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Network Working Group H. Yokota
Request for Comments: 5271 KDDI Lab
Category: Informational G. Dommety
Cisco Systems, Inc.
June 2008
Mobile IPv6 Fast Handovers for 3G CDMA Networks
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract
Mobile IPv6 is designed to maintain its connectivity while moving
from one network to another. It is adopted in 3G CDMA networks as a
way to maintain connectivity when the mobile node (MN) moves between
access routers. However, this handover procedure requires not only
movement detection by the MN, but also the acquisition of a new
Care-of Address and Mobile IPv6 registration with the new care-of
address before the traffic can be sent or received in the target
network. During this period, packets destined for the mobile node
may be lost, which may not be acceptable for a real-time application
such as Voice over IP (VoIP) or video telephony. This document
specifies fast handover methods in the 3G CDMA networks in order to
reduce latency and packet loss during handover.
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RFC 5271 3G CDMA Fast Handover June 2008
Table of Contents
1. Introduction ....................................................2
2. Requirements Notation ...........................................3
3. Terminology .....................................................3
4. Network Reference Model for Mobile IPv6 over 3G CDMA Networks ...4
5. Fast Handover Procedures ........................................6
5.1. Predictive Fast Handover ...................................7
5.2. Reactive Fast Handover ....................................12
5.3. Considerations on the Link Indications ....................15
6. Message Format .................................................15
6.1. Handover Assist Information Option ........................15
6.2. Mobile Node Identifier Option .............................16
6.3. New Flag Extension to FBU Message .........................17
6.4. New Flag Extension to PrRtAdv Message .....................17
7. Security Considerations ........................................18
8. IANA Considerations ............................................18
9. Acknowledgements ...............................................19
10. References ....................................................19
10.1. Normative References .....................................19
10.2. Informative References ...................................19
1. Introduction
Mobile IPv6 [2] allows mobile nodes (MNs) to maintain persistent IP
connectivity while the MN moves around in the IPv6 network. It is
adopted in 3G CDMA networks for handling host-based mobility
management [12]. During handover, however, the mobile node (MN)
needs to switch the radio link to obtain a new Care-of Address (CoA)
and to re-register with the home agent (HA), which may cause a
communication disruption. This is not desirable for real-time
applications such as VoIP and video telephony. To reduce this
disruption time or latency, a fast handover protocol for Mobile IPv6
[3] is proposed. RFC 4260 [7] further describes how this Mobile IPv6
Fast Handover could be implemented on link layers conforming to the
IEEE 802.11 suite of specifications. However, 3G CDMA and IEEE
802.11 networks are substantially different in the radio access, the
representations of the network nodes or parameters, and the network
attachment procedures; for example, the beacon scanning or New Access
Router (NAR) discovery based on [Access Point Identifier, Access
Router-info (AP-ID, AR-info)] tuples specified in RFC 4260 can not be
directly applied to 3G CDMA networks. This document therefore
specifies how Mobile IPv6 fast handovers can be applied in the 3G
CDMA networks.
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RFC 5271 3G CDMA Fast Handover June 2008
2. Requirements Notation
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 [1].
3. Terminology
This document refers to [3] for Mobile IPv6 fast handover
terminology. Terms that first appear in this document are defined
below:
Access Network Identifier (ANID): An identifier that is used by the
Packet Data Serving Node (PDSN) to determine whether the MN is
being handed off from the access network that was not previously
using this PDSN. Anytime the MN crosses into a new region, which
is defined by the ANID, it must re-register with that access
network. The ANID is further composed of the System ID (SID),
Network ID (NID), and Packet Zone ID (PZID) and these values are
administered by the operator. The lengths of the SID, NID, and
PZID are 2 octets, 2 octets, and 1 octet, respectively. Thus,
that of the ANID occupies 5 octets [11].
Forward Pilot Channel: A portion of the Forward Channel that carries
the pilot. The Forward Channel is a portion of the physical layer
channels transmitted from the 3G CDMA access network to the MN.
Further, several sets of pilots (e.g., the active set or neighbor
set) are defined to determine when and where to handover.
