Re: [Mipshop] WG last call on MIH solutiondocument (draft-ietf-mipshop-mstp-solution-01.txt)

Thanks Ashutosh for your comments.
We will address them in the next version of the draft.

Telemaco

-----Original Message-----
From: mipshop-bounces@ietf.org [mailto:mipshop-bounces@ietf.org] On
Behalf Of Ashutosh Dutta
Sent: Thursday, March 06, 2008 5:24 AM
To: Vijay Devarapalli
Cc: 'Mipshop'
Subject: Re: [Mipshop] WG last call on MIH solutiondocument
(draft-ietf-mipshop-mstp-solution-01.txt)

Vijay,
       I think Yoshi and Kevin have given some useful comments and 
covered most of it, here are some of mine that start with AD>

Regards
Ashutosh

1.  Introduction

    This document proposes a solution to the issues identified in the
    problem statement document [I-D.ietf-mipshop-mis-ps] for the layer 3
    transport of IEEE 802.21 MIH protocols.

    The MIH Layer 3 transport problem is divided in two main parts: the
    discovery of a node that supports specific Mobility Services (MoS)
    and the transport of the information between a mobile node (MN) and
    the discovered node.  The discovery process is required for the MN
to
    obtain the information needed for MIH protocol communication with a
    peer node.  The information includes the transport address (e.g.,
the
    IP address) of the peer node and the types of MoS provided by the
    peer node.

    This document lists the major MoS deployment scenarios.  It next
    describes the solution architecture, including the MSTP reference
    model and MIHF identifiers.  A description follows of MoS discovery
    procedures when the MN is in a home or remote network.

    AD> Sentence structure above is not correct.

    The remainder
    of the document describes the MIH transport architecture, example
    message flows for several signaling scenarios, and security issues.

    AD> What is meant by signaling scenarios here?

2.  Terminology

    The following acronyms and terminology are used in this document:

    MIH  Media Independent Handover: the handover support architecture
       defined by the IEEE 802.21 working group that consists of the MIH
       Function (MIHF), MIH Network Entities, MIH Event messages, and
MIH
       command messages.

  AD> What is the definition of MIH entities above, we also need to 
mention Information Service Messages.

    MIHF  Media Independent Handover Function: a cross-layer function
       that provides handover services including the Event Service (ES),
       Information Service (IS), and Command Service (CS), through
       service access points (SAPs) defined by the IEEE 802.21 working
       group.

AD> Do we need to say cross-layer function here. Instead cannot we just
say logical function or just function?

    MIHF User  an MIH client that uses the MIH SAPs to access MIHF
       services, and which is responsible for initiating and terminating
       MIH signaling

    MIHFID  Media Independent Handover Function Identifier: an
identifier
       required to uniquely identify the MIHF endpoints for delivering
       mobility services (MoS); it is implemented as either a FQDN or
       NAI.

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    MoS  Mobility Services: those services, as defined in the MIH
problem
       statement document [I-D.ietf-mipshop-mis-ps] , which include the
       MIH IS, CS, and ES services defined by the IEEE 802.21 standard.

    MoSh  Mobility Services assigned in the mobile node's Home Network

    MoSv  Mobility Services assigned in the Visited Network, which is
any
       network other than the mobile node's home network

    MoS3  Mobility Services assigned in a 3rd Party Network, which is a
       network that is neither the Home Network nor the current Visited
       Network.

    MN Mobile Node: an Internet device whose location changes, along
with
       its point of connection to the network.

    NN Network Node: an Internet device whose location and network point
       of attachment do not change

    MSTP  Mobility Services Transport Protocol: a protocol that is used
       to deliver MIH signaling messages from an MIHF to other MIH-aware
       nodes in a network.

    IS Information Service: a MoS that originates at the lower or upper
       layers and sends information to the local or remote upper or
lower
       layers.  It can use secure or insecure ports to transport
       information elements (IEs) and information about various
       neighboring nodes.  Its architecture is outside the scope of the
       IEEE 802.21 draft document.

AD> Add protocol stack after lower or upper layers (e.g., lower or upper

layers of a protocol stack)

    ES Event Service: a MoS that originates at a remote MIHF or the
lower
       layers and sends information to the local MIHF or local higher
       layers.  The purpose of the ES is to report changes in link
status
       (e.g.  Link Going Down messages) and transmission status.

AD> change lower layers to (lower layers of protocol stack) unless it is

implicit

    CS Command Service: a MoS that sends commands from the remote MIHF
or
       local upper layers to the local lower layers to switch links or
to
       get link status.

    FQDN  Fully-Qualified Domain Name: a complete domain name for a host
       on the Internet, consisting of a host name followed by a domain
       name (e.g. hostname.domain.org)

    NAI  Network Access Identifier: the user ID that a user submits
       during PPP authentication.  For mobile users, the NAI identifies
       the user and helps to route the authentication request message.

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    NAT  Network Address Translator: A device that implements the
Network
       Address Translation function described in [RFC3022], in which
       local or private network layer addresses are mapped to valid
       network addresses and port numbers.

    DHCP  Dynamic Host Configuration Protocol: a protocol described in
       [RFC2131] that allows Internet devices to obtain IP addresses,
       subnet masks, default gateway addresses, and other IP
       configuration information from DHCP servers.

    DNS  Domain Name System: a protocol described in [RFC1035] that
       translates domain names to IP addresses.

    AAA  Authentication, Authorization and Accounting: a set of network
       management services that respectively determine the validity of a
       user's ID, determine whether a user is allowed to use network
       resources, and track users' use of network resources.

