Internet Draft Seok J. Koh Internet Engineering Task Force KNU draft-sjkoh-mobile-sctp-mobileip-04.txt Qiaobing Xie Expires December 2004 Motorola June 2004 Mobile SCTP with Mobile IP for Transport Layer Mobility 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 [1]. 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. Abstract Mobile SCTP (mSCTP) is defined as SCTP with the ADDIP extension. The mSCTP can be used for providing seamless handover by exploiting its multi-homing feature. On the other hand, the Mobile IP basically provides the location management. In this document, we discuss the use of mSCTP along with Mobile IP for Internet mobility support in the transport layer. The use of SCTP with Mobile IP is focused on the mobile sessions that are initiated by CN to MN. Koh and Xie [Page 1]
Internet Draft mSCTP with Mobile IP June 2004 Table of Contents 1. Introduction..................................................3 2. Terminology...................................................3 3. Mobility Support by Mobile IP.................................3 3.1 Location Management in Mobile IP..........................3 3.2 Handover Management in Mobile IP..........................4 4. Overview of mobile SCTP.......................................4 5. Location Management in mSCTP with Mobile IP...................5 6. Use of SCTP with Mobile IP....................................6 6.1 Basic SCTP Initialization.................................6 6.2 Association Initiation in mSCTP with Mobile IP............6 6.3 Data Transport and Handover during the Association........9 6.4 Usage Scenarios for SCTP with Mobile IPv6.................9 7. Discussion....................................................9 7.1 Requirements for SCTP over Mobile IP......................9 7.2 Route Optimization........................................9 7.3 Other Issues.............................................10 8. Security Considerations......................................10 9. Acknowledgement..............................................10 10. References..................................................10 10.1 Normative References....................................10 10.2 Informative References..................................10 Author's Addresses..............................................11 Full Copyright Statement........................................12 Intellectual Property...........................................12 Koh and Xie [Page 2]
Internet Draft mSCTP with Mobile IP June 2004 1. Introduction The Stream Control Transmission Protocol (SCTP) [3] that provides the multihoming feature. Without support of routers in the networks, the SCTP with the ADDIP extension [4] that is called mobile SCTP (mSCTP) can be used to provide seamless handover for the mobile sessions that are originated by Correspondent Nodes (CN) toward to Mobile Nodes (MN) [5, 6]. The mSCTP can also be used to support Internet mobility for the sessions that are initiated by CN toward MN, if it is used along with the Mobile IP [7, 8]. In this case, the Mobile IP is used for location management, and then the mSCTP will be used for seamless handover instead of the MIP-based handover schemes [9, 10]. Specifically, Mobile IP will be used only for the CN to find the current location of MN and to establish an SCTP association. Once the SCTP association has been established, the SCTP session will be supported by the mSCTP seamless handover procedures [5, 6]. This document is intended to continue a discussion to explore the use of SCTP for Internet mobility support. Please send comments to the mailing list <mobile@sctp.de>. To subscribe to this mailing list, please send a mail to <mobile-request@sctp.de>. 2. 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 RFC 2119 [2]. 3. Mobility Support by Mobile IP Generically, Internet mobility issues are divided into Location Management and Handover Management. 3.1 Location Management in Mobile IP Location Management is to identify the current location of a mobile node and keep track of its changes as it moves on. Basically, the location management is done so as to prepare the call setup for the sessions that are requested to mobile nodes (MN) from correspondent nodes (CN). With help of location management, the CN will be able to locate the MN and to establish a session via an appropriate call setup process. Koh and Xie [Page 3]
