCE, the LMA keeps using the previous + forwarding information towards the pMAG binding as forwarding + information until the transient BCE gets turned into active. The LMA + acknowledges the PBU by means of sending a PBA to the nMAG. The nMAG + now has relevant information available, such as the MN's HNP, to set + up a radio bearer and send a Router Advertisement to the MN. While + the MN's BCE at the LMA has a transient characteristic, the LMA + forwards uplink packets from the MN's pMAG as well as from its nMAG. + The nMAG may recognize when the MN's IF2 is able to send and receive + data packets and sends a new PBU to the LMA without including the + Transient Binding option to initiate turning the MN's transient BCE + into an active BCE [G]. As a result of successfully turning the MN's + transient BCE into an active BCE, downlink packets will be forwarded + towards the MN's IF2 via the nMAG [H]. + + +------+ +----+ +----+ +---+ + | MN | |pMAG| |nMAG| |LMA| + +------+ +----+ +----+ +---+ + IF2 IF1 | | | + | | | | | + | |- - - - - - - - - Attach | | + | | |---------------PBU--------------->| + | | |<--------------PBA----------------| + | |--------RtSol------->| | | + | |<-------RtAdv--------| | | + | Addr. | | | + | Conf. | | | + | |<------------------->|==================data============|<---> + | | | | | + |- - - - - - - - - - - - - - - - - Attach | + | | | |----PBU(transient)--->| + | | | |<---PBA(transient)---[F] + |------RAT Configuration--------------| | + | |<--------------------|==================data============|<--- + |-------RtSol-(optional)------------->| | + |<-----------RtAdv--------------------| | + Addr. | | | | + Conf | | | | + |------------NSol-------------------->|---------PBU-------->[G] + | | | |<--------PBA----------| + |<------------------------------------|========data=========[H]<--> + | | | | | + | | | | | + | | | | | + + Figure 6: Late path switch with PMIPv6 transient BCEs + + + + + +Liebsch, et al. Experimental [Page 32] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +Appendix B. Applicability and Use of Static Configuration at the LMA + + During the working group discussion of the functionality introduced + by this document, it was mentioned that some current Home Agents are + already handling some features and functionality introduced in this + document via some static configuration. This Appendix captures the + analysis that describes which functionality can be handled securely + using a static configuration and which can not. In these cases where + static configuration can be used, this section documents the possible + disadvantages versus using the procedures captured in this document. + +B.1. Early Uplink Traffic from the nMAG + + This use case is related to the handoff scenario when the access + network establishes the uplink tunnel to the LMA before the downlink + portion is done. Consequently, when the mobile node is attached to + the nMAG and in the case of active handoff, the UE will start sending + uplink traffic to the LMA through the nMAG. + + Since the LMA has a proxy BCE for this mobile node that points to the + Proxy-CoA that is hosted at the pMAG, the LMA has a routing entry for + the MN HNP that points to the pMAG-LMA tunnel. Any uplink packet + coming from the nMAG will be dropped by the LMA. + + Allowing the LMA to forward the received uplink traffic from the nMAG + to the Internet while the MN BCE points to the Proxy-CoA hosted at + the pMAG is a violation of all mobility protocols that require a + secure signaling exchange between the nMAG and the LMA before + forwarding such traffic to the Internet. Otherwise, the LMA will be + modifying the mobile node's routing entry based on an unsecured data + traffic packet coming from the nMAG. + + Therefore, this case cannot be addressed by any statically configured + information on the LMA. On the contrary, a secure signaling using + Transient Binding option as detailed in this document is required to + create a transient state for the mobile node BCE at the LMA. This + transient state will allow a temporary routing entry of the mobile + node to point to the nMAG Proxy-CoA. + +B.2. Late Uplink Traffic from the pMAG + + This case is a very common case where the mobile node is handing over + to another MAG while there is still some uplink traffic in flight + coming from the pMAG. In this case, the LMA has the MN BCE points to + the mobile node location before the handoff, i.e., pMAG Proxy-CoA. + Then the LMA receives a PBU from the nMAG over a secure signaling + tunnel, e.g., IPsec tunnel, which indicates some type of handoff as + per the value in the handoff indicator mobility option. + + + +Liebsch, et al. Experimental [Page 33] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + + If the PBU received from the nMAG was sent using the secure tunnel + and successfully processed by the LMA, the LMA according to [RFC5213] + switches the IP-in-IP tunnel to point to the nMAG Proxy-CoA. + However, as the LMA is fully aware of the mobile node movement via + secure signaling from the nMAG and the content of the PBU, which, in + particular, contains the Handoff Indicator mobility option, the LMA + can process some intelligence to allow the mobile node's late + in-flight uplink traffic coming over the pMAG-LMA tunnel to proceed + to the Internet. + + In order to handle all handoff circumstances, the activation + mechanism as described in this document is preferable over a + statically configured timer, and it would dynamically help in ending + the late forwarding from the pMAG based on a protected signaling from + the pMAG. + +B.3. Late Switching of Downlink Traffic to nMAG + + One main use case of transient bindings is the late switching of + downlink traffic routing at the LMA. This allows IP mobility + protocol signaling between nMAG and LMA to be performed decoupled + from the setup of the new link-layer connectivity, e.g., for + performing a handover to an interface with time-consuming link setup + procedures or for a make-before-break handover between interfaces. + + LMA behavior according to [RFC5213] does not allow for late path + switching. The LMA, according to [RFC5213], can only act upon the + Handover Indicator and has no information on the time of completion + of link layer setup. Even if an LMA implementation would be + configured to delay the path switching by a fixed time, which would + violate [RFC5213], this would not lead to smooth handover performance + but would even add latency to the handover. Only additional + signaling as provided by this document provides the information that + late switching is applicable and enables a synchronization of the + handover sequence, i.e., the switching is adapted both to the + finalization of the link between mobile terminal and nMAG and to the + release of the link between mobile terminal and pMAG, whatever comes + first. Stable handover performance is achieved using protected + PMIPv6 signaling as per [RFC5213]. + + + + + + + + + + + + +Liebsch, et al. Experimental [Page 34] + +RFC 6058 Transient Binding for Proxy Mobile IPv6 March 2011 + + +Authors' Addresses + + Marco Liebsch (editor) + NEC Laboratories Europe + NEC Europe Ltd. + Kurfuersten-Anlage 36 + 69115 Heidelberg, + Germany + + Phone: +49 6221 4342146 + EMail: marco.liebsch@neclab.eu + + + Ahmad Muhanna + Ericsson + 2201 Lakeside Blvd. + Richardson, TX 75082, + USA + + Phone: +1 (972) 583-2769 + EMail: ahmad.muhanna@ericsson.com + + + Oliver Blume + Alcatel-Lucent Deutschland AG + Bell Labs + Lorenzstr. 10 + 70435 Stuttgart, + Germany + + Phone: +49 711 821-47177 + EMail: oliver.blume@alcatel-lucent.com + + + + + + + + + + + + + + + + + + + +Liebsch, et al. Experimental [Page 35] + |