Home Link Prefix (HLP): The prefix address assigned to the home link
where the MN should send the binding update message. This is also
called Home Network Prefix (HNP) and one of the bootstrap
parameters for the MN.
International Mobile Subscriber Identity (IMSI): The IMSI is a
string of decimal digits, up to a maximum of 15 digits, that
identifies a unique mobile terminal or mobile subscriber
internationally. The IMSI consists of three fields: the Mobile
Country Code (MCC), the Mobile Network Code (MNC), and the Mobile
Subscriber Identification Number (MSIN). An example of the IMSI
is "440701234567890", where "440" is the MCC, "70" is the MNC, and
"1234567890" is the MSIN. The IMSI conforms to the ITU-T E.212
numbering standard [6]. In this specification, IMSI is an ASCII
string that consists of not more than 15 decimal digits (ASCII
values between 30 and 39 hexadecimal), one character per IMSI
digit. The above example would therefore be encoded as "34 34 30
37 30 31 32 33 34 35 36 37 38 39 30" in hexadecimal notation.
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RFC 5271 3G CDMA Fast Handover June 2008
Mobile Identity (MN ID): An identifier of the Mobile Node that is
used by the access network. The value (e.g., IMSI) is unique
within the operator's network.
Packet Data Serving Node (PDSN): An entity that routes MN originated
or MN terminated packet data traffic. A PDSN establishes,
maintains, and terminates link-layer sessions to MNs. A PDSN is
the access router in the visited access provider network.
Sector Address Identifier (SectorID): A typical cell divides its
coverage area into several sectors. In 3G CDMA systems, each
sector uses a different PN (Pseudo Noise) code offset and is
associated with SectorID. The SectorID is 128 bits long and can
be represented in the IPv6 address format [8].
4. Network Reference Model for Mobile IPv6 over 3G CDMA Networks
Figure 1 shows a simplified reference model of the Mobile IP enabled
3G CDMA networks. The home agent (HA) and Authentication,
Authorization, and Accounting (AAA) server of the mobile node (MN)
reside in the home IP network, and the MN roams within or between the
access provider network(s). Usually, the home IP network is not
populated by the MNs, which are instead connected only to the access
provider networks. Prior to the Mobile IPv6 registration, the MN
establishes a 3G CDMA access technology specific link-layer
connection with the access router (AR). When the MN moves from one
AR to another, the link-layer connection is re-established, and a
Mobile IPv6 handover is performed. Those ARs reside in either the
same or different access provider network(s). The figure shows the
situation, where the MN moves from the Previous Access Router (PAR)
to the New Access Router (NAR) via the radio access network (RAN).
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RFC 5271 3G CDMA Fast Handover June 2008
Home IP Network
+........................+
. +--------+ +--------+ .
. | HA |--| AAA | .
. +--------+ +--------+ .
+../......\..............+
/ \
Access Provider Network(s)
+.............+ +.............+
. +---------+ . . +---------+ .
. | PAR | . . | NAR | .
. +---------+ . . +---------+ .
. |: . . :| .
. |:L2link L2link:| .
. |: . . :| .
. +----+:---+ . . +---:+----+ .
. | RAN | . . | RAN | .
. +----+:---+ . . +---:+----+ .
. |: . . :| .
. +----+ . . +----+ .
. | MN | ---------> | MN | .
. +----+ . . +----+ .
