Transcript Mobile IP

Mobile Systems
Presented by:
Eddy & Kevin
Directed by:
Professor Joung
Introduction

Computing and communications are
becoming inseparable synergistic
activities independent of time and
location, i.e., with mobility.
Computation
Mobility
Mobile
Computing
Communication
Introduction

3 components:
Computation includes the computing devices with
their dramatically increasing processing power.
Communication systems include the different wireless
and wired networks and span a wide range of
bandwidths.
Mobility is an aspect of user behavior.
Link Layer Consideration

A great deal of attention is paid to
methods for establishing links between
mobile computers (or mobile nodes)
and base stations (or access points)
that make use of both wired and
wireless communications.
Link Layer Consideration
Hidden terminals
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Having multiple computers in a cell can give rise to
the hidden terminal problem.
Under this problem, the simultaneous transmission of
two mobile nodes can’t hear each other but are both
received by the same access point or destination
station.
Link Layer Consideration

Hidden terminal problem
Link Layer Consideration

Hidden terminal problem

Possible solution #1
A sender ask to transmit its data(e.g., by a RTS, or
request to send), and then waits until the intended
receiver grants permission(e.g., CTS, or clear to
send).
Link Layer Consideration

Hidden terminal problem

Possible solution #2

Applying CDMA (or code division multiple access)
schemes, we assign the minimum number of
orthogonal codes to eliminate the hidden terminal
interference.
Note: The receivers are code-agile, namely, able to
communicate over several codes, in which case it is
a transmitter-oriented code assignment (TOCA)
scheme.
Link Layer Consideration
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Code Assignment for hidden terminal
interference ~ in a ring network
Link Layer Consideration

Code Assignment for hidden terminal
interference ~ in binary tree networks
Network Layer Consideration

IP traditionally makes next-hop
decisions based on the IP address of
the destination, but it is now modified to
tunnel packets to a mobile node at it’s
current point of attachment to the
Internet.
Network Layer Consideration
Tunneling
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A tunnel is the path followed by a first packet while it
is encapsulated within the payload portion of a
second packet.
mobile node: a node which can change its point-ofattachment to the Internet from one link to another by
using only its (permanent) IP home address
home agent: a router with an interface on the mobile
node’s home link
foreign agent: a router on a mobile node’s foreign link
Network Layer Consideration
Tunneling
Network Layer Consideration
Triangle Routing vs. Optimized Routing
Network Layer Consideration
Triangle Routing
Packets sent by a correspondent to a mobile node
are routed first to the home agent and then tunneled
to the care-of address.
Packets sent by the mobile node are routed directly
to the correspondent, thus forming a triangle.
Optimized Routing
The mobile node informs correspondents of its careof address and have them tunnel directly bypassing
the home agent, in so-called binding updates.
Transport Layer Consideration

Several mechanisms in TCP perform
as well, and others need modified to
accommodate themselves to the mobile
system.
Transport Layer Consideration
Asymmetry

The mobile node may send directly to some Internet
nodes but receive by another routing path around the
tunneling, that causes the different data rate.
The ACK can’t be supplied normally.
Transport Layer Consideration
Congestion
The problem comes when errors are mistaken as
evidence of congestion.
The packets should be retransmitted right away,
but the window-based self-clocking mechanism
causes a slowdown in the data rate!
Transport Layer Consideration
The WTCP approach
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Rate-based transmission control
Inter-packet delay as the main
mechanism for transmission control
Predicting the cause of packet loss
and adjusting transmission rate
accordingly
Transport Layer Consideration
The WTCP approach
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Performing transmission control
computation at the receiver
Variable granularity rate adjustment
Start-up behavior
Transport Layer Consideration
Handoff
Whenever the process requires the transfer of state
information from the old connection point to the new
one, a handoff has to occur.
Issues: any kinds of packets can be lost during the
handoff period.
Transport Layer Consideration
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Before the handoff
Transport Layer Consideration
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Handoff between 2 foreign networks
Transport Layer Consideration
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After the handoff
Transport Layer Consideration
Handoff

Possible solution:
We may allow the data packets to be stored at the
foreign agent; thus when a handoff occurs, the old
foreign agent would forward all the stored packets to
the new foreign agent.
Enter the Mobile IP
Introduction
How does Mobile IP work ??
 OSI Reference Model
 Why Mobile IP??

– What happens when a node changes link??
– The existing solution to the problem.

What problems does Mobile IP solve??
How does Mobile IP work ??

A change-of-address postcard to everyone
– These postcards would have to be sent every time
you moved to a new location.
– You would have to be sure to send a postcard to
every conceivable correspondent.
– Some prankster form sending bogus change-ofaddress cards to your correspondents in order to
redirect your mail to some undesirable person or
place.
How does Mobile IP work ??

