One document matched: draft-kuntz-dmm-summary-00.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
<!ENTITY idPatilDmm PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.patil-mext-dmm-approaches'>
<!ENTITY idChanDmm PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.chan-distributed-mobility-ps'>
<!ENTITY idYokotaDmm PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.yokota-dmm-scenario'>
<!ENTITY idLiuDmm1 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.liu-mext-distributed-mobile-ip'>
<!ENTITY idLiuDmm2 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.liu-distributed-mobility'>
<!ENTITY idLiuDmmAnalysis PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.liu-distributed-mobility-traffic-analysis'>
<!ENTITY idSeiteDmm PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.seite-netext-dma'>
<!ENTITY idKassiDmm PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.kassi-mobileip-dmi'>
<!ENTITY idHARPDmm PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-mip6-hareliability'>
<!ENTITY idWakikawaDmm PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.wakikawa-mext-global-haha-spec'>
<!ENTITY idChanDmm2 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.chan-netext-distributed-lma'>
<!ENTITY idBernardosDmm PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.bernardos-mext-dmm-cmip'>
<!ENTITY rfchmipv6 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.5380'>
<!ENTITY idNgTnlLoop PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ng-intarea-tunnel-loop'>
<!ENTITY idLaganierCga PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.laganier-mext-cga'>
<!ENTITY rfc5026 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.5026'>
]>
<?rfc toc="yes"?>
<?rfc tocompact="no"?>
<?rfc tocdepth="6"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<rfc ipr='trust200902' category="info" docName="draft-kuntz-dmm-summary-00">
<front>
<title abbrev="DMM Summary"> A Summary of Distributed Mobility Management </title>
<!-- Authorship -->
<author fullname="Romain Kuntz" initials="R.K." surname="Kuntz">
<organization abbrev="Toyota ITC"> Toyota InfoTechnology Center USA, Inc. </organization>
<address>
<postal>
<street>465 Bernardo Ave</street>
<city>Mountain View</city>
<code>94045</code>
<region>California</region>
<country>USA</country>
</postal>
<phone>+1-650-694-4152</phone>
<facsimile>+1-650-694-4901</facsimile>
<email> rkuntz@us.toyota-itc.com </email>
</address>
</author>
<author fullname="Divya Sudhakar" initials="D.S." surname="Sudhakar">
<organization> UCLA </organization>
<address>
<phone>+1-408-896-7526</phone>
<email> divyasudhakar@ucla.edu</email>
</address>
</author>
<author fullname="Ryuji Wakikawa" initials="R.W." surname="Wakikawa">
<organization abbrev="Toyota ITC"> Toyota InfoTechnology Center USA, Inc. </organization>
<address>
<postal>
<street>465 Bernardo Ave</street>
<city>Mountain View</city>
<code>94045</code>
<region>California</region>
<country>USA</country>
</postal>
<email> ryuji@us.toyota-itc.com </email>
</address>
</author>
<author fullname="Lixia Zhang" initials="L.Z." surname="Zhang">
<organization> UCLA </organization>
<address>
<postal>
<street>3713 Boelter Hall</street>
<city>Los Angeles</city>
<code>90095-1596</code>
<region>California</region>
<country>USA</country>
</postal>
<email> lixia@cs.ucla.edu </email>
</address>
</author>
<date year="2011"/>
<area> Internet Area </area>
<workgroup> MEXT Working Group </workgroup>
<!-- Abstract -->
<abstract>
<t>
As stated in the MEXT charter, the working group will "work on operational
considerations on setting up Mobile IPv6 networks so that traffic is distributed
in an optimal way". This topic, referred to as Distributed Mobility Management (DMM),
has motivated the submission of multiple problem statement and solution drafts.
This document aims at summarizing the current status of the DMM effort, in order
to initiate more discussions within the working group.
</t>
</abstract>
<!--
<note title="Requirements Language">
<t>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 <xref target="RFC2119">RFC 2119</xref>.
</t>
</note>
-->
</front>
<!-- Romain -->
<middle>
<!-- Introduction -->
<section title="Introduction">
<t>
In its charter, the MEXT working group mentions the need to work on
"operational considerations on setting up Mobile IPv6 networks so that
traffic is distributed in an optimal way". The expected deliverable
is an Internet Draft on "Operational considerations for distributed use
of Mobile IPv6" for publication as an informational document.