+.............+ +.............+
Figure 1: Reference Model for Mobile IP
In 3G CDMA networks, pilot channels transmitted by base stations
allow the MN to obtain a rapid and accurate C/I (carrier to
interference) estimate. This estimate is based on measuring the
strength of the Forward Pilot Channel or the pilot, which is
associated with a sector of a base station (BS). The MN searches for
the pilots and maintains those with sufficient signal strength in the
pilot sets. The MN sends measurement results, which include the
offsets of the PN code in use and the C/Is in the pilot sets, to
provide the radio access network (RAN) with the estimate of sectors
in its neighborhood. There are several triggers for the MN to send
those estimates, e.g., when the strength of a pilot in the pilot sets
exceeds that of the current pilot, the MN sends the estimates to the
access network. As long as the sector to which the MN is going to
move belongs to the same access network, the mobility within that
access network is handled by the access-specific interfaces [10] and
the link-layer connection between the MN and AR can be maintained
without a re-establishment. The MN can continually search for pilots
without disrupting the data communication and a timely handover is
assisted by the network. If, however, the serving access network
finds that the sector associated with the highest pilot strength
belongs to a different AR, it attempts to close the connection with
the MN. The MN then attempts to get a new traffic channel assigned
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RFC 5271 3G CDMA Fast Handover June 2008
in the new access network, which is followed by establishing a new
connection with the new AR. This could cause a noticeable
communication disruption and lead to a serious degradation of the
user experience. In order to minimize the service degradation,
during the handover between ARs, an IP-level fast handover approach
as defined in RFC 5268 needs to be involved. If the air interface
information can be used as a trigger for the handover between access
routers, fast and smooth handover of Mobile IPv6 can be realized in
3G CDMA networks. The MN can continually search for pilots without
disrupting the data communication and a timely handover is assisted
by the network.
To assist the handover of the MN to the new AR, various types of
information can be considered: the pilot sets, which include the
candidates of the target sectors or BSs, the cell information where
the MN resides, the serving nodes in the radio access network, and
the location of the MN, if available. To identify the access network
that the MN moves to or from, the Access Network Identifiers (ANID)
or the subnet information can be used [9][10]. In this document, a
collection of such information is called "handover assist
information". In 3G CDMA networks, the Link-Layer Address of the New
Access Point (AP) defined in [3] may not be available. If this is
the case, the Handover Assist Information option defined in this
document SHOULD be used instead.
5. Fast Handover Procedures
There are two modes defined in [3] according to the time of sending
the FBU (Fast Binding Update); one is called "predictive mode", where
the MN sends the FBU and receives the FBAck (Fast Binding
Acknowledgment) on the PAR's (Previous Access Router's) link and the
other is called "reactive mode", where the MN sends the FBU from the
NAR's (New Access Router's) link. In the predictive mode, the time
and place the MN hands off must be indicated sufficiently before the
time it actually happens. In cellular systems, since handovers are
controlled by the network, the predictive mode is well applied.
However, if the network is not configured to be able to identify the
new AR, to which the MN is moving next, in a timely manner, the
reactive mode is better applied.
Section 2 of RFC 4907 [20] suggests architectural principles on the
link indication and the effectiveness of the optimization. The link
indication of this document relies on 3G CDMA networks and the
effectiveness of the optimization is attributed to RFC 5268. The
above principles are thus considered by the related specifications
referenced in this document.
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RFC 5271 3G CDMA Fast Handover June 2008
5.1. Predictive Fast Handover
Figure 2 shows the predictive mode of MIPv6 fast handover operation.
When the MN finds a sector or a BS whose pilot signal is sufficiently
strong, it initiates handover according to the following sequence:
(a) A router solicitation for proxy router advertisement is sent to
the PAR. Handover assist information for the target 3G CDMA
network is attached to this message.
(b) Based on the received handover assist information, the NAR is
determined and a proxy router advertisement (PrRtAdv) containing
the prefix of the NAR is sent back to the MN. The MN also
checks that the R flag is not set in the PrRtAdv message, which
indicates the network supports the predictive fast handover mode
(defined later).
(c) The MN creates an NCoA (new CoA) and sends the Fast Binding
Update (FBU) with the NCoA to the PAR, which in turn sends the
Handover Initiate (HI) to the NAR.
(d) The NAR sends the Handover Acknowledge (HAck) back to the PAR,
which in turn sends the FBU acknowledgment (FBAck) to the MN.
(e) The PAR starts forwarding packets toward the NCoA and the NAR
captures and buffers them.
(f) The link-layer connection associated with the PAR is closed and
a new traffic channel is assigned in the new access network.
(g) The MN attaches to the new access network. The attachment
procedure is access technology specific and that for 3G CDMA
network including the PPP transactions is described later.
