IETF Seamoby Working Group
Internet Draft Marco Liebsch
Ajoy Singh
(Editors)
Hemant Chaskar
Daichi Funato
Eunsoo Shim
draft-ietf-seamoby-card-protocol-02.txt
Expires: December 2003 June 2003
Candidate Access Router Discovery
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
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Abstract
To enable seamless IP-layer handover of a mobile node (MN) from one
access router (AR) to another, the MN is required to discover the
identities of candidate ARs (CARs) for handover, along with their
capabilities, prior to the initiation of the IP-layer handover. The
act of discovery of CARs has two aspects to it: Identifying the IP
addresses of the CARs and finding the capabilities of those CARs.
This process is called "candidate access router discovery" (CARD).
At the time of IP-layer handover, that CAR, whose capabilities is a
good match to the preferences of the MN, may be chosen as the target
AR for handover. The protocol described in this document allows a
mobile node to perform CARD.
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TABLE OF CONTENTS
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 4
2. TERMINOLOGY. . . . . . . . . . . . . . . . . . . . . . . . . 5
3. CARD PROTOCOL FUNCTIONS. . . . . . . . . . . . . . . . . . . 6
3.1 Reverse Address Translation. . . . . . . . . . . . . . . . 6
3.2 Discovery of CAR Capabilities. . . . . . . . . . . . . . . 6
4. CARD PROTOCOL OPERATION. . . . . . . . . . . . . . . . . . . 7
4.1 Conceptual Data Structures . . . . . . . . . . . . . . . . 10
4.2 Mobile Node - Access Router Operation. . . . . . . . . . . 10
4.2.1 Mobile Node Operation. . . . . . . . . . . . . . . . . 10
4.2.2 Current Access Router Operation. . . . . . . . . . . . 11
4.3 Current Access Router - Candidate Access Router Operation. 12
4.3.1 Current Access Router Operation. . . . . . . . . . . . 12
4.3.2 Candidate Access Router Operation. . . . . . . . . . . 12
4.4 CARD Signaling Failure Recovery. . . . . . . . . . . . . . 13
4.4.1 MN-AR Signaling Failure. . . . . . . . . . . . . . . . 13
4.4.2 AR-AR Signaling Failure. . . . . . . . . . . . . . . . 13
4.5 CARD Protocol Message Piggybacking on the MN-AR Interface. 14
4.6 CARD Protocol Security . . . . . . . . . . . . . . . . . . 14
5. PROTOCOL MESSAGES. . . . . . . . . . . . . . . . . . . . . . 15
5.1 CARD Messages for the Mobile Node-Access Router interface. 15
5.1.1 CARD Main Header Format. . . . . . . . . . . . . . . . 15
5.1.2 CARD Options Format. . . . . . . . . . . . . . . . . . 17
5.1.2.1 CARD Request Option. . . . . . . . . . . . . . . . 18
5.1.2.2 CARD Reply Option. . . . . . . . . . . . . . . . . 18
5.1.3 Sub-Options Format . . . . . . . . . . . . . . . . . . 19
5.1.3.1 L2 ID Sub-Option . . . . . . . . . . . . . . . . . 20
5.1.3.2 Preferences Sub-Option . . . . . . . . . . . . . . 21
5.1.3.3 Requirements Sub-Option. . . . . . . . . . . . . . 21
5.1.3.4 Capability Container Sub-Option. . . . . . . . . . 22
5.1.3.5 Address Sub-Option . . . . . . . . . . . . . . . . 23
5.1.4 Capability AVP Encoding Rule . . . . . . . . . . . . . 23
5.2 CARD Messages for the inter-Access Router Protocol
Operation . . . . . . . . . . . . . . . . . . . . . . 24
5.2.1 Protocol Transport . . . . . . . . . . . . . . . . . . 24
5.2.2 Protocol Main Header . . . . . . . . . . . . . . . . . 25
5.2.3 Protocol Payload Types . . . . . . . . . . . . . . . . 25
5.3 Overview on sub-options'/payload types' usage. . . . . . . 26
6. SECURITY CONSIDERATIONS. . . . . . . . . . . . . . . . . . . 27
6.1 Assumptions . . . . . . . . . . . . . . . . . . . . . . . 27
6.2 Security Association between AR and AR . . . . . . . . . . 27
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6.3 Security Association between AR and MN . . . . . . . . . . 28
6.4 DoS Attack . . . . . . . . . . . . . . . . . . . . . . . . 28
7. PROTOCOL CONSTANTS . . . . . . . . . . . . . . . . . . . . . 29
8. IANA CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . 29
9. NORMATIVE REFERENCES . . . . . . . . . . . . . . . . . . . . 30
10. INFORMATIVE REFERENCES . . . . . . . . . . . . . . . . . . . 30
11. AUTHORS' ADDRESSES . . . . . . . . . . . . . . . . . . . . . 31
12. IPR STATEMENTS . . . . . . . . . . . . . . . . . . . . . . . 32
13. COPYRIGHT NOTICE . . . . . . . . . . . . . . . . . . . . . . 32
14. ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . 32
Appendix A MAINTENANCE OF ADDRESS MAPPING TABLES IN
ACCESS ROUTERS . . . . . . . . . . . . . . . . . . . 33
Appendix A.1 Centralized Approach using a Server Functional
Entity . . . . . . . . . . . . . . . . . . . . . . 33
Appendix A.1.1 Approach . . . . . . . . . . . . . . . . . . . 33
Appendix A.1.2 Associated Protocol Operation . . . . . . . . . 34
Appendix A.1.3 Associated Protocol Messages. . . . . . . . . . 36
Appendix A.1.3.1 CARD Message Transport for the Interface
between an AR and the CARD Server . . . . . . . . . 36
Appendix A.1.3.2 Protocol Main Header. . . . . . . . . . . . 36
Appendix A.1.3.3 Protocol Payload Types. . . . . . . . . . . 37
Appendix A.1.4 Associated Security Considerations. . . . . . . 37
Appendix A.1.4.1 Security Associations . . . . . . . . . . . 37
Appendix A.1.4.2 DoS Attack. . . . . . . . . . . . . . . . . 38
Appendix A.1.4.3 CAR Table Contamination . . . . . . . . . . 38
Appendix A.1.5 Associated IPR statements . . . . . . . . . . . 39
Appendix A.2 Decentralized Approach using Mobile Terminals'
Handover . . . . . . . . . . . . . . . . . . . . . 40
Appendix A.2.1 Approach. . . . . . . . . . . . . . . . . . . . 40
Appendix A.2.2 Associated Protocol Operation . . . . . . . . . 40
Appendix A.2.3 Associated Protocol Messages. . . . . . . . . . 42
Appendix A.2.4 Associated Security Considerations. . . . . . . 43
Appendix A.2.5 Associated IPR Statements . . . . . . . . . . . 43
Appendix B APPLICATION SCENARIOS. . . . . . . . . . . . . . . . 44
Appendix B.1 CARD Operation in a Mobile-IPv6 Enabled Wireless
LAN Network . . . . . . . . . . . . . . . . . . . . 44
Appendix B.2 CARD operation in a Fast Mobile-IPv6 enabled
network . . . . . . . . . . . . . . . . . . . . . . 47
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Conventions used in this document
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 [1].
1. INTRODUCTION
IP mobility protocols, such as Mobile IP, enable mobile nodes to
execute IP-level handover among access routers. Additionally, work
is underway [7][15] to extend the mobility protocols to allow
seamless IP handover. The pre-requisite for the seamless IP mobility
protocols is the knowledge of candidate access routers (CARs) to
which a mobile node can be handed over to. The CAR discovery
protocol enables to acquire information about the access routers
that are candidates for the mobile node's next handover.
The CAR discovery involves identifying a CAR's IP address as well as
its capabilities that the mobile node might use for its handover
decision. There are cases when a mobile node has a choice of
candidates to perform handover to different CARs. The mobile node
would choose one based on a match between the mobile node's
requirements on a handover candidate and the CAR's capabilities.
However, the decision algorithm itself is out of scope of this
document.
The problem statement of the CAR discovery is discussed in [2]. In
this document, a protocol is described to perform CAR discovery.
Section 3 describes two main functions of the CAR discovery
protocol. Then, section 4 describes the core part of the CARD
protocol operation. Finally, the protocol messages' format is
described in section 5.
In Appendix A, two optional approaches are described to build a
local table (CAR table), holding CARs' IP addresses and associated
access points' layer-2 addresses, dynamically in access routers.
This mapping is required in access routers to identify an individual
CAR's IP address and to perform reverse address translation.
However, the core protocol, as described in this document up to
section 5, assumes this local CAR table (section 4.1) in access
routers to be available and filled with the IP addresses of the CARs
(and their associated APs' L2 addresses) throughout the core part of
the draft.
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2. TERMINOLOGY
This document uses terminology defined in TERMS [6].
In addition, the following terms are used:
Mobile Node (MN)
A Mobile Node is an IP host capable of moving its point of
attachment to the Internet.
Access Point (AP)
A radio transceiver by which a MN obtains Layer 2 connectivity with
the wired network.