</t>
<t>
This topic of Distributed Mobility Management (DMM) has motivated the submission
of multiple problem statement and solution drafts, that often share
common concepts and ideas. This document first summarizes the motivation and
problem statement documents submitted in the MEXT working group. Then,
we expose an overview of six representative proposed approaches. In the
conclusion, we analyze the benefits and drawbacks of each approach.
</t>
<t>
The goal of this document is to initiate discussion within the working
group towards an agreement on the needed requirements and a unified
DMM solution.
</t>
</section>
<!-- Problem statement summary. Reviewed draft:
[1] http://tools.ietf.org/html/draft-patil-mext-dmm-approaches-00
[2] http://tools.ietf.org/html/draft-chan-distributed-mobility-ps-01
[3] http://tools.ietf.org/html/draft-liu-mext-distributed-mobile-ip-00
[4] http://tools.ietf.org/html/draft-yokota-dmm-scenario-00
[5] http://tools.ietf.org/html/draft-liu-distributed-mobility-02
[6] http://tools.ietf.org/html/draft-liu-distributed-mobility-traffic-analysis-00
-->
<section title="Summary of the Problem Statement">
<section title="Issues of centralized mobility solutions">
<t>
The following Internet Drafts have been considered in this section:
<list style="symbols">
<t>
<xref target="I-D.chan-distributed-mobility-ps" />,
</t>
<t>
<xref target="I-D.liu-mext-distributed-mobile-ip" />
(that shares a vast portion of text with the previously mentioned
draft),
</t>
<t>
<xref target="I-D.patil-mext-dmm-approaches" />.
</t>
</list>
</t>
<t>
Centralized mobility solutions (i.e. which rely on the use of a single mobility
anchor) suffer from the following drawbacks:
<list style="symbols">
<t>
Non-optimal routes, especially as Content Delivery Network (CDN) servers
are being placed closer to the edge of the network. This results in long delays
between mobile clients and content servers, as well as unnecessary load in the
core network.
</t>
<t>
Low scalability that requires the deployment of several mobility anchors along
with the increasing number of mobile nodes. Furthermore, more and more traffic
is to be expected from and to these mobile devices, which could result in
congestions at the mobility anchor.
</t>
<t>
Mobility support is performed per node, and not per flow, which makes offloading
(i.e. the possibility to bypass the mobility anchor) impossible for some of the
traffic. We cannot expect route optimization capabilities to exists at every correspondent
node. In such cases, all of the traffic from and towards a mobile node has to go
through the centralized mobility anchor, which worsens the previously mentioned
issues.
</t>
<t>
The mobility anchor is a single point of failure: if a large number of mobile
nodes share the same mobility anchor, they can all be affected by a single outage.
In the specific case of Mobile IPv6, this issue is however supposed to be solved by
the standardization of the Home Agent Reliability Protocol (HARP)
<xref target="I-D.ietf-mip6-hareliability" />.
</t>
<t>
Signaling messages of the mobility protocol, as well as reliability protocols
such as HARP, can represent a significant overhead, both for the MN and the mobility
anchor. This is also true when considering route optimization modes that involves the MN,
the mobility anchor and the CN.
</t>
</list>
</t>
</section>
<section title="Requirements of DMM">
<t>
The following Internet Drafts have been considered in this section:
<list style="symbols">
<t>
<xref target="I-D.yokota-dmm-scenario" />,
</t>
<t>
<xref target="I-D.liu-distributed-mobility" />,
</t>
<t>
<xref target="I-D.liu-distributed-mobility-traffic-analysis" />.
</t>
</list>
</t>
<t> DMM should be achieved by considering the following requirements:
<list style="symbols">
<t>
The distribution of the mobility anchors (e.g. the Home Agents) in
order to achieve a more flat design. This would improve scalability
and robustness of the mobility infrastructure.
</t>
<t>
Placing the mobility management closer to the edge of the network
(e.g. at the Access Router level) in order to attain routing optimality
and lower delays. Beside, offloading near the edge of the network would
become possible, to the benefit of the core network load.
</t>
<t>
The dynamic use of mobility support by allowing the split of data
flows along different paths that may travel through either the mobility anchor
or non-anchor nodes, even though no specific route optimization support is available
at the correspondent node. This would further improve the previously mentioned
benefits.
</t>
<t>
Separating control and data planes by splitting location and
routing anchors. Keeping the control plane centralized while distributing
the data plane, as previously suggested, could minimize the signaling
overhead between the mobility anchors.
</t>
<t>
Reusing existing protocols while minimizing changes, in order to allow
faster adoption of the technology.