    AAA home  AAA server: an AAA server located on the MN's home network

AD> The sentence is ambiguous, should be AAAH Home AAA server

    AAA visited  AAA server: an AAA server located a visited network
that
       is not the MN's home network

AD> The sentence is ambiguous, suggested change AAAV Visited AAA Server

    MIH ACK  MIH Acknowledgement Message: a MIH signaling message that a
       MIHF sends in response to an MIH message from a sending MIHF,
when
       UDP is used as the MSTP.

    PoS  Point of Service, a network-side MIHF instance that exchanges
       MIH messages with a MN-based MIHF

    NAS  Network Access Server: a server to which a MN initially
connects
       when it is trying to gain a connection to a network and which
       determines whether the MN is allowed to connect to the NAS's
       network

AD> Is it a standard IETF definition, if not can we improve the
definition?

    UDP  Network Access Server: a server to which a MN initially
connects
       when it is trying to gain a connection to a network and which
       determines whether the MN is allowed to connect to the NAS's
       network

AD> The definition does not sounds correct, seems like repetition of the

previous sentence

    TCP  Transmission Control Protocol: a stream-oriented transport
layer
       protocol that provides a reliable delivery service with
congestion
       control, defined in RFC 793.

    RTT  Round-Trip Time: a estimation of the time required for a
segment
       to travel from a source to a destination and an acknowledgement
to
       return to the source that is used by TCP in connection with timer
       expirations to determine when a segment is considered lost and

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       should be resent.

    MTU  Maximum Transmission Unit: the largest size packet that can be
       sent on a network without requiring fragmentation [RFC1191].

    TLS  Transport Layer Security Protocol: an application layer
protocol
       that assures privacy and data integrity between two communicating
       network entities [RFC4346].

3.  Deployment Scenarios

    This section describes the various possible deployment scenarios for
    the MN and the MoS.  The relative positioning of MN and MoS affects
    resource discovery as well as the performance of the MIH signaling
    service.

3.1.  Scenario S1: Home Network MoS

    In this scenario, the MN and the services are located in the home
    network.  We refer to this set of services as MoSh as in Figure 1.
    The MoSh can be located at the access point the MN uses to connect
to
    the home network, or it can be located elsewhere.

    +--------------+  +====+
    | HOME NETWORK |  |MoSh|
    +--------------+  +====+
         /\
         ||
         \/
    +--------+
    |   MN   |
    +--------+

                      Figure 1: MoS in the Home network

AD> Please change "Access Point" above to "Access Network"

3.2.  Scenario S2: Visited Network MoS

    In this scenario, the MN is in the visited network and mobility
    services are provided by the visited network.  We refer to this as
    MoSv as shown in Figure 2.

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              +--------------+
              | HOME NETWORK |
              +--------------+
                    /\
                    ||
                    \/
     +====+ +-----------------+
     |MoSv| | VISITED NETWORK |
     +====+ +-----------------+
                    /\
                    ||
                    \/
                +--------+
                |   MN   |
                +--------+

                    Figure 2: MoSV in the Visited Network

3.3.  Scenario S3: Roaming MoS

    In this scenario, the MN is located in the visited network and all
    MIH services are provided by the home network, as shown in Figure 3.

     +====+   +--------------+
     |MoSh|   | HOME NETWORK |
     +====+   +--------------+
                    /\
                    ||
                    \/
           +-----------------+
           | VISITED NETWORK |
           +-----------------+
                    /\
                    ||
                    \/
                +--------+
                |   MN   |
                +--------+

             Figure 3: MoS provided by the home while in visited

3.4.  Scenario S4: Third party MoS

    In this scenario, the MN is in its home network or in a visited
    network and services are provided by a 3rd party network.  We refer
    to this situation as MoS3 as shown in Figure 4.  (Note that MoS can
    exist both in hom enad in visited).

AD> Typo "both in home and in visited"

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                                       +--------------+
                                       | HOME NETWORK |
    +====+    +--------------+         +--------------+
    |MoS3|    | THIRD PARTY  |  <===>        /\
    +====+    +--------------+               ||
                                             \/
                                     +-----------------+
                                     | VISITED NETWORK |
                                     +-----------------+
                                             /\
                                             ||
                                             \/
                                         +--------+
                                         |   MN   |
                                         +--------+

                      Figure 4: MoS form a third party

    Different types of MoS can be provided independently of other types
    and there is no strict relationship between ES, CS and IS, nor is
    there a requirement that the entities that provide these types be
co-
    located.  However, while IS tends to involve large amounts of static
    information, ES and CS are dynamic services and some relationship
    between them can be expected, e.g. a handover command (CS) could be
    issued upon reception of a link event (ES).  Hence, while in theory
    MoS can be implemented in different locations, it is expected that
ES
    and CS will be co-located, whereas IS can be co-located with ES/CS
or
    located elsewhere.  Therefore, having the flexibility at the MSTP to
    discover different services in different locations is an important
    feature that can be used to optimize handover performance.  Resource
    discovery is discussed in more detail in Section 5.

4.  Solution Overview

    As mentioned in Section 1 the solution space is being divided into
    two functional domains: discovery and transport.  The following
    assumptions have been made:

    o  The solution is aimed at supporting IEEE 802.21 MIH services,
       namely Information Service (IS), Event Service (ES), and Command
       Service (CS).

    o  If the MIHFID is available, FQDN or NAI's realm is used for
       mobility service discovery.

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    o  The solutions are chosen to cover all possible deployment
       scenarios as described in Section 3.

    o  MoS discovery can be performed during initial network attachment
       or thereafter.

    The MN could know or not the realm of the MoS to be discovered.

AD> MN may or may not know

  In
    any case after the acquisition of the target realm (e.g. via
    Information Server or statically configured) the MN could either be
    pre-configured with the address of the MoS, or this address could be
    obtained through DHCP or DNS.  The dynamic assignation methods are
    described in Section 5.

    The configuration of the MoS could be executed either upon network
    attachment or after successful IP configuration.  The methodology to
    be used depends on the considered deployment scenario.