Access Router (AR)
An IP router residing in an access network and connected to one or
more APs. An AR offers IP connectivity to MNs.
Candidate AR (CAR)
An AR to which a MN has a choice of performing IP-level handover.
Capability of an AR
A characteristic of the service offered by an AR that may be of
interest to a MN when the AR is being considered as a handover
candidate.
L2 ID
Identifier of an AP that uniquely identifies that AP. For example,
in 802.11 PCF, this could be a MAC address of an AP.
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3. CARD PROTOCOL FUNCTIONS
A CARD protocol accomplishes the following functions.
3.1 Reverse Address Translation
If a MN can listen to L2 IDs of new APs prior to making decision
about IP-level handover to CARs, a mechanism is needed for reverse
address translation. This function of the CARD protocol enables the
MN to map the received L2 ID of an AP to the IP address of the
associated CAR that connects to the AP. To get the CAR's IP address,
the MN sends the L2 ID of the AP to the current AR and the current
AR provides the associated CAR's IP address to the MN.
In cases where the MN can acquire IP connectivity with CARs prior to
making handover decisions, this functionality is trivially realized,
since the MN can request CARs individually for reverse address
translation.
3.2 Discovery of CAR Capabilities
Information about capabilities of CARs can assist the MN in making
optimized handover decisions. This capability information serves as
input to the target AR selection algorithm. Some of the capability
parameters of CARs can be static, while some others can change with
time.
Definition of capabilities is out of scope of the CARD protocol
design. Encoding rules for capabilities and the format of a
capability container for capability transport are specified in
section 5.
There are two approaches for MNs to acquire address and capability
information of CARs. One is that the MN sends an explicit request to
its current AR and the current AR provides address and capability
information to the MN. The other is that the current AR either
periodically transmits address and capability information of CARs to
the MNs over download channels, or link-layer mechanisms trigger
unsolicited transmission of CARs' address and capability
information.
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4. CARD PROTOCOL OPERATION
The CARD protocol is used to allow MNs resolving the L2 ID of one or
more APs, which are candidates the MN may initiate a handover to, to
the IP address of the associated CARs, as well as to discover these
CARs' capabilities. Furthermore, the protocol allows populating
ARs' CAR tables (section 4.1) with the capabilities of CARs.
For this, the CARD protocol makes use of a CARD Request and CARD
Reply protocol message handshake between a MN and its current AR,
and between a MN's current AR and individual CARs respectively. CARD
Request and CARD Reply messages are used on the interface between a
MN and its current AR to allow MNs retrieving CARs' address and
capability parameter specific information from the network. To allow
ARs populating and maintaining their local CAR table with capability
parameter information of CARs, a CARD Request and CARD Reply
protocol message handshake is also used on the interface between a
MN's current AR and CARs to allow updating ARs' CAR table entries
with CARs' capability information.
An access point's L2 ID, a CAR's IP address and associated
capability information is carried as CARD protocol message parameter
with a CARD Request or a CARD Reply message respectively. A CAR's
capabilities are specified as a list of attribute-value pairs, which
is conveyed in a Capability Container message parameter.
The CARD protocol enables the MN's current AR to exchange
capabilities with CARs and to subsequently convey appropriate
capabilities to the connected MNs. Information about the CAR(s) and
associated capabilities MAY be used by the MN to perform target
access router selection during its IP handover. The current AR
initiates capability exchange with a CAR either when it receives a
CARD Request message from a MN, containing possibly parameters
carrying identifier(s) (L2 ID) of newly discovered AP(s), or when it
detects that some of its CAR table's capability entries are about to
expire. Upon completion of the MN-solicited capability exchange
between a MN's current AR and CARs, the current AR MUST notify the
desired capabilities to the MN by sending a CARD Reply message
having the desired message parameters appended. The current AR MAY
also send periodically unsolicited CARD Reply messages to all
connected MNs. This behavior of the AR SHALL depend upon the local
policies of the network service providers and need to be configured
administratively.
The unsolicited CARD Reply SHALL be broadcast from ARs to all the
connected MNs. For unsolicited CARD Reply messages sent to connected
MNs, the AR MUST set the U-flag of the CARD Reply to indicate to MNs
that this particular CARD Reply message has been sent unsolicited.
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The CARD protocol also enables a MN to optionally indicate its
preferences on capabilities of interest to its current AR, which
allows the MN's current AR performing optional capability pre-
filtering for optimization purposes. Appending the optional
Preferences message parameter for a CARD Request message, which is
sent to the MN's current AR, the MN can indicate a list of
capability attributes, which are of interest to the MN, to its
current AR. The AR now returns only these capabilities of interest
to the requesting MN. The format of this optional Preferences
message parameter is described in section 5.1.3.2.
Optionally, the MN can provide its current AR with a list of
capability attribute-value pairs, indicating not only the capability
parameters (attributes) as required for capability pre-filtering,
but also a specific value for a particular capability. This allows
the MN's current AR performing CAR pre-filtering and to send only
address and capability information of CARs, whose capability values
meet the requirements of the MN, back to the requesting MN. The
format of this optional Requirements message parameter is described
in section 5.1.3.3.
As an example, using the optional Preferences message parameter, a
MN may indicate to its current AR that it is interested only in
IEEE802.11 interface specific capability parameters, since this is
the only interface the MN has implemented. Hence, the MN's current
AR sends back only CARs' IEEE802.11 specific capabilities.
Similarly, using the optional Requirements message parameter, a MN
MAY indicate to its current AR that it is only interested in CARs
that can satisfy a given QoS constraint. Here, a MN sends the
respective QoS attribute with the QoS constraint value to its
current AR using the optional Requirements message parameter. The
QoS constraint is denoted as an attribute-value pair and
encapsulated with the Requirements message parameter, which is
appended to the MN-originated CARD Request message. Based on the
received optional list of attributes in the Preferences parameter or
a list of attribute-value pairs in the Requirements message
parameter, the MN's current AR MAY use these parameters for deciding
the content of the solicited CARD Reply message, which is to be sent
back to the MN. Alternatively, in case no optimization with regard
to capability or CAR pre-filtering is performed by the MN's current
AR, the current AR MAY choose to silently ignore the optional
Requirements and Preferences message parameter as received in the
CARD Request message.
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The CARD protocol operation, as described in this section,
distinguishes signaling messages exchanged between a MN and its
connecting AR and signaling messages exchanged between ARs. Hence,
description of signaling messages described in the following
sections have a preceding identifier, referring to the associated
interface. Messages that are exchanged between a MN and AR are
precluded with "MN-AR", messages between ARs with "AR-AR"
respectively.
+--------------+ (3)AR-AR CARD Request +----------+
| Current |------------------------->| CAR |
| AR |<-------------------------| |
+--------------+ (4)AR-AR CARD Reply +----------+
^ |
| | MN-AR
MN-AR | | CARD Reply(5)
CARD Request(2) V
+--------------+
| Mobile |
| Node |<-- CARD Init Trigger
+--------------+ (1)
Figure 1: MN initiated CARD Protocol Overview
Figure 1 describes the operation of the MN initiated CARD
Request/Reply-based protocol operation. On reception of access
points' L2 IDs or the appearance of a CARD initiation trigger (1),
the MN passes on one or more L2 ID(s) to its current AR using the
MN-AR CARD Request message (2). The MN's current AR resolves the L2
ID to the IP address of the associated CAR or, in case the MN has
not attached one or more L2 ID message parameters, it just reads out
all CARs' IP address information using the reverse address
translation information (L2 ID to IP address mapping) from its local
CAR table. In case one or more capability entries have expired in
the current AR's CAR table, the current AR then directly contacts
the CAR and performs capability discovery with it by performing an
AR-AR CARD Request (3) and AR-AR CARD Reply (4) protocol message
handshake to retrieve individual CARs' capability information. The
current AR then updates capability entries in its local CAR table
and passes on the IP address of the CAR(s) and associated
capabilities to the MN using the MN-AR CARD Reply message (5).
Since the MN-AR CARD Request is sent when a MN discovers new AP(s)
during link layer scanning, sometimes a MN might send frequent MN-AR
CARD Requests, thereby overwhelming its current AR with CARD Request
signaling messages. To counteract this problem, the AR SHOULD set
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the R-flag (rate limiting) of a subsequent CARD Reply message for
flow-control purposes (section 5.1.2.2), thereby requesting the MN
to reduce the generation rate of MN-AR CARD Requests. Upon receipt
of the MN-AR CARD Reply with the R-flag set, the requesting MN MUST
reduce the rate of generation of MN-AR CARD Requests. The exact
implementation of a rate-limiting algorithm should be decided by the
implementers.
4.1 Conceptual Data Structures
AR(s) SHALL maintain a L2-L3 address mapping table (CAR table) that
will be used to resolve L2 IDs of candidate APs to the IP address of
associated CARs. This address-mapping table can be configured
statically for the CARD protocol operation. Optionally, the CAR
table MAY be populated dynamically, using either a server-based or a
handover-based approach, as described in appendices A.1 and A.2
respectively.