</t>
</list>
</t>
</section>
</section>
<!-- Divya -->
<section title="Solution Space">
<t>
A number of solutions for distributing mobility management and flattening the
centralized architecture have been proposed for Mobile IPv6 and Proxy Mobile IPv6. Some of these solutions attempt this distribution of mobility management by moving the mobility functionality closer to the edge of the network while others distribute the same functionality among several mobility agents near the core. In this draft, we summarize six representative approaches that all aim at
achieving this purpose.
</t>
<section title="Hierarchical Mobile IPv6 (HMIPv6)">
<t>
When talking about moving mobility functionality closer to the edge of the network, mention must be made of Hierarchical Mobile IPv6 (HMIPv6) <xref target="RFC5380" />. HMIPv6 suggests the implementation of an additional mobility agent called the Mobility Anchor Point (MAP) in addition to or instead of the HA (in case of nomadic operations of the MN where a permanent HA is not required). The MAP can be implemented at different levels of the routing hierarchy, even in access routers where it can be most beneficial to the MN in reducing mobility handoff overhead. If the MN is mobile but its movements are very small, then there is a lot of overhead in binding its new location with the HA which could potentially be very far. In this scenario having a MAP closer to the edge of the network and thus closer to the MN can help reduce the time for signaling and handoff.
</t>
<t>
In HMIPv6, each MN is associated with 3 addresses: the HoA obtained from the HA, the Local Care of Address (LCoA) obtained on link and the Regional Care of Address (RCoA) obtained from stateless configuration using the prefix set advertised by the MAP. When the MN enters the MAP domain, it identifies the MAP it wants to use from router updates and configures its LCoA and RCoA. It then sends a local binding update (local BU) to the MAP to bind its LCoA with its RCoA. After the success of this local BU, the MN binds the RCoA with its HoA at the HA (and its CNs if the MN wants to perform route optimization) (Figure 1). Once this binding is in place, any movement of the MN within the domain of the MAP is hidden from the HA and the CNs as only the LCoA of the MN would change and the RCoA would remain the same. Thus only a local BU to the MAP with the new LCoA would be required and this is faster than sending a new binding update to the HA which could be much further away than the MAP.
</t>
<figure>
<artwork>
<![CDATA[
CN HA MAP MN
| | | |
| | |+------| MN binds LCoA to RCoA at MAP
| |+--------------| MN binds RCoA to HoA at HA
|------>|======>|======>| CN->MN without route optimization
: : : :
|+----------------------| MN binds RCoA to HoA at CN for RO
|-------------->|======>| CN->MN with route optimization
|<--------------|<======| MN->CN
]]>
</artwork>
<postamble> Figure 1: Packet routing when MN is anchored at MAP and acquires LCoA on link and RCoA from MAP.</postamble>
</figure>
<t>
HMIPv6 allows the MN to bind with multiple MAPs simultaneously. This could allow the MN to use MAPs at different levels of the routing hierarchy. However, although HMIPv6 distributes mobility functionality amongst several MAPs, there still remains a centralized HA which is a single point of failure and failure of this HA could cause the location information of the MNs being serviced by the HA to be lost. The MAP also adds an additional layer of indirection to the architecture which may not always be desirable.
</t>
</section>
<section title="Flat Access and Mobility Architecture (FAMA)">
<t>
In <xref target="I-D.bernardos-mext-dmm-cmip" />, a decentralized architecture
called the Flat Access and Mobility Architecture (FAMA) is proposed. FAMA
suggests moving the functionality of the Home Agent (HA) closer to the edge of
the network and placing it in the default gateways that provide IP connectivity
to the mobile nodes (MNs). Thus the first elements to provide access to the
internet for these MNs also perform mobility management. These elements are
called Distributed Access Routers (DARs) in FAMA.
</t>
<t>
When an MN attaches to a DAR, it gets a topologically correct IP address anchored
at that DAR. The MN uses this IP address for all its flows while connected to
the DAR. When the MN moves, it connects to a new DAR and gets an IP address
anchored to the new DAR and uses this IP address for its connections. If, for
some reason, the MN decides to retain use of and connectivity to its old IP
address anchored with the old DAR, then the MN sends a binding update to the
old DAR and the old DAR would then bind the old IP address with the new IP
address of the MN (Figure 2). Thus, in MIPv6 terminology, the old DAR becomes the
HA of the MN and the old IP address becomes the home address (HoA). Thus any DAR
has the potential to act as HA if the MN decides to retain use of an IP address
anchored at the DAR.