(h) The MN sends the Unsolicited Neighbor Advertisement (UNA).
(i) The NAR starts delivering packets to the MN.
(j) The MN sends the Binding Update (BU) to the HA to update the
Binding Cache Entry (BCE) with the NCoA, and the HA sends back
the Binding Acknowledgment (BA) to the MN.
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RFC 5271 3G CDMA Fast Handover June 2008
MN PAR NAR HA AAA
| RtSolPr | | | |
(a) |------------->| | | |
| PrRtAdv | | | |
(b) |<-------------| | | |
| FBU | Hl | | |
(c) |------------->|-------------->| | |
| FBack | HAck | | |
(d) |<-------------|<--------------| | |
| |forward packets| | |
(e) | |==============>|(buffering) | |
| | | | |
(f) handover | | | |
| | | | |
+--------------------------------------------------------------+
(g) | Attachment procedure |
+--------------------------------------------------------------+
| UNA | | |
(h) |----------------------------->| | |
| deliver packets | | |
(i) |<=============================| | |
| | BU/BA | | |
(j) |<------------------------------------------->| |
| | | | |
Figure 2: MIPv6 Fast Handover Operation (Predictive Mode)
It is assumed that the NAR can be identified by the PAR leveraging
the handover assist information from the MN. To perform the
predictive mode, the MN MUST send the FBU before the connection with
the current access network is closed. If the MN fails to send the
FBU before handover, it SHOULD fall back to the reactive mode. Even
if the MN successfully sends the FBU, its reception by the PAR may be
delayed for various reasons such as congestion. If the NAR receives
the HI triggered by the delayed FBU after the reception of the UNA
((c) comes after (h)), then the NAR SHOULD send the HAck with
handover not accepted and behave as the reactive mode.
In (a), Router Solicitation for Proxy Advertisement (RtSolPr) is
supposed to include the New Access Point and the MN Link-Layer
Address (LLA) options (Option Code=1 and 2, respectively) according
to [3]. The New AP-LLA option MAY be replaced by the handover assist
information option in 3G CDMA networks. As for the MN-LLA option, if
the LLA for the MN is not available, 3G specific IDs such as IMSI[11]
MAY be used. If this is the case, the MN ID option defined in
Section 6.2, which can support other types of IDs and a length that
is not necessarily multiples of 8 octets, SHOULD be used instead of
the MN-LLA option.
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RFC 5271 3G CDMA Fast Handover June 2008
In (b), PrRtAdv MUST include options for the IP address of the NAR,
which may be the link-local address, and the prefix for the MN. The
PAR SHOULD be able to identify the NAR from the handover assist
information provided by the MN.
Figure 3 shows the call flow for the initial attachment in the 3G
CDMA network [12]. After the traffic channel is assigned, the MN
first establishes a link-layer connection between itself and the
access router. As a link-layer protocol, PPP is considered in this
figure, and a PPP handshake is depicted as an example. After a
link-layer connection is established, the MN registers with the HA by
sending a Binding Update message. There are several parameters for
using Mobile IPv6 such as the home address (HoA), the Care-of Address
(CoA), the home agent address (HA), and the home link prefix (HLP).
In [12], obtaining these values is called bootstrapping, and the
bootstrapping information can be obtained during the link-layer
establishment phase and/or the mobility binding phase [13].
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RFC 5271 3G CDMA Fast Handover June 2008
MN PAR NAR HA AAA
/ | (serving PDSN) (target PDSN) | |
| | LCP | | | |
| (1) |<----------------------->| | |
| | CHAP/PAP | Access-Request/Accept |
| (2) |<----------------------->|<-------------|------->|
| | | +------+ | | |
| (3) | | | HA |<---------+ |
| | | +------+ | |
|+........................................+ | |
|. | | . | |
|. | IPv6CP(IF-ID) | . | |
|.(4)* |<---------|------------->| . | |
(g)< . +---------+ | | | . | |
|.(5)*| LL-addr |<-+ | | . | |
|. +---------+ | | . | |
|. | | . | |
|. | RA(prefix) | . | |
|.(6)* |<---------|--------------| . | |
|. +-----+ | | | . | |
|.(7)*| CoA |<-----+ | | . | |
|. +-----+ | | . | |
|+........................................+ | |
| | DHCPv6(HA) | | |
| (8) |<---------------+------->| | |
| +-----+ | | | | |
| (9) | HA |<-----------+ | | |
| +-----+ | | | |
| | | | | |
\ | | | | |
Figure 3: Attachment Procedure in 3G CDMA Network
The procedure for the initial attachment is as follows:
(g) The link-layer connection establishment and the bootstrapping
phase.