Internet Draft mSCTP with Mobile IP June 2004 In Mobile IPv4 [7], Home Agent (HA) and Foreign Agent (FA) are employed for location management. The Home Address (HoA) is used as a host identifier of an MN, whereas the Care-of Address (CoA) is used as a location identifier of the MN. The HA maintains the information on the current location of each mobile node by binding CoA of FA to HoA of MN. In case that a Collaborated CoA (CCoA) is used instead of CoA, MIPv4 need not use the FA. By this, an external CN will be able to establish a session with an MN. In Mobile IPv6 [8], the HA is employed for location management. Similar to MIPv4, HoA and CoA are used as a host identifier and a location identifier of the MN, respectively. The CoA of MIPv6 is the same as CCoA of MIPv4. By using MIPv6, an external CN will be able to establish a session with an MN. In Mobile IP, it is noted that the HoA is also used by the applications of an MN, since the MN binds its applications to the HoA. In this respect, HoA is also used for IP packet data transport. 3.2 Handover Management in Mobile IP Handover Management is used to provide mobile hosts for seamless handover, whenever they move into different IP network regions during a session. The main objective of the seamless handover is to minimize the service disruption due to data loss and/or latency during the handover period. In Mobile IP, the Low Latency handover for MIPv4 [9] and Fast Handover for MIPv6 [10] have been designed for handover management. These MIP-based handover schemes rely on the tunneling between old and new Access Routers (ARs). 4. Overview of mobile SCTP In terms of mobile Internet services, a session involved by a mobile node can be classified into one of the following two types: a. Session originated from MN toward CN b. Session originated from CN toward MN The mobile sessions in (a) seem to be a natural extension of the classical client-server model, in which the mobile host originating the session can be viewed as a client, while the counter endpoint will function as a server. For this type of session, the location management is not a crucial requirement. Only the seamless handover will be required in terms of Internet mobility management. Koh and Xie [Page 4]
Internet Draft mSCTP with Mobile IP June 2004 On the other hand, the case (b) requires the location management by which the session originator, CN, can locate the mobile host, MN, as supported in Mobile IP. Mobile SCTP (mSCTP) [5, 6], in its present form, is targeted for mobile sessions that are initiated by MNs toward CNs located in the fixed networks. The mSCTP is used to provide seamless handover for mobile nodes that change their IP addresses by continual moving across different IP subnets. These sessions do not require location management. The detailed schemes for seamless handover using mSCTP are described with some implementation issues in [5, 6]. The mSCTP can be used to provide an alternative scheme for seamless handover instead of the LMIPv4 and FMIPv6 schemes. The basic difference between the MIP-based handover schemes and mSCTP is that the mSCTP intrinsically realizes the handover in the transport layer without any support of network routers, whereas the MIP-based schemes rely on the support of routers support for tunneling between old and new ARs. To support the mobile sessions that are initiated by a CN toward an MN, the mSCTP may be used along with a location management scheme such as Mobile IP. In this scenario, the MIP will be used for a CN to locate an MN and to establish an SCTP association with the MN. After an SCTP association is successfully setup, the mobile SCTP will be used for providing seamless handover for the MN, as described in [5, 6]. 5. Location Management in mSCTP with Mobile IP For the present, the use of SCTP with MIP is focused on the mobile sessions that are initiated by CN to MN. The sessions initiated by MN can be supported only by mobile SCTP. Specifically, Mobile IP will be used only for location management, by which the CN locates the location of MN and establishes an SCTP association. Once the SCTP association has been established, the on-going SCTP session will be supported by the mSCTP seamless handover procedures [5, 6]. A part of the MIP functionality for data transport, will not be used in SCTP with MIP. If once the association is established, the data transport between MN and CN relies on SCTP over IP. The tunneling between HA and MN is not used. Furthermore, the Home Address (HoA) of MN is not used for the data transport. Note that the HoA is used for only the location management. Koh and Xie [Page 5]