    Once the MIHF peer has been discovered, MIH information can be
    exchanged between MIH peers over a trasnport protocol such as UDP or
    TCP.  The usage of transport protocols is described in Section 6.

4.1.  Architecture

    Figure 5 depicts the MSTP reference model and its components within
a
    node.  The topmost layer is the MIHF user.  This set of applications
    consists of one or more MIH clients that are responsible for such
    operations as maintaining MIH databases associated with the IS,

AD> suggested change, for operations such as generating query and
response

    processing Layer 2 triggers as part of the ES, and initiating and
    carrying out handover operations as part of the CS.  Beneath the
MIHF
    user set is the MIHF itself.

AD> Above sentence is not very clear

   This function is responsible for MoS
    discovery, as well as creating, maintaining, modifying, and
    destroying MIH signaling associations with other MIHFs located in
MIH
    peer nodes.  Below the MIHF are various transport layer protocols as
    well as address resolution functions.

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     +--------------------------+
     |       MIHF User          |
     +--------------------------+
                  ||
     +--------------------------+
     |           MIHF           |
     +--------------------------+
         ||         ||       ||
     +---------+ +------+ +-----+
     | TCP/UDP | | DHCP | | DNS |
     +---------+ +------+ +-----+

                             Figure 5: MN stack

    The MIHF relies on the services provided by TCP and UDP for
    transporting MIH messages, and relies on DHCP and DNS for peer
    discovery.  In cases where the peer MIHF IP address is not pre-
    configured, the source MIHF needs to discover it either via DHCP or
    DNS or a combination of both as described in Section 5.  Once the
    peer MIHF is discovered, MIHF must exchange messages with its peer
    over either UDP or TCP.  Specific recommendations regarding the
    choice of transport protocols are provided in Section 6.

    The above reference architecture however does not include other
    services such as message fragmentation and security.  Depending upon
    the MIH service type (e.g., ES, CS and IS) the message size can be
    very large.  In case where the underlying layers do not support
    fragmentation, this may be an issue.  There are no security features
    currently defined as part of the MIH protocol level.  However,
    security can be provided either at the transport or IP layer where
it
    is necessary.  Section 8 provides some guidelines and
recommendations
    for security.

4.2.  MIHF Identifiers (FQDN, NAI)

    An MIHFID is an identifier required to uniquely identify the MIHF
end

AD. Not sure if An is needed here

    points for delivering the mobility services (MoS).  Thus an MIHF
    identifier needs to be unique within a domain where mobility
services
    are provided and invariant to interface IP addresses.  An MIHFID
MUST
    be represented either in the form of an FQDN [RFC2181] or NAI
    [RFC4282].  An MIHFID can be pre-configured or discovered through
the
    discovery methods described in Section 5.

5.  MoS Discovery

    The MoS discovery method depends on whether the MN attempts to
    discover an MoS in the home network, in the visited network, or in a

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    3rd party remote network that is neither the home network nor the
    visited network.

    In case MoS is provided locally (scenarios S1 and S2) , the
discovery
    techniques described in [I-D.bajko-mos-dhcp-options] and
    [I-D.bajko-mos-dns-discovery] are both applicable and either one MAY
    be used to discover the MoS.

    In case MoS is provided in the home network while the MN is in the
    visited network (scenario S3), the DNS based discovery described in
    [I-D.bajko-mos-dns-discovery] is applicable, while the DHCP based
    discovery method would require an interaction between the DHCP and
    the AAA infrastructure, similarly to what specified in
    [I-D.ietf-mip6-bootstrapping-integrated-dhc] .  This latter case
    assumes that MoS assignment is performed during access
authentication
    and authorization.

    In case MoS is provided in a remote network other than visited or
    home network (scenario S4), only the DNS based discovery method
    described in [I-D.bajko-mos-dns-discovery] is applicable.

5.1.  MoS Discovery when MN and MoSh are in the home network (Scenario
       S1)

    To discover an MoS in the home network, the MN SHOULD use the DNS
    based MoS discovery method described in
    [I-D.bajko-mos-dns-discovery].  In order to use that mechanism, the
    MN MUST first find out the domain name of its home network.  Home
    domains are usually pre-configured in the MNs, thus the MN can
simply
    read its configuration data to find out the home domain name
    (scenario S1).  The DNS query option is shown in Figure 6b.
    Alternatively, the MN MAY use the DHCP options for MoS
    discovery[I-D.bajko-mos-dhcp-options] as shown inFigure 6a.

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                               +-------+
                +----+         |Domain |
                | MN |-------->|Name   |
                +----+         |Server |
                               +-------+
                 MN@xyz.com

                              (a) using DNS Query

                             +-----+      +------+
                +----+       |     |      |DHCP  |
                | MN |<----->| DHCP|<---->|Server|
                +----+       |Relay|      |      |
                             +-----+      +------+

                              (b)  Using DHCP Option

     Figure 6: MOS Discovery (a) Using DNS query, (b) using DHCP option

5.2.  MoS Discovery when MIN is in visited network and MoSv is also in
       visited network (Scenario S2)

    To discover an MoS in the visited network, the MN SHOULD attempt to
    use the DHCP options for MoS discovery [I-D.bajko-mos-dhcp-options]
    as shown in Figure 7a.  If the DHCP method fails, the MN SHOULD
    attempt to use the DNS based MoS discovery method described in
    [[I-D.bajko-mos-dns-discovery] as shown in Figure 7b.  In order to
    use that, the MN MUST first learn the domain name of the local
    network.  There are a number of ways how the domain name of a
network
    can be learned:

    DHCP --  In order to find out the domain name of the local network,
       the MN SHOULD use the dhcpv4 option 15 for learning the domain
       name [RFC1533].  A similar solution is available for dhcpv6
       [I-D.ietf-dhc-dhcpv6-opt-dnsdomain] .

