MIPSHOP Working Group Heejin Jang
Internet-Draft Samsung AIT
Intended status: Informational Junghoon Jee
Expires: January 9, 2008 ETRI
Youn-Hee Han
KUT
Soohong Daniel Park
Samsung Electronics
Jaesun Cha
ETRI
July 8, 2007
Mobile IPv6 Fast Handovers over IEEE 802.16e Networks
draft-ietf-mipshop-fh80216e-02.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
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Abstract
This document describes how a Mobile IPv6 Fast Handover can be
implemented on link layers conforming to the 802.16e suite of
specifications.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. IEEE 802.16e Handovers Overview . . . . . . . . . . . . . . . 6
4. Network Topology Acquisition and Cell Selection . . . . . . . 8
5. Interaction between FMIPv6 and IEEE 802.16e . . . . . . . . . 9
5.1. Access Router Discovery . . . . . . . . . . . . . . . . . 9
5.2. Handover Preparation . . . . . . . . . . . . . . . . . . . 9
5.3. Handover Execution . . . . . . . . . . . . . . . . . . . . 10
5.4. Handover Completion . . . . . . . . . . . . . . . . . . . 10
6. The Examples of Handover Scenario . . . . . . . . . . . . . . 11
6.1. Predictive Mode . . . . . . . . . . . . . . . . . . . . . 11
6.2. Reactive Mode . . . . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 16
9. Normative References . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . . . 19
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1. Introduction
Mobile IPv6 (MIPv6) [RFC3775] is currently available to provide the
session continuity during handover. It is capable of handling IP
handovers between different subnets in a transparent way for higher-
level connections. However, the handover latency resulting from
MIPv6 is often unacceptable to real-time traffic such as Voice over
IP, and Mobile IPv6 Fast Handover protocol (FMIPv6) [RFC4068] has
been proposed as a mechanism to reduce the handover latency by
predicting and preparing the impending handover in advance.
As [RFC4260] pointed out, FMIPv6 assumes the support from the link-
layer technology, but the specific link-layer information available,
as well as the timing of its availability (before, during or after a
handover occurs), differs according to the particular link-layer
technology in use.
This document describes Mobile IPv6 Fast Handovers over 802.16
networks. We begin with a summary of a handover procedure of
[802.16e], the amendment of 802.16 for mobility. Then the
interaction between 802.16e and FMIPv6 is presented with the
primitives proposed by IEEE 802.21 [802.21] for the close interaction
between Layer 2 and Layer 3. Lastly, the examples of handover
scenario are described for both predictive mode and reactive mode.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document is to be interpreted as described in [RFC2119].
Most of terms used in this draft are defined in MIPv6 [RFC3775] and
FMIPv6 [RFC4068].
The following terms come from IEEE 802.16e specification [802.16e].
MOB_NBR-ADV
IEEE 802.16e neighbor advertisement message sent periodically
by a base station.
MOB_MSHO-REQ
IEEE 802.16e handover request message sent by a mobile node.
MOB_BSHO-RSP
IEEE 802.16e handover response message sent by a base station.
MOB_BSHO-REQ
IEEE 802.16e handover request message sent by a base station.
MOB_HO-IND
IEEE 802.16e handover indication message sent by a mobile node.
BSID
IEEE 802.16e base station identifier.
Additionally, the following primitives are proposed by [802.21] and
the standardization is in progress. We also referred to
[I-D.irtf-mobopts-l2-abstractions].
Link_Detected (LD)
A trigger from the link layer to the IP layer in a mobile node
to report that a new link is detected.
Link_Going_Down (LGD)
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A trigger from the link layer to the IP layer in a mobile node
to report that a link down event will be fired in the near
future.
Link_Up (LUP)
A trigger from the link layer to the IP layer in a mobile node
to report that the mobile node completes the link layer
connection establishment with a new BS.
Handover_Commit (HC)
A control command from the IP layer to the link layer in a
mobile node in order to force the mobile node to switch from an
old BS to a new BS.
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3. IEEE 802.16e Handovers Overview
Compared with the handover in the wireless LAN, the 802.16e handover
mechanism consists of more steps since 802.16e embraces the
functionality for elaborate parameter adjustment and procedural
flexibility.