</t>
<figure>
<artwork>
<![CDATA[
CN2 CN1 H-DAR DAR2 MN
| | | | |
| | |+--------------| Binding Update to H-DAR
| |------>|==============>| CN1->MN to HoA anchored at H-DAR
| |<------|<==============| MN->CN1 from HoA anchored at DAR1
| | | | |
|<----------------------|<------| MN->CN2 from HoA anchored at DAR2
|---------------------->|------>| CN2->MN to HoA anchored at DAR2
]]>
</artwork>
<postamble> Figure 2: Packet routing when MN is anchored at DAR2 and uses
the HoA anchored at DAR2 as well as an HoA anchored at some previously
visited DAR1.</postamble>
</figure>
<t>
FAMA allows an MN to simultaneously use several IP addresses anchored at different
DARs. However, FAMA does not specify when and under what conditions an MN would
want to retain use of its old IP address. FAMA also does not specify whether the MN
is associated with a permanent address that can be used to reach it by default. The
use of multiple anchored address mandates a mechanism (such as DNS) on the correspondent
node side to retrieve a proper and valid destination address for the MN. Care should
also be taken to avoid routing loops between DARs and routing dead ends whenever the MN
mutually binds a new and old address to two different DARs. This issue is however not
peculiar to FAMA. <xref target="I-D.ng-intarea-tunnel-loop" /> discusses this issue and
exposes solutions.
</t>
</section>
<section title="Dynamic Mobile IP (DMI)">
<t>
Dynamic Mobile IP (DMI) proposed in <xref target="I-D.kassi-mobileip-dmi" /> suggests
a use case for establishing when an MN would want to retain use of its old IP address. It
proposes that an MN only requires use of an old IP address when there is an ongoing
connection/session that has been established using that IP address.
Thus, Mobile IP functionality to retain IP address obtained from an old subnet after
moving to a new subnet is put to use only when there is ongoing communication while
the MN is in motion between subnets. At all other times, regular IP networking using
topologically correct IP addresses is used. Thus DMI suggests a different mode for
mobility usage in IP networks. This helps reduce the signaling overhead and the
number of binding cache entries that have to be maintained by Correspondent Node
(CN) in regular MIPv6.
</t>
<t>
Each MN is associated with a permanent home subnet having a permanent HA
which gives the MN a permanent HoA. As long as the MN is anchored to the
permanent home subnet, usual IP communication takes place without any need for
Mobile IP. When the MN moves from the home subnet and anchors itself to a new subnet
(referred to as the temporary home subnet), it identifies the mobility agent in that
subnet (referred to as the temporary HA) and obtains a temporary HoA
from it. The MN sends a binding update to the permanent HA to register its
current location (Figure 3). The MN then proceeds to use its temporary HoA and
regular IP connections for all flows initiated after the move has taken place.
Mobility routing functions would only be required when there exist flows that have
been initiated in the permanent home subnet using the permanent HoA. In this case,
triangular routing would have to be performed, in order to maintain location
transparency for the CN which sees only the permanent HoA.
</t>
<figure>
<artwork>
<![CDATA[
CN1 P-HA T-HA1 MN T-HA2 CN2
| | | | | |
| |+------------| | | Binding update to P-HA
| | |+-----| | | Binding update to previous T-HA
|------------>|=====>| | | CN1->MN to old temporary HoA
|<------------|<=====| | | MN->CN1 from old temporary HoA
| | | |------------>| MN->CN2 from new temporary HoA
| | | |<------------| CN2->MN to new temporary HoA
| | | | | |
]]>
</artwork>
<postamble>
Figure 3: Packet routing when MN is associated and registered with permanent HA (P-HA)
and has moved from temporary HA1 (T-HA1) to T-HA2. MN uses the HoA acquired form T-HA1
for ongoing flows with CN1 and the HoA acquired from T-HA2 for new flows with CN2.
</postamble>
</figure>
<t>
Every time the MN moves from one subnet to another, the MN sends a binding update
to the permanent HA and then continues to use regular IP connections using
the new temporary HoA obtained at the new subnet for all flows initiated after the
move. If there are any ongoing flows using an old IP address (from an old temporary
or permanent subnet), the MN has to additionally perform a binding update with
the home agent that provided the IP address with which the flow had been initiated.
Thus any temporary HA might have to perform binding updates and mobility
routing if an MN initiates a flow using an IP address obtained from that temporary
home agent and moves to a different subnet. By ensuring that mobile IP is used
only when strictly required, DMI reduces the number of control messages required
in MIPv6.