    Reverse dns query --  When DHCP does not provide the required domain
       name, the MN MAY use reverse DNS (DNS PTR record) to find the
       domain name associated with the IP address it is using in the
       visited network.  Note, that when a NAT device exists between the
       MN and the visited network, the MN will first need to find out
the
       external IP address of the NAT device.  Some possible methods for
       determining the NAT's external IP address are STUN [RFC3849] or
       UPnP [UPnP_IDG_DCP].  Once the MN has determined the external IP
       address of the NAT device, it MUST use that address in the
reverse

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       DNS query.

                          +-----+      +------+
             +----+       |     |      |DHCP  |
             | MN |<----->| DHCP|<---->|Server|
             +----+       |Relay|      |      |
                          +-----+      +------+

                    (a) MOS Discovery using DHCP options

                            +-------+
             +----+         |Domain |
             | MN |-------->|Name   |
             +----+         |Server |
                            +-------+

                     (b) Reverse DNS Query (starting from the IP
address)

          Figure 7: Discovery (a) using DHCP option, (b) Using DNS

    It should be noted, that the usage of DHCP options to discover an
MoS
    in this particular scenario is recommended because of its simplicity
    over the DNS based discovery method: the DNS discovery method
    requires the MN to learn the domain name of the local network first,
    possibly using DHCP, and then perform the DNS query.  The usage of
    the DHCP based discovery method does not require any additional
    procedure.

5.3.  MOS Discovery when the MN is in a visited Network and Services are
       at the Home network (Scenario S3)

    To discover an MoS in the visited network when MIH services are
    provided by the home network, both the DNS based discovery method
    described in [I-D.bajko-mos-dns-discovery] and the DHCP based
    discovery method described in [I-D.bajko-mos-dhcp-options] are
    applicable.

    To discover the MoS at home while in a visited network using DNS,
the
    MN SHOULD use the procedures described in section Section 5.1

    Alternatively, the MN MAY also use the DHCP based discovery method.
    Using the DHCP based discovery may be required in deployments where
    the usage of MoS located in the home network is enforced and
included
    in the subscription profile.  Similarly to

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    [I-D.ietf-mip6-bootstrapping-integrated-dhc] in this integrated
    scenario the mobile node is required to perform network access
    authentication before it can bootstrap MoS information.

AD: Suggested change, before it can obtain the MOS information

    This allows
    for MoS discovery at the time of access authentication and
    authorization.  Also, the mechanism defined in this document
requires
    the NAS to support MIH specific AAA attributes and a collocated DHCP
    relay agent.  In order to provide the mobile node with information
    about the assigned MoS, the AAAh conveys the assigned MoS's
    information to the NAS via AAA protocol similarly to
    [I-D.ietf-dime-mip6-integrated] and described in [REF TO NEW DOC].

AD> suggested change: as defined in
    [I-D.ietf-dime-mip6-integrated] and described in 
[draft-stupar-mos-diameter-options-00. The relation
    between functional components supporting such procedure is shown in
    Figure 8.

    In these deployment scenarios the AAAh sends the MoS address at home
    to the AAAv during the network access authentication.  The relation
    beween functional components supporting such procedure is shown in
    Figure 8.

AD> The above sentence can be take out in view of the previous one

    The mobile node executes the network access authentication procedure
    (e.g., IEEE 802.11i/802.1X) and it interacts with the NAS.  The NAS
    is in the visited and it interacts with the AAAh to authenticate the

AD> visited network, interacts with  AAAh via AAAv

    mobile node.  In the process of authorizing the mobile node, the
AAAh
    verifies in the AAA profile that the mobile node is allowed to use
    MoS services.  The AAAh assigns the MoS in the home and returns this
    information to the NAS.  The NAS may keep the received information
    for a configurable duration or it may keep the information for as
    long as the MN is connected to the NAS.

    The mobile node sends a DHCPv6 Information Request message [RFC3315]
    to the All_DHCP_Relay_Agents_and_Servers multicast address.  In this
    message the mobile node (DHCP client) MUST include the Option Code
    for MoS Identifier Option [I-D.bajko-mos-dhcp-options] in the
    OPTION_ORO.  The mobile node MUST also include the OPTION_CLIENTID
to
    identify itself to the DHCP server.

    The Relay Agent intercepts the Information-request from the mobile
    node and forwards it to the DHCP server.  The Relay Agent also
    includes the received MoS information from the AAAh in the IPv6
Relay
    Agent MoS Option [I-D.bajko-mos-dhcp-options].  If a NAS
    implementation does not store the received information as long as
the
    MN's session remains in the visited,

AD> Change the visited to visited network

and if the MN delays sending
    DHCP request, the NAS/DHCP relay does not include the IPv6 Relay
    Agent MoS Option in the Relay Forward message.

    The DHCP server identifies the client by looking at the DUID for the
    client in the OPTION_CLIENTID.  The DHCP server determines that the
    home agent is allocated by the AAAh by looking at the IPv6 Relay

AD> What is home agent, should it be MOS instead?

    Agent Sub-Option in the IPv6 Relay Agent MoS Option.  The DHCP
server
    extracts the allocated home agent information from the IPv6 Relay
    Agent Sub-Option and includes it in the MoS Information Option

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    [I-D.bajko-mos-dhcp-options] in the Reply Message.  If the requested
    information is not available in the DHCP server, it follows the
    behavior described in [RFC3315].

    The Relay Agent relays the Reply Message from the DHCP server to the
    mobile node.  At this point, the mobile node has the MoS information
    that it requested.

    In should be noted, that using the DHCP Options and procedures
    defined in [I-D.bajko-mos-dhcp-options] the MN can not specify the
    network (local or home) where it wants the MoS address from.
Whether
    the MN receives an MoS address from local or home network will
depend
    on the actual network deployment (scenario S2 or S3).