ARs SHALL also keep and maintain individual CARs' capabilities in
the local CAR table, taking the associated capability lifetime into
account. If the lifetime of an individual capability entry has
expired, the respective capability is to be discovered and to be
updated when requested from a connected MN. The ARs' CAR table may
be implemented differently by the different implementations, hence
additional details are not provided here.
4.2 Mobile Node - Access Router Operation
4.2.1 Mobile Node Operation
To initiate CARD, a MN sends a CARD Request to its current AR,
requesting it to resolve the L2 ID of nearby access points to the IP
address of associated CARs, and also to obtain capability parameters
associated with these CARs. In case the requesting MN want its
current AR to resolve specific L2 IDs, the MN-AR CARD Request SHOULD
contain the CARD protocol specific L2 ID message parameters,
carrying the L2 ID of respective access points, for which reverse
address translation to associated CARs' IP address as well as CARs'
capability information is being requested. The CARD Request MAY also
contain the Preferences or Requirements message parameter,
indicating the MN's preferences on capability attributes of interest
or its requirements on CARs' capability attribute-value pairs to its
current AR. For example, using the Preferences message parameter, a
MN may indicate that it is only interested in these CAR(s)
supporting a specific air interface technology. Similarly, using the
Requirements message parameter, a MN can indicate the list of
capability attributes and associated capabilities' values to its
current AR. The Requirements message parameter may be used to
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indicate the cut off values of the capabilities for the desired
CAR(s). The MN's current AR MAY use the Preferences and Requirement
message parameter to decide about a sub-set of the CAR(s) that can
satisfy the MN's need.
Upon receipt of the corresponding MN-AR CARD Reply message, which
has been sent by the MN's current AR in response to the MN's
previously sent request, the MN processes all MN-AR CARD Reply
message parameters to retrieve its CARs' address and capability
information.
4.2.2 Current Access Router Operation
Upon receipt of the requesting MN's MN-AR CARD-Request, containing
one or multiple L2 ID message parameters, the connected AR SHALL
resolve the requested APs' L2 ID to the IP address of the associated
CAR(s). In case no L2 ID parameter has been sent with the MN-AR CARD
Request message, the MN's current AR retrieves all CARs' IP address
and capability information from its local CAR table. Optionally,
when allowed by local policies and supported by respective ARs, the
AR MAY retrieve a subset of capabilities or CARs, satisfying the
optionally appended Preferences and Requirement message parameter,
from its local CAR table. CARs' address information along with
associated capabilities are then delivered to the MN using the MN-AR
CARD Reply message, having the Address message parameters and
appropriate Capability Container parameters appended. The CARs' IP
address as well as the capabilities SHALL be encoded according to
the format for CARD protocol message parameters as defined in
section 5.1.3 of this document. The capabilities are encoded as
attribute-value pairs, which are to be encapsulated in a Capability
Container message parameter according to the format defined in
section 5.1.3.4. The responding current AR shall copy the sequence
number received in the MN-AR CARD Request to the MN-AR CARD Reply.
The CARD protocol optionally allows service providers to configure
AR to send periodic unsolicited CARD Reply Messages to all connected
mobile nodes. The unsolicited CARD Reply is delivered as broadcast
message to MN(s). The current AR sets the U-flag of the unsolicited
CARD Reply to indicate that the message is being sent unsolicited.
The interval between consecutive periodic broadcast is a
configurable parameter and SHALL be configured by the network
administrators.
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4.3 Current Access Router - Candidate Access Router Operation
4.3.1 Current Access Router Operation
The MN's current AR MAY initiate capability exchange with CARs
either when it receives a MN-AR CARD Request or when it detects that
one or multiple of its local CAR table's capability entries'
lifetime is about to expire.
Upon receipt of a MN-AR CARD Request, the MN's current AR retrieves
the IP address of the associated CAR(s) from its local CARD table.
Then the AR SHOULD issue an AR-AR CARD Request to the respective
CAR(s) if complete capability information of a CAR is not available
in the current AR's CAR table. The AR MAY also issue the AR-AR CARD
Request when it detects that one or multiple of its local CAR
table's entries are about to expire. The AR-AR CARD Request message
format is defined in section 5.2.2. The AR MUST set the sequence
number of the CARD Request to one more than the previously used
sequence number value. The AR MAY append its own capabilities,
encoded as attribute-value pairs and encapsulated with the
Capability Container message parameter, to the released AR-AR CARD
Request. The MN's current AR SHALL use the IPsec ESP for
authenticating the AR-AR CARD Request. The IPsec ESP MAY be also
used for encrypting the capability information.
Upon receipt of the AR-AR CARD Reply, which has been sent by the CAR
in response to the previously sent request, the MN's current AR
SHALL extract the capability information from the payload of the
received message and buffer the received capabilities in its local
CAR table. The lifetime of individual capabilities is to be set
according to the lifetime indicated for each capability received.
The value of the table entries' timeout shall depend upon the nature
of individual capabilities. Then the AR MUST send the MN-AR CARD
Reply to the Mobile Node.
4.3.2 Candidate Access Router Operation
Upon receipt of a AR-AR CARD Request, a CAR shall extract the
capabilities of the MN's current AR from the payload of the received
message. The CAR SHALL buffer the received capabilities in its CAR
table and set the timer for individual capabilities appropriately.
The value of the table entries' timeout depends upon the nature of
capabilities received. The CAR then MUST respond with the AR-AR CARD
Reply message. The CAR MUST include the same sequence number
received in AR-AR CARD Request message to the AR-AR CARD Reply
message. The AR-AR CARD Reply shall include the CAR's capabilities
as list of attribute-value pairs in the Capability Container message
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parameter. The CAR SHALL use IPsec ESP for authentication or
optionally encryption of the AR-AR CARD Reply message.
4.4 CARD Signaling Failure Recovery
For a variety of reasons, the packets carrying CARD protocol
signaling may be dropped. In this section we consider mechanisms for
recovery from the CARD signaling failures. Broadly the CARD
signaling failures can be categorized in MN-AR signaling failures
and AR-AR signaling failures.
4.4.1 MN-AR Signaling Failure
It is likely that either a CARD Request or CARD Reply may be dropped
due to poor radio link conditions. A MN SHALL detect the loss of a
MN-AR CARD Request or MN-AR CARD Reply Message using a timeout
mechanism (MN_AR_CARD_TIMEOUT). The AR SHALL start a timer
(MN_AR_CARD_TIMER) after sending a MN-AR CARD Request message with
the given sequence number. The MN SHALL stop the timer as soon as
the reply to the MN-AR CARD Request is received by it. Upon
expiration of the MN_AR_CARD_TIMER, the MN SHALL declare the
outstanding message as lost, resends the same message and restart
the MN_AR_CARD_TIMER. The MN shall retry the MN-AR CARD Request for
a pre-configured number of times (MN_AR_CARD_RETRIES) before
declaring the protocol message exchange aborted. The MN SHALL
silently discard any duplicate MN-AR CARD Reply messages received
from its current AR.
4.4.2 AR-AR Signaling Failure
It is likely that a AR-AR CARD Request or AR-AR CARD Reply may be
dropped due to congestion at the intermediate routers or poor link
conditions. The MN's current AR SHALL detect the loss of an AR-AR
CARD Request or an AR-AR CARD Reply message using a timeout
mechanism (AR_AR_CARD_TIMEOUT). The current AR SHALL start a timer
(AR_AR_CARD_TIMER) after sending the AR-AR CARD Request with the
given sequence number. The current AR SHALL stop the timer as soon
as the reply to the AR-AR CARD Request is received by it. Upon
expiration of the AR_AR_CARD_TIMER, the MN's current AR SHALL
declare the outstanding AR-AR CARD Request as lost and then resends
the same message to the CAR. The current AR SHALL retry the AR-AR
CARD Request message for a pre-configured number of times
(AR_AR_CARD_RETRIES) before declaring the protocol message exchange
as aborted. The current AR SHALL silently discard any duplicate AR-
AR CARD Reply received from the CAR.
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4.5 CARD Protocol Message Piggybacking on the MN-AR Interface
To allow MNs and ARs appending the ICMP-option type CARD Request and
CARD Reply (section 5.1.2) to the ICMP-type Fast Mobile IPv6
signaling messages (CARD protocol message piggybacking), MN and AR
should know about the signaling peer's capability for CARD protocol
message piggybacking. This requires dynamic discovery of
piggybacking capability using the P-flag in the MN-AR CARD Request
and the MN-AR CARD Reply message, as well as in the Capability
Container message parameter, as described in detail in section 5.1.
When not receiving an unsolicited CARD Reply message from the MN's
current AR, the MN sends the very first CARD Request to its current
AR using the ICMP-type CARD main header for transport, as described
in section 5.1.1. In case the MN supports CARD protocol message
piggybacking, the P-flag in this very first CARD Request message is
to be set. On reception of the CARD Request message, the MN's
current AR learns about the MN's piggybacking capability. To
indicate its own capability to convey CARD protocol messages with
Fast Mobile IPv6 protocol messages, the AR sets the P-flag in the
CARD Reply message. In case the AR does not support CARD protocol
message piggybacking, all subsequent CARD protocol messages between
the MN and this particular AR are to be sent stand-alone, using the
CARD main header. In case both nodes, the MN and its current AR,
support CARD protocol message piggybacking, subsequent CARD protocol
messages can be conveyed as an option via the Fast Mobile IPv6
RtSolPr and PrRtAdv message. During the CARD process, a MN learns
about its CARs' piggybacking capability already during the discovery
phase, since the Capability Container, as described in section
5.1.3.4, carries also a P-flag, which is to be set appropriately
from respective CARs whose capabilities are encapsulated. This
allows the MN to immediately perform CARD protocol message
piggybacking after a handover to a selected CAR, assumed this CAR
supports CARD protocol piggybacking.