Internet Draft mSCTP with Mobile IP June 2004 6. Use of SCTP with Mobile IP 6.1 Basic SCTP Initialization When the CN has the knowledge of the current location of the MN, the basic SCTP initialization, as described in RFC 2960 [1] is done from CN to MN as follow (also see Figure 1): a. CN sends INIT chunk to MN for triggering the association setup. b. MN responds with INIT-ACK chunk to CN. c. Then, CN and MN exchange COOKIE-ECHO and COOKIE-ACK each other. CN MN | | | INIT | |-------------------->| | | | INIT-ACK | |<--------------------| | | | COOKIE-ECHO | |-------------------->| | | | COOKIE-ACK | |<--------------------| Figure 1. SCTP Initialization As shown in the figure, the establishment of an SCTP association is ready by exchanging INIT and INIT-ACK and completed by exchanging COOKIE-ECHO and COOKIE-ACK between CN and MN. 6.2 Association Initiation in mSCTP with Mobile IP In Mobile IP, the HA will have information on the current location of an MN, which is updated by Registration or Binding Update procedures of the MN located at a foreign link. The location management of Mobile IP can be used to convey the INIT chunk message of CN to the MN via HA. After receiving the INIT chunk, the MN responds with INIT-ACK chunk directly to CN (not by way of HA) so as to complete the initiation of SCTP association. The responding INIT-ACK must contain the CCoA (in MIPv4) or CoA (in MIPv6), which can be addressable to the MN. Koh and Xie [Page 6]
Internet Draft mSCTP with Mobile IP June 2004 Mobile IPv4 considers two options to represent the location of the foreign link: CoA and CCoA. The CoA is the IP address of FA (possibly a router), whereas the CCoA is dynamically assigned by using an address allocation mechanism such as DHCP. Unfortunately, the CoA in MIPv4 cannot be applicable to SCTP, since it is an address of FA and thus cannot be used within the MN host (for its SCTP association). Note that SCTP is an end-to-end transport layer protocol, not a network-layer one. On the other hand, the CCoA in MIPv4 can be used within the SCTP hosts. Specifically, the SCTP of MN could bind the CCoA to an SCTP association. For this reason, in this document, we focus on the use of SCTP over MIPv4 for the MN hosts with CCoA in a foreign link. The case of using CoA is for further study. Let us consider an example of MIPv4 networks, which consists of CN, MN and HA. The MN is now at Location A (a foreign link), and will then move into Location B, as shown in Figure 2. [1.1.1.2] +----+ | CN | +----+ || ******* *** *** ** ** ############## ** Internet **---# Home Agent # ** ** ############## ** ** [1.1.1.1] *** *** || ******** || || || ####### ####### # AR1 # # AR2 # ####### ####### | | Location A | | Location B | | +----+ +----+ | MN |=========>| MN | +----+ +----+ CCoA=[2.2.2.2] CCoA=[3.3.3.2] HoA=[1.1.1.2] HoA=[1.1.1.2] Figure 2. SCTP with Mobile IPv4 using CCoA Koh and Xie [Page 7]
Internet Draft mSCTP with Mobile IP June 2004 We assume that the MN has already obtained a CCoA ([2.2.2.2]) from the DHCP server attached to AR1, and also registered the CCoA with HA by using the MIPv4 Registration Procedures. We also assume that the applications of MN can initially bind the CCoA as well as HoA via the socket interface. After initialization of SCTP association, the HoA may be released from the application, as described below. It is noted that the HoA will still be used for MN to update its new CCoAs to HA according to the MIPv4 mechanisms. Now the CN initiates an SCTP association with the MN by sending INIT chunk message over HoA ([1.1.1.2]). The INIT chunk will first be routed to HA, and the HA then forwards the INIT chunk to MN by referring to CCoA ([2.2.2.2]) and using a tunneling mechanism. CN HA MN | | | | INIT | INIT | |-------------------->|-------------------->| | | | | INIT-ACK (CCoA=primary address) | |<------------------------------------------| | | | | COOKIE-ECHO (over CCoA) | |------------------------------------------>| | | | | | COOKIE-ACK | |<------------------------------------------| | | | | SCTP Data Transport | |<----------------------------------------->| | | | Figure 3. SCTP Initiation in SCTP with MIPv4 In response to the INIT chunk, the MN sends INIT-ACK chunk to the CN. The INIT-ACK contains the CCoA address (as the Primary address) and HoA address. Here, the HoA address may only be used for the CN to check whether the responding MN is the authorized host or not (for somewhat security reason). In fact, the HoA will not be referred to by CN (see the Section 4 for more detailed discussion). The source address and destination address of IP packet containing the INIT-ACK chunk are CCoA [2.2.2.2] and CN [1.1.1.2], respectively. In turn, the COOKIE-ECHO and COOKIE-ACK chunks will be exchanged between CN and MN. Koh and Xie [Page 8]
