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IEEE 802.21 MEDIA INDEPENDENT HANDOVER DCN:21-09-0164-06-0secTitle: Detailed analysis on MIA/MSA architectureDate Submitted: January 5, 2010Present at IEEE 802.21 meeting in January 2010 San Diego.Authors or Source(s): Fernando Bernal, Rafa Marín-LópezAbstract: This document discusses specific details on the MIA/MSA architecture, addressing different key distribution models (push and pull) and providing entities’ required functionalities.

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IEEE 802.21 presentation release statementsThis document has been prepared to assist the IEEE 802.21 Working Group. It is

offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

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The contributor is familiar with IEEE patent policy, as stated in Section 6 of the IEEE-SA Standards Board bylaws <http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and in Understanding Patent Issues During IEEE Standards Development http://standards.ieee.org/board/pat/faq.pdf> 

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Differences with previous versions• The motivation of MIA is now explicitly

explained.• We have added and described a new key

distribution: proactive pull key distribution.• Some deployment analysis has been added.

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Intra-MIH Authenticator

Media Specific Authenticator and

Key Holder (MSA-KH)

Media Specific Authenticator and

Key Holder (MSA-KH)

POA1POA1

Media Independent Authenticator and

Key Holder (MIA-KH)

Media Independent Authenticator and

Key Holder (MIA-KH)

MIHFMIHF

POA2POA2

Media Specific Authenticator and

Key Holder (MSA-KH)

Media Specific Authenticator and

Key Holder (MSA-KH)

POA1POA1 POA2POA2

Media IndependentAccess Functions (MIH POS+)

Med

ia Spe

cific

Acces

s Fun

ction

s

MNMN MNMNServing Access

Network

Candidate AccessNetwork

RP1RP1

Inte

rface

_M

IA-K

H-MSA-K

H

RP1RP1

Interface _MIA-KH

-MSA-KH

Media Specific

Access Functions

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Inter-MIH Authenticator

Media Specific Authenticator and

Key Holder (MSA-KH)

Media Specific Authenticator and

Key Holder (MSA-KH)

POA1POA1

Media Independent Authenticator and

Key Holder (MIA-KH)

Media Independent Authenticator and

Key Holder (MIA-KH)

MIHFMIHF

POA2POA2

Media Specific Authenticator and

Key Holder (MSA-KH)

Media Specific Authenticator and

Key Holder (MSA-KH)

POA1POA1 POA2POA2

Media Independent

Access Functions

(MIH POS+)

Med

ia S

pecif

ic

Acces

s Fun

ctio

ns

MNMN MNMN

Media Independent Media Independent Authenticator and Authenticator and

Key HolderKey Holder (MIA-KH)(MIA-KH)

Media Independent Media Independent Authenticator and Authenticator and

Key HolderKey Holder (MIA-KH)(MIA-KH)

MIHFMIHF

Serving Access Network

Candidate AccessNetwork

RP5RP5

RP1RP1 RP2RP2 RP1RP1

Int_

MIA

-KH

-MSA

-KH

Int_M

IA-KH-M

SA-KH

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Motivation of MIA architecture• Provide support to enable secure media independent handover

services• These services include the management of different types of key

distribution mechanisms:– Push Key Distribution– Reactive Pull Key Distribution– Proactive Pull Key Distribution

• To securely provide and control the access to these services, an authentication and key establishment are required.

• Goals – Security– Reduce the handover time

– Try to achieve a smooth deployment

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Notation

Primitives for EAP authentication

Primitives for (reactive or proactive) pull key distribution

Primitives for push key distribution

Out of scope of 802.21a

MIH-SAP

Unprotected MIH signalling between MIHF

Protected MIH signalling between MIHF

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General Call FlowCandidate

MIAServing

MIAMN

Step 1: Negotiation phase between MN andCandidate MIA

Step 2 & 2’: Media Independent Authentication between MN and Candidate MIA and Key Installation for PULL Key Distr.

Step 3: PUSH Key distribution or (Reactive or Proactive) PULL Key distr. execution.

Target MSA-KH

Step 4: Session Finalization

. . .

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General MI Authentication PhasesMIHF

MN

MIHF

MIA

Negotiationphase

Authenticationphase

(Step 2 and 2’)

Authenticated&

Authorizedphase

(Step 3)

Finalizationphase

(Step 4)

(Step 1)

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General Message Exchange• Negotiation phase

– In this phase both the MN and MIA exchange messages in order to agree on the type of key distribution service (push, reactive pull, proactive pull) and other parameters.