AD> You may want to add and operator policy

   In an
    integrated scenario, where the network access authentication is
    performed by the home network the MoS information will anyway be
sent
    to the AAAV, then stored in the relay agent and ultimately sent to
    the MN if the MN asks for it, using the procedures defined in
    [I-D.bajko-mos-dhcp-options].

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                            Visited             |          Home
                                                |
                                                |
                            +-------+           |        +-------+
                            |       |           |        |       |
                            |AAAV   |-----------|--------|AAAH   |
                            |       |           |        |       |
                            |       |           |        |       |
                            +-------+           |        +-------+
                                |               |
                                |               |
                                |               |
                                |               |
                                |               |       +--------+
                                |               |       |        |
                                |               |       |  MoSh  |
                            +-----+    +------+ |       +--------+
                +----+      |     |    |DHCP  | |
                | MN |------| NAS/|----|Server| |
                +----+      | DHCP|    |      | |
                            |Relay|    |      | |
                            +-----+    +------+ |
                                                |

           AAAv -- Visited AAA
           AAAH -- Home AAA
           NAS  -- Network Access Server

    Figure 8: MOS Discovery using Network Access Authentication and DHCP
                                   options

5.4.  MoS discovery when MIH services are in a 3rd party remote network
       (scenario S4)

    To discover an MoS in a remote network other than home network, the
    MN MUST use the DNS based MoS discovery method described in
    [I-D.bajko-mos-dns-discovery].  The MN MUST first learn the domain
    name of the network containing the MoS it is searching for.  If the
    MN does not yet know the domain name of the network, learning it may
    require more than one operation, as pre-configuration and DHCP
    methods can not be used.  The MN MAY attempt to first discover an
MoS
    in either the local or home network (as in Figure 9 part (a)) and
    query that MoS to find out the domain name of a specific network or
    the domain name of a network at a specific location (as in Figure 9
    part (b)).  Alternatively, the MN MAY query an MoS previously known
    to learn the domain name of the desired network (e.g., via an IS
    Query).  Finally the MN MUST use DNS queries to find MoS in the

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    remote network as inFigure 9 part(c).  It should be noted that step
c
    can only be performed upon obtaining the domain name of the remote
    network.

AD> as described in Figure 9 ..
                                    +-------+
                     +----+         |DHCP   |
                     | MN |-------->|       |
                     +----+         |Server |
                                    +-------+
                      MN@xyz.com

            (a) Discover MoS in local network with DHCP
                                +------------+
                 +----+         |            |
                 |    |         |Information |
                 | MN |-------->| Server     |
                 |    |         |(previously |
                 +----+         |discovered) |
                                +------------+

       (b) Using IS query to find the FQDN on the remote network

                                  +-------+
                   +----+         |Domain |
                   | MN |-------->|Name   |
                   +----+         |Server |
                                  +-------+
                    MN@xyz.com

             (c) using DNS Query in the remote network

      Figure 9: MOS Discovery using (a) DHCP Options, (b) IS Query to a
                         known Server, (c) DNS Query

AD> IS Query to a known IS Server

6.  MIH Transport Options

    Once the Mobility Services have been discovered, MIH peers MAY
    exchange information over TCP, UDP or any other transport supported
    by both the server and client, as described in
    [I-D.rahman-mipshop-mih-transport].  The client MAY use the DNS
    discovery mechanism to discover which transport protocols are
    supported by the server in addition to TCP and UDP.  While either
    protocol can provide the basic transport functionality required,
    there are performance trade-offs and unique characteristics
    associated with each that need to be considered in the context of
the
    MIH services for different network loss and congestion conditions.
    The objectives of this section are to discuss these trade-offs for

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    different MIH settings such as the MIH message size and rate, and
the
    retransmission parameters.  In addition, factors such as NAT
    traversal are also discussed.  Given the reliability requirements
for
    the MIH transport, it is assumed in this discussion that the MIH ACK
    mechanism is to be used in conjunction with UDP, while it is
    preferred to avoid using MIH ACKs with TCP since TCP includes
    acknowledgement and retransmission functionality

6.1.  MIH Message size

    Although the MIH message size varies widely from about 30 bytes (for
    a broadcast capability discovery request) to around 65000 bytes (for
    an IS MIH_Get_Information response primitive), a typical MIH message
    size for the ES/CS service ranges between 50 to100 bytes
[IEEE80221].
    Thus, considering the effects of the MIH message size on the
    performance of the transport protocol brings us to discussing two
    main issues, related to fragmentation of long messages in the
context
    of UDP and the concatenation of short messages in the context of
TCP.
    Since transporting long MIH messages may require fragmentation that
    is not available in UDP, if MIH is using UDP a limit MUST be set on
    the size of the MIH message, unless fragmentation functionality is
    added to the MIH layer or IP layer fragmentation is used instead.
In
    this latter case, the loss of an IP fragment leads to the
    retransmission of an entire MIH message, which in turn leads to poor
    end-to-end delay performance in addition to wasted bandwidth
    utilization.  Additional recommendations in
    [I-D.ietf-tsvwg-udp-guidelines] apply for limiting the size of the
    MIH message when using UDP and assuming IP layer fragmentation.  In
    terms of dealing with short messages, TCP has the capability to
    concatenate very short messages in order to reduce the overall
    bandwidth overhead.  However, this reduced overhead comes at the
cost
    of additional delay to complete an MIH transaction, which may not be
    acceptable for CS and ES services.  Note also that TCP is a stream
    oriented protocol and measures data flow in terms of bytes, not
    messages.  Thus it is possible to split messages across multiple TCP
    segments if they are long enough.  Even short messages can be split
    across two segments.  This can also cause unacceptable delays,
    especially if the link quality is severely degraded as is likely to
    happen when the MN is exiting a wireless access coverage area.