An application scenario of the CARD-function enabled Fast Mobile-
IPv6 protocol, which carries CARD protocol messages between a MN and
its current AR by means of CARD protocol message piggybacking, is
described in Appendix B.2.
4.6 CARD Protocol Security
The MN-AR and AR-AR messages SHALL be protected using IPsec ESP
[10]. It is safe to assume that there will be an appropriate SA
between a MN and its connected AR, which MAY be used to secure MN-AR
CARD Message. It is also assumed that neighboring ARs SHALL
establish an appropriate SA to secure the AR-AR CARD messages.
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5. PROTOCOL MESSAGES
5.1 CARD Messages for the Mobile Node-Access Router Interface
5.1.1 CARD Main Header Format
Hosts and Access Routers use the CARD ICMP-type main header when
CARD protocol messages, which are to be exchanged between a MN and
an AR, cannot be conveyed via another outgoing ICMP-type message, as
for example the Fast Mobile-IPv6 'Router Solicitation for Proxy' or
'Proxy Router Advertisement' [7] messages.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+- - - -
IP Fields:
Source Address:
An IP address assigned to the sending
interface.
Destination Address:
An IP address assigned to the receiving
interface.
Hop Limit: 255
Encapsulating Security Payload (ESP) Header:
The sender SHOULD include the Encapsulating
Security Payload (ESP) Header, based on the
previously established Security Association
between the sender and the receiver.
ICMP Fields:
Type T.B.A (To be assigned)
Code 0
Checksum The ICMP checksum.
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Reserved This field is currently unused. It MUST be
initialized with zero by the sender and MUST be
ignored by the receiver.
Valid Options:
CARD Request: The CARD Request allows entities to request CARD
specific information from ARs. To process the
CARD Request message on the receiver side,
further sub-options must be carried, serving as
input to the reverse address translation
function and/or capability discovery function.
CARD Reply: The CARD Reply carries parameters, previously
requested with a CARD Request, back to the
sender of the CARD Request. In case of
unsolicited address information and capabilities
are to be sent to a node, the sender uses the
CARD Reply without getting an explicit CARD
Request before. Further sub-options will be
associated with the CARD Reply message.
Valid Sub-Options:
Layer-2 ID (mandatory):
The Layer-2 ID sub-option carries information
about the type of an access point as well as
the Layer-2 address of the access point
associated with the CAR, whose IP address and
capability information is to be resolved.
Preferences sub-option (optional):
The Preferences sub-option carries information
about attributes of interest to the requesting
entity. Attributes are encoded according to the
AVP encoding rule as described in section
5.1.4. For proper settings of AVP Code and Data
field, please see section 5.1.3.2. This sub-
option is used only in case of performing
optional capability pre-filtering on ARs and
allows for providing only capabilities of
interest to a requesting MN.
Requirements (optional):
The Requirements sub-option carries information
about attribute-value pairs required for pre-
filtering of CARs on a MN's current AR. This
parameter conveys MN specific attribute-value
pairs to allow a MN's current AR to send only
CARs of interest, meaning CARs matching the
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MN's requirements according to the attributes'
values, back to the requesting MN. CARs are
filtered on ARs according to CARs' capability
parameters and given policy or threshold, as
encoded in the Requirements sub-option.
Attribute-value pairs are encoded according to
the AVP encoding rule as described in section
5.1.4. Setting rules of AVP Code and Data field
for the Requirements sub-option are described
in section 5.1.3.3.
Capability container (mandatory):
The Capability container sub-option carries
information about a single CAR's capabilities.
The format of this sub-option is described in
section 5.1.3.4.
Address (mandatory):
The Address sub-option carries information on
an individual CAR's resolved IP address. The
format of the Address sub-option is described
in section 5.1.3.5.
5.1.2 CARD Options Format
All options are of the form:
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 | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Type: 8-bit identifier of the type of option. The
options defined in this document are:
Option Name Type
--------------------------------------------------
MN-AR CARD Request T.B.A
MN-AR CARD Reply T.B.A
Length: 8-bit unsigned integer. The length of the
option including the type and length fields in
units of octets. The value 0 is invalid.
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5.1.2.1 CARD Request Option
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 |P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Options
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - -
Fields:
Type: T.B.A
Length: The length of the option in units of octets, including
the type and length fields as well as sub-options.
Flags: P-flag: Indicates CARD protocol message piggybacking
capability of the CARD Request message sender.
A description for proper use of this flag can
be found in section 4.5 of this document.
Reserved bits MUST be initialized with 0.
Sequence Number:
Allows correlating requests with replies.
Valid Sub-Options:
- L2 ID sub-option
- Preferences sub-option
- Requirements sub-option
5.1.2.2 CARD Reply Option
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 |P|U|R| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Options
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - -
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Fields:
Type: T.B.A
Length: The length of the option in units of octets, including
the type and length fields as well as sub-options.
Flags: P-flag: Indicates CARD protocol message piggybacking
capability of the CARD Request message sender.
A description for proper use of this flag can
be found in section 4.5 of this document.
U-flag: Indicates an unsolicited CARD Reply.
A description for proper use of this flag can
be found in section 4 of this document.
R-flag: Indicates exceeding CARD Request rate
limitation. A description for proper use of
this flag can be found in section 4 of this
document.
Reserved bits MUST be initialized with 0.
Sequence Number:
Allows correlating requests with replies.
Valid Sub-Options:
- L2 ID sub-option
- Capability Container sub-option
- Address sub-option
5.1.3 Sub-Options Format
All Sub-Options are of the form:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-Option Type|Sub-Option Len | Sub-Option Data . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sub-Option Type: 8-bit identifier of the type of option. The
Sub-Options defined in this document are:
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Sub-Option Name Type
--------------------------------------------
L2 ID T.B.A
Preferences T.B.A
Requirements T.B.A
Capability Container T.B.A
Address T.B.A
Option-Length: 8-bit unsigned integer. The length of the
option including the type and length fields in
units of octets. The value 0 is invalid.
5.1.3.1 L2 ID Sub-Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-Option Type|Sub-Option Len | Context-ID |M| L2-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2 ID . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - -
Sub-Option Type:
T.B.A
Sub-Option Length:
Length of the Sub-Option (including type and length
fields as well as L2 type indicator) in units of 8
octets.
Context-ID: Identifies associated L2 ID, IP address and
capability information, when coming with separated
sub-options.
M-flag: This flag indicates that the Context-ID of this
particular L2 ID sub-option has been modified by the
MN's current AR and set to the same value as a
preceding L2 ID received in the same CARD Request
message. This adjustment appears in case this L2 ID's
associated access point is served by the same CAR as
a preceding access point's L2 ID, hence, the same
Capability Container and Address sub-option,
describing a CAR's IP address and associated
capabilities, is valid for this particular L2 ID.
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L2 type: Indicates the interface type (optional)
(Ethernet, IEEE802.11b, ...).
If the L2 type indicator is not used, this field MUST
be set to 0.
L2 ID: The variable length layer-2 identifier of an
individual CAR's access point.
5.1.3.2 Preferences Sub-Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-Option Type|Sub-Option Len | Preferences
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sub-Option Type:
T.B.A
Sub-Option Length:
Length of the Sub-Option (including type and length
fields) in units of 8 octets.
Preferences: AVP encoded preferences (see section 5.1.4).
AVPs MUST be encoded according to the AVP encoding rule described in
section 5.1.4. Only ATTRIBUTES (AVP Code) need to be set. The VALUE
indicator (Data) will not be processed and can be omitted. The 'AVP
Length' field is to be set appropriately.
The use of the Preferences sub-option is optional and for
optimization purpose.
5.1.3.3 Requirements Sub-Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-Option Type|Sub-Option Len | Requirements
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sub-Option Type:
T.B.A
Sub-Option Length:
Length of the Sub-Option (including type and length
fields) in units of octets.
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Requirements: AVP encoded requirements (see section 5.1.4)
AVPs MUST be encoded according to the rule described in section
5.1.4. Both, ATTRIBUTES (AVP Code) and VALUES (Data) MUST be set.
The use of the Requirements sub-option is optional and for
optimization purpose.
5.1.3.4 Capability Container Sub-Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-Option Type|Sub-Option Len | Context-ID |P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVPs
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - -
Sub-Option Type:
T.B.A
Sub-Option Length:
Length of the Sub-Option (including type and length
fields as well as AVPs) in units of 8 octets.
Context-ID: Identifies L2 ID, IP address and capability triples,
coming with separate sub-options.
