Network Working Group Z. Zhu
Internet-Draft UCLA
Intended status: Informational R. Wakikawa
Expires: April 22, 2010 TOYOTA ITC
L. Zhang
UCLA
October 19, 2009
A Survey of Mobility Support In the Internet
draft-zhu-mobility-survey-00.txt
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Abstract
Over the last two decades many research efforts have been devoted to
developing solutions for mobility support over the global Internet
and resulted in a variety of proposed solutions. We conducted a
survey of the previous efforts to deepen our understanding on the
overall solution space of mobility support. This draft reports on
our finding and identifies remaining issues in providing ubiquitous
and efficient global scale mobility support.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Basic Components in Mobility Support Protocols . . . . . . . . 4
4. Existing Mobility Support Protocols . . . . . . . . . . . . . 5
4.1. Columbia Protocol . . . . . . . . . . . . . . . . . . . . 6
4.2. Sony Protocol . . . . . . . . . . . . . . . . . . . . . . 7
4.3. LSR Protocol . . . . . . . . . . . . . . . . . . . . . . . 9
4.4. Mobile IP . . . . . . . . . . . . . . . . . . . . . . . . 10
4.5. MSM-IP . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.6. Cellular IP, HAWAII and TIMIP . . . . . . . . . . . . . . 13
4.7. Hierarchical Mobile IP . . . . . . . . . . . . . . . . . . 14
4.8. NEMO . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.9. E2E and M-SCTP . . . . . . . . . . . . . . . . . . . . . . 16
4.10. Host Identity Protocol . . . . . . . . . . . . . . . . . . 16
4.11. Connexion and WINMO . . . . . . . . . . . . . . . . . . . 17
4.12. ILNP . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.13. Global HAHA . . . . . . . . . . . . . . . . . . . . . . . 19
4.14. Proxy Mobile IP . . . . . . . . . . . . . . . . . . . . . 20
4.15. Mobile Me . . . . . . . . . . . . . . . . . . . . . . . . 21
4.16. LISP-Mobility . . . . . . . . . . . . . . . . . . . . . . 22
5. Different Directions towards Mobility Support . . . . . . . . 23
5.1. Routing-based Approach v.s. Mapping-based Approach . . . . 23
5.2. IP Layer Indirection v.s. Mobility Exposure . . . . . . . 24
5.3. Operator-Controlled Approach v.s. User-controlled . . . . 26
5.4. Local and Global Scale Mobility . . . . . . . . . . . . . 27
6. Discussions . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.1. Backward Compatibility . . . . . . . . . . . . . . . . . . 29
6.2. Undisrupted TCP Connection . . . . . . . . . . . . . . . . 29
6.3. Interconnecting Heterogeneous Mobility Support Systems . . 30
6.4. Flat-id Based Routing . . . . . . . . . . . . . . . . . . 31
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34
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1. Introduction
This draft reports our findings from a historical survey of the
Internet mobility research and standardization efforts since the
early '90s. Our survey was motivated by two factors. First,
supporting mobility over the Internet has been an active research
area and has produced a variety of solutions; some specific solutions
have become the Internet standards. Yet new issues and new solutions
continue to arise, making one wonder how much more we are yet to
discover about the problem space as well as the solution space. The
second motivation is the rapid growth in Internet access via mobile
devices in recent years, which will inevitably lead to new Internet
application development in coming years and further underscore the
importance of Internet mobility support. We believe that a
historical review of all the proposed solutions not only can help us
better understand their commonalities and differences, but can also
help shed insight on future efforts.
In the rest of this document, we provide an overview of the mobility
support solutions from the early works to the most recent proposals.
In the process we also discuss the essential components in mobility
support, analyze the design space and try to initiate an open
discussion by sharing our understanding about the general direction
for future mobility support.
2. Terminology
This document uses a number of terms to refer to the entities or
functions that are required in mobility support. Readers are also
encouraged to scan [RFC3753] before reading this document.
Identifier
A stable piece of information that can be used to identify a mobile
node. Anything could be used as an identifier as long as it remains
unchanged when the mobile node roams around.
Locator
The IP address that indicates the mobile node's current location. It
could be the IP address of the mobile node itself, or the IP address
of the network entity that is currently serving the mobile node.
Mapping
In this document, mapping specifically means the mapping between a
mobile's identifier and it's Locator.
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Rendezvous Point
The place where the mapping is held. Some other functions such as
data forwarding may also be placed on the rendevzvous point.
Global Mobility Management
The mobility management in a global scale. It keeps the mobile's
reachability during the mobile's long distance moving, either
geographically or topologically.
Local Mobility Management
The mobility management within a topologically local domain. It
tries to keep the mobile's local movements transparent to the network
entity that manages the mobile's mobility in a global scale. It also
tries to improve the handoff performance.
Operator Controlled Mobility Management
The mobile node does not get involved in mobility management.
Instead, the network entities, which are controlled by the network
operators, do all the mobility related signalling job on behalf of
the mobile node.
User Controlled Mobility Management
The mobile node participates in the mobility management. Typically,
the mobile updates the mapping after it changes locations and refresh
the mapping at a user-defined frequency.
3. Basic Components in Mobility Support Protocols
Mobility support can be provided through through multiple different
ways. The basic question is how to make data reach a moving receiver
(a mobile in short; here we do not distinguish between mobile nodes
and mobile subnets). Whoever sending data to a mobile must be able
to identity the receiver via a piece of stable information, which
"stable" means that the information does not change as the mobile
moves. However if the sender's knowledge about the mobile does not
change while the mobile moves, some means must exist to bind that
unchanged identifier of the mobile with its dynamically changing
locations.
The above intuitive reasoning leads to the following observation--
mobility support essentially involves three basic components:
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o a stable identifier for a mobile;
o a locator, which is usually an IP address;
o and a mapping between the two.
In the next section we show that different mobility support designs
are merely different ways to choose mobile identifiers and different
approaches to provide mapping between the identifiers and the
mobiles' current IP addresses.
4. Existing Mobility Support Protocols
In this section, we review the existing mobility support protocols
roughly in time order (There are exceptions: for the sake of
convenience, we group closely related protocols together). We
briefly describe their design and point out how they implement the
three basic components defined in last section.
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Figure 1 shows a list of the protocol names and the time when they
were first proposed.