• Authentication phase– The MN authenticates against the MIA in order to achieve access to the security services. – After this authentication key material is shared between them and the rest of the MIH

communication can be protected.– At the end, the negotiated parameters in the previous phase are confirmed.– An authentication session is established

• Authenticated & Authorized phase– At this point, MIH signalling is protected and MN is authenticated and authorized to use

the services provided by the MIA.– Regarding key distribution:

• If Push Key Distribution was negotiated, some protected MIH signalling is required in order the MN to inform the MIA to install a key in a target MSA.

• If Reactive Pull Key Distribution is agreed, no need of MIH signalling is required but some state is needed in the MIA that will act as AAA server.

• If Proactive Pull Key Distribution is agreed, authentication L2 frames are tunnelled to the MIA from the MN; and from the MIA to the target MSA in order to perform a proactive media-specific authentication with the target MSA. That is, the MIA provides a proxy service.

• Finalization phase– MN and MIA finish the session.

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ServingMSA-KH

TargetMSA-KH

* Auth. Trigger

0*. Media-specific network access authentication

1. Negotiation

MSKMSK

Media Independent Authentication (I)

0*. Only required if the MN has no already access to the network through Serving MSA-KH

MIH User

MIHF

MNMAC

MIH User

MIHF

MIAH-AAAL-AAA

AAA

I1

Key Distribution Method agreed

Key Distribution Method agreed

2. Media-independent authentication . . .I1 I2 I3 I4I2

Key Distribution Method confirmed

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ServingMSA-KH

TargetMSA-KH

MSK’/rMSK

MI-PMK

Media Independent Authentication (II)MIH User

MIHF

MNMAC

MIH User

MIHF

MIA

MS-PMKMS-PMK

MS-PMK

H-AAAL-AAA

AAA

MSK’/rMSK

MI-PMK

MS-PMK

MS-PMK

MS-PMK I5I6

2’. Key installation for (reactive or proactive) PULL just after media-independent authentication

I2 I2

. . .

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Media Independent Authentication• 802.21a scope

– Interface I1• This interface transports EAP or an authentication protocol over MIH signaling. In the case

of transporting EAP, the MIHF implements an EAP lower-layer functionality. – Interface I2

• For Media Independent Authentication it is an internal interface used by the MIA to exchange EAP packets (or any other authentication protocol packets) between the MIHF and the MIH-USER (which is the EAP stack when EAP is used or the authentication protocol implementation).

• For key distribution, I2 is used to install the derived MS-PMKs and required parameters to the corresponding MIH-USER (e.g. key manager).

– This interface is used just after Media Independent Authentication for Reactive or Proactive PULL Key Distribution.

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Media Independent Authentication• Outside 802.21a scope

– Interface I3• Internal interface to communicate MIH user with AAA client in the MIA-KH order to

forward authentication to H-AAA.– Interface I4

• Interface to transport EAP or authentication protocol to the H-AAA in order to perform the authentication (e.g. AAA protocol).

– Interface I5• This interface is used by the Reactive or Proactive PULL Key Distribution in order to

provide the MS-PMK(s) to the AAA server in the MIA. So that, when the MN moves to the target MSA-KH, all key material is available and a fast media-specific re-authentication can be performed.

– Interfaces (I6)• This interface allows to installa the MS-PMK in the MAC layer (MN side).

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Summary Media Independent Authentication

EAP layer

EAP peer layer

EAP Peer / MN

EAP method layer

MIH EAP lower- layer (MIHF)

EAP Authenticator / MIA-KH

AAA/IP AAA/IP

EAP(serv.) layer

EAP/AAA Server

EAP method layer

MIH EAP lower-layer (MIHF)

EAP layer

Primitives for EAP authentication

Primitives for pull key distribution

MIH USER

MIHF

MIH USERMIH USER

(e.g.) Key Manager

EAP layer

EAP auth. layer

EAP method layer

MIH USERMIH USER

(e.g.) Key Manager

I1

I2I2

I2 I3 I5

I4

Out of scope of 802.21a

I2

MIH signalling between MIHF

MIH-SAP

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Key Dist. Trigger 3. Proactive (Push) Key Dist. signaling

Handoff to target MSA-KH

MS-PMK

MS-PMK

MI-PMKMI-PMK

MS-PMK

Push Key distributionServingMSA-KH

TargetMSA-KH

MIH User

MIHF

MNMAC

MIHF

MIA

MIH User

MS-PMK

Security Association Protocol

I2I7

I2

I6

I1

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Push Key distribution• Interface (I1)

– This interface is used to request the MIA-KH the installation of a key (MS-PMK) in the target MSA-KH using MIH signaling.