Flags: P-flag: Indicates piggybacking capability of a CAR.
This flag allows a MN already after a CARD process to
know about a selected new AR's piggybacking
capability.
Reserved bits MUST be initialized with 0.
AVPs: AVPs are a method of encapsulating capability
information relevant for the CARD protocol. See
section 5.1.4 for the AVP encoding rule.
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5.1.3.5 Address Sub-Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-Option Type|Sub-Option Len | Context-ID | Address Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - -
Sub-Option Type:
T.B.A
Sub-Option Length:
Length of the Sub-Option (including type and length
fields) in units of octets.
Context-ID: Identifies L2 ID, IP address and capability triples,
coming with separate sub-options.
Address Type: Indicates the type of the address.
0x01 IPv4
0x02 IPv6
Address: The Candidate Access Router's IP address.
5.1.4 Capability AVP encoding rule
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Code |S| Res | AVP Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attribute Lifetime (present if S = 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - -
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AVP Code: Identifies the attribute uniquely.
Flags: S-flag (Static) 1: identifies a static attribute,
lifetime field is not present.
Data will follow immediately
after the AVP Length field.
0: identifies a dynamic attribute,
lifetime field indicates the
attribute's lifetime.
Reserved (Res) flags MUST be set to 0.
Lifetime: Specifies the lifetime of the encoded capability
in seconds. This field is only present if the encoded
capability has a lifetime associated and the S-bit
has not been set.
AVP Length: The two octet AVP length field indicates the
number of octets in this AVP, including the AVP Code,
AVP Flags, AVP Length, Lifetime (if present) and
Data.
In case the encoded capability is static and does not change with
the time, the S-flag MUST be set and the 32-bit Lifetime field is
not present in the encoded capability. In this case the Data field
follows immediately the AVP length field. If there is a timeout
associated with the encoded capability, the S-flag MUST NOT be set
and the Lifetime field MUST be present.
Note: This document provides no detailed information on how to
encode the capability attribute's value, which is to be encoded in
the Data field of the generic message format described above. Also
details on the interpretation of individual capability parameters is
out of scope of this document.
5.2 CARD Messages for the inter-Access Router Protocol Operation
5.2.1 Protocol Transport
For the CARD protocol operation on the network side between a MN's
current AR and CARs, UDP [9] is used as transport for CARD protocol
messages. The associated UDP port for the CARD protocol operation is
T.B.A.
To authenticate protocol messages between ARs, the IPsec ESP SHOULD
be used [10].
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5.2.2 Protocol Main Header
Protocol main header comprises the first 8 octets:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Res. | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - -
Version: Indicates the version of the protocol.
The version described in this document is version 1.
Res.: This field is currently reserved and MUST be
set to 0.
Type: Message type.
Message types specified for this interface:
Message Type
--------------------------------------
AR-AR CARD Request 0x01
AR-AR CARD Reply 0x02
Length: Length of the subsequent payload in octets.
Sequence number:
Allows correlating requests with responses.
5.2.3 Protocol Payload Types
Payload types and encoding rules are the same as described for the
various sub-option types in section 5.1 for the MN-AR interface. The
same TLV-encoded format is used to attach the options as payload to
the protocol main header.
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5.3 Overview on sub-options'/payload types' usage
The following table indicates, which sub-options or payload types
are relevant for the various interfaces in CARD protocol functions.
Description Type Interface
| | / \
| | MN-AR AR-AR
---------------------------------------------------------------
L2 ID T.B.A x
Preferences T.B.A x x
Requirements T.B.A x
Capability Container T.B.A x x
Address T.B.A x
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6. SECURITY CONSIDERATIONS
6.1 Assumptions
It is important to note that it is assumed in the protocol that each
AR has the correct information in the CAR table about the identities
of the geographically neighboring APs and their associated ARs and
the association relationship between the APs and the ARs. It is
assumed that the ARs registered in the CAR table at each AR are
authorized to participate in the CARD protocol.
So any security concern regarding the procedure to discover the
identities is not considered here. Verifying the authorization
status of particular ARs with respect to participating in the CARD
protocol is a part of the discovery procedures and thus is not
considered here either. The appendices of this draft describe
procedures for discovering the identities of the geographically ARs
and APs and relevant security considerations.
It is assumed also that each AR has the correct information about
APs associated with the AR or capability to get it. It could be done
as static configuration at the AR or a protocol could be used
between the AR and the APs for dynamic discovery and exchange of
information such as MAC addresses and operating channels of the APs.
It is out of scope of this draft.
6.2 Security Association between AR and AR
Each AR receives capability information from its neighboring ARs. If
the message is not protected from modification, a malicious attacker
can modify the information, which can cause undesirable impacts on
the applications using the information. Also if the information is
delivered in plain text, a third party can read it.
To prevent the information from being compromised, the CARD REPLY
messages between ARs SHOULD be authenticated. The messages also MAY
be encrypted for privacy of the information.
How to establish a security association is out of scope of this
memo. But it is assumed that the two CARs can establish a security
association. IPsec ESP is the default mechanism for message
authentication between ARs. Also, IPsec ESP is the default method
for message encryption.
Which capability information is collected in the CAR table and
allowed to be disclosed depends on the administration policy. In
particular, if the CARD protocol runs between ARs in different
domains as well as within the same domain, different policies could
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be established regarding capability information disclosure. The
policy can be implemented locally at each AR and thus it is not
dealt with here.
6.3 Security Association between AR and MN
A malicious node can send bogus CARD REPLY messages to MNs by
masquerading the AR. So the MN SHOULD authenticate the CARD REPLY
messages from the AR.
6.4 DoS Attack
An AR can be overwhelmed with CARD REQUEST messages or even CARD
REPLY messages. A MN can also be overwhelmed with CARD REPLY
messages. The AR or MN SHOULD implement a rate limiting policy about
sending or responding to the messages so that it does not send or
process more than a certain number of messages per period. The AR
should also implement a rate limiting policy in accepting CARD
REQUEST messages from any particular AR or MN.
An attacker can send a huge list of capability information by
masquerading ARs. It can cause overflow in the buffer for the CAR
table at ARs or MNs. So the AR or the MN should put a limit on the
size of the capability information for an AR.
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7. PROTOCOL CONSTANTS
MN_AR_CARD_TIMEOUT: This timer value indicates the timeout of an
expected CARD Reply message on a MN after a
previously released CARD Request message has
been sent to the MN's current AR.
MN_AR_CARD_RETRIES: This value indicates the number of retries when
sending a MN-AR CARD Request from a MN before
declaring the message exchange aborted.
AR_AR_CARD_TIMEOUT: This timer value indicates the timeout of an
expected CARD Reply message on an AR after a
previously released CARD Request message has
been sent to a CAR.
AR_AR_CARD_RETRIES: This value indicates the number of retries when
sending an AR-AR CARD Request from a MN's
current AR to a CAR before declaring the message
exchange aborted.
8. IANA CONSIDERATIONS
This section is to provide the Internet Assigned Numbers Authority
(IANA) with guidelines to allow assignment and registration of
values related to the Candidate Access Router Discovery protocol, in
accordance with [11].
The protocol described in this document requires a new ICMP type to
be assigned by the IANA for the CARD protocol main header (section
5.1.1). Furthermore, two new ICMP-option types (section 5.1.2) are
to be assigned through IETF consensus [11] for the protocol
operation between a Mobile Node and its current Access Router. The
new ICMP options to be assigned by the IANA shall be used for the
CARD Request (section 5.1.2.1) and the CARD Reply (section 5.1.2.2)
options. The protocol also requires a UDP port number to be assigned
through IETF consensus for the inter-Access Router CARD protocol
operation (section 5.2.1).
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9. NORMATIVE REFERENCES
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] Kempf, J.,"Problem Description: Reasons For Performing Context
Transfers Between Nodes in an IP Access Network", RFC 3374,
September 2002.
[8] Narten, T., et al., "Neighbor Discovery for IP Version 6
(IPv6)", RFC 2461, December 1998.
[9] Postel, J., "User Datagram Protocol", RFC 768, August 1980.
[10]Atkinson, R., Kent, S.,"IP Encapsulating Security Payload
(ESP)", RFC 2406, November 1998.
[11]Narten, T., Alvestrand, H., "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 2434, October 1998.
10. INFORMATIVE REFERENCES
[2] Trossen, D., Krishanmurthi, G. Chaskar, H., Kempf, J. "Issues in
candidate access router discovery for seamless IP-level
handoffs", draft-ietf-seamoby-cardiscovery-issues-04.txt, work
in progress, October 2002.
[3] Krishanmurti, G., "Requirements for CAR Discovery Protocolsö,
draft-ietf-seamoby-card-requirements-02.txt, work in progress,
October 2002.
[5] Kenward, B.,"General Requirements for Context Transfer", draft-
ietf-seamoby-ct-reqs-05.txt, work in progress, October 2002.
[6] Manner, J., Kojo, M. (Ed), "Mobility Related Terminology",
draft-ietf-seamoby-mobility-terminology-04.txt, work in
progress, April 2003.