+----------------+-----+---------------+-----+
| Protocol Name |Year | Protocol Name |Year |
+----------------+-----+---------------+-----+
| Columbia |1991 | TIMIP |2001 |
+----------------+-----+---------------+-----+
| Sony |1991 | M-SCTP |2002 |
+----------------+-----+---------------+-----+
| LSR |1993 | HIP |2003 |
+----------------+-----+---------------+-----+
| Mobile IP |1996 | Connexion |2004 |
+----------------+-----+---------------+-----+
| MSM-IP |1997 | ILNP |2005 |
+----------------+-----+---------------+-----+
| Cellular IP |1998 | Global HAHA |2006 |
+----------------+-----+---------------+-----+
| HMIP |1998 | PMIP |2006 |
+----------------+-----+---------------+-----+
| HAWAII |1999 | Mobile Me |2007 |
+----------------+-----+---------------+-----+
| NEMO |2000 | WINMO |2008 |
+----------------+-----+---------------+-----+
| E2E |2000 | LISP-Mobility |2009 |
+----------------+-----+---------------+-----+
Figure 1
4.1. Columbia Protocol
This protocol was originally designed to provide mobility support in
a campus. A router named Mobile Support Station (MSS) is set up in
each wireless cell, which is the default access router for all mobile
nodes in that cell. Mobile node obtains an IP address from a special
block of IP addresses and keeps it regardless of it's current
location. Each MSS keeps a list of mobile nodes that are currently
in its cell. When a correspondent node sends a packet to a mobile
node, the packet is first routed to the closest MSS near
correspondent node. This MSS will deliver the packet directly to the
mobile node if the mobile node happens to be in its cell, or forward
the packet to the MSS that serves the mobile node. In the latter
case, a MSS sends a query message to all other MSSs in the campus in
order to find out current location of the mobile node. Each MSS in
turn checks its tracking list of mobile nodes, and sends a reply if
the target mobile node is on the list.
Here, the three basic components are:
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o Identifier: the mobile node's IP address from the special IP
block;
o Locator: the IP address of the serving MSS;
o Mapping: no explicit mapping; query flood is used to find out the
mobile's location.
The illustration of Columbia Approach is shown in Figure 2.
+---------+
| |
.------>| MAS |
| | |
| +---------+
| query
|
+--------+ query +--------+
| | -------------->| |
| MAS | <------------- | MAS |
| | reply | |
+--------+ ==============>+--------+
/\ data ||
|| ||
|| \/
+--------+ +---------+
| | | |
| CN | | MN |
| | | |
+--------+ +---------+
===>: data packets
--->: signaling packets
Figure 2
4.2. Sony Protocol
In this protocol, the IP header is modified so that each mobile node
has two IP addresses: a Virtual IP address and a conventional IP
address. Virtual IP address is the IP address that a mobile node
obtains from its home network, whereas a conventional IP address is
the IP address a mobile node obtains from its access router. Every
time the mobile node changes its location, it sends a special packet
containing the mapping between its Virtual IP address and
conventional IP address to its home network, which in turn stores the
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mapping. Routers in the middle as well as the correspondent hosts
can also cache a set of mappings for mobile nodes.
To deliver data to the mobile node, the correspondent node sets the
destination IP address the same as mobile node's Virtual IP address.
If a router along the way from correspondent node to mobile node's
home network happens to have a valid mapping for mobile node, it
modifies the destination IP address field and forwards the packets to
the new destination; otherwise, the packet will flow to mobile node's
home network, which then delivers the packets to mobile node
according to the mapping. Note that the destination IP address field
can be modified again if the packet encounters a router with newer
mapping.
The three basic components are easy to find:
o Identifier: the mobile node's Virtual IP address;
o Locator: the mobile node's conventional IP address;
o Mapping: the mapping between Virtual IP address and conventional
IP address; it could be stored in home network, as well as in
routers and end host.
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Figure 3 shows how sony protocol works.
,---. +-------+
/ \ | CN |
( Router)<====| |
+---------+ //\ / | |
| | // `---' +-------+
| | ,---. //
| | / \ //
| Home |<--- Router)//
| Network | \ / \\
| | `---' \ \\
| | \ \\,---. +-------+
| | \ / \=======>| |
| | ( Router)<------+ MN |
| | \ / | |
| | `---' +-------+
+---------+
===>: data packets
--->: location update message
Figure 3
4.3. LSR Protocol
Each mobile node has a designated router that manages its mobility,
called Mobile Router. Mobile Router assigns an IP address for each
mobile node it manages and announce reachability to those IP
addresses. Another network entity required is Mobile Access Station
(MAS), which, as indicated by its name, gives a mobile node access to
the Internet regardless of the mobile node's IP address. The mobile
node always reports the current serving MAS to its Mobile Router.
If the correspondent node and the mobile node are attached to the
same MAS, then it's easy: the MAS can just forwards packets between
the two; otherwise, the packet sent by the correspondent node would
be routed to the Mobile Router according to rules of the IP routing.
The Mobile Router exams the mappings, finds the serving MAS of the
mobile node, and inserts the loose source routing (LSR) option into
the IP header of the packet with the IP address of the MAS on it.
This way, the packet is redirect to the MAS and then to the mobile
node. After that, the mobile node reverses the LSR and replies to
the correspondent node; the correspondent node, similarly, sends the
following packets along an optimal path by reversing the LSR.
Let's identify the three basic components for this protocol:
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o Identifier: the mobile node's IP address;
o Locator: the IP address of the serving MAS;
o Mapping: the mapping between the two, managed by the Mobile
Router.
Figure 4 shows the basic operation of LSR protocol.
+---------+
| |
___________________| CN |
| | |
| +---------+
V /\
+-------+ ||
|Mobile | ||
|Router | ||
| | || Reversing LSR
+---+---+ ||
| \/
| +---------+ +----------+
| LSR Inserted | |<====>| |
+------------------->| MAS | | MN |
| |----->| |
+---------+ +----------+
-->: first data packet
==>: following data packets
Figure 4
4.4. Mobile IP
IETF begun its effort in mobility support area following the path of
the above three protocols. In 1996, the first version of Mobile IP
was finished. Later, IETF further made Mobile IPv4 [RFC3220] and
Mobile IPv6 [RFC3775] standards in 2002 and 2004 respectively.
Let's take Mobile IPv6 as an example. Each mobile node has a Home
Agent, from which it acquires its Home Address (HoA). Unlike in LSR
protocol, however, the mobile node also obtains a Care-of Address
(CoA) from its access router to the Internet. Whenever the mobile
node changes its point of attachment and gets a new CoA, it sends a
Binding Update message to notify the Home Agent about the new CoA.
The correspondent node simply sets the destination field in the IP
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header to the HoA of the mobile node, and the packets are routed to
the Home Agent since Home Agent is announcing the reachability to the
HoA. Home Agent then encapsulates the packets to mobile node's CoA
according to the mapping. If the correspondent node supports Route
Optimization, then it can also keep a mapping between the mobile
node's HoA and CoA; as specified by the protocol, the mobile node
would update the mapping in correspondent node as well. Thus the
correspondent node can tunnel packets to the mobile node directly,
bypassing the Home Agent and resulting in a shorter data path.