Leave a forwarding notice at your home
post office
– Arrange with your previous post office to
forward any subsequently arriving mail to
your current post office.
– Inform your correspondents that if they do
not see a reply form you within a
reasonable period of time then they should
resend their letter to you.
How does Mobile IP work ??

Letter
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Forwarding
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Internet Protocol data
packet
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Tunneling
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Mobile IP-enhanced
router
Post office
How does Mobile IP work ??
Most network protocols were designed
back in the days when almost all
computers did not move very often.
 Mobile IP

– Allows a mobile computer to change its
location without restarting its applications
and without disrupting any ongoing
communication.
OSI Reference Model
IP Network
Why Mobile IP??
Why Mobile IP??

The existing solution to the problem
– Host-Specific Routes
– Changing IP Address
– Some existing link-layer solutions
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CDPD
IEEE 802.11
Host-Specific Routes
Host-Specific Routes
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Minimally, host-specific routes must be
propagated to all nodes along the path between
a mobile node’s home link and its foreign link.
Some (in the worst case all) of these routes
must be updated every time the node moves
from one link to another.
We expect millions of mobile nodes to be
operation in the Internet within the coming years.
Thus, we must multiply the number if hostspecific routes suggested by the first two items
by a million-or-so in order to determine the full
impact of this solution.
Host-Specific Routes
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Unless host-specific routes are propagated to
a much larger set of routes than the minimal
set described in the first item above, then the
Internet’s ability to route around isolated node
and link failures is negated by host-specific
routing.
There are serious security implications to
using host-specific routes to accomplish node
mobility in the Internet, which would require
authentication and complicated key
management protocols to address.
Changing IP Address
Terminate any ongoing communications
at the old link and then restart them at
the new link
 Mobility vs. Nomadicity

Some existing link-layer solutions

CDPD (Cellular Digital Packet Data)
– Limitations in the media over which they
can run

IEEE 802.11
– Limitations in geographic applicability
What problems does Mobile IP solve??
If a node moves from one link to
another without changing its IP address,
it will be unable to receive packets at
the new link.
 If a node changes its IP address when it
moves, it will have to terminate and
restart any ongoing communications
each time it moves.

Mobile IP
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Mobile IP was produced by the IP Routing for
Wireless/Mobile Hosts working group of the
Internet Engineering Task Force (IETF),
which was formed in June 1992.
Mobile IP was approved by the Internet
Engineering Steering Group (IESG) in June
1996 and published as a Proposed Standard
in November 1996.
Mobile IP

The Mobile IP standards documents include the
following Request For Comments (RFCs):
– RFC 2002, which defines the Mobile IP protocol itself
– RFC 2003,2004, and 1701,which define three respective
types of tunneling used in Mobile IP
– RFC 2005, which describes the applicability of Mobile IP
– RFC 2006, which defines the Mobile IP Management
Information Base(MIB).The Mobile IP MIB is a collection of
variables within a node which implements Mobile IP that can
be examined or configured by a manager station using
version 2 of the Simple Network Management Protocol
(SNMPv2) [RFC 1905]
Mobile IP
What problems does Mobile IP solve??
 The scope of the Mobile IP solution
 The requirements for Mobile IP
 The design goals for Mobile IP
 Where does Mobile IP reside??
 At a 10,000-foot level, how does Mobile
IP work??

What does Mobile IP solve??

Mobile IP is a solution for mobility on
the global Internet which is scalable,
robust, secure, and which allows nodes
to maintain all ongoing communications
while changing links. Specifically,
Mobile IP provides a mechanism for
routing IP packets to mobile nodes
which may be connected to any link
while using their permanent IP address.
The scope of the Mobile IP solution

Mobile IP is a network-layer solution to
node mobility in the Internet.
– Mobile IP accomplishes its task by setting
up the routing tables in appropriate nodes,
such that IP packets can be sent to mobile
nodes not connected to their home link.

Mobile IP is completely independent of
the media over which it runs.
The scope of the Mobile IP solution
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Heterogeneous mobility
– The ability of a mobile node to move between
different media types while retaining its ability to
communicate.

Homogenous mobility
– CDPD and IEEE 802.11

Mobile IP is unique in its ability to
accommodate heterogeneous mobility in
addition to homogenous mobility.
The requirements for Mobile IP


A mobile node must be able to communicate
with other nodes after changing its link-layer
point-of-attachment to the Internet.
A mobile node must be able to communicate
using only its home (permanent) IP address,
regardless of its current link-layer point-ofattachment to the Internet.
The requirements for Mobile IP
A mobile node must be able to
communicate with other computers that
do not implement the Mobile IP mobility
functions.
 A mobile node must not to be exposed
to any new security threats over and
above those to which any fixed node on
the Internet is exposed.