[7] Koodli, R, et al., "Fast handoffs for Mobile IPv6", draft-ietf-
mobileip-fast-mipv6-06.txt, work in progress, March 2003.
[12]Funato, D. et al.,"Geographically Adjacent Access Router
Discovery Protocolö, draft-funato-seamoby-gaard-01.txt, work in
progress, June 2002.
[13]Trossen, D. et al.,"A Dynamic Protocol for Candidate Access-
Router Discovery", draft-trossen-seamoby-dycard-01.txt, work in
progress, March 2003.
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[14]Shim, E., Gitlin, R.,"Fast Handoff Using Neighbor Information",
draft-shim-mobileip-neighbor-00.txt, work in progress,
November 2000.
[15]El Malki, K. et. al, "Low Latency Handoffs in Mobile IPv4",
draft-ietf-mobileip-lowlatency-handoffs-v4-05.txt, work in
progress, June 2003.
11. AUTHORS' ADDRESSES
Hemant Chaskar
Nokia Research Center
5 Wayside Road
Burlington, MA 01803, USA
Phone: +1 781-993-3785
Email: Hemant.Chaskar@nokia.com
Daichi Funato
NTT DoCoMo USA Labs
181 Metro Drive, Suite 300
San Jose, CA 95110, USA
Phone: +1 408-451-4736
Email: funato@docomolabs-usa.com
Marco Liebsch
NEC Network Laboratories
Kurfuersten-Anlage 36 , 69115 Heidelberg
Germany
Phone: +49 6221-90511-46
Email: marco.liebsch@ccrle.nec.de
Eunsoo Shim
NEC Laboratories America, Inc.
4 Independence Way
Princeton, NJ 08540, USA
Phone: +1 609-951-2909
Email: eunsoo@nec-labs.com
Ajoy Singh
Motorola Inc
1501 West Shure Dr, USA
Phone: +1 847-632-6941
Email: asingh1@email.mot.com
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12. IPR STATEMENTS
The IETF has been notified of intellectual property rights claimed
in regard to some or all of the specification contained in this
document. For more information consult the online list of claimed
rights.
Please refer to http://www.ietf.org/ietf/IPR for more information.
13. COPYRIGHT NOTICE
"Copyright (C) The Internet Society (date). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
14. ACKNOWLEDGEMENTS
The CARD design team would like to thank Erik Nordmark for providing
valuable insight about the piggybacking of CARD options upon Fast
Mobile-IPv6 messages. In addition, the design team would like to
thank (in alphabetical order) Dirk Trossen, Govind Krishnamurthi,
James Kempf, Madjid Nakhjiri, Pete McCann, Rajeev Koodli, Robert C.
Chalmers and other members of the Seamoby WG for their valuable
comments on the previous versions of the draft as well as for the
general CARD related discussion and feedback.
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APPENDIX A: MAINTENANCE OF ADDRESS MAPPING TABLES IN ACCESS ROUTERS
This appendix gives information on two optional CAR table
maintenance schemes for reverse address mapping in access routers.
Appendix A.1 Centralized Approach using a Server Functional Entity
Appendix A.1.1 Approach
The centralized approach works when the MN has IP-layer connectivity
with only the current AR. However, the MN can scan L2 beacons from
neighboring AP(s) and thereby deduce their L2 ID(s). For example,
802.11 families of MN or cellular handsets with the mobile-assisted
handover capability can do this.
Figure A.1.1 illustrates the centralized CARD operation. In this
operation, ARs have registered their address information with a CARD
server in advance. When a MN discovers the L2 ID of APs during L2
scanning, the MN passes one or more L2 ID(s) to its current AR and
the AR resolves it to the IP address of the AR. For this, the AR
first checks whether the mapping information is locally available in
its CAR table. If not, the MN's current AR queries a CARD server
with the L2 ID. In response, the CARD server returns the IP address
of the CAR to the current AR. Then, the current AR directly contacts
the respective CAR and performs capability discovery with it. The
current AR then passes the IP address of the CAR and associated
capabilities to the MN. The current AR stores the resolved IP
address within its local CAR table.
The centralized CARD protocol operation introduces additional
signaling messages, which are exchanged between the MN's current AR
and the CARD server. The signaling messages are shown with the
preceding identifier "AR-Server", referring to the associated
interface.
An initial idea of performing reverse address translation using a
centralized server has been described in [12].
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+----------+
+------------>| CARD |<-------------+
|+------------| Server |-------------+|
|| +----------+ ||
|| ||
|| ~~~~~~~~~~~ ||
(3)AR-Server||(4)AR-Server{ } || (0) CARD
CARD || CARD { } ||Registration
Request || Reply { IP Cloud } |Request/Reply
|| { } ||
|| { } ||
|V ~~~~~~~~~~~ V|
+---------+ (5)AR-AR CARD Request +-----+-----+
| Current |------------------------->| CAR | CAR |
| AR |<-------------------------| 1 | 2 |
+---------+ (6)AR-AR CARD Reply +-----+-----+
^ | | |
(2)MN-AR | |(7)MN-AR | |
CARD | | CARD | |
Request| V REPLY +---+ +---+
+--------------+ (1) AP1 L2 ID +--|AP1| |AP2|
| Mobile |<---------------------+ +---+ +---+
| Node |<--------------------------------+
+--------------+ (1) AP2 L2 ID
Figure A.1.1: Centralized Approach for L2-L3 mapping
Appendix A.1.2 Associated Protocol Operation
Figure A.1.2 shows the timing diagram of the centralized CARD
protocol operation. In this figure, the CAR registration process is
done before the CARD discovery process (0). CARs register with the
CARD server when the CAR is initialized or when the status of the
APs' L2 ID, which are associated with the CAR, changes. The CAR MAY
also periodically register with the CARD server to update the list
of current AP(s) that it supports.
The CAR discovery process in the centralized approach is initiated
as soon as a MN discovers the L2 ID of a nearby AP during the
periodic L2 scanning. The MN sends the L2 ID to its current AR with
a MN-AR CARD Request message. If the identity and capability
information of the requested CAR is not available in the AR's local
CAR table, the current AR subsequently sends an AR-Server CARD
Request message to the CARD server to resolve the IP address of the
serving AR of the newly discovered AP. The CARD server then resolves
the received L2 ID(s) to the IP address of the associated CAR(s) and
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returns the identity of the CAR(s) to the requesting AR using the
AR-Server CARD Reply message.
MN current AR CARD Server CAR
| | | (Candidate
| | | Access
| | | Router)
| | | |
| | | Registration Req |
| | |<--------------------|
| <~ ~ ~ L2-SCAN (1) | | Registration Reply |
| | |-------------------->|
| | | |
| | | |
|MN-AR CARD Request(2)| | |
|-------------------->| | |
| | AR-Server | |
| | CARD Request(3) | |
| |------------------>| |
| | AR-Server | |
| | CARD Reply(4) | |
| |<----------------- | |
| | | |
| | AR-AR CARD Request(5) |
| |---------------------------------------->|
| | | |
| | AR-AR CARD Reply (6) |
| |<----------------------------------------|
| | | |
| MN-AR CARD Reply(7) | | |
|<--------------------| | |
| | | |
| | | |
| | | |
Figure A.1.2 CARD procedure using a server function for maintenance
of reverse address translation information in ARs' CAR
tables.
Upon receipt of the AR-Server CARD Reply message, the MN's current
AR extracts the IP address of the CAR and subsequently requests
remaining capabilities by sending an AR-AR CARD Request message to
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the CAR. The CAR conveys its capabilities to the requesting AR in an
AR-AR CARD Reply message. Upon receipt of the AR-AR CARD Reply
message, the current AR caches the CAR's capabilities as well as the
associated L2-L3 mapping information in its local CAR table and
conveys the requested capabilities and address information to the MN
using the MN-AR CARD Reply message.
Appendix A.1.3 Associated Protocol Messages
A.1.3.1 CARD Message Transport for the interface between an AR
and the CARD Server
For the centralized CARD operation between an AR and the CARD
server, UDP is used as transport protocol for CARD protocol
messages. A UDP port is T.B.A.
To authenticate protocol messages between ARs, IPsec ESP is to be
used.
A.1.3.2 Protocol Main Header
The protocol main header for this interface is the same as used for
the interface between ARs on network side, and is described in
section 5.2.2.
Because ARs need to register with the CARD server function, two
additional message types have been specified, which is a CARD
Registration Request and a CARD Registration Reply message.
The following table lists message types specified for CARD as used
between an AR and the CARD server function:
Message types specified for this interface:
Message Type
------------------------------------
AR-Server CARD Request 0x03
AR-Server CARD Reply 0x04
CARD Registration Request 0x05
CARD Registration Reply 0x06
For the registration related message types, an additional payload
type is required and described in section A.1.3.3.
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A.1.3.3 Protocol Payload Types
Payload types and encoding rules are the same as described for the
various sub-option types in section 5.1 for the MN-AR interface. The
same TLV-encoded format is used to append the options to the
protocol main header.
For the registration of an AR with a CARD server function, an
additional payload type is required to indicate the lifetime of the
associated AR's registration. The lifetime option is encoded as
follows:
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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: T.B.A
Length: 0x08 - Length of the lifetime payload option in octets
(including type and length fields).