</t>
<t>
In principles, DMI and FAMA are very similar. FAMA explicitly places the mobility anchor at the access router. DMI better defines when the MN retains use of its old IP addresses. Since the MN is always associated with a permanent HoA, it can always be reached by a CN
that does not know the MN's current location. Failure of the permanent HA does not cause
the MN to lose connectivity to the network. It can still continue flows that have been initiated using the temporary HoAs. </t>
</section>
<section title="Dynamic Mobility Anchoring (DMA)">
<t>
In Dynamic Mobility Anchoring (DMA) proposed in <xref target="I-D.seite-netext-dma" />,
the best ideas of FAMA and DMI are combined to propose a Proxy Mobile IP (PMIP) approach
in a flattened architecture where mobility functions are distributed among access routers.
The access routers are mobility-enabled and provide traffic anchoring and location
management functionalities to the MNs. These mobility-enabled access routers (MARs)
allocate Home Network Prefixes (HNP) for MNs. When an MN is anchored at a MAR, it uses
the HNP provided by that MAR and regular IPv6 routing applies for flows initiated at
the MAR. When an MN moves to another MAR, it acquires a HNP from the new MAR and uses
this HNP for new flows. A routing tunnel must now be set up between the old MAR and
new MAR if there are any ongoing flows during the IP handover.
</t>
<t>
The new MAR thus acts as a Home MAR (H-MAR) for flows using HNP allocated by itself
and as a Visited MAR (V-MAR) for flows using HNP allocated by a previously visited
MAR (Figure 4). As a result, any MAR can act as both an H-MAR and a V-MAR for flows
belonging to the same MN. Even if the MN is moving across several MARs, the tunnel
endpoints are always on the initial H-MAR (whose HNP is being used) and the current
V-MAR.
</t>
<figure>
<artwork>
<![CDATA[
CN2 CN1 MAR1 MAR2 MN
| | | | |
| | |+------| | Binding registration with H-MAR
| |------>|======>|----->| MAR1 acts as H-MAR and MAR2 acts as
| |<------|<======|<-----| V-MAR for flow between MN and CN1
|<---------------------|<-----| MAR2 acts as H-MAR for flow between
|--------------------->|----->| MN and CN2
| | | | |
]]>
</artwork>
<postamble> Figure 4: Packet routing when MN moves from MAR1 to MAR2 but has an
ongoing flow with CN1 during the movement. After the movement MN initiates flow
with CN2. </postamble>
</figure>
<t>
DMA's dynamic provision of flow based traffic indirection can also be applied to multiple
interfaces and IP flow mobility. However, DMA suffers from some of the same issues as
FAMA. It fails to specify whether the MN will be associated with a permanent address it
can be reached with and in the absence of such, how a CN will lookup MN's address to
initiate communication. In addition, DMA also requires that each MAR advertises different
per-MN prefixes set.
</t>
</section>
<section title="Global Ha to HA (GHAHA)">
<t>
Global HA to HA (GHAHA) <xref target="I-D.wakikawa-mext-global-haha-spec" />
builds on the Home Agent Reliability Protocol (HARP) proposed in
<xref target="I-D.ietf-mip6-hareliability" />. HARP provides reliability and
availability of HAs by having several redundant HAs form a group. One HA from the
group becomes the active HA and receives binding requests and updates from the MNs.
The other HAs in the group are standby HAs and are state-synchronized with the
active HA. When the active HA fails, one of the HAs in the group takes over as
active HA and sends a switch message to all the MNs which will cause them to bind
with the new HA. The aliveness of the HAs is determined through periodic HA-Hello
messages exchanged among the HAs in the group. The HAs in the group may be either
on the same link or on different links (to provide geographic redundancy). The HA
switch may also occur when the active HA wants to go offline for maintenance
operations.
</t>
<t>
GHAHA uses the redundant HA architecture suggested by HARP to provide distributed
mobility management. A number of geographically distributed HAs form a global HA
set and the HAs in the global set form HA links among themselves. All of them
advertise the same HA subnet prefix to leverage anycast routing. The MN discovers
the topologically closest HA using dynamic home agent address discovery protocol
or DNS and binds to it. This HA becomes the primary HA for that MN. When the binding
registration with the primary HA is complete, the primary HA sends a state
synchronization message to all other HAs in the global set which then create a
routing entry for the MN with the primary HA as the next hop.