(g-1) The LCP (Link Control Protocol) configure-request/response
messages are exchanged.
(g-2) User authentication (e.g., Challenge Handshake Authentication
Protocol (CHAP) or Password Authentication Protocol (PAP)) is
conducted.
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RFC 5271 3G CDMA Fast Handover June 2008
(g-3) The static bootstrapping information is conveyed from the AAA
and stored in the NAR (target PDSN). The HoA and HLP can be
dynamically assigned by the HA in the mobility binding phase.
This step can be skipped in the handover case.
(g-4) Unique interface IDs are negotiated in IPv6 Control Protocol
(IPv6CP).
(g-5) The MN configures its link-local address based on the obtained
interface ID.
(g-6) A router advertisement containing the prefix is received by
the MN.
(g-7) The MN configures its CoA based on the obtained prefix.
(g-8) DHCPv6 is used to obtain the static bootstrap information
(e.g., the HA address). This step is performed in the initial
attachment and can be skipped once the MN obtains those
parameters.
(g-9) The MN installs the bootstrap information for further
procedures (e.g., the mobility binding).
As is shown in Figure 3, it takes a considerable amount of time to
establish a link-layer connection and almost all of the above
sequences run every time the MN attaches to a new access network. It
is therefore beneficial if packets in transit to the MN are saved not
only during the time period when the MN switches to the new radio
channel but also during the time period when the MN establishes the
link-layer connection.
There are several ways to configure a unique IP address for the MN.
If a globally unique prefix is assigned per link as introduced in
[12], the MN can use any interface ID except that of the other peer
(the AR to which the MN is attached) to create a unique IP address.
If this is the case, however, the PAR cannot provide the MN with a
correct prefix for the new network in the PrRtAdv since such a prefix
is selected by the NAR and provided in the router advertisement. The
MN therefore configures a temporary NCoA with the prefix provided by
the PAR and the correct NCoA MUST be assigned by the NAR. Therefore,
in 3G CDMA network, the PAR MUST send the HI with the S flag set when
it receives the FBU from the MN at step (c) in Figure 2.
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The UNA is supposed to include the MN-LLA [3], but the point-to-point
link-layer connection may be able to uniquely identify the MN. The
most required information by the UNA is the NCoA to check if there is
a corresponding buffer. Therefore, in (h), the function of the UNA
can be realized in several ways:
o Since the establishment of the link-layer connection in (g)
indicates readiness of data communication on the MN side, the NAR
immediately checks if there is a buffer that has packets destined
for the NCoA, which was configured at steps (c) - (d), and starts
delivering, if any (substitution of UNA).
o The MN sends the UNA as defined in [3]. Instead of the MN-LLA in
the LLA option, the MN ID MAY be included in the MN ID option
(standard implementation of UNA).
The primary benefit of the predictive fast handover mode is that the
packets destined for the MN can be buffered at the NAR, and packet
loss due to handover will be much lower than that of the normal MIPv6
operation. Regarding the bootstrapping, the following benefit can be
obtained, too:
o Since the NCoA can be configured via the fast handover procedures,
a router advertisement is not required.
Therefore, the procedures (g-4) to (g-7) can be skipped from the
standard MIPv6 operation in Figure 3.