• Interfaces (I2, I7)– After MN requests a PUSH Key Distribution with I1, the MIHF in the MIA provides the

MS-PMK and other useful information (e.g. key lifetime) to the MIH User (by using I2), which knows how to install the MS-PMK in the target MSA-KH (I7).

• Interfaces (I2, I6)– After requesting a PUSH Key Distribution through I1, the MIHF in the MN provides the

MS-PMK and other useful information (e.g. MS-PMK lifetime) to the MIH User (acting as key manager) (I2) which is in charge of export the MS-PMK to the MAC layer (I6).

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MAC

Summary Push Key Distribution

MN

MIHF

MIA-KH

MIHF

MIHFPrimitives for push key distribution

MIH User (e.g. Protocol X for push key

installation)

MIH User (e.g. Key Manager/Store)

TargetMSA-KH

MIH USER

I1

I2 I2

I6 I7

Protected MIH signaling between MIHF

Out of scope of 802.21a

MIH-SAP

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Reactive Pull Key Distribution

Handoff to target MSA-KH

ServingMSA-KH

TargetMSA-KH

MIH User

MIHF

MNMAC

MIHF

MIA

MIH User

MS-PMK

Security Association Protocol

MSK

3. Media-specific network access re-authentication [MN’s identity = *MN-MIHF-ID@MIA-MIHF-ID]

*NOTE = Regarding identity’s format, it must still be defined.

MS-PMK

MSK

AAA

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Reactive Pull Key Distribution

• Assuming that the MS-PMK used by the EAP (fast) re-authentication mechanism for pull key distribution has been already sent to the MIH user during the authentication phase (see slide 10):- No MIHF intervention is required (see slide 17)

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Proactive Pull Key Distribution(over MIH Signalling)

ServingMSA-KH

TargetMSA-KH

MIH User

MIHF

MNMAC

MIA

AAA

3. Authentication L2 frames over MIH Tunnel[MN’s identity for media-specific auth. = *MN-MIHF-ID@MIA-MIHF-ID or user@homedomain]

I1

I9

I2

H-AAAL-AAA

I10

Security Association Protocol

I2

MIH UserMIHF

MS-PMK MS-PMK

MN’s identity = MN-MIHF-ID@MIA-MIHF-ID

MN’s identity = MN-MIHF-ID@MIA-MIHF-ID

I11

MN’s identity = user@homedomainMN’s identity = user@homedomainI11

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ServingMSA-KH

TargetMSA-KH

MIH User

MIHF

MNMAC

MIHF

MIAMIH User AAA

3. Authentication L2 frames over dynamically established tunnel[MN’s identity for media-specific auth. = *MN-MIHF-ID@MIA-MIHF-ID or user@homedomain]

I9

MN’s identity = MN-MIHF-ID@MIA-MIHF-ID

MN’s identity = MN-MIHF-ID@MIA-MIHF-ID

I11

H-AAAL-AAA

I12

MN’s identity = user@homedomainMN’s identity = user@homedomain

Security Association Protocol

TN-PMK

MI-PMK

I11

Proactive Pull Key Distribution(over DYNAMIC TUNNEL)

Dynamically established secure tunnel using TN-PMKDynamically established secure tunnel using TN-PMK

I10

TN-PMK

TN-PMK

MI-PMK

TN-PMK

I2 I2

MS-PMK MS-PMK

3. Authentication L2 frames over Secure Tunnel

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Proactive Pull Key distribution• Interface I1

– This interface is used to transport the media-specific authentication L2 frames from the MN to the MIA.

– These messages are protected by the key material provided after the media independent authentication.

• Interface I2– Over MIH Signalling. It is used to tranfer L2 frames from MIHF to MIH user and viceversa. – Over Dynamic secure tunnel. It is used to set a TN-PMK that allows to establish a secure tunnel (e.g.