6.2.  MIH Message rate

    The frequency of MIH messages varies according to the MIH service
    type.  It is expected that CS/ES message arrive at a rate of one in
    hundreds of milliseconds in order to capture quick changes in the
    environment and/ or process handover commands.  On the other hand,
IS
    messages are exchanged mainly every time a new network is visited
    which may be in order of hours or days.  Therefore a burst of either

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    short CS/ES messages or long IS message exchanges (in the case of
    multiple MIH nodes requesting information) may lead to network
    congestion.  While the built-in rate-limiting controls available in
    TCP may be well suited for dealing with these congestion conditions,
    this may result in large transmission delays that may be
unacceptable
    for the timely delivery of ES/CS messages.  On the other hand, if
UDP
    is used, a rate-limiting effect similar to the one obtained with TCP
    may be obtained by adequately adjusting the parameters of a token
    bucket regulator as defined in the MIH specifications [IEEE80221].
    Recommendations for tocken bucket parameter settings are specific to
    the scenario considered.

6.3.  Retransmission

    For TCP, the retransmission timeout is adjusted according to the
    measured RTT.  However due to the exponential backoff mechanism, the
    delay associated with retransmission timeouts may increase
    significantly with increased packet loss.

    If UDP is being used to carry MIH messages, MIH SHOULD use MIH ACKs.
    An MIH message is retransmitted if its corresponding MIH ACK is not
    received by the generating node within a timeout interval set by the
    MIHF.  This approach does not include an exponential backoff and
    therefore tends to degrade more gracefully than TCP when the packet
    loss rate becomes large, in the sense that the expected delay does
    not increase exponentially.  The number of retransmissions is
    limited, which reduces head-of-line blocking of other MIH messages,
    but this can cause important ES/CS messages to be lost.

    Additionally, instead of retransmitting an unacknowledged message,
    the MIH may choose to update the information and transmit a new
    message.

6.4.  NAT Traversal

    There are no known issues for NAT traversal when using TCP.  The
    default connection timeout of 24 hours is considered adequate for
MIH
    transport purposes.  However, issues with NAT traversal using UDP
are
    documented in [I-D.ietf-tsvwg-udp-guidelines].  Communication
    failures are experienced when middleboxes destroy the per-flow state
    associated with an application session during periods when the
    application does not exchange any UDP traffic.  Hence, communication
    between the MN and the MoS SHOULD be able to gracefully handle such
    failures and implement mechanisms to re-establish their UDP
sessions.
    In addition and in order to avoid such failures, MIH messages MAY be
    sent periodically, similarly to keep-alive messages, to attempt to
    refresh middlebox state (e.g.  ES reports could be used for this
    purpose).  As [RFC4787] requires a minimum state timeout of two

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    minutes or more, MIH messages using UDP as transport SHOULD be sent
    once every two minutes.

6.5.  General guidelines

    Since ES and CS messages are small in nature and have tight latency
    requirements, UDP in combination with MIH acknowledgement SHOULD be
    used for transporting ES and CS messages.  On the other hand, IS
    messages are more resilient in terms of latency constraints and some
    long IS messages could exceed the MTU of the path to the
destination.
    Therefore, TCP SHOULD be used for transporting IS messages.  For
both
    UDP and TCP cases, if a port number is not explicitly assigned (e.g.
    by the DNS SRV), MIH messages sent over UDP, TCP or other supported
    transport MUST use the default port number defined for that
    particular transport..

    MOS server MUST support both UDP and TCP for MIH transport and the
MN
    MUST support TCP.  Additionally, the server and MN MAY support
    additional transport mechanisms.  The MN MAY use the procedures
    defined in [I-D.bajko-mos-dns-discovery] to discover additional
    transport protocols supported by the server.

7.  Operation Flows

    Figure 10 gives an example operation flow between MIHF peers when an
    MIH user requests for an IS service.  Scenario 1 is in effect, i.e.
    the MoS and the MN are both in the MN's home network.  Thus DHCP is
    used for MoS discovery and TCP is used for establishing a transport
    connection to carry the IS messages.  When MOS is not
pre-configured,
    the MIH user needs to discover the IP address of MOS to communicate
    with the remote MIHF.  Therefore the MIH user sends a discovery
    request message to the local MIHF as defined in [IEEE80221]

    In this example, we assume that MoS discovery is performed before a
    transport connection is established with the remote MIHF, and the
    DHCP client process is invoked via some internal APIs.  DHCP Client
    sends DHCP INFORM message according to standard DHCP and with the
MoS
    option as defined in [I-D.bajko-mos-dhcp-options].  DHCP server
    replies via DHCP ACK message with the IP address of the MoS.  The
MOS
    address is then passed to the MIHF locally via some internal APIs.
    MIHF generates the discovery response message and passes it on to
the
    corresponding MIH user.  The MIH user generates an IS query
addressed
    to the remote MoS.  MIHF invokes the underlying TCP client which
    establishes a transport connection with the remote peer.  Once the
    transport connection is established, MIHF sends the IS query via MIH
    protocol REQUEST message.  The message and query arrive at the
    destination MIHF and MIH user respectively.  The MoS MIH user

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    responds to the corresponding IS query and the MoS MIHF sends the IS
    response via MIH protocol RESPONSE message.  The message arrives to
    the source MIHF which passes the IS response on to the corresponding
    MIH user.