The three basic components in Mobile IP are:
o Identifier: the mobile node's HoA;
o Locator: the mobile node's CoA;
o Mapping: the mapping between HoA and CoA; Home Agent always holds
the mapping, and correspondent nodes can also store the mappings
if they support Route Optimization.
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Figure 5 illustrates the data path of Mobile IPv6 without Route
Optimization.
+---+-----+
|HoA|DATA |
+---+-----+ +-------+
+----------------------| CN |
| +------------------->| |
| | +-------+
| |
V |
+--------+
| Home | Mapping: HoA <=> CoA
| Agent |
| |
+--------+
|| /\
|| || +-------+
|| +====================| |
|| | MN |
+=======================>| |
+-----+---+---+ +-------+
|DATA |HoA|CoA|
+-----+---+---+
==>: Tunnel
-->: regular IP
Figure 5
4.5. MSM-IP
MSM-IP stands for Mobility Support using Multicast in IP. As one can
learn from its name, it leverages the IP multicast routing to support
the mobility. In IP multicast, a host can join a group regardless of
to which network it attaches, and all the packets sent to the group
can be received after that. Thus, as claimed by the designers of
MSM-IP, mobility is naturally supported if IP multicast problem is
solved. Note that their purpose is not to show the feasibility of
supporting mobility with current IP multicast architecture, but
rather the possibility of reusing IP multicast, if it is well
supported in the future, to solve mobility support problem.
MSM-IP [MSM-IP] assigns each mobile node a unique multicast IP
address. When the mobile node moves into a new network, it initiates
a join to its own address, which makes the multicast router in that
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subnet join the multicast distribution tree. Whoever wants to
communicate with the mobile node can just send the data to the
mobile's multicast IP address.
In order to make this approach deployable in wide-area networks, a
hierarchical location management service is also proposed. In the
location server for each mobile node, the IP address of the multicast
router that serves mobile node is stored. Thus, a new multicast
router can always query the location server to find out how to join
the multicast distribution tree.
Also note that, due to the nature of multicast routing, the mobile
node can have the new multicast router join the group to cache
packets in advance before it detaches the old one, resulting in
smoother handoff.
The three basic components here are:
o Identifier: the mobile node's multicast IP address;
o Locator: the IP address of the multicast router that is currently
serving the mobile node;
o Mapping: the mapping between the above two; this mapping is stored
in location server.
4.6. Cellular IP, HAWAII and TIMIP
This is a group of protocols that share the common idea of seting up
host route for the mobile node in the local domain. They are all
intended to work with Mobile IP as a local mobility management
protocol. We introduce them together so that it is much clearer to
show the differences by comparison.
Cellular IP [CIP] handles the local mobility in a network consists of
Cellular IP nodes, which are essentially special routers that
integrates location tracking service with routing. The mobile node
registers the local gateway node's IP address to Home Agent as the
regional CoA, and retains its assigned IP address when it roams
within the Cellular IP network. The network monitors the packets
originated from mobile node and maintains a distributed, hop-by-hop
reverse path which can be used to route packets back to the mobile
node. It utilizes paging technique from cellular network to track
the location of mobile node efficiently, by allowing mobile node to
update its location (via the way of sending dummy packets) with a
relatively long period. When a packet from correspondent node
arrives at the gateway node, controlled flooding query is initiated
if the gateway node has no idea about the exact location of mobile
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node. However, a much more precise reverse path is maintained later
when the communication between mobile node and correspondent node is
going on.
Similarly, HAWAII [HAWAII] also aims to provide efficient local
mobility support with two main differences from Cellular IP. First,
it dynamically setup routes to mobile node by installing host-based
forwarding entry in specific routers, usually the ones located in the
shortest path between the old and new serving base stations. Second,
it uses IP multicast to page idle mobile nodes when they have
incoming packets arrived at the border router and there are no
routing entries available for these addresses.
TIMIP [TIMIP], which stands for Terminal Independent Mobile IP,
integrated Cellular IP and HAWAII together. On one hand, it
refreshes the routing paths with dummy packets if there is no traffic
for the mobile node. On the other hand, handoff within a domain
results in the changes of routing tables in the routers. Besides,
the IP layer is coupled with layer 2 handoff mechanisms and special
nodes can work as Mobile IP proxies for legacy nodes that do not
support Mobile IP. Thus, as long as it roams within the domain, a
legacy node has the same degree of mobility support as a Mobile IP
capable node.
Given the similarity of the three protocols, the implementation of
the three basic components in them are listed as below:
o Identifier: the mobile node's IP address that are unchanged when
it roams within the domain;
o Locator: the network node that gives network access to the mobile
node;
o Mapping: no explicit mapping; host-based entries in local routers
instead tracks the mobiles' locations.
4.7. Hierarchical Mobile IP
This [RFC4140] is a simple extension to Mobile IP introduced in 1998.
It aims to work with Mobile IP as a local mobility support protocol.
A level of hierarchy is added to Mobile IP in the following way. A
Mobility Anchor Point (MAP) is responsible for handling the mobility
of mobile node in a local region. Simply speaking, MAP is the local
Home Agent for the mobile node. The mobile node, if it supports
Hierarchical Mobile IP (HMIP), obtains a Regional CoA and register it
to Home Agent as its current CoA; at the same time, it also obtains a
Local CoA from the subnet it attaches to. When roaming with the
region, mobile node only needs to keep the mapping between Regional
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CoA and Local CoA updated in MAP. In this way, the handoff
performance is usually better due to the short round-trip time, and
it also enhance the scalability of Mobile IP.
The basic components here are:
o Identifier: the mobile node's HoA;
o Locator: the mobile node's Local CoA;
o Mapping: the mapping between HoA and Local CoA, stored in MAP.
4.8. NEMO
It is not unusual for a group of hosts to move together. Consider
vehicles such as ships, trains, airplanes which contain networks with
a large number of nodes that need global mobility support. Mobile IP
is not efficient when handling such mobility scenarios.
Consequently, NEMO [RFC3963], as a backward compatible extension to
Mobile IP, was introduced in 2000 to handle the network mobility
support problem.
A new entity call Mobile Router (note that this is different from the
"Mobile Router" in LSR protocol) is introduced. Every mobile network
has at least one Mobile Router via which it can be accessed. Mobile
Router is a special mobile node as in original Mobile IP, with more
powerful functions. After establishing bidirectional tunnel with
Home Agent, the Mobile Router will distribute the network's pefixes
(namely Mobile Prefixes) through the tunnel to Home Agent, but never
leaks them to the infrastructure at its point of attachment (i.e. the
access router never knows that it can reach the Mobile Prefixes via
the Mobile Router). The Home Agent in turn announces the
reachability to these Mobile Prefixes. Packets to and from mobile
network always flow through the bidirectional tunnel to their
destinations.