IKEv2-PSK).• Interface l9

– Interface used between the target MSA-KH and MIA. This interface transports authentication L2 frames to the target MSA-KH from the MIA.

• Interface l10– Interface for transporting the media-specific auth. L2 frames to the MAC layer in the MN.

• Interface l11– Interface used by the target MSA-KH to communicate with the AAA server. The AAA

server may be the MIA or the home AAA.• Interface I12

– A dynamically established secure tunnel to transport auth. L2 frames

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MAC

Summary Proactive PULL Key Distribution (over MIH Signalling)

MN

MIHF

MIA

MIHF

MIH User MIH User (e.g. Key

Manager/Store)

TargetMSA-KH

Auth. L2 frames over MIH (I1)

I2 I2

I10 I9

MIHFPrimitives for pull key distribution

MIH USERProtected MIH signaling between MIHFs

Out of scope of 802.21aMIH-SAP

AAA/IP

I11

AAA/IPEAP(serv.) layer

AAA Server

EAP method layer

EAP layer

I11

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MAC

Summary Proactive PULL Key Distribution (over DYNAMIC TUNNEL)

MN

MIHF

MIA

MIHF

MIH User

MIH User (e.g. Key Manager/Store)

TargetMSA-KH

I2 I2

I10I9

MIHFPrimitives for pull key distribution

MIH USERProtected MIH signaling between MIHFMIH or dynamically Tunnel

Out of scope of 802.21aMIH-SAP

AAA/IP

I11

L2 frames over Dynamically established secure tunnel using TN-PMKL2 frames over Dynamically established secure tunnel using TN-PMK

AAA/IPEAP

(serv.) layer

EAP/AAA Server

EAP method layer

EAP layer

I11

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ServingMSA-KH

TargetMSA-KH

4. Session Finalization. . .

Session FinalizationMIH User

MIHF

MNMAC

MIH User

MIHF

MIA

AAA

I1

I2 I5I2

I7

I2

I6

I2

I6

4b. For Push Key Dist.

Remove KeysRemove Keys

4a. For (Reactive or Proactive) Pull Key Dist.

Remove dynamically established tunnelRemove dynamically established tunnel

I12

Remove KeysRemove Keys

4a’. Only for Proactive Pull Key Dist. over Dynamic tunnel

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Interfaces summaryMedia Independent

Proactive authentication

Reactive PULL Key Distribution

Proactive PULL Key Distribution

PUSH Key Distribution

MN I1 I2 I2 I6 I1 I10 I2 I12 I1 I6 I2Serving MSA-KH

Target MSA-KH I9 I11 I7MIA I2 I3 I4 I2 I5 I1 I11 I2 I12 I1 I7 I2AAA I4 I11

Outside 802.21a scope

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DEPLOYMENTANALYSIS

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PUSH Key Distribution

• The target MSA-KH needs to provide an interface to allow the MIA to push (or remove) a key.

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Reactive PULL Key Distribution

• A new MN re-authentication identity must be provided to the MN during the authentication.

• Once the target MSA-KH receives the MN re-authentication identity, two options are possible: 1. The MSA-KH routes the AAA messages using the realm part of the new MN re-

authentication identity to the appropiate MIA MSA-KH AAA routing table has to be updated to point out to the MIA.

2. The target MSA-KH , usings its default AAA route, sends the AAA messages to its default local AAA server, which must be configured to act as AAA proxy for the identity’s realm provided and to forward the AAA messages to the corresponding MIA. Local AAA proxy has to add a new entry in AAA routing table to point out the MIA.

• Summary:– In either options, no changes to the media-specific wireless technology are

required.– Moreover, option 2 does not need any change in the configuration parameters in

the deployed MSA-KHs.

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Proactive PULL Key Distribution

• Similar analysis as Reactive PULL Key Distribution is applicable to Proactive PULL Key Distribution but...

• ... since the MIA provides a proxy service for authentication L2 frames.– The MSA-KHs must be modified in order to accept L2 authentication

wireless frames through the wired interface. – A protocol to transport these frames from the MIA to the target MSA-

KH is required. (out of the scope of 802.21a)• Depending on the MN’s identity:

– If the MN uses its original home domain identity (e.g. user@homedomain), the target MSA contacts the home AAA and MIA does not need to act as AAA server.