The design goals for Mobile IP

To make Mobile IP suitable for use over a
wide range of wireless links and the
increasing number of nodes using it.
– Make the size and the frequency of these updates
as small as possible.
– Make it as simple as possible to implement mobile
node software.
– Avoid solutions which require mobile nodes to use
multiple addresses, or which require large pools of
address to be made available for use by mobile
nodes,unless absolutely necessary.
Where does Mobile IP reside??

Mobile Node
– A node which can change its point-ofattachment to the Internet from one link to
another while maintaining any ongoing
communications and using only its
(permanent) IP home address.
Where does Mobile IP reside??

Home Agent
– A router with an interface on the mobile node’s
home link which:
a.the mobile node keeps informed of its current location, as
represented by its care-of address, as the mobile node
moves from link to link.
b.in some cases, advertises reachability to the networkprefix of mobile node’s home address, thereby attracting
IP packets that are destined to the mobile node’s home
address.
c.intercepts packets destined to the mobile node’s home
address and tunnels them to the mobile node’s current
location; I.e, to the care-of address.
Where does Mobile IP reside??

Foreign Agent
– A router on a mobile node’s foreign link which:
a.assists the mobile node in informing its home agent of its
current care-of address;
b.in some cases, provides a care-of address and detunnels packets for the mobile node that have been
tunneled by its home agent; and
c.serves as a default router for packets generated by the
mobile node while connected to this foreign link.
Where does Mobile IP reside??
Where does Mobile IP reside??

Tunneling
– A tunnel is the path followed by a first packet while
it is encapsulated within the payload portion of a
second packet.

Home address
– An IP address assigned to the mobile node
“permanently”.

Home link
– The link which has been assigned the same
network-prefix as the network-prefix of the mobile
node’s ho,e address.
Where does Mobile IP reside??
Where does Mobile IP reside??

Care-of address
– A care-of address is specific to the foreign link
currently being visited by a mobile node.
– A mobile node’s care-of address generally
changes every time the mobile node moves from
one foreign link to another.
– Packets destined to a care-of address can be
delivered using existing Internet routing
mechanisms.
Where does Mobile IP reside??

Care-of address
– A care-of address is used as the exit-point of a
tunnel from the home agent toward the mobile
node.
– A care-of address is almost never used as the IP
Source or Destination Address in a mobile node’s
conversations with other nodes.Specifically, the
care-of address will never be returned by a
Domain Name Sever when another node looks up
the mobile node’s hostname.
– Foreign agent care-of address vs. collocated careof address
At a 10,000-foot level,
how does Mobile IP work??
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Home agents and foreign agents advertise their
presence on any attached links by periodically
multicasting or broadcasting special Mobile IP
messages called Agent Advertisements.
Mobile nodes listen to these Agent Advertisements
and examine their contents to determine whether
they are connected to their home link or a foreign
link.While connected to their respective home links,
mobile nodes act just like stationary nodes—that is,
they make use of no other Mobile IP functionality.
The rest of the steps which follow, therefore,
assume that a mobile node has discovered that is
connected to a foreign link.
At a 10,000-foot level,
how does Mobile IP work??

A mobile node connected to a foreign link
acquires a care-of address. A foreign agent
care-of address can be read from one of the
fields within the foreign agent’s Agent
Advertisement. A collocated care-of address
must be acquired by some assignment
procedure, such as the Dynamic Host
Configuration Protocol, the Point-to-Point
Protocol’s IP Control Protocol, or manual
configuration.
At a 10,000-foot level,
how does Mobile IP work??

The mobile node Register the care-of
address acquired in step3 with its home
agent, using a message-exchange defined by
Mobile IP. In the registration procedure, the
mobile node asks for service from a foreign
agent, if one is present on the link. In order to
prevent remote denial-of-service attacks, the
registration messages are required to be
authenticated.
At a 10,000-foot level,
how does Mobile IP work??

The home agent or some other router on the
home link advertises reachability to the
network-prefix of the mobile node’s home
address, thus attracting packets that are
destined to the mobile node’s home address.
The home agent intercepts these packets,
possibly by using proxy ARP, and tunnels
them to the care-of address that the mobile
node registered in step4.
At a 10,000-foot level,
how does Mobile IP work??


At the care-of address—at either the foreign
agent or one of the interfaces of the mobile
node itself—the original packet is extracted
form the tunnel and then delivered to the
mobile node.
In the reverse direction, packets sent by the
mobile node are routed directly to their
destination, without any need for tunneling .
The foreign agent serves as a router for all
packets generated by a visiting mobile node.
At a 10,000-foot level,
how does Mobile IP work??
At a 10,000-foot level,
how does Mobile IP work??
Future Topics & Open Issues
Mobility for IP version 6
 Performance of TCP
 Support for real-time traffic
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Conclusion

A total mobility solution involves more
than simply the ability to route IP
packets to mobile computers, the latter
being solved by Mobile IP.