</t>
<t>
When a CN anywhere in the internet tries to send a packet to the MN, the packet is
routed to the HA in the global set that is nearest to the CN via anycast routing (Figure 5).
This HA then looks up its global binding entries and tunnels the packet to the primary
HA of the MN. The primary HA then tunnels the packet to the MN. When an MN tries to
send a packet to a CN, the packet is tunneled to the primary HA which then routes
it to the CN.
</t>
<figure>
<artwork>
<![CDATA[
MN HA1 HA2 CN
| | | |
|-----+(Primary) | | Binding Registration
| |--------+| | State Synchronization
|<========|<========|<--------| Data from CN to MN
|========>|------------------>| Data from MN to CN
| | | |
]]>
</artwork>
<postamble> Figure 5: Packet routing when the MN is anchored to HA1 which is now
the primary HA for the MN. HA1 and HA2 have HA links established. HA2 is the
closest HA to CN. </postamble>
</figure>
<t>
The HAs in a global set periodically transmit HA-Hello messages that can be used for
checking the aliveness of the HAs. When a HA fails, the nearest HA takes over as the
new primary HA for the MNs anchored to the failed HA.
</t>
<t>
When the MN moves and reattaches to a different subnet, it sends a binding update
to its last known primary HA. This binding update gets routed to the currently
closest HA via anycast routing. This HA would then forward the binding update to
the intended HA. The intended HA would recognize that the packet has been forwarded by
a different HA and thus informs the MN that it must now switch to the topologically
closest HA. The MN sends a binding request to the new primary HA. All the other HAs
modify their global binding when the binding registration and synchronization process
is complete.
</t>
<t>
GHAHA eliminates the problem of single point of failure. Failure of the primary
HA does not cause the MN to lose connectivity. The synchronization between all the HAs in the global set ensure that the MN's flows are not disrupted as another HA takes over as the primary HA for the client. Since the HAs are globally distributed, the overhead due to triangular routing is also minimized. GHAHA's major disadvantage is the signaling overhead due to the need to synchronize the state all the HAs. This overhead grows linearly with the number of HAs in the system. The use of anycast routing has also raised concerns on security, as IPsec cannot be applied to communications which endpoints are anycast addresses, and on its impact on the BGP routing system scalability.
</t>
</section>
<section title="Dynamic Local Mobility Anchors (DLMA)">
<t>
The Dynamic Local Mobility Anchors (DLMA) scheme suggested in
<xref target="I-D.chan-netext-distributed-lma" /> builds on the distributed
architecture proposed by GHAHA while offsetting some of the disadvantages of GHAHA in
requiring complete synchronization of all the HAs in a global set and the large
amount of signaling traffic required for this complete synchronization. DLMA
decouples the logical functionalities of a mobility anchor into:
<list style="format (%d)">
<t>
Allocation of HoA or HNPs to MNs,
</t>
<t>
Location management which includes managing IP addresses and locations
of MNs,
</t>
<t>
Mobility routing which includes intercepting and forwarding packets.
</t>
</list>
</t>
<t>
DLMA then centralizes functionalities (1) and (2) in a Home Location Mobility
Anchor (H-LMA) while distributing functionality (3) across several Visited
Location Mobility Anchors (V-LMAs). The term Visited LMA here is used loosely,
regardless of whether the MN has visited the subnet or not. All the LMAs advertise
the same prefix
using anycast routing. However it is required that the HoA or HNP assigned to
an MN is unique to an H-LMA, i.e. it is possible to uniquely identify the
H-LMA of an MN from its HoA.
</t>
<t>
An MN acquires a HoA (or HNP) from its H-LMA. When it moves out of the home
subnet and anchors itself to a V-LMA, the V-LMA informs the H-LMA of the MN
that it is the current anchoring point of the MN. The H-LMA then maintains
this location information for the MN. When a CN anywhere in the Internet tries
to send a packet to the MN, the packet is intercepted by the V-LMA closest to
the CN via anycast routing. This V-LMA, called the O-LMA, tunnels the packet
to the H-LMA of the MN which then tunnels the packet to the V-LMA where the
MN is currently anchored. This V-LMA is called the D-LMA which then delivers
the packet to the MN (Figure 6). Thus O-LMA and D-LMA for a flow are the V-LMAs
that are closest to the CN and MN of that flow respectively.