When an MN stays in a link, it listens to L2 neighbor advertisement
messages, named MOB_NBR-ADV, from its serving BS. A BS broadcasts
them periodically to identify the network and announces the
characteristics of neighbor BSs. Once receiving this, the MN decodes
this message to find out information about the parameters of neighbor
BSs for its future handover. With the provided information in
MOB_NBR-ADV, the MN may minimize the handover latency by obtaining
the channel number of neighbors and reducing the scanning time, or
may select the better target BS based on the signal strength, QoS
level, service price, etc.
In 802.16e, the handover procedure is conceptually divided into two
steps: ``handover preparation'' and ``handover execution''
[SH802.16e]. The handover preparation can be initiated by either MN
or BS. During this period, neighbors are compared by the metrics
such as signal strength or QoS parameters and a target BS is selected
among them. If necessary, the MN may try to associate (initial
ranging) with candidate BSs to expedite a future handover. Once the
MN decides handover, it notifies its intent by sending a MOB_MSHO-REQ
message to the serving BS. The BS then replies with a MOB_BSHO-RSP
containing the recommended BSs to the MN after negotiating with
candidates. Optionally it may confirm handover to the target BS over
backbone when the target is decided. The BS alternatively may
trigger handover with a MOB_BSHO-REQ message.
After handover preparation, handover execution starts. When the MN
selects the target BS and is about to move to the new link, it sends
a MOB_HO-IND to the serving BS as a final indication for handover and
conducts handover. Once the MN makes a new attachment, it conducts
802.16e ranging through which it can acquire physical parameters from
the target BS, tuning its parameters to the target BS. After ranging
with the target BS successfully, the MN negotiates basic capabilities
such as maximum transmit power, modulator/demodulator type, etc. It
then performs authorization and key exchange procedures, and finally
registers with the target BS. If the target BS has already learned
some contexts such as authentication or capability parameters through
backbone, it may omit the corresponding procedures. For the detailed
procedures of the 802.16 network entry, refer to section 6.3.22 of
[802.16e]. After completing registration, the target BS starts to
serve the MN and communication via target BS is available. However,
when the MN moves to a different subnet, it should re-configure a new
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IP address and re-establish IP connection. To resume the active
session of previous link, the MN should perform IP layer handover
additionally.
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4. Network Topology Acquisition and Cell Selection
An MN can learn the network topology and acquire the link information
in two ways. One method is via L2 neighbor advertisements. A BS
supporting mobile functionality shall broadcast a MOB_NBR-ADV message
including the network topology periodically (maximum interval,
1sec.). This message includes the BSID and channel information of
neighbor BSs, and is used to facilitate the MN's synchronization with
neighbor BSs. An MN can collect the necessary information of the
neighbor BSs for its future handover through this message.
Another method for acquisition of network topology is scanning, which
is the process to seek and monitor available BSs in order to find
suitable handover targets. While a MOB_NBR-ADV message includes
static information about neighbor BSs, scanning provides rather
dynamic parameters such as link quality parameters. Since the
MOB_NBR-ADV message delivers a list of neighbor BSIDs periodically
and scanning provides a way to sort out some adequate BSs, it is
recommended that when new BSs are found in the advertisement, the MN
identifies them via scanning and resolves their BSIDs to the
information of the subnet where the BS is connected. The
association, an optional initial ranging procedure occurring during
scanning, is one of the helpful methods to facilitate the impending
handover. The MN is able to get ranging parameters and service
availability information for the purpose of proper selection of the
target BS and expediting a potential future handover to it. The
detailed explanation of association is described in section 6.3.22 of
[802.16e].
After learning about neighbors, the MN may compare them to find a BS
which can serve better than the serving BS. The target BS may be
determined by considering various criteria such as required QoS,
cost, user preference, policy, etc. How to select the target BS is
not in the scope of this draft.
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5. Interaction between FMIPv6 and IEEE 802.16e
In this section, we describe the desirable FMIPv6 handover procedure
in 802.16 networks. We introduce four primitives proposed by IEEE
802.21 WG [802.21] for the close interaction between FMIPv6 and
802.16e, and present the detailed interaction procedures.