Reserved:
To be initialized with 0.
Lifetime:
Indicates the lifetime of a registration in seconds.
If the lifetime is set to '0', this indicates a de-
registration with a CARD server function.
Appendix A.1.4: Associated Security Considerations
A.1.4.1 Security Associations
The AR-CARD Server communication must be protected using IPsec ESP
and a previously established security association.
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A.1.4.2 DoS Attack
The MN-AR communication presents opportunities to an attacker. A
rogue MN can use CARD as a denial-of-service (DoS) attack against an
AR. It could also flood the backend AR-Server and AR-AR
communications. If the MN undertakes a DoS attack by flooding its
current AR with real or bogus L2 IDs, the CARD protocol should
prevent it.
When the AR has an authentication scheme for MNs, it is difficult
for a rogue MN to change its identity. Hence, one possible solution
is to limit the number of requests from an identical MN within a
unit of time.
A.1.4.3 CAR Table Contamination
When an AR allows caching, CAR table contamination could occur. A MN
provides the current AR with unauthenticated observations of AP
identifiers that it can hear. Then the AR asks for the authenticated
AR information using the CARD server. The CARD server can tell only
that there is a registered AR with the given L2 ID, but it cannot
tell whether the AR is a CAR of the current AR. (Note that CAR needs
to have an access point geographically adjacent to current AR's
APs). The current AR relies on the fact that a MN provided the L2 ID
that matches a registered AR. A malicious MN may provide a L2 ID,
which is the L2 ID of a registered AR but not a CAR of the current
AR, that is, has no overlapping coverage with the current AR. Then
the current AR would build a CAR table with the IP addresses of ARs
that are not CARs. This has implications on the size of CAR table
that can be allowed on ARs. A more serious implication is that, if a
large number of non-CAR entries appear in the AR'S CAR table, the AR
spends processing resources in exchanging capabilities with them.
There is a possible solution for this. The ARs can handle this by
making the CARD information soft state, so that it times out the AP
addresses if it does not receive a confirmation from another MN
within a certain period of time. Thus, any bogus information has
only a limited lifetime, and even within that lifetime, it cannot do
more than to occupy a table slot in the AR's memory. In fact, the AR
can use the number of MNs reporting a particular address to weight
the relevance of a reported AP. So, if 20 MNs report it, the AP
address is more likely to stick around than if only one MN reports
it. This is an issue for implementation rather than a protocol
issue.
However, this issue could not be a problem in actual handover cases.
At the time of handover, the MN or AR receives the L2 ID of the AP
to which the MN is moving. Or the MN matches the AP L2 ID in the CAR
table with the address of the APs it can hear. Thus, an AP's L2 ID
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that is provided by a malicious MN, but has no wireless connectivity
to the CAR, is filtered out when a MN or AR uses the information for
handover, so this can do no harm at the time of handover.
Appendix A.1.5 Associated IPR statements
The IETF has been notified of intellectual property rights claimed
in regard to some or all of the specification contained in this
Appendix A.1. For more information consult the online list of
claimed rights.
Please refer to http://www.ietf.org/ietf/IPR for more information.
[Page 39]
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Appendix A.2 Decentralized Approach using Mobile Terminals'
Handover
Appendix A.2.1 Approach
This approach performs CARD over the MN-AR interface as described in
Section 4. However, it employs one additional message, called the
Router Identity message, over the MN-AR interface to enable ARs to
learn about the reverse address translation tables of their
neighboring ARs, without being dependent on any centralized server.
In this approach, CAR identities in the CAR table of an AR are
maintained as soft states. In other words, the entries for CARs are
removed from CAR table if not refreshed before the timeout period.
The entries for CAR identities in CAR table are created/refreshed
according to following mechanism.
The key idea behind the decentralized approach is to bootstrap and
maintain the association between two ARs as neighbors of each other,
using the actual handover of MNs occurring between them as input.
The first handover between any two neighboring ARs serves as the
bootstrap handover, which invoke the discovery procedure and the
subsequent handover serve to refresh the association between the
neighboring ARs. After the bootstrap handover, the MNs can perform
CARD and thus seamless handover using the CAR information. This idea
was presented in [13] and [14].
Appendix A.2.2 Associated Protocol Operation
CAR table maintenance using the Router Identity message:
Upon the completion of an inter-AR handover, the MN SHOULD send a
Router Identity message to its current AR. This message contains the
identity (IP address) of the previous AR (pAR), which is already
known to the MN. This message is sent as a specific sub-option in
the MN-AR CARD Request (see below). It SHOULD be acknowledged with
the MN-AR CARD Reply. The Router Identity message enables the MN's
current AR to learn that the pAR (still) has an AP whose coverage
overlaps with one of the APs of the current AR and vice versa. With
this information, the MN's current AR can create or refresh an entry
for the pAR as its neighbor. If handover cease between two
particular ARs, the associated entries will eventually timeout and
removed from each AR's CAR table.
Prior to trusting the MN's report, however, the current AR may
perform a number of checks to ensure the validity of the received
information. As one simple method to verify the accuracy of the
Router Identity message, the current AR sends an AR-AR CARD Request
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message to the pAR. The AR-AR CARD Request includes the identity of
the MN. Upon receiving this message, the pAR has to verify that the
said MN was indeed attached to it during a reasonable past and
respond to the current AR. In this way, each handover of a MN
results in a bi-directional discovery process between the two
participating ARs.
Upon receiving positive verification response, the current AR
creates or refreshes as applicable, the entry for the pAR in its
local CAR table. In the former case, the current AR and the pAR
exchange capabilities using the AR-AR CARD Request and AR-AR CARD
Reply protocol messages. When a new entry is created, the ARs MUST
exchange their reverse address translation tables. They may exchange
other capabilities at this time or may defer it to later time when
some MN undergoing handover between them performs CARD as described
in Section 4. In the later (refresh) case, ARs may exchange
capabilities or defer it until later time when some MN undergoing
handover between them performs CARD as described in Section 4.
+--------------+ (4)AR-AR CARD Request +----------+
| Current |------------------------->| pAR |
| AR |<-------------------------| |
+--------------+ (5)AR-AR CARD Reply +----------+
^ | .
| |(3) ACK .
Router | | .
Identity V .
Message (2)+--------------+ +---------------+
| Mobile | | Mobile |
| Node |<-- Inter AR Handoff | Node |
+--------------+ (1) +---------------+
Figure A.2.1 Use of Router Identity Message for CAR Table
Maintenance
Finally, note that, in a handover-based protocol, a first handover
between a pAR and a MN's current AR (without regard to direction, MN
identity and which APs are involved) cannot use CARD, as this
handover would bootstrap the CAR table. However, it is hoped that in
long term such handover will only amount to a small fraction of
total successful handover between pAR and the MN's current AR. Also,
if the user of the MN engaging in such first handover is running a
non-delay sensitive application at the time of handover, the user
may not even realize its impact.
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Appendix A.2.3 Associated Protocol Messages
Router Identity Message Format:
The dynamic handover based approach requires a MN to convey the
pAR's IP address to its current AR. The pAR's IP address is conveyed
from the MN to its current AR as using the following CARD protocol
message sub-option.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-Option Type|Sub-Option Len | pAR ID ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - -
Sub-Option Type:
T.B.A
Sub-Option Length:
Length of the Sub-Option in units of octets.
pAR ID: IP address of the pAR.
The MN's current AR SHOULD acknowledge the receipt of the Router
Identity message using the ACK sub-option described below.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-Option Type|Sub-Option Len | ACK |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sub-Option Type:
T.B.A
Sub-Option Length:
Length of the Sub-Option in units of octets.
ACK: All 1's.
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Appendix A.2.4 Associated Security Considerations
In the design of this protocol, a few assumptions have been made
about the security model in place between the MN and the AR, and
between ARs. In particular, it has been assumed that prior to any
protocol messaging, the AR has authenticated and authorized the MN
to participate in CARD. Moreover, in order for two ARs to cooperate
without introducing serious security concerns, they must be able to
establish a security association. For intra-domain routers, this
could be as simple as a shared secret key. For the inter-domain
scenario, the two domains must have a previously established
relationship that can be leveraged to derive an adequate session
key. All messages listed herein should be protected by means of
IPsec ESP to provide authentication and to ensure message integrity.
Appendix A.2.5 Associated IPR Statements
The IETF has been notified of intellectual property rights claimed
in regard to some or all of the specification contained in this
Appendix A.2. For more information consult the online list of
claimed rights.
Please refer to http://www.ietf.org/ietf/IPR for more information.
[Page 43]
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APPENDIX B: APPLICATION SCENARIOS
This section provides two examples of an application scenario for
the CARD protocol operation. One scenario describes CARD protocol
operation in a Mobile IPv6 (MIPv6) enabled network, providing access
to the infrastructure via wireless LAN Access Points and associated
Access Routers. A second scenario describes CARD protocol operation
in a Mobile IPv6 enabled network, which has enhanced support for
fast handover integrated (Fast Mobile-IPv6), also providing wireless
LAN access to the infrastructure.