This is the route taken by a packet from the CN to the MN when there
is no route optimization. When there is route optimization, the O-LMA caches location
information about the MN from its H-LMA and thereafter directly tunnels the packet
to its D-LMA. When an MN moves from D-LMA to another, an update must be sent to
the previous D-LMA in addition to the H-LMA if route optimization is used,
in case some O-LMA has cached information about the old D-LMA of the MN.
The old D-LMA could then tunnel packets to the new D-LMA of the MN and also
inform the O-LMA to update the location information in its cache. In the
reverse direction, a packet sent by the MN is captured by its D-LMA and
routed to the CN directly.
</t>
<figure>
<artwork>
<![CDATA[
MN D-LMA H-LMA O-LMA CN
| | | | |
| | | | |
|=======>|--------------------->| MN->CN
|<=======|<======|<======|<-----| CN->MN without route optimization
: : : : :
|<=======|<==============|<-----| CN->MN with route optimization
| | | | |
]]>
</artwork>
<postamble> Figure 6: Packet routing to and from the MN. The LMA closest
to the MN becomes the D-LMA and the LMA closest to the communication CN
becomes the O-LMA. The H-LMA is the LMA that handles location information
for the MN.</postamble>
</figure>
<t>
Every LMA acts as a H-LMA for a subset of MNs for which it assigns HoAs or HNPs
and maintains location information. It also performs mobility routing for MNs not
in this subset (i.e.) acts as a V-LMA for these MNs. The DLMA scheme works for both
Mobile IPv6 and Proxy Mobile IPv6. The mobility functionalities can also be moved to
the edge of the routers and packets may be tunneled directly to and from the mobile
access gateways (MAGs) bypassing the V-LMAs.
</t>
<t>
It is worth noting that the Scalable Approach for Wide-Area IP Mobility <xref target="SAIL" />
proposes a very similar approach by distributing the binding management with one-hop DHT.
Through a performance evaluation, it has proven being prone to failure as well as
reducing GHAHA's overhead while achieving equal or even better end-to-end delay in
most cases.
</t>
</section>
</section>
<!-- Conclusion section -->
<section title="Conclusion">
<t>
A summary of each approach is presented in Table 1.
The base protocol on which the solution relies is stated in the "Reuse protocol"
column. "(P)MIPv6" means that the scheme can apply to both MIPv6 and PMIPv6.
</t>
<figure>
<artwork>
<![CDATA[
+------+--------+-----------+--------+----------+-------------------+
|Scheme| Reuse |Distributed|Dynamic |Splitting | Number of HoAs |
| name |protocol| mobility |mobility| location | per MN |
| | | anchors |support | & routing| |
+------+--------+-----------+--------+----------+-------------------+
|HMIPv6| MIPv6 | Yes | No | No | Single one |
+------+--------+-----------+--------+----------+-------------------+
| FAMA | MIPv6 | Yes | Partial| No | 1 per visited net.|
+------+--------+-----------+--------+----------+-------------------+
| DMI | MIPv6 | Yes | Partial| No | 1 per visited net.|
+------+--------+-----------+--------+----------+-------------------+
| DMA | PMIPv6 | Yes | Partial| No | 1 per visited net.|
+------+--------+-----------+--------+----------+-------------------+
| GHAHA| MIPv6 | Yes | No | No | Single one |
+------+--------+-----------+--------+----------+-------------------+
| DLMA |(P)MIPv6| Yes | No | Yes | Single one |
+------+--------+-----------+--------+----------+-------------------+
]]>
</artwork>
<postamble>Table 1: Summary of the solution space.</postamble>
</figure>
<t>
All of the previously mentioned solutions propose a distributed approach for
mobility management, by locating multiple mobility anchors closer to the edge of the network.
FAMA and DMA locate them at the access router, i.e. at the first element to provide
access to the internet to the MNs. DMI and DLMA requires that a mobility anchor is
located in the same IP network than the MN (not necessarily co-located with the
access router). HMIPv6 and GHAHA are more flexible as mobility anchors do not need to be
located in every IP network where the MN will travel. However, having more mobility
anchors improves performance and reliability in case of a failure and decreases
latency. HMIPv6 still relies on a centralized HA, which makes it prone to failure
and triangular routing.
</t>
<t>
The use of multiple mobility anchors raise the question of how the IPsec Security
Associations (SA) would be deployed and enforced on all of them. This is a matter of
concern especially for securing the signaling messages. For that purpose, FAMA proposes
to use Cryptographically Generated Addresses, as introduced in <xref target="I-D.laganier-mext-cga" />.