5.1. Access Router Discovery
Once a new BS is detected through the reception of a MOB_NBR-ADV and
scanning, an MN may try to learn the associated AR information as
soon as possible. In order to enable quick discovery of the
associated AR information in the IP layer, the link layer (802.16)
triggers a Link_Detected primitive to the IP layer (FMIPv6) on
detecting the new BS.
Receiving the Link_Detected from the link layer, the IP layer tries
to learn the associated AR information by exchanging the RtSolPr
(Router Solicitation for Proxy Advertisement) and PrRtAdv (Proxy
Router Advertisement) with the PAR. The result of resolving BSIDs is
a list of [BSID, AR-Info] tuple(s). AR-Info consists of AR's prefix,
IP address and link layer address.
5.2. Handover Preparation
As mentioned in section 4, an MN initiates handover by sending a
MOB_MSHO-REQ to the BS and receives a MOB_BSHO-RSP from the BS as a
response. Alternatively, the BS can initiate handover by sending a
MOB_BSHO-REQ to the MN. After receiving either MOB_BSHO-RSP or
MOB_BSHO-REQ message, the MN sends an FBU (Fast Binding Update) to
the PAR. At this time, the Link_Going_Down (LGD) is used to signal
the IP layer of the arrival of MOB_BSHO-REQ/MOB_BSHO-RSP in the link
layer as soon as possible. According to 7.3.6 of [802.21], this
notification is designed to be triggered when the link layer
connection is expected to go down (Link_Down) within a certain time
interval, as a consequence, it can be used for making adequate a
priori preparation to before actual handover
On receiving LGD, the IP layer sends an FBU to the PAR. Before
sending an FBack (Fast Binding Acknowledgement) to the MN, the PAR
sets up tunnel between PCoA (Previous CoA) and NCoA (New CoA) by
exchanging HI (Handover Initiate) and HAck (Handover Acknowledge)
messages with the NAR, and forwards the packets destined for the MN
to NCoA. During this time, an available NCoA is confirmed with a
HAck message.
After the MN sends a MOB_HO-IND to the serving BS, data packet
transfer between MN and BS is not allowed any more. Therefore, if
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possible, the MN should exchange an FBU and an FBack message with the
PAR before sending a MOB_HO-IND to the BS so as to operate in
predictive mode.
5.3. Handover Execution
When an FBack message arrives before handover, an MN runs in
predictive mode. If the MN can not acquire an FBack message on the
current link, it should run in reactive mode after handover. Note
that when a MOB_HO-IND is sent before an FBack arrives, the MN will
operate in reactive mode because the serving BS releases MN's all
connections and resources after it receives a MOB_HO-IND The BS may
retain the resource until the resource retain timer expires.
When an FBack message arrives, a Handover_Commit (HC) may be issued
from the IP layer to the link layer so as to promote the issue of
MOB_HO-IND message immediately. Until the HC occurs, the link-layer
may keep the current link and postpone sending a MOB_HO-IND message
as long as possible to operate in predictive mode. Similar concept
has already introduced for the wireless LAN in
[I-D.irtf-mobopts-l2-abstractions]. An HC is provided by MIH (Media
Independent Handover) command service of the [802.21].
After switching links, the MN synchronizes with the target BS and
performs the 802.16e network entry procedure. The MN exchanges the
RNG-REQ/RSP, SBC-REQ/RSP, PKM-REQ/RSP and REG-REQ/RSP messages with
the target BS. Some of these messages may be omitted if the
(previously) serving BS transferred the context to the target BS over
the backbone beforehand. On completion of the network entry
procedure, according to WiMAX model, the initial connection between
the MN and the NAR such as initial service flow (ISF) needs to be
established by the network. For more detailed description, refer to
[WiMAX-NWG]. After that, the 802.16 layer informs the IP layer of
the fact with a Link_Up (LUP) primitive, forcing the IP layer to send
an FNA (Fast Neighbor Advertisement) to the NAR. In case of reactive
mode, the MN should include an FBU within an FNA message.
5.4. Handover Completion
When an MN establishes link connectivity with the NAR, it sends an
FNA message to the NAR. When an NCoA in the FNA is acceptable, in
predictive mode, the NAR stops defending the NCoA and delivers the
buffered packets to the MN. In reactive mode, the MN sends the FNA
containing the FBU. If the NAR detects the NCoA is already in use,
it MUST discard the FBU and reply with Router Advertisement with
Neighbor Advertisement Acknowledge (NAACK) option to the MN.