Note that, mobility is transparent to the nodes in the moving
network.
Hence, in this protocol, the basic components are:
o Identifier: the Mobile Prefixes;
o Locator: the CoA of the Mobile Router;
o Mapping: the mapping between two, stored in the Home Agent.
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4.9. E2E and M-SCTP
E2E (End-to-End communication) gets the name from its end-to-end
architecture, and is the first formal proposal that utilizes existing
DNS infrastructure to track mobile node's current location. It works
in a conceptually simple way: Dynamic DNS update is used to refresh
the current IP address of the mobile node in DNS server; to keep the
ongoing TCP connection unaffected by mobility, a TCP Migrate option
is introduced, which enables both ends to replace the IP addresses
and ports in TCP 4-tuple on the fly. Migration security is protected
based on token and sequence number.
Inspired by E2E, M-SCTP [M-SCTP] was proposed in 2002. Similarly, it
uses Dynamic DNS to track the mobile nodes and allows both ends to
add/delete IP addresses use in SCTP in order to keep the SCTP
association during the move.
The three components hence are:
o Identifier: the domain name of the mobile node;
o Locator: the current IP address of the mobile node;
o Mapping: the DNS records kept in the Dynamic DNS server.
4.10. Host Identity Protocol
Host Identify Protocol (HIP) [RFC5201] introduces a new name space
consisting of cryptographic keys, and places a Host Identity layer
between transport and network layers. As a result, the Host
Identities, which are essentially public keys, are used to identify
the mobile nodes; while at the same time, IP addresses are only used
for routing purpose. For the convenience of reusing existing code,
Host Identity Tag, a 128-bit hash value of the Host Identity, is used
in the upper layer connections.
Dynamic DNS again can serve as the rendezvous point and holds the
mappings for HIP. Nevertheless, HIP has also specified its own
static infrastructure Rendezvous Servers, in expectation of better
rendezvous service. Each mobile node has a designated Rendezvous
Server (RVS), which tracks the current location of mobile node. When
a correspondent node wants to communicate with mobile node, it
queries DNS with mobile node's HIT to obtain the IP address of mobile
node's RVS, and sends out the first packet (I1) of Base Exchange,
which is a four-packet handshake with the purpose of establishing an
IPSec Encapsulated Security Payload and Security Association pair.
After receiving this packet, RVS will relay it to mobile node. Then
mobile node and correspondent node can finish Base Exchange and start
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communication directly. If mobile node moves to a new address, it
simples notifies correspondent node by sending HIP UPDATE with
LOCATOR parameter indicating the new IP address.
The basic components here are:
o Identifier: Host Identity or Host Identity tag of a mobile node;
o Locator: the current IP address of the mobile node;
o Mapping: the mapping between the two; either kept in Dynamic DNS
server or in Rendezvous Server.
4.11. Connexion and WINMO
Connexion [Boeing] is a service provided by Boeing that uses BGP to
support mobility. Every mobile network is assigned a /24 prefix.
When the plane moves between ground stations, which are the access
points to Internet, it withdraws its prefix from the BGP table in the
older ground station, and announce the prefix via the new ground
station. Thus, the location change of the plane is effectively
propagated to the rest of the world. However, if the number of
moving networks soars, an avalanche of BGP updates will be generated
to the whole Internet, resulting in severe global routing
instability.
WINMO [WINMO] (which stands for Wide-Area IP Network Mobility) was
later designed in 2008 to address the routing instability problem of
Connexion.
Like Connexion, WINMO also assigns each mobile network a stable
prefix, however, WINMO made the BGP updates overhead for mobile
networks orders of magnitude lower than that of Connexion by the
following two approaches. First, WINMO uses various heuristics to
reduce the propagation scope of routing updates caused by mobile
movements. Consequently, not every router may know all the mobiles'
current locations. Resolving this issue led to the second, and more
fundamental approach taken by WINMO: adoption of the basic idea from
Mobile IP. WINMO assumes that each mobile subnet is assigned a
prefix out of a small set of well defined Mobile Prefixes. These
Mobile Prefixes are announced by a small set of Aggregation Routers,
which keep track of the mobile networks. Thus one may view WINMO's
Aggregation Routers as playing the role of Home Agents in Mobile IP.
To prevent frequent iBGP routing changes due to the movement of
mobile networks within an AS, WINMO also adopts the Mobile IP way.
It introduced a Home Agent for the Mobile Prefixes within an AS: only
a designated BGP speaking router (DBR) acts as the origin of Mobile
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Prefixes; mobile networks always update their addresses of attachment
points to DBR, which resembles the binding updates in Mobile IP.
Thus, packets destined to mobile networks will be routed to DBR after
it enters the border of AS, and DBR will be responsible to tunnel
them to the right receivers. A BGP community name Packet State is
also created to eliminate the triangle routing problem caused by DBR,
in a way similar to Route Optimization, by leaking CoA to
corresponding node.
The basic components in Connexion are:
o Identifier: the prefixes of the moving network;
o Locator: the serving ground station;
o Mapping: no explicit mapping; BGP tables in different routers
collectively track the location of the mobile network.
The basic components in WINMO are:
o Identifier: the Mobile Prefixes of the moving network;
o Locator: the point of attachment to the Internet;
o Mapping: mapping between the two, kept in Aggregation Routers and
DBR.
4.12. ILNP
ILNP [ILNP] stands for Identifier/Locator Network Protocol. It
splits IPv6 address into two parts: high-order 64 bits as a Locator
field and low-order 64 bits as an Identifier field. Locator is used
for IP packet delivery, while Identifier is used by all upper layer
protocols, just as HIT in HIP. During the movement, the mobile node
updates the binding entry between Locator and Identifier via Dynamic
DNS Update; it also updates Locator to correspondent nodes with a new
ICMP Locator Update message.
The basic components in ILNP are clear:
o Identifier: the low-order 64 bits of the mobile's IP address;
o Locator: the high-order 64 bits of the mobile's IP address;
o Mapping: the mapping between the two, kept in Dynamic DNS server
and correspondent node.
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4.13. Global HAHA
Global HAHA [HAHA], first proposed in 2006, aims to eliminate the
triangle routing problem in Mobile IP and NEMO by distributing Home
Agents in a wide area. A set of Home Agents joins an IP anycast
group and forms an overlay network. The same home prefixes are
announced by all the Home Agents at different locations. Each mobile
node can register with any Home Agent that is closest to it. The
Home Agent that accepts the binding request of mobile node, namely
the primary Home Agent, is responsible to notify all other Home
Agents in the overlay network, so that the binding information
databases in all Home Agents are always synchronized.