5.2. Reactive Fast Handover
When the network does not support the predictive fast handover mode,
the reactive fast handover is applied. In this document, a new flag
is defined in PrRtAdv to inform the MN about the capability of the
network (see Section 6.4). To minimize packet loss in this
situation, the PAR instead of the NAR can buffer packets for the MN
until the MN regains connectivity with the NAR. The NAR obtains the
information of the PAR from the MN on the NAR's link and receives
packets buffered at the PAR. In this case, the PAR does not need to
know the IP address of the NAR or the NCoA and just waits for the NAR
to contact the PAR. However, since the PAR needs to know when to
buffer packets for the MN, the PAR obtains the timing of buffering
from the MN via the FBU or the lower-layer signaling, e.g., an
indication of the release of the connection with the MN. Details of
the procedure are as follows:
(a) A router solicitation for proxy router advertisement MAY be sent
to the PAR.
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RFC 5271 3G CDMA Fast Handover June 2008
(b) The proxy router advertisement MAY be sent to the MN. If the
information on the NAR is not available by the PAR, "0::0" MUST
be used for the options related to the NAR (e.g., IP address of
the NAR).
(c) The MN sends the FBU or the access network indicates the close
of the connection with the MN by the lower-layer signaling. If
the MN cannot formulate the NCoA, "0::0", MUST be used for the
NCoA in the FBU. If the B flag is set in the FBU, the PAR
SHOULD start buffering packets destined for the PCoA.
(d) The link-layer connection associated with the PAR is closed and
a new traffic channel is assigned in the new access network.
(e) The MN attaches to the new access network. This part is the
same as described in Section 5.1 and illustrated in Figure 3.
(f) The MN sends the UNA to the NAR.
(g) The MN sends the Fast Binding Update (FBU) to the PAR via the
NAR.
(h) The NAR forwards the FBU from the MN to the PAR.
(i) The PAR sends the Handover Initiate (HI) to the NAR with the
Code set to 1.
(j) The NAR sends the Handover Acknowledge (HAck) back to the PAR.
(k) The PAR sends the FBAck to the NAR.
(l) If the PAR is buffering packets destined for the PCoA, it starts
forwarding them as well as newly arriving ones to the NAR.
(m) The NAR delivers the packets to the MN.
(n) The MN sends the BU to the HA to update the BCE with the NCoA
and the HA sends back the BA to the MN.
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RFC 5271 3G CDMA Fast Handover June 2008
MN PAR NAR HA AAA
| RtSolPr | | | |
(a) |------------->| | | |
| PrRtAdv | | | |
(b) |<-------------| | | |
| FBU | | | |
(c) |- - - - - - ->|(buffering) | | |
| | | | |
(d) handover | | | |
| | | | |
+--------------------------------------------------------------+
(e) | Attachment procedure |
+--------------------------------------------------------------+
| UNA | | |
(f) |----------------------------->| | |
| FBU | | |
(g) |----------------------------->| | |
| | FBU | | |
(h) | |<--------------| | |
| | HI | | |
(i) | |-------------->| | |
| | HAck | | |
(j) | |<--------------| | |
| | FBack | | |
(k) | |-------------->| | |
| |forward packets| | |
(l) | |==============>| | |
| deliver packets | | |
(m) |<=============================| | |
| | BU/BA | | |
(n) |<------------------------------------------->| |
| | | | |
Figure 4: MIPv6 Fast Handover Operation (Reactive Mode)
To indicate the PAR to buffer packets destined for the PCoA, in step
(c), a new flag 'B' is defined in the FBU. When the PAR receives the
FBU with this flag set, it SHOULD buffer packets for the MN. The PAR
MAY also start buffering packets for the MN based on lower layer
signal during handover. Since the packets are buffered at the PAR in
this scenario, the UNA, which is received and processed by the NAR,
can not be used to trigger to forward the buffered packets at the
PAR. In Figure 4, the HAck from the NAR is used as the trigger for
the forwarding of any buffered packets.
The handover indication from the lower layer of 3G CDMA system is
reasonably reliable by the periodical reports from the MN; however,
there are several situations where the target link is not available
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RFC 5271 3G CDMA Fast Handover June 2008
after the handover (step (d)) and the MN comes back to the PAR, or
the MN is not able to move to the target link for some reason after
the connection was closed. If this is the case, the attachment
procedure is performed on the previous link. The packets buffered at
the PAR SHOULD be delivered to the MN after the connection is
re-established.