Otherwise, the NAR forwards the inner FBU to the PAR, establishes the
tunnel, and finally delivers packets destined for the NCoA to the MN.
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6. The Examples of Handover Scenario
In this section, the recommended handover procedure over 802.16
network is shown for both predictive mode and reactive mode. In
following scenarios, an MN is assumed to move to a different subnet.
6.1. Predictive Mode
The procedure is described briefly as follows.
1. A BS broadcasts a MOB_NBR-ADV periodically.
2. If an MN discovers a new neighbor BS in this message, it
may perform scanning for the BS.
3. When a new BS is found through the MOB_NBR-ADV and
scanning, the MN's link layer notifies it to the IP layer
(FMIPv6) by a Link_Detected primitive.
4. Then the MN tries to resolve the new BS's BSID to the
associated AR by exchange of RtSolPr and PrRtAdv messages
with the PAR.
5. The MN initiates handover by sending a MOB_MSHO-REQ message
to the BS and receives a MOB_BSHO-RSP from the BS.
Alternatively, the BS may initiate handover by sending a
MOB_BSHO-REQ to the MN.
6. When the MN receives either MOB_BSHO-RSP or MOB_BSHO-REQ
from the BS, its link layer triggers a Link_Going_Down
primitive to the IP layer.
7. On reception of a Link_Going_Down, the MN's IP layer sends
an FBU message to the PAR. If the PAR receives this, it
establishes tunnel with the NAR by exchange of HI and HAck
messages. During this time, the NAR confirms NCoA
availability in the new link via HAck.
8. The MN receives an FBack message before its handover and
operates in predictive mode after handover. It sends a
MOB_HO-IND message as a final indication of handovers.
Issue of a MOB_HO-IND may be promoted by using a
Handover_Commit command from the IP layer.
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9. The MN conducts handover to the target BS and performs
802.16e network entry procedure.
10. As soon as the network entry procedure is completed, the
MN's link layer signals the IP layer with a Link_Up and
the MN issues an FNA to the NAR.
11. When the NAR receives the FNA from the MN, it delivers
the buffered packets to the MN.
---------- ----------
MN L3 MN L2 | s-BS PAR | | NAR t-BS |
---------- ----------
| | | | | |
|<-LD--|<-----MOB_NBR-ADV-------| | | |
| | & Scanning | | | |
|--------------(RtSolPr)-------------->| | |
|<--------------PrRtAdv----------------| | |
| | | | | |
| | [MN initiation] | | | |
| |------MOB_MNHO-REQ----->| | | |
|<-LGD-|<-----MOB_BSHO-RSP------| | | |
| | or | | | |
| | [BS initiation] | | | |
|<-LGD-|<-----MOB_BSHO-REQ------| | | |
| | | | | |
|------------------FBU---------------->| | |
| | | |-----HI---->| |
| | | |<---HACK----| |
|<-----------------FBack---------------|--> | |
|(HC)>|--------MOB_HO-IND------>| forward========>| |
disconnect | packets | |
| connect | | | |
|<-LUP-|<-------------802.16 network entry---------------->|
connect | | | |
|-------------------------FNA---------------------->| |
|<===============================================deliver |
| | | | packets |
Figure 3. Predictive Fast Handover in 802.16
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6.2. Reactive Mode
The procedure is described as follows in case of reactive mode.
1.~ 7. The same as the case of predictive Mode.
8. In case the MN cannot receive an FBack message before its
handover, it operates in reactive mode after handover.
It sends a MOB_HO-IND message as a final indication of
handovers.
9. The MN conducts handover to the target BS and performs
802.16e network entry procedure.
10. As soon as the network entry procedure is completed, the
MN's link layer signals the IP layer with a Link_Up and
the MN issues an FNA encapsulating an FBU to the NAR.
11. Receiving the FNA, the NAR verifies the availability of
NCoA and forwards the inner FBU to the PAR, establishing
the tunnel. If the NAR detects an NCoA is already in use,
it MUST discard the FBU and reply with Router Advertisement
with NAACK option to the MN. Otherwise, it delivers the
packets destined for NCoA to the MN.