Packets from correspondent node are delivered to the nearest Home
Agent by anycast routing. This Home Agent then forwards these
packets through the overlay network to the target Home Agent that is
currently serving mobile node, which will finally deliver the packets
to mobile node after striping the tunneling headers. In the reverse
direction, this approach works exactly the same as Mobile IP. If the
distribution of Home Agents are carefully designed, the triangle
routing problem is solved naturally without Route Optimization.
Thus, the basic components in Global HAHA are:
o Identifier: the HoA of the mobile node;
o Locator: the CoA of the mobile node (in the primary Home Agent);
the IP address of primary Home Agent (in other Home Agents).
o Mapping: the mapping between the two.
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The data flow in Global HAHA is shown in Figure 6.
+------+ +------+ +-----+
| HA |_____________| HA | | |
| | | | | CN |
+--+---+ .'+++----+ +-----+
| .' || /\
| .' || ||
| .-' || ||
| .' || ||
+--+---+.' || ||
| |<==============+ ||
| HA |==============================+
+-++---+
|| /\
\/ ||
+---++-+ ===>: data flow
| | ----: HA overlay network
| MN |
+------+
Figure 6
4.14. Proxy Mobile IP
Proxy Mobile IP [RFC5213] was proposed in 2006. The two new types of
network nodes, Local Mobility Anchor (LMA) and Mobile Access Gateway
(MAG), together handle the local mobility without interference from
mobile node. LMA serves as a local Home Agent and assigns a local
Home Network Prefix for each mobile node. MAGs monitor the attaching
and leaving events of mobile node, and performs Proxy Binding Update
to LMA on behalf of mobile node during handoff. After the success of
binding, LMA updates mobile node's Proxy-CoA with the IP address of
the MAG that is currently serving mobile node. The MAG then emulates
mobile node's local Home Link by advertising mobile node's local Home
Network Prefix in Router Advertisement. When roaming in the PMIP
domain, mobile node always obtains its local Home Prefix, and
believes that its on local Home Link.
Here, the basic components are:
o Identifier: the Home Network Prefix of a mobile node;
o Locator: the Proxy-CoA, which is the IP address of the current
MAG;
o Mapping: the mapping between the two kept in LMA.
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4.15. Mobile Me
Mobile Me [BTMM] is a pragmatic approach to support mobility and has
been deployed as real-world commercial service since 2007 (with Mac
OS leopard release). In this approach, Apple provides DNS server for
all Mobile Me users. Each mobile node performs secure DNS update to
dynamically refresh its current location. In the DNS database, an
AAAA RR represents mobile node's identifier, which is an IPv6
address, and a SRV [RFC2782] RR records mobile node's current
location with IPv4 address, and port number in case of NAT traversal.
Every node establishes long-lived query (llq) with DNS, which means
that the DNS will automatically notify the node if the answer to the
query changes. In this way, the node only need to refresh the llq
after a certain period, avoiding the frequent queries for the up-to-
date location of the other communicating end host. A node uses the
IPv6 address in all applications. It then uses UDP/IPv4
encapsulation to deliver the IPv6 packets according to the DNS reply.
Note that the IPv6 address is only for identification purpose and not
used in routing. In fact, it could be any form of identifier (e.g.
HIT in HIP, domain name, etc.); IPv6 address was chosen simply
because the designer do not want to change the IP header and cause
problems of reusing existing code.
Mobile ME is perhaps the first large-scale commercial host mobility
support in Internet with millions of subscribers as of today. It is
simple and requires little budget to deploy. However, it does not
fully support mobility yet.
We can also list the basic components for Mobile Me:
o Identifier: the IPv6 address of a mobile node;
o Locator: the IPv4 address (and port in the case of NAT) of a
mobile node;
o Mapping: the mapping between them, kept in Dynamic DNS server.
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Figure 7 shows an example communication scenario of Mobile Me.
+----------+ dynamic DNS update
llq | |<------------------+
+-------->| DNS | |
| | | <------------+ |
| +----------+ llq | |
| | |
| | |
V V |
+-------+ ,---. +-----+-+
| | UDP/IPv4 / \ | |
| Mac1 |<=============>( NAT )<---->| Mac2 |
| | tunnel \ / | |
+-------+ `---' +-------+
Figure 7
4.16. LISP-Mobility
LISP-Mobility[LISP-Mobility] is a relatively new idea, in which the
designer hopes to support mobility via LISP[LISP] functionality.
Conceptually, however, it is very similar to some protocols we have
mentioned so far, such as ILNP and Mobile IP. Light-weight Ingress
Tunnel Router and Egress Tunnel Router are implemented on each mobile
node, encapsulating/decapsulating the packets to and from the mobile
node. Each mobile node is assigned a static Endpoint ID, which is
used in upper layer connections, as well as a pre-configed Map-
Server. When a mobile node roams into a network and obtains a new
Routing Locator, it updates its Routing Locator set in the Map-Server
and also in the Ingress Tunnel Routers or Proxy Tunnel Routers of the
correspondent nodes. Thus the correspondent node can always learn
the location of the mobile node via the resolution of its Endpoint
ID, and the data would always travel through the shortest path. Note
that both Endpoint IDs and Routing Locators are essentially IP
addresses.
It is trivial to list the basic components in this protocol:
o Identifier: the Endpoint ID of the mobile node;
o Locator: the Routing Locator the mobile node;
o Mapping: the mapping between them, kept in Map-Server or the
Ingress Tunnel Router of the Correspondent.
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5. Different Directions towards Mobility Support
What would be the best way to provide global scale ubiquitous
mobility support for an essentially unlimited number of mobile
devices with unknown future applications? No one has the crystal
ball that clearly shows the future. Nevertheless, we identified
several different directions towards mobility support by studying
various existing protocols. We believe a thorough understanding of
these directions will help us make wise decisions when designing
mobility support system for the future.
5.1. Routing-based Approach v.s. Mapping-based Approach
All existing mobility support designs can be broadly classified into
two basic approaches.
The first one is to support mobility through dynamic routing, in
which case there is not explicit "mapping" component as we discussed
in last section. In such designs, a mobile keeps its IP address
regardless of its location changes, thus the IP address can be used
both to identify the mobile and to deliver packets to it. As a
result, these designs do not require explicit mapping function.
Rather, the routing system must continuously keep track of mobile's
movements and reflect their current positions in the network on the
routing table, so that at any given moment packets carrying the
(stable) receiver's IP address can be delivered to the right place.
Supporting mobility through dynamic routing is conceptually simple as
it does not require a mapping function; it can also provide robust
and efficient routing, assuming that the routing system can keep up
with the mobile movements. However, because the whole network must
be informed of every movement by every mobile, this approach is
feasible only in small scale networks with a small number of mobiles;
it does not scale well in large networks or for large number of
mobiles.