                 MN                                             MoS
|====================================|    |======|
|===================|
  + ---------+                                                 +
---------+
  | MIH USER |       +------+  +------+    +------+   +------+ | MIH
USER |
  | +------+ |       | TCP  |  |DHCP  |    |DHCP  |   | TCP  | |
+------+ |
  | | MIHF | |       |Client|  |Client|    |Server|   |Server| | | MIHF
| |
  +----------+       +------+  +------+    +------+   +------+
+----------+
      |                 |         |           |          |          |
      |MIH Discovery    |         |           |          |          |
      |Request          |         |           |          |          |
      |(MIH User-> MIHF)|         |           |          |          |
      |======>          |         |           |          |          |
      |                 |         |           |          |          |
      |Invoke DHCP Client         |           |          |          |
      |(Internal process with MoS)|DHCP INFORM|          |          |
      |==========================>|==========>|          |          |
      |                 |         |           |          |          |
      |                 |         |           |          |          |
      |                 |         |  DHCP ACK |          |          |
      |                 |         |<==========|          |          |
      |    Inform MoS address     |           |          |          |
      |<==========================|           |          |          |
      |    (internal process)     |           |          |          |
      |                           |           |          |          |
      |Discovery        |         |           |          |          |
      |Response         |         |           |          |          |
      |<======          |         |           |          |          |
      |(MIH User<- MIHF)|         |           |          |          |
      |                 |         |           |          |          |
      |IS Query         |         |           |          |          |
      |=======>         |         |           |          |          |
      |(MIH User-> MIHF)|         |           |          |          |
      |                 |         |           |          |          |
      |Invoke TCP Client|         |           |          |          |
      |================>|         |           |          |          |
      |(Internal process|         |           |          |          |
      |with MOS)        |         |           |          |          |
      |                 |         |           |          |          |
      |                 |  TCP connection established    |          |
      |                 |<==============================>|          |
      |                 |         |           |          |          |
      |                 |         |           |          |          |
      |                 |         |           |          |          |

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      |                 IS  QUERY REQUEST (via MIH protocol)        |
      |============================================================>|
      |                 |         |           |          |          |
      |                 |         |           |          |          |
      |                 |         |           |          |          |
      |                 |         |           |          |  IS QUERY|
      |                 |         |           |          |   REQUEST|
      |                 |         |           |          |=========>|
      |                 |         |           |    (MIHF-> MIH User)|
      |                 |         |           |          |          |
      |                 |         |           |          |     QUERY|
      |                 |         |           |          |  RESPONSE|
      |                 |         |           |          |   <======|
      |                 |         |           |  |(MIHF <-MIH User) |
      |                 |         |           |          |          |
      |                 | IS QUERY RESPONSE (via MIH protoco        |
      |<============================================================|
      |                 |         |           |          |          |
      |    IS           |         |           |          |          |
      |RESPONSE         |         |           |          |          |
      |<========        |         |           |          |          |
      |(MIH User <-MIHF)|         |           |          |          |
      |                 |         |           |          |          |

           Figure 10: Example Flow of Operation Involving MIH User

AD> What do you mean by internal process with MOS?

8.  Security Considerations

    There are a number of security issues that need to be taken into
    account during node discovery and information exchange via a
    transport connection [I-D.ietf-mipshop-mis-ps]

    In case where DHCP is used for node discovery and authentication of
    the source and content of DHCP messages are required, it is
    recommended that network administrators should use DHCP
    authentication option described in [RFC3118], where available or
rely
    upon link layer security.  This will also protect the denial of
    service attacks to DHCP server.[RFC3118] provides mechanisms for
both
    entity authentication and message authentication.

    In case where DNS is used for discovering MoS, fake DNS requests and
    responses may cause DoS and the inability of the MN to perform a
    proper handover, respectively.  Where networks are exposed to such
    DoS, it is recommended that DNS service providers use the Domain
Name
    System Security Extensions (DNSSEC) as described in [RFC4033].
    Readers may also refer to [RFC4641] to consider the aspects of
DNSSEC
    Operational Practices.

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    In case where reliable transport protocol such as TCP is used for
    transport connection between two MIHF peers, TLS [RFC4346] should be
    used for message confidentiality and data integrity.  In particular,
    TLS is designed for client/server applications and to prevent
    eavesdropping, tampering, or message forgery.  Readers should also
    follow the recommendations in [RFC4366] that provides generic
    extension mechanisms for the TLS protocol suitable for wireless
    environments.

    In case where unreliable transport protocol such as UDP is used for
    transport connection between two MIHF peers, DTLS [RFC4347] should
be
    used for message confidentiality and data integrity.  The DTLS
    protocol is based on the Transport Layer Security (TLS) protocol and
    provides equivalent security guarantees.

    Alternatively, generic IP layer security, such as IPSec [RFC2401]
may
    be used where neither transport layer security for a specific >
    transport is available nor server only authentication is required.

9.  IANA Considerations

    This document registers the following TCP and UDP port(s) with IANA:

  Keyword         Decimal   Description
  -------        -------    -----------
  ieee-mih-IS    XXX/tcp    Media Independent Handover Information
Services
  ieee-mih-IS    XXX/udp    Media Independent Handover Information
Services
  ieee-mih-ES    XXX/tcp    Media Independent Handover Event Services
  ieee-mih-ES    XXX/udp    Media Independent Handover Event Services
  ieee-mih-CS    XXX/tcp    Media Independent Handover Command Services
  ieee-mih-CS    XXX/udp    Media Independent Handover Command Services

10.  Acknowledgements

    The authors would like to thank Patrick Stupar for his valuable
    comments and fruitful discussions.

11.  References

11.1.  Normative References

    [I-D.bajko-mos-dhcp-options]
               Bajko, G., "Dynamic Host Configuration Protocol (DHCPv4
               and DHCPv6) Options for Mobility  Servers (MoS)",
               draft-bajko-mos-dhcp-options-00 (work in progress),

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               August 2007.

    [I-D.bajko-mos-dns-discovery]
               Bajko, G., "Locating Mobility Servers",
               draft-bajko-mos-dns-discovery-00 (work in progress),
               August 2007.