5.3. Considerations on the Link Indications
This section discusses if the link indications assumed in this
document meet the principles defined in Section 2 of RFC 4907[20],
which suggests 11 architectural principles on the link indication and
the effectiveness of the optimization. This document relies on the
3G CDMA network regarding the link indication, which is precisely
specified by 3GPP2. Therefore, principles (1) to (5), (7), (8), and
(11), that is, "Model Validation", "Clear Definition", "Robustness",
"Recovery from Invalid Indications", "Congestion Control",
"Interoperability", "Race Condition", and "Transport of Link
Indications" are considered by those specs. Principle (6)
"Effectiveness" mentions the effectiveness of the optimization. This
document bases its effectiveness on RFC 5268. Therefore, this
principle is dealt by that RFC. Principle (9) "Metric Consistency"
mentions inconsistencies between link and routing layer metrics. The
spec of this document does not change the routing metrics and
multi-homing is not considered. Finally, principle (10) "Layer
Compression", mentions an overhead reduction scheme and
interoperability. This document does not deal with overhead
reduction and therefore this principle does not apply.
6. Message Format
6.1. Handover Assist Information Option
If the lower layer information of the new point of attachment is not
represented as the link-layer address, the following option SHOULD be
used. The primary purpose of this option is to convey the handover
assist information described in Section 4.
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 | Option-Code | HAI-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HAI-Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
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Type 29
Length The size of this option in 8 octets including the
Type, Length, Option-Code, and HAI-Length (Handover
Assist Information-Length) fields.
Option-Code
1: Access Network Identifier (AN ID)
2: Sector ID
HAI-Length The size of the HAI-Value field in octets.
HAI-Value The value specified by the Option-Code.
If those that received this message do not support this option, they
SHOULD treat this option as opaque and MUST NOT drop it.
Option-Code indicates the particular type of handover assist
information. Currently, two types of information are defined to
assist the discovery of the NAR (see Section 3).
Depending on the size of the HAI-Value field, appropriate padding
MUST be used to ensure that the entire option size is a multiple of 8
octets. The HAI-Length is used to disambiguate the size of the
HAI-Value.
The handover assist information MAY replace the New Access Point
Link-Layer Address in 3G CDMA networks.
6.2. Mobile Node Identifier Option
This option is used to transfer the Identifier of the MN, which is
not its link-layer address.
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 | Option-Code | MN ID-Length |
+---------------------------------------------------------------+
| MN ID ...
+-----------------------------
Type 30
Length The size of this option is in 8 octets including the
Type, Length, and Option-Code.
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Option-Code
1: NAI [4]
2: IMSI (See Section 3)
MN ID-Length The length of the MN ID in octets.
MN ID MN ID value
The MN ID MAY replace the MN Link-Layer Address in 3G CDMA networks.
6.3. New Flag Extension to FBU Message
The MN MUST send the FBU to the PAR with the following new (B) flag
set in the previous network to indicate the PAR to buffer packets
destined for the PCoA. The rest of the Binding Update message format
remains the same as defined in [2] and with the additional (M), (R),
and (P) flags as specified in [14], [15], and [16], respectively.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L|K|M|R|P|B| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
B flag: If the 'B' flag is set, the PAR SHOULD start buffering
the packets destined for the MN as specified in
Section 5.2.
6.4. New Flag Extension to PrRtAdv Message
A new flag 'R' is defined in the PrRtAdv to inform the MN about the
fast handover mode that the network supports.
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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subtype |R| Reserved | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
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R flag: If the 'R' flag is set, the network supports only the
reactive handover mode. Otherwise, the network
supports both the predictive and reactive fast
handover mode.
7. Security Considerations
The security considerations for Mobile IPv6 fast handover are
described in [3]. When a 3G CDMA network is considered, it can be
assumed that the PAR and the NAR have a trust relationship and the
links between them and those between the ARs and the MN are secured.