Internet Draft mSCTP with Mobile IP June 2004 6.3 Data Transport and Handover during the Association After the association is established, the CN transmits data chunks to MN over the CCoA address, and the MN sends data chunks to CN directly. When the MN moves from Location A to Location B, the MN gets a new CCoA address [3.3.3.2] from Location B. According to the MIPv4 mechanism, the MN will update its new location to HA, which is done in the Mobile IP layer regardless of the on-going SCTP association. On the other hand, the MN will perform the seamless handover, as it moves into a new IP subnet area, according to the mobile SCTP by adding the new IP address to the on-going association, as described in Section 4 of [6]. These procedures will be repeated until the association has been completed. 6.4 Usage Scenarios for SCTP with Mobile IPv6 The usage scenarios for SCTP with MIPv6 are similar to those for SCTP with MIPv4 that are described so far. In MIPv6, the CoA is used instead of CCoA in MIPv4. The CoA may be obtained from the foreign location via DHCPv6 or stateless address auto-configuration. 7. Discussion This section discusses comparison of SCTP/MIP with the MIP-only scheme and some issues. Again, this comparison is valid for the mobile sessions that are initiated by CN toward to MN. 7.1 Requirements for SCTP over Mobile IP The requirement for using SCTP over Mobile IP is that the CN and MN hosts must be aware of the mobile SCTP. In addition, the MN must be able to bind the CoA as well as HoA to its applications. In MIP, only HoA is bound to the applications of MN. 7.2 Route Optimization The SCTP intrinsically provides the route optimization for data transport between CN and MN. No additional route optimization procedures are required, differently from MIPv4. No binding update between MN and CN is needed, differently from MIPv6. As a result, the tunneling of data packets between HA and MN is not required too. Koh and Xie [Page 9]
Internet Draft mSCTP with Mobile IP June 2004 7.3 Other Issues In the proposed scheme for use of SCTP over MIP, the home address (HoA) of MN is not involved in the data transport between CN and MN. The reason for this is to exploit the intrinsic route optimization feature of mobile SCTP. Note that the additional tunneling or binding update procedures are required in case that the HoA is used in the SCTP association. The HoA may be used as a backup IP address in the event of path failure of the primary address, CCoA or CoA. This is for further study. 8. Security Considerations This document discusses architecture of SCTP mobility support. The associated security issues will be identified as further works go on. 9. Acknowledgement The Authors would like to give special thanks to the following people for their valuable contributions and discussion: Hee Young Jung, ETRI Mee Jeong Lee, Ewha Women University Moon Jung Chang, Ewha Women University Randall Stewart, Cisco Systems Maximilian Riegel, Siemens AG Michael Tuexen, University of Applied Science in Muenster 10. References 10.1 Normative References [1] S. Bradner, " Intellectual Property Rights in IETF Technology", BCP 79, RFC 3668, February 2004. [2] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP, RFC 2119, March 1997. [3] Stewart, R., et al., "Stream Control Transmission Protocol", RFC 2960, October 2000 10.2 Informative References Koh and Xie [Page 10]
INTERNET DRAFT mSCTP with Mobile IP June 2004 [4] Stewart, R., "Stream Control Transmission Protocol (SCTP) Dynamic Address Reconfiguration", draft-ietf-tsvwg-addip-sctp-07, February 2003 [5] Riegel, M. and Tuexen M., "Mobile SCTP", draft-riegel-tuexen- mobile-sctp-03, August 2003 [6] Koh, S. J., et al., "Mobile SCTP for Transport Layer Mobility", draft-sjkoh-sctp-mobility-04, June 2004 [7] Perkins, C. (ed.), "IP mobility Support for IPv4", RFC 3344, August 2002 [8] Johnson, D., et al., "Mobility Support in IPv6", draft-ietf- mobileip-ipv6-24, June 2003 [9] Malki, K. L., et al., "Low Latency Handoffs in Mobile IPv4", draft-ietf-mobileip-lowlatency-handoffs-v4-09, June 2004 [10] Koodli, R., et al., "Fast Handovers for Mobile IPv6", draft- ietf-mipshop-fast-mipv6-01, January 2004 Author's Addresses Seok J. Koh sjkoh@knu.ac.kr Department of Computer Science Kyungpook National University, Korea Qiaobing Xie Qiaobing.Xie@motorola.com Motorola, Inc., USA Koh and Xie [Page 11]
INTERNET DRAFT mSCTP with Mobile IP June 2004 Full Copyright Statement Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Koh and Xie [Page 12]