– if the MN uses a new MN re-authentication identity (e.g. MN-MIHF-ID@MIA-MIHF-ID), the MIA has to act as AAA server.

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Some conclusions• 802.21a defines EAP (or any other authentication protocol)

transport for proactive authentication, key hierarchy and an MIH-SAP primitives with the MIH-USER to support three key distribution models.

• How the parameters passed by means of the MIH-SAP primitives are used by the media-specific lower layers is out of the scope.

• 802.21a specification may contain call flows for guidelines to show how these parameters can be used by the media-specific lower-layers.

• The call flows if contained are only informational.• Depending on how these parameters are used, it may or may not

require changes to the lower-layer standards and/or implementations.– Reactive PULL Key Distribution do not require these modifications and PUSH

Key Distribution and proactive PULL Key Distribution may require these ones (e.g. at firmware level)

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REQUIRED FUNCTIONALITIES FOR

EACH ENTITY

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For media-specific network access authentication

• If MN needs to get network access through the Serving MSA (step 0, slide 9).– EAP peer for a media-specific authentication.– Media specific EAP lower layer.– Secure Association protocol client for the specific media

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For the Media Independent Authentication• MN

– If EAP is used for media-independent authentication• EAP peer for media-independent authentication• Media-independent EAP lower-layer (MIHF)

– If EAP is NOT used for (proactive) media-independent authentication• authentication protocol implementation• media-independent client transport for the authentication protocol.

• Serving MSA-KH– EAP authenticator for media-specific authentication.– AAA protocol client for a specific media– Secure Association protocol server for the specific media

• MIA– If EAP is used for media-independent authentication

• EAP authenticator for media-independent authentication• Media-independent EAP lower-layer

– If EAP is NOT used for (proactive) media-independent authentication• authentication protocol implementation• media-independent client transport for the authentication protocol.

– AAA protocol client for media independent authentication• (H) AAA Server

– EAP server for media specific authentication– EAP server for proactive media-independent authentication– AAA protocol for media specific authentication– AAA protocol for (proactive) media independent authentication

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For PUSH Key distribution• MN

– Media independent client protocol for indicating proactive key distribution.

• This signaling indicates that key distribution is push model– Key derivation mechanism to derive MS-PMK.– Secure Association protocol client for the specific media

• Target MSA-KH– Interface with MIA-KH that allows to receiving a key in a push fashion.– Secure Association protocol server for the specific media

• MIA– Media independent server protocol for proactive key distribution.– Interface with MSA-KH for sending a key in a push fashion.

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For Reactive PULL Key Distribution

• MN– Media independent client protocol for indicating proactive key distribution.

• This signaling indicates that key distribution is pull model• The MN receives from MIA information about MIA’s realm that it is useful for AAA

routing.– EAP peer for a media-specific authentication.– Media specific EAP lower layer.– Secure Association protocol client for the specific media

• Target MSA-KH– EAP authenticator for a specific media– AAA client for a specific media– Secure Association protocol server for the specific media

• MIA– EAP server for media-specific authentication– AAA protocol server for media-specific authentication

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For Proactive PULL Key Distribution• MN

– Interface to obtain/set L2 Frames from/to the MAC layer.– Media independent protocol for transporting L2 frames between the MN and the MIA (Over MIH signalling

option).– Secure tunnel protocol for transporting L2 frames between the MN and the MIA (Over dynamic secure tunnel

option).– Key derivation mechanism to derive MS-PMK and TN-PMK– EAP peer for a media-specific authentication.– Media specific EAP lower layer.– Secure Association protocol client for the specific media.

• Target MSA-KH– EAP authenticator for a specific media– AAA client for media-specific (proactive) authentication.– Protocol to receive/send wireless (auth.) L2 frames from/to MIA over the wired interface.– Secure Association protocol server for the specific media

• MIA– AAA protocol for media-specific (proactive) authentication [NOTE: When MN uses a MN re-authentication

identity].– Protocol to receive/send wireless (auth.) L2 frames from/to the target MSA over the wired interface.– Media independent protocol for transporting L2 frames between the MN and the MIA (Over MIH signalling

option).– Secure tunnel protocol for transporting L2 frames between the MN and the MIA (Over dynamic secure tunnel

option).

• Home AAA– AAA protocol for media-specific (proactive) authentication. [NOTE: When MN uses its home domain identity]

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Future work

• More detailed definition of the interfaces in 802.21a scope.