The MN is authenticated every time it attaches to the new link;
therefore, the AR can securely identify the MN. Depending on the
operator's policy, however, SEcure Neighbor Discovery (SEND) [18] and
the shared handover key defined in [17] can also be applied.
8. IANA Considerations
This document defines two new IPv6 Neighbor Discovery options that
have been assigned from the same space as the IPv6 Neighbor Discovery
Options defined in [19].
29: Handover Assist Information Option (Section 6.1)
30: Mobile Node Identifier Option (Section 6.2)
This document creates two new registries for the Option-Code field in
the Handover Assist Information Option and that in the Mobile Node
Identifier Option. The values for the Option-Code must be within the
range 0-255. New values for both registries can be allocated by
Standards Action or IESG approval [5].
The Option-Code values that have been assigned by IANA are as
follows:
Option-Code for Handover Assist Information Option
Value Description Reference
----- ---------------------------- ----------
0 Reserved
1 ANID Section 6.1
2 Sector ID Section 6.1
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Option-Code for Mobile Node Identifier Option
Value Description Reference
----- ---------------------------- ----------
0 Reserved
1 NAI Section 6.2
2 IMSI Section 6.2
9. Acknowledgements
The authors would like to thank Kuntal Chowdhury, Ashutosh Dutta, Ved
Kafle, and Vijay Devarapalli for providing feedback and support for
this work. The authors would also thank Sebastian Thalanany for
3GPP2 expert review.
10. References
10.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[3] Koodli, R., Ed., "Mobile IPv6 Fast Handovers", RFC 5268, June
2008.
[4] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The Network
Access Identifier", RFC 4282, December 2005.
[5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[6] ITU-T Recommendation, "The international identification plan
for mobile terminals and mobile users", ITU-T E.212, May 2004.
10.2. Informative References
[7] McCann, P., "Mobile IPv6 Fast Handovers for 802.11 Networks",
RFC 4260, November 2005.
[8] 3GPP2 TSG-C, "cdma2000 High Rate Packet Data Air Interface
Specification", C.S0024-A v.2.0, July 2005.
[9] 3GPP2 TSG-A, "3GPP2 Access Network Interfaces Interoperability
Specification", A.S0001-A v.2.0, June 2001.
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RFC 5271 3G CDMA Fast Handover June 2008
[10] 3GPP2 TSG-A, "Interoperability Specification for High Rate
Packet 1 2 Data (HRPD) Access Network Interfaces - Rev A.",
A.S0007-A v.2.0, May 2003.
[11] 3GPP2 TSG-A, "Interoperability Specification (IOS) for High
Rate Packet Data (HRPD) Access Network Interfaces", 3GPP2
A.S0008-0 v3.0, May 2003.
[12] 3GPP2 TSG-X, "cdma2000 Wireless IP Network Standard: Simple IP
and Mobile IP services", X.S0011-002-D v.1.0, February 2006.
[13] Devarapalli, V., Patel, A., Keung, K., and K. Chowdhury,
"Mobile IPv6 Bootstrapping for the Authentication Option
Protocol", Work in Progress, September 2007.
[14] Soliman, H., Castelluccia, C., El Malki, K., and L. Bellier,
"Hierarchical Mobile IPv6 Mobility Management (HMIPv6)", RFC
4140, August 2005.
[15] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
"Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
January 2005.
[16] Gundavell, S., Ed., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", Work in Progress, February
2008.
[17] Kempf, J., Ed. and R. Koodli, "Distributing a Symmetric FMIPv6
Handover Key using SEND", RFC 5269, June 2008.
[18] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[19] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[20] Aboba, B., Ed., "Architectural Implications of Link
Indications", RFC 4907, June 2007.
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Authors' Addresses
Hidetoshi Yokota
KDDI Lab
2-1-15 Ohara, Fujimino
Saitama, 356-8502
JP
Phone: +81 49 278 7894
Fax: +81 49 278 7510
EMail: yokota@kddilabs.jp
Gopal Dommety
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
US
Phone: +1 408 525 1404
EMail: gdommety@cisco.com
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RFC 5271 3G CDMA Fast Handover June 2008
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