

 Internet Draft                                             Seok Joo Koh 
 Internet Engineering Task Force                                    ETRI 
 Expires February 2004                                      Qiaobing Xie 
 August 2003                                                    Motorola 
                                                                         
     
                                       
            mSCTP with Mobile IP for Transport Layer Mobility 
                                      
                <draft-sjkoh-mobile-sctp-mobileip-02.txt> 
                                       
                                       
                                       
 Status of this Memo 
  
    This document is an Internet-Draft and is in full conformance with 
    all provisions of Section 10 of RFC 2026 [1]. 
  
    Internet-Drafts are 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 a "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] 
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                            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 SCTP Initialization.......................................6 
       6.2 Association Initiation in mSCTP with Mobile IP............7 
       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 
    Author's Addresses..............................................11 
     
     
  
     


















  
  
  Koh and Xie                                                 [Page 2] 
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 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] 
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    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] 
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    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] 
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 6. Use of SCTP with Mobile IP  
     
 6.1 SCTP Initialization 
     
    As described in RFC 2960 [1], the SCTP initialization is done from CN 
    and 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. 
     
    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] 
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 6.2 Association Initiation in mSCTP with Mobile IP 
     
    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] 
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    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 
    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] 
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 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 2.2.1. 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] 
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 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 
    
   [1] S. Bradner, "The Internet Standards Process -- Revision 3", BCP, 
      RFC 2026, October 1996.  
    
   [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 
    


  
  
  Koh and Xie                                                [Page 10] 
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   [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-02, February 2003 
    
   [6] Koh, S. J., et al., "Architecture of Mobile SCTP for IP Mobility 
      Support", draft-sjkoh-sctp-mobility-02, June 2003 
    
   [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-ipv6-21, February 2003 
    
   [9] Malki, K. L., et al., "Low Latency Handoffs in Mobile IPv4", 
      draft-ietf-mobileip-lowlatency-handoffs-v4-04, June 2002 
    
   [10] Koodli, R., et al., "Fast Handovers for Mobile IPv6", draft-
      ietf-mobileip-fast-mipv6-06, March 2003 
    
    
 Author's Addresses 
       
       
      Seok Joo Koh 
      sjkoh@etri.re.kr 
      ETRI, Korea 
       
      Qiaobing Xie 
      Qiaobing.Xie@motorola.com 
      Motorola, Inc., USA 



















 Koh and Xie                                                [Page 11] 