    [I-D.ietf-dhc-dhcpv6-opt-dnsdomain]
               Yan, R., "Domain Suffix Option for DHCPv6",
               draft-ietf-dhc-dhcpv6-opt-dnsdomain-04 (work in
progress),
               June 2007.

    [I-D.ietf-dime-mip6-integrated]
               Korhonen, J., Bournelle, J., Tschofenig, H., Perkins, C.,
               and K. Chowdhury, "Diameter Mobile IPv6: Support for
               Network Access Server to Diameter Server  Interaction",
               draft-ietf-dime-mip6-integrated-07 (work in progress),
               November 2007.

    [I-D.ietf-mip6-bootstrapping-integrated-dhc]
               Chowdhury, K. and A. Yegin, "MIP6-bootstrapping for the
               Integrated Scenario",
               draft-ietf-mip6-bootstrapping-integrated-dhc-05 (work in
               progress), July 2007.

    [I-D.ietf-mip6-hiopt]
               Jang, H., Yegin, A., Chowdhury, K., and J. Choi, "DHCP
               Option for Home Information Discovery in MIPv6",
               draft-ietf-mip6-hiopt-10 (work in progress), January
2008.

    [I-D.ietf-mipshop-mis-ps]
               Melia, T., Hepworth, E., Sreemanthula, S., Ohba, Y.,
               Gupta, V., Korhonen, J., and Z. Xia, "Mobility Services
               Transport: Problem Statement",
               draft-ietf-mipshop-mis-ps-05 (work in progress),
               November 2007.

    [I-D.ietf-tsvwg-udp-guidelines]
               Eggert, L. and G. Fairhurst, "UDP Usage Guidelines for
               Application Designers",
draft-ietf-tsvwg-udp-guidelines-05
               (work in progress), February 2008.

    [IEEE80221]
               "Draft IEEE Standard for Local and Metropolitan Area
               Networks: Media Independent Handover Servicesinnn", IEEE
               LAN/MAN Draft  IEEE P802.21/D07.00, July 2007.

    [RFC1533]  Alexander, S. and R. Droms, "DHCP Options and BOOTP
Vendor

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               Extensions", RFC 1533, October 1993.

    [RFC1536]  Kumar, A., Postel, J., Neuman, C., Danzig, P., and S.
               Miller, "Common DNS Implementation Errors and Suggested
               Fixes", RFC 1536, October 1993.

    [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

    [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP
Vendor
               Extensions", RFC 2132, March 1997.

    [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
               Specification", RFC 2181, July 1997.

    [RFC2401]  Kent, S. and R. Atkinson, "Security Architecture for the
               Internet Protocol", RFC 2401, November 1998.

    [RFC2988]  Paxson, V. and M. Allman, "Computing TCP's Retransmission
               Timer", RFC 2988, November 2000.

    [RFC3118]  Droms, R. and W. Arbaugh, "Authentication for DHCP
               Messages", RFC 3118, June 2001.

    [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
               and M. Carney, "Dynamic Host Configuration Protocol for
               IPv6 (DHCPv6)", RFC 3315, July 2003.

    [RFC3849]  Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix
               Reserved for Documentation", RFC 3849, July 2004.

    [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
               Rose, "DNS Security Introduction and Requirements",
               RFC 4033, March 2005.

    [RFC4282]  Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
               Network Access Identifier", RFC 4282, December 2005.

    [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
               (TLS) Protocol Version 1.1", RFC 4346, April 2006.

    [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
               Security", RFC 4347, April 2006.

    [RFC4366]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen,
J.,
               and T. Wright, "Transport Layer Security (TLS)
               Extensions", RFC 4366, April 2006.

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    [RFC4641]  Kolkman, O. and R. Gieben, "DNSSEC Operational
Practices",
               RFC 4641, September 2006.

    [RFC4787]  Audet, F. and C. Jennings, "Network Address Translation
               (NAT) Behavioral Requirements for Unicast UDP", BCP 127,
               RFC 4787, January 2007.

11.2.  Informative References

    [I-D.rahman-mipshop-mih-transport]
               Rahman, A., "Transport of Media Independent Handover
               Messages Over IP", draft-rahman-mipshop-mih-transport-03
               (work in progress), July 2007.

Authors' Addresses

    Telemaco Melia (editor)
    CISCO

    Email: tmelia@cisco.com

    Gabor Bajko
    Nokia

    Email: Gabor.Bajko@nokia.com

    Subir Das
    Telcordia

    Email: subir@research.telcordia.com

    Nada Golmie
    NIST

    Email: nada.golmie@nist.gov

    Sam Xia
    Huawei

    Email: xiazhongqi@huawei.com

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    Juan Carlos Zuniga
    InterDigital

    Email: j.c.zuniga@ieee.org

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Full Copyright Statement

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Acknowledgment

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Melia, et al.            Expires August 15, 2008               [Page 29]

Vijay Devarapalli wrote:
> Hello folks,
> 
> This is to announce a working group last call for the MIH
> solution document (draft-ietf-mipshop-mstp-solution). You
> can find the document at the following URL.
> 
>
http://www.ietf.org/internet-drafts/draft-ietf-mipshop-mstp-solution-01.
txt
> 
> The last call expires on March 5 2008. (Its a three week
> last call because of Internet Draft submission deadlines
> on the 18th and 25th).
> 
> The intended status for this document is Standards Track.
> 
> Please post any issues or comments on this document to the
> MIPSHOP WG mailing list. In case you have reviewed the
> document and found no issues, please send an email saying
> you support advancing this document.
> 
> Vijay
> _______________________________________________
> Mipshop mailing list
> Mipshop@ietf.org
> http://www.ietf.org/mailman/listinfo/mipshop
_______________________________________________
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