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---------- ----------
MN L3 MN L2 | s-BS PAR | | NAR t-BS |
---------- ----------
| | | | | |
|<-LD--|<-----MOB_NBR-ADV-------| | | |
| | & Scanning | | | |
|--------------(RtSolPr)-------------->| | |
|<--------------PrRtAdv----------------| | |
| | | | | |
| | [MN initiation] | | | |
| |------MOB_MSHO-REQ----->| | | |
|<-LGD-|<-----MOB_BSHO-RSP------| | | |
| | or | | | |
| | [BS initiation] | | | |
|<-LGD-|<-----MOB_BSHO-REQ------| | | |
| | | | | |
|-----------------(FBU)--------------->| | |
| |-------MOB_HO-IND------>| | | |
disconnect| | | | |
| connect | | | |
|<-LUP-|<-------------802.16 network entry---------------->|
connect | | | |
|-------------------------FNA[FBU]----------------->| |
| | | |<---FBU-----| |
| | | |----FBack-->| |
| | | forward | |
| | | packets=========>| |
|<================================================deliver |
| | | | packets |
Figure 4. Reactive Fast Handover in 802.16
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7. Security Considerations
The security consideration of the FMIPv6 specification [RFC4068] is
applicable to this document. Particularly, 802.16e architecture
supports a number of mandatory authorization mechanisms, for example,
EAP-TTLS, EAP-SIM and EAP-AKA, as well as, secure IP address
management between the MN and its network entity. That will allow
secure handover operation between the MN and the network entity.
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8. Acknowledgment
Many thanks IETF Mobility Working Group members of KWISF (Korea
Wireless Internet Standardization Forum) for their efforts on this
work. In addition, we would like to thank Alper E. Yegin, Jinhyeock
Choi, Yoshihiro Ohba and Behcet Sarikaya who have provided the
technical advice.
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9. Normative References
[I-D.irtf-mobopts-l2-abstractions]
Teraoka, F., "Unified L2 Abstractions for L3-Driven Fast
Handover", draft-irtf-mobopts-l2-abstractions-03 (work in
progress), May 2007.
[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.
[RFC4068] Koodli, R., "Fast Handovers for Mobile IPv6", RFC 4068,
July 2005.
[RFC4260] McCann, P., "Mobile IPv6 Fast Handovers for 802.11
Networks", RFC 4260, November 2005.
[802.16e] IEEE 802.16 TGe Working Document, "Amendment 2: Physical
and Medium Access Control Layers for Combined Fixed and
Mobile Operation in Licensed Bands and Corrigendum 1",
IEEE Std 802.16e¢â-2005 and IEEE Std 802.16¢â-2004/
Cor 1-2005, February 2006.
[802.21] IEEE 802.21 Working Group Document,"Draft IEEE Standard
for Local and Metropolitan Area Networks: Media
Independent Handover Services", IEEE P802.21/D05.00,
April 2007.
[SH802.16e] Kim, K., Kim, C., and T. Kim, "A Seamless Handover
Mechanism for IEEE 802.16e Broadband Wireless Access",
International Conference on Computational Science,
vol. 2, pp. 527-534, 2005.
[WiMAX-NWG] WiMAX Network Working Group, "WiMAX Forum Network
Architecture (Stage 3: Detailed Protocols and Procedures)",
Release 1.0.0, March 28, 2007.
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Authors' Addresses
Heejin Jang
Samsung Advanced Institute of Technology
P.O. Box 111
Suwon 440-600
Korea
Email: heejin.jang@samsung.com
Junghoon Jee
Electronics and Telecommunications Research Institute
161 Gajeong-dong, Yuseong-gu
Daejon 305-350
Korea
Email: jhjee@etri.re.kr
Youn-Hee Han
Korea University of Technology and Education
Email: yh21.han@gmail.com
Soohong Daniel Park
Samsung Electronics
416 Maetan-3dong, Yeongtong-gu
Suwon 442-742
Korea
Email: soohong.park@samsung.com
Jaesun Cha
Electronics and Telecommunications Research Institute
161 Gajeong-dong, Yuseong-gu
Daejon 305-350
Korea
Email: jscha@etri.re.kr
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