The second approach to mobility support is to provide a mapping
between a mobile's stable identifier and its dynamically changing IP
address. Instead of notifying the world on every movement, a mobile
only needs to update a single binding location about its location
changes. In this approach, if one level of indirection at IP layer
is used, as in the case of Mobile IP, it has a potential side effect
of introducing triangle routing; otherwise, if the two end nodes need
to be aware of each other's movement, which means that both ends have
to support the same mobility protocol.
Yet there is the third case in which the protocols combine the above
approaches, in the hope of keeping the pros and eliminating some cons
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of the two. WINMO is a typically protocol in this case.
In Figure 8 we show the classification of the existing protocols
according to the above analysis.
_.--------.
,-'' `--.
,-' `-.
,' +----+ `.
,-------. / +----+ |ILNP| +----+ \
,+--------+ `-,' |Sony| +----+ |HMIP| `.
,' |Columbia| / `. +----+ +----+ \
,' +--------+ / `. +---+ +------+ \
/ ; \ +----+ |E2E| |M-SCTP| :
/ +---------+ ;+-----+ \ |NEMO| +---+ +------+ :
; |Connexion| ; |WINMO| : +----+ +---------+ :
; +---------+ | +-----+ : +---+ |Mobile Me| |
; +-----+ | : +---+ |HIP| +---------+ |
| |TIMIP| | +------+ | |LSR| +---+ |
: +-----+ : |MSM-IP| ; +---+ +---------+ ;
: +------+ :+------+ ; +----+ |Mobile IP| ;
: |HAWAII| : ; |PMIP| +---------+ ;
\ +------+ \ / +----+ +-----------+ /
\ +-----------+ \ / |Global HAHA| /
`. |Cellular IP| `. ,' +-----------+ ,'
`+-----------+ ,' +-------------+ /
`-. ,-' `. |LISP-Mobility| ,'
`-------' '-+-------------+ ,-'
`--. _.-'
`--------''
Routing-based Mapping-based
Figure 8
5.2. IP Layer Indirection v.s. Mobility Exposure
One critical choice in mapping-based systems is the choice of
rendezvous point, i.e. where to locate the mapping function and
whether or not the rendezvous point provides other functions except
storing mapping information.
Several mobility support designs provide the mapping function at IP
layer, which both the identifier and the current location of a mobile
are represented by IP addresses. In this approach, the IP address
which is used as the mobile's identifier points to the rendezvous
point that keeps track of the mobile's current location. Such
designs offer an advantage of hiding the mobility from correspondent
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nodes through one level of indirection. When a correspondent node
sends packets to an IP address which is a mobile's identifier, the
packets will be delivered to the location where the mapping
information of the mobile is kept (e.g. the Home Agent in Mobile IP),
and later they will be forwarded to the mobile's current location via
either encapsulation or destination address translation.
Although this one level of indirection at IP layer makes mobility
transparent, it has a potential side effect of introducing triangle
routing: the path taken by the packets via the rendezvous point can
be much longer than the direct path between the correspondent and the
mobile's current location. Besides, as increasing number of mobile
devices are connected to Internet (why hide mobility to them), some
mobility solutions have opted to expose mobility to both ends and let
them communicate directly. One common approach taken by these
protocols is to use DNS for the mapping function to keep track of
mobiles' current locations. Mobiles use dynamic DNS updates to keep
their DNS servers updated with their current locations. This
approach re-utilizes the DNS infrastructure, which is ubiquitous and
quite reliable, and makes the mobility support protocol simple and
easy to deploy.
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Figure 9 shows the two categories of mobility protocols according to
their choices of rendezvous point. Note, however, protocols like
Mobile IP can also expose mobility to the other end if Route
Optimization is supported.
,-------.
,-' `-.
,' +---------+ `. ,-----.
/ |Mobile IP| \ ,-' `-.
,' +---------+ `. / +----+ \
; : ,' |ILNP| `.
; +----+ : ; +----+ :
/ |HMIP| +-----------+ \ ; +------+ :
; +----+ |Global HAHA| : / +---+ |M-SCTP| \
| +-----------+ | ; |E2E| +------+ :
| +---+ | | +---+ +---------+ |
| |LSR| +----+ | | |Mobile Me| |
: +---+ +----+ |NEMO| ; | +---+ +---------+ |
\ |Sony| +----+ / : |HIP| ;
: +----+ ; \ +---+ /
: ; : +-------------+ ;
`. +----+ ,' : |LISP-Mobility| ;
\ |PMIP| / `. +-------------+'
`. +----+ ,' \ /
'-. ,-' `-. ,-'
`-------' `-----'
IP Layer Indirection Mobility Exposure
Figure 9
5.3. Operator-Controlled Approach v.s. User-controlled
At the time when this draft was written, the largest global mobility
support today is provided by cellular networks, using a service model
that bundles together the device control, network access control and
mobility support. The tremendous success of cellular market speaks
loudly that the current cellular service model is a viable one, and
is likely to continue for foreseeable future. As a result, there is
a strong advocate in IETF that we continue the cellular way of
handling mobility, i.e. the mobile do not necessarily need to
participate in the mobility related signaling; instead, the network
entities deployed by the operators will take care of any signaling
process of mobility support. A typical example is Proxy Mobile IP,
in which LMA work together with MAGs, assuring that the mobile always
obtains its Home Prefixes as long as it roams within the domain.
The main reason for this approach is perhaps backward compatibility.
By not requiring the participation of mobiles in control signaling
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process, it avoids any changes to the mobile nodes, which essentially
means that the mobile nodes can stay simple and all the legacy nodes
can obtain the same level of mobility services as the most fancy
mobile devices. According the the claim of 3G vendors and operators,
this is a key aspect as they learn from their deployment experience.
On the contrary, most mobility support protocols so far focus on
mobility support only. And the mobile nodes typically need to update
their locations by themselves to the rendezvous points chosen by the
user. In these protocols, only the node implementing them can
benefit from mobility support. However, the users get more
flexibility and freedom, e.g. they can choose whatever mobility
services available as long as their software support that protocol,
and they can also tune the parameters to get the services that are
most suitable to them.
Which one is better? No one knows. We expect them to co-exist as
they do today. However, as the technology advances and the hand-hold
devices becomes more and more powerful, the latter approach seems to
be a much simpler way to move forward with.
5.4. Local and Global Scale Mobility
The works done on mobility management can also be divided according
to their scale into two categories: local mobility management and
global mobility management.
