Internet Draft Seok Joo Koh
Internet Engineering Task Force Hee Young Jung
Expires December 2003 Jun Seob Lee
June 2003 Sung Han Kim
ETRI
mSCTP with Mobile IP for IP Mobility Support
<draft-sjkoh-mobile-sctp-mobileip-01.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
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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 IP mobile support in the
harmonized manner. The use of SCTP with Mobile IP is focused on the
mobile sessions that are initiated by CN to MN.
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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
Full Copyright Statement........................................12
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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 IP 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 IP 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, IP 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.
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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 IP mobility management.
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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.
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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.
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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
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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.
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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.
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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:
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
[4] Stewart, R., "Stream Control Transmission Protocol (SCTP) Dynamic
Address Reconfiguration", draft-ietf-tsvwg-addip-sctp-07, February
2003
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[5] Riegel, M. and Tuexen M., "Mobile SCTP", draft-riegel-tuexen-
mobile-sctp-02, February 2003
[6] Koh, S. J., et al., "SCTP with Mobile IP for IP Mobility Support",
draft-sjkoh-mobile-sctp-mobileip-01, 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
361 Kajung-Dong Yusung-Gu,Taejon 305-350, Korea
Hee Young Jung
hyjung@etri.re.kr
361 Kajung-Dong Yusung-Gu,Taejon 305-350, Korea
Jun Seob Lee
juns@etri.re.kr
361 Kajung-Dong Yusung-Gu,Taejon 305-350, Korea
Sung Han Kim
sh-kim@etri.re.kr
361 Kajung-Dong Yusung-Gu,Taejon 305-350, Korea
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