GHAHA relies on HARP to perform such IPsec SA synchronization. The other solutions do not mention how
this could be achieved.
</t>
<t>
The approaches that grant the MN the capability to register to multiple mobility anchors
at the same time (HMIPv6, FAMA, DMI) should also implement a mechanism to avoid
routing loops between them (e.g.when the MN mutually binds a new and old address to two
different mobility anchors). For example, [I-D.ng-intarea-tunnel-loop]
discusses this issue and proposes solutions.
</t>
<t>
Dynamic mobility (i.e. the ability for flows to travel through either the
mobility anchor or non-anchor nodes, even though no specific route optimization
support is available at the correspondent node), is only partially supported in FAMA,
DMI and DMA. These protocols indeed reduce triangular routing by assigning
topologically valid IP addresses to the MN every time it moves in a new
network. However, it is still unclear how applications could select the desired
source address for their sessions. For example, in the case of DMI, one could
be interested in using the permanent address anchored at the permanent HA,
or the newly assigned address in the network where the MN resides. In other words, how could
one bind a specific address to a specific socket? A mobility-aware API, as described by Section
6 of <xref target="I-D.patil-mext-dmm-approaches" />, could help making such decisions.
In addition, more work may be needed to better define use-cases for dynamic mobility.
For example, the benefits offered depend on how frequently the MN changes its anchor
point, how long the sessions last, and also where the correspondent nodes are located.
</t>
<t>
By design, FAMA, DMI and DMA relies on the use of multiple anchored addresses. With DMI,
the MN is always associated with a permanent HoA, and thus can always be reached by a CN
that does not know the MN's current location. However, FAMA and DMA fail to specify
whether the MN will be associated with a permanent address. In the absence of such,
reachability of the MN from the CN is not guaranteed, so mechanisms should be specified
for the CN to chose a valid destination address. The dynamic DNS update as specified by
<xref target="RFC5026" /> cannot be used in this case. Beside, how HoAs would be assigned
is not clearly defined by these solutions. Especially, how does it affect the HoA bootstrapping
mechanism defined by <xref target="RFC5026" />? Last but not least, how would the HoAs
be recycled? They need to be released at some point and put back by the mobility anchor
into the pool of available HoAs. As HMIPv6, DLMA and GHAHA always rely on a single permanent
address, these solutions are not affected by these issues.
</t>
<t>
The idea of splitting location and routing management as exposed by DLMA or SAIL could
improve GHAHA scalability by reducing the signaling overhead caused by the HA's
synchronization. However, in the case of DMLA, care should be taken to avoid that the
location anchor becomes a single point of failure.
</t>
<t>
It is clear that there are several issues that must be kept in mind and tradeoffs that
have to be made while designing an effective DMM solution. Some (not all) of them are:
<list style="format (%d)">
<t>Ensuring reachability of the MN by the CN, </t>
<t>Signaling overhead and binding latency, </t>
<t>More vs less mobility agents, </t>
<t>Distribution of mobility functions among these mobility agents, </t>
<t>Assigning and recycling addresses to MNs, </t>
</list>
We have presented, what we hope would be the first steps to reinitiating discussion within the MEXT WG on DMM which in turn would lead to a robust and efficient DMM solution.
</t>
</section>
</middle>
<back>
<!--
<references title="Normative References">
</references>
-->
<references title="Informative References">
&idPatilDmm;
&idChanDmm;
&idYokotaDmm;
&idLiuDmm1;
&idLiuDmm2;
&idLiuDmmAnalysis;
&rfchmipv6;
&idBernardosDmm;
&idSeiteDmm;
&idKassiDmm;
&idHARPDmm;
&idWakikawaDmm;
&idChanDmm2;
&idNgTnlLoop;
&idLaganierCga;
&rfc5026;
<reference anchor="SAIL">
<front>
<title>SAIL: A Scalable Approach for Wide-Area IP Mobility</title>
<author initials="Z.Z." surname="Zhu" fullname="Zhenkai Zhu">
<organization>UCLA</organization>
</author>
<author initials="R.W." surname="Wakikawa" fullname="Ryuji Wakikawa">
<organization>UCLA</organization>
</author>
<author initials="L.Z." surname="Zhang" fullname="Lixia Zhang">
<organization>Toyota InfoTechnology Center</organization>
</author>
<date month="April" year="2011" />
</front>
<seriesInfo name="INFOCOM 2011" value="MobiWorld Workshop" />
</reference>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-24 10:06:28 |