Global mobility management is typically supposed to support mobility
of unlimited number of nodes in a geographically as well as
topologically large area. Consequentially, it pays a lot of
attentions to the scalability issues. For the availability concern,
it also tries to avoid failure of single point.
Local mobility management on the other hand is designed to work
together with global mobility management, and thus focuses more on
performance issues, such as shorten handoff delay, reduce handoff
loss, short local data path and etc. Since it is typically used in a
small scale with no-so-large number of mobile nodes, sometimes the
designers can use some fine-tune mechanisms that are not scale with
large network (such as host route) to improvement performance. As a
side effect of local mobility management, the number of location
updates sent by mobile nodes to their global rendezvous points is
substantially reduced. Thus, the existence of local mobility
management also contribute to the scalability of global mobility
management.
One problem of the local mobility management is that it often
requires many infrastructure support, such as MAGs in PMIP, or MAPs
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in HMIP. These kind of local devices are essentially required in all
small domains, which can be a huge investment.
Neverthe less, the mobility managements in two scale make it possible
for designers to design protocols that fit into specific user
requirements; it also enables the gradual deployment of local
enhancement while not losing the ability of global roaming. The co-
existence of the two seems to be a right choice in the foreseeable
future.
Figure 10 shows the classification of the studied protocols according
to their serving scale.
_.------------.
,-------. _.-'' `---.
,-+--------+`-. ,-'' +---+ +---------+ `--.
,' |Columbia| `,' |HIP| |Mobile IP| `.
,' +--------+ ,' `. +---+ +---------+ `.
/ +----+ / \ \
/ |PMIP| ,'+-----+\ +---+ +------+ +----+ `.
; +----+ ; |WINMO| : |E2E| |MSM-IP| |NEMO| :
;+----+ ; +-----+ : +---+ +------+ +----+ :
; |HMIP| +-----+ ; : :
| +----+ |TIMIP| +-----------+| +------+ +---+ |
: +-----+ |Global HAHA|; |M-SCTP| |LSR| +----+ ;
: +-----------++-----------+ +------+ +---+ |ILNP| ;
: |Cellular IP| : ; +---------+ +----+ ;
\ +-----------+ `. / +----+ |Mobile Me| ,'
\ +------+ \ / |Sony| +---------+ /
`. |HAWAII| `. ,' +----+ +---------+ ,'
`. +------+ ,'. |Connexion| ,'
`-. ,-' `--. +---------+ _.-'
`-------' `---. _.-''
`------------''
Local Mobility Management Global Mobility Management
Figure 10
6. Discussions
In last section we discussed the different directions towards
mobility support. We now turn our attention to identify both new
opportunities and remaining open issues in providing global scale
mobility support for unlimited number of online mobility devices. We
are not trying to identify the solutions to these issues, but rather,
the goal is to share our opinions and to initiate an open discussion.
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6.1. Backward Compatibility
The Internet has been running for more than two decades, and the
scale of the Internet gets so large that it is impossible to upgrade
the whole system over night. As a result, it is not possible for a
mobility support system designer to overlook this problem: how
important the backward compatibility is?
As one can expect, different designers have different opinions.
Some assume that the other end is by a large chance also mobility
capable (as of today, more people are accessing the Internet via
mobile devices than a desktop), and thus do not provide backward
compatibility at all; but as a tradeoff, the system design becomes
much simpler and the data path is always the shortest one. The
examples of protocols fall into this categories could be HIP, Mobile
Me and etc.
Some take a more conservative approach. They do not want to lose the
ability of communicating with legacy nodes during the movement, and
they also do not want the rest of the world (meaning, the static
nodes) to be bothered by the mobility of mobile nodes. Thus they add
a level of indirection at IP layer, and hide the mobility of the
mobile nodes. The mobile node thus can benefit from mobility support
even when communicating with legacy node. And when the other end
also supports mobility, it is also possible to achieve the shortest
data path, but with additional complexity. The Mobile IP related
protocols fall into this category.
Others want to cater to the inertness of the Internet (and the users)
and keep everything status quo, at least from the users' point of
view. And thus they take backward compatibility more serious and
hide the mobility completely, even for the mobile node itself. Proxy
Mobile IP represents this approach.
We all know that backward compatibility is important in system
design. But how important is that? How much effort should we make
for this issue? At least for now, the answer is not clear yet.
6.2. Undisrupted TCP Connection
TCP is the most widely used transport layer protocol in the Internet,
and the majority of the data traffic today is TCP traffic. In order
for the users to benefit from the mobility support, it is of vital
importance to keep the established TCP connections undisrupted during
the mobile's movement.
Basically there are three approaches to do this: 1) make the mobile
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node keep its IP address regardless of its point of attachment to the
Internet; 2) add a level of indirection and use a static IP address
in the TCP pseudo header; 3) modify the TCP protocol.
The routing-based protocols typically make the mobile node keep a
stable IP address and thus the first approach is the right one for
them. Proxy Mobile IP, however, also takes the first approach. No
overhead or complexity is introduced in order to maintain TCP
connections in this approach.
A large number of protocols take the second approach. This approach
could be achieved via a forwarding agent, as in the case of Mobile
IP; or the two end nodes can directly set up a tunnel and use a
stable IP address in TCP pseudo headers, as in the case of Mobile Me.
In order to maintain the TCP connections undisrupted via this
approach, an extra IP header is appended to every data packets, and
the possible forwarding agent also introduce problems such as single
point of failure, triangle routing, bottleneck of bandwidth and
processing power, etc.
A few protocols also take the third approach. In this approach, the
TCP protocol itself is modified, either to 1) put an identifier
rather than an IP address as connection id or to 2) allow the TCP
connections to change the IP address of both ends. HIP, ILNP uses
designated ID in TCP layer (they can be in the format of IP address
though), while E2E allows using dynamically changing IP addresses.
This approach faces the difficulty of changing the TCP protocol
itself, which will introduce serious backward compatibility problem.
What is the best choice for the future? Although it seems that most
people favor the second approach, whether or not it is the right
direction is still uncertain.
6.3. Interconnecting Heterogeneous Mobility Support Systems
As our survey suggests, multiple solutions of mobility support are
already running today, and it is almost for sure that the mobility
support systems in the future are going to be heterogeneous.
However, as of today, the inter-operation between different protocols
is still problematic. For example, when a mobile node supporting
Mobile IP only wants to communicate with another mobile with only HIP
support, both of them can not benefit from mobility support.
This situation reminds us the days before IP were adopted. In that
time, the hosts in different networks are not able to communicate
with each other. It is the IP that merged the networks and created
the Internet, where each host can freely communicate with any other
host. Is it necessary to introduce something like IP to the mobility
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support in the future? Is it possible to design an architecture, so
that it glues all the mobility support systems together? We believe
the answer to both questions is yes.