Appendix B.1 CARD Operation in a Mobile-IPv6 Enabled Wireless LAN
Network
This application scenario assumes a moving MN having access to the
infrastructure through wireless LAN (IEEE802.11) APs. Location
tracking is performed using the Mobile IPv6 protocol.
The following figure illustrates the assumed network sector for
description of CARD protocol operation.
-----------------------------
/ \ +----+
| NETWORK |---| HA |
\ / +----+
-----------------------------
| |
+-----+ +-----+
| AR1 |---------+ | AR2 |
+-----+ | +-----+
| subnet 1 | |subnet 2
+-----+ +-----+ +-----+
| AP1 | | AP2 | | AP3 |
+-----+ +-----+ +-----+
^ ^ ^
\
\
\
v
+-----+
| MN | - - ->>>- - - ->>>
+-----+
Figure B.1: Assumed network topology
A Mobile IPv6 Home Agent (HA), which is connected to the network,
maintains location information of the MN in its binding cache.
According to Figure B.1, the MN holds currently a care-of address
for the subnet 1, supported by AR1, which is registered with its HA.
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According to the MN's movement, the MN's current environment offers
two further wireless LAN APs with increasing link-quality as
candidate APs for a handover. To allow the MN taking a decision, on
which AP might be the better choice, not only access link quality
parameters, but also parameters associated with ARs should be taken
into account for the decision process. These AR-related parameters
can be, for example, available QoS resources or the type of access
technologies supported from an AR. To learn about these candidate
ARs' capabilities and associated IP address information, the MN
performs CARD. This requires retrieving information about candidate
APs' L2 ID, which is broadcast via beacon information from
respective APs. Furthermore, associated link-quality parameters are
to be retrieved to ascertain, whether or not approaching APs are
eligible candidates for a handover. Assume AP2 and AP3 to be
suitable candidate APs. The MN encapsulates both L2 IDs (AP2 and
AP3) into a CARD Request message, using the L2 ID sub-option, and
sends it to its current AR (AR1).
AR1 resolves each L2 ID, listed as L2 ID options in the received
CARD Request, to the associated IP address of the respective AR,
making use of its local CAR table. According to the environment
illustrated in Figure B.1, the associated AR IP address of the
candidate AP2 will be the same as the MN is currently attached to,
which is AR1. Respective IP address of the candidate AR, to which
AP3 is connected to, is the address of AR2. Since IP addresses of
the MN's CARs are now known to AR1, AR1 retrieves CARs' capabilities
from the CAR table, assumed it has valid entries for respective
capability parameters in the local CAR table. To ascertain dynamic
capabilities, of which lifetime in AR1's CAR table has been expired,
AR1 performs inter-AR CARD for capability discovery. Since
capability information of AR1 is known to AR1, a respective inter-AR
CARD Request is to be sent only to AR2. AR2 in response sends a CARD
Reply message back to AR1, having the requested capability
parameters encapsulated with the signaling message, all assembled in
a capability container sub-option.
Now, AR1 sends its own capabilities and the dynamically discovered
ones of AR2 back to the MN via a CARD Reply message. Furthermore,
AR1 stores the capability parameters of AR2 with the associated
lifetimes in its local CAR table.
On reception of the CARD Reply message, the MN performs target AR
selection, taking AR1's and AR2's capability parameters as well as
associated APs' link-quality parameters into account. In case the
selected AP is AP2, no IP handover needs to be performed. In case
AP3 and the associated AR2 are selected, the MN needs to perform an
IP handover according to the Mobily-IPv6 protocol scenario.
Figure B.2 illustrates the signaling flow of the previously
described application scenario of CARD within a Mobile-IPv6 enabled
network.
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MN AP1 AR1 AP2 AP3 AR2
| | | | | |
| connected | | | | |
0-------------0-------0 | | |
| | | | | |
| | | | | |
| | | |
| <~~~~~~~~~L2-SCAN (AP2)~~~~~| | |
| <~~~~~~~~~L2-SCAN (AP3)~~~~~~~~~~~~~~~~~| |
| | | |
| (MN-AR) CARD Req | | | |
|-------------------->| (AR-AR) CARD Req |
| | |---------------------------------------->|
| | | (AR-AR) CARD Repl |
| (MN-AR) CARD Repl |<----------------------------------------|
|<--------------------| | | |
| | | | | |
[target AR | | | | |
selection] | | | | |
| | | | | |
// // // // // //
[either...] | | | | |
| | | | | |
|-------- L2 attach --------->| | |
| | | | | |
| connected | | | |
0---------------------0-------0 | |
| | | | | |
// // // // // //
[... or] | | | | |
| | | | | |
|--------------- L2 attach -------------->| |
| | | | | |
| connected | | | |
0-----------------------------------------0---------------------0
| | | | | |
| | |
| MIPv6 Binding Update to the HA | |
|------------------------------------------------ - - - > |
| | | | | |
Figure B.2: CARD protocol operation within a Mobile-IPv6 enabled
wireless LAN network.
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Appendix B.2 CARD Operation in a Fast Mobile-IPv6 Enabled Network
This application scenario assumes ARs to be able to perform the fast
handover protocol sequence for Mobile IPv6 [7]. The MN scans for new
APs to handover to, similar to what Figure B.1 illustrates. To
discover candidate APs' associated ARs (CARs), the MN attaches a MN-
AR CARD Request option to the ICMP-type Fast Mobile-IPv6 RtSolPr
message, which is sent to the MN's current AR (pAR, previous AR).
Candidate APs' L2 IDs are encapsulated using the CARD protocol's L2
ID sub-options, which allows the MN to send multiple L2 IDs of
candidate APs to its current AR (potentially replaces the "New
Attachment Point Link-Layer Address" option of the Fast Mobile-IPv6
protocol).
The pAR resolves the received list of candidate APs' L2 IDs to the
IP address of associated CARs. Furthermore, the pAR checks its local
CAR table to retrieve information about the CARs' capabilities. In
case one or multiple associated capability entries of a CAR have
expired, the pAR acquires this CAR's capabilities by means of
sending an AR-AR CARD Request to the respective CAR. The CAR replies
to the requesting pAR with an AR-AR CARD Reply message, having all
capabilities encapsulated in a capability container sub-option and
attached to the CARD Reply option. On reception of the CARs'
capability information, the pAR updates its local CAR table and
forwards the address and capability information of the MN's CAR(s)
to the MN by means of attaching a MN-AR CARD Reply option, carrying
appropriate address and capability container sub-options, to the
Fast Mobile-IPv6 PrRtAdv message. When the MN's handover is
imminent, the MN selects its new AR and the associated new AP from
the discovered list of CARs. According to the Fast Mobile-IPv6
protocol, the MN notifies the pAR of the selected new AR with the
Fast Binding Update (F-BU) message, which allows the pAR to perform
further protocol sequences for a fast handover according to the Fast
Mobile-IPv6 protocol.
Optionally, the pAR could perform selection of an appropriate new AR
on behalf of the MN after the pAR has the MN's CARs' addresses and
associated capabilities available. To allow for selection of an
appropriate new AR out of the list of CARs, the MN must send its
requirements for the selection process to its pAR together with the
MN-MN CARD Request message, appended as a list of attribute-value
pairs carried with the CARD protocol's Requirements sub-option.
After the pAR has selected the MN's new AR, the address and
associated capabilities of the chosen new AR are notified to the MN
with the CARD Reply option, which is conveyed to the MN with the
Fast Mobile-IPv6 PrRtAdv message.
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Note: Since the CARD protocol functions and the CARD Request and
CARD Reply message provide all information of the RtSolPr and
PrRtAdv in a flexible way with regard to discovery and selection of
a new AR during a handover process, the CARD Request and CARD Reply
options could potentially replace the Fast Mobile-IPv6 RtSolPr and
PrRtAdv protocol messages respectively.
Figure B.3 illustrates how CARD protocol messages and functions
could perform together with the Fast Mobile-IPv6 protocol.
MN pAR NAR CAR2
| | as CAR1 |
| | | |
|-------RtSolPr------>| | |
| [MN-AR CARD Req] |-- AR-AR CARD Req*->| |
| |-- AR-AR CARD Req*------------>|
| |<--AR-AR CARD Repl*------------|
| |<--AR-AR CARD Repl*-| |
|<------PrRtAdv-------| | |
| [MN-AR CARD Repl] | | |
| | | |
NAR selection | | |
|------F-BU---------->|--------HI--------->| |
| |<------HACK---------| |
| <--F-BACK--|--F-BACK--> | |
| | | |
Disconnect | | |
| forward | |
| packets===============>| |
| | | |
| | | |
Connect | | |
| | | |
RS (with FNA option)======================>| |
|<-----------RA (with NAACK option)--------| |
|<=================================== deliver packets |
| | |
Figure B.3: Fast Handover protocol sequence with
CARD protocol options
*): The CARD protocol interaction between the pAR and CARs is only
required in case the lifetime of one or multiple capability entries
of the pAR's local CARD table have been expired. Otherwise, the pAR
can respond to the requesting MN immediately after having the CARs'
address and capability information retrieved from its local CAR
table.
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