The basic idea for the solution is simple, as the famous quote says:
"Every problem in Computer Science can be solved by adding a level of
indirection. However, the devil is in the details and we still need
to figure that out.
6.4. Flat-id Based Routing
Up until now, all our discussions are based on an implication that
the underlying global routing systems is not fundamentally changed,
that is, the location of the mobile node is always indicated by an IP
address. However, recently there are a lot of works that challenge
this "classic" idea. Flat-id based routing schemes [VRR] [ROFL][VIR]
are especially popular.
With flat-id based routing, mobility as well as multihoming are
naturally incorporated. And most of these protocols are
mathematically elegant. However, although the notion of flat-id
space has been widely adopted in peer-to-peer network, it seems that
the Internet is not going to undertake such revolutionary changes
(from hierarchical IP Address based routing to flat-id based routing)
in the foreseeable future due to the inertness of the extremely huge
system and also the backward compatibility problem.
Nevertheless, whether or not flat-id based routing will be a good
solution to the mobility support problem, or perhaps more generally,
the routing problem is not determined yet.
7. References
[BTMM] Nakamoto, R., Zhu, Z., Lau, D., and B. Allen,
"Understanding Apple's Back to My Mac Service", UCLA CS217
Project, 2009.
[Boeing] Andrew, L., "A Border Gateway Protocol 4 (BGP-4)",
Boeing White Paper, 2006.
[CIP] Valko, A., "Cellular IP: A New Approach to Internet Host
Mobility", ACM SIGCOMM, 1999.
[E2E] Snoeren, A. and H. Balakrishnan, "An End-to-End Approach
to Host Mobility", ACM Mobicom, 2000.
[HAHA] Wakikawa, R., Valadon, G., and J. Murai, "Migrating Home
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Agents Towards Internet-scale Mobility Deployment",
ACM CoNEXT, 2006.
[HAWAII] Ramjee, R., Varadhan, K., and L. Salgarelli, "HAWAII: A
Domain-based Approach for Supporting Mobility in Wide-are
Wireless Networks", IEEE/ACM Transcations on Networking,
2002.
[I-TCP] Bakre, A. and B. Badrinath, "I-TCP: Indirect TCP for
Mobile Hosts", Proceedings of the 15th International
Conference on Distributed Computing System, 1995.
[ILNP] Atkinson, R., "An Overive of the Identifier-Locator
Network Protocol", Research Note, 2005.
[LISP] Farinacci, D., Fuller, V., Lewis, D., and D. Meyer,
"Locator/ID Separation Protocol (LISP)",
draft-farinacci-lisp-12.txt (work in progress), 2009.
[LISP-Mobility]
Farinacci, D., Fuller, V., Lewis, D., and D. Meyer, "LISP
Mobility Architecture", draft-meyer-lisp-mn-00.txt (work
in progress), 2009.
[LSR] Bhagwat, P. and C. Perkins, "A Mobile Networking System
Based on Internet Protocol (IP)", Mobile and Location-
Independent Computing Symposium, 1993.
[M-SCTP] Xing, W., Karl, H., and A. Wolisz, "M-SCTP: Design and
Prototypical Implementaion of An End-to-End Mobility
Concept", 5th Intl. Workshop on the Internet Challenge,
2002.
[MSA] Ioannidis, J., Duchamp, D., and G. Maguire, "IP-based
Protocols for Mobile Internetworking", ACM SIGCOMM CCR,
1991.
[MSM-IP] Mysore, J. and V. Bharghavan, "A New Multicast-based
Architecture for Internet Host Mobility", ACM Mobicom,
1997.
[MSOCKS] Ferguson, P. and D. Senie, "MSOCKS: An Architecture for
Transport Layer Mobility", IEEE INFOCOM, 1998.
[RFC2002] Perkins, C., "IP Mobility Support", RFC 2002,
October 1996.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
Zhu, et al. Expires April 22, 2010 [Page 32]
Internet-Draft Mobility Survey October 2009
Specifying the Location of Services (DNS SRV)", RFC 2782,
2000.
[RFC3007] Willington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, 2000.
[RFC3220] Perkins, C., "IP Mobility Support for IPv4", RFC 3220,
2002.
[RFC3753] Manner, J. and M. Kojo, "Mobility Related Terminology".
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "IP Mobility
Support in IPv6", RFC 3775, 2004.
[RFC3963] Devarapalli, V., Wakikawa, R., Peterson, A., and P.
Thubert, "Network Mobility (NEMO) Basic Support Protocol",
RFC 3963, 2005.
[RFC4140] Soliman, H., Castelluccia, C., Malki, K., and L. Bellier,
"Hierarchical Mobile IPv6 Mobility Management (HMIPv6)",
RFC 4140, 2005.
[RFC5201] Nikander, P., Moskowitz, R., Jokela, P., and T. Henderson,
"Host Identity Protocol", RFC 5201, 2008.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, 2008.
[ROFL] Caesar, M., Condie, T., Kannan, J., Lakshminarayanan, K.,
Stoica, I., and S. Shenker, "ROFL: Routing on Flat
Labels", ACM Sigcomm, 2006.
[Sony] Teraoka, F., Yokote, Y., and M. Tokro, "A Network
Architecture Providing Host Migration Transparency",
ACM SIGCOMM CCR, 1991.
[TIMIP] Grilo, A., Estrela, P., and M. Nunes, "Terminal
Independent Mobility For IP", IEEE Communications
Magazine, 2001.
[VIR] Lu, G., Jain, S., Chen, S., and Z. Zhang, "Virtual Id
Routing", ACM MobiArch, 2008.
[VRR] Caesar, M., Castro, M., Nightingale, E., O'Shea, G., and
A. Rowstron, "Virtual Ring Routing: Network Routing
Inspired by DHTs", ACM Sigcomm, 2006.
[WINMO] Hu, X., Li, L., Mao, Z., and Y. Yang, "Wide-Area IP
Zhu, et al. Expires April 22, 2010 [Page 33]
Internet-Draft Mobility Survey October 2009
Network Mobility", IEEE INFOCOM, 2008.
Authors' Addresses
Zhenkai Zhu
UCLA
4805 Boelter Hall, UCLA
Los Angeles, CA 90095
US
Phone: +1 310 993 7128
Email: zhenkai@cs.ucla.edu
Ryuji Wakikawa
TOYOTA ITC
465 Bernardo Avenue
Mountain View, CA 94043
US
Email: ryuji@jp.toyota-itc.com
Lixia Zhang
UCLA
3713 Boelter Hall, UCLA
Los Angeles, CA 90095
US
Phone: +1 310 825 2695
Email: lixia@cs.ucla.edu
Zhu, et al. Expires April 22, 2010 [Page 34]
