Transcript unit10 - WCU Computer Science

CSC 600
Internetworking
with
TCP/IP
Unit 10: Mobile IP
(Ch. 19)
Dr. Cheer-Sun Yang
Spring 2001
Mobile IP
• How can IP design be changed so that
portable computers can be moved from one
network to another with disconnection and
reconnection?
Why Mobile IP?
• A computer can logon to a home network from
within an airplane, a car, yacht, etc.
• New ways of connection are now available
including radio frequency, infrared LAN, etc.
• For example, if an access point is installed, a
computer user who just finished preparing for the
presentation material can carry the laptop to the
conference room without shutting down and then
restoring the communication links in the new
room.
Mobile IP vs. Wireless
Communication
• When Mobile IP talks about computers,
wireless communication has to do with
cellular phones.
• Wireless communication requires a phone
company to make changes in their system,
whereas infrared or radio LAN attachments
are typically made without charge.
Mobility vs. Portability
• Mobility requires a host connecting to a network
to change its location without disconnecting the
connection.
• Portability allows a host to be moved from one
location to another with the possibility of
reconnection.
• Mobility is often associated with wireless
technology, e.g., wireless PC, whereas portability
is often associated with laptop computers.
Mobil IP Topics
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Mobility, Routing, and Addressing
Mobil IP Operations
Mobil Addressing
Foreign Agency Discovery
Agent Registration
Tunneling: The Two-Crossing Problem
Portability
• The protocols such as Point-to-Point (PPP),
Dynamic Host Configuration Protocol
(DHCP) and Domain Name System (DNS)
are devised to support portability.
Mobile IP
• Mobile allows a single host to hold two
addresses simultaneously.
– The primary address is permanent and fixed. It
is the address applications and transport
protocols use.
– The secondary address is temporary and
changes as the host moves.
Architectural Model of the IETF
Protocol
• In the IETF Mobile IP Protocol, the location
directory (LD) is present at the same node on the
home network that implements the readdressing
function. The readdressing node on the home
network is called the home agent.
• Correspondingly, a foreign agent fulfills the
inverse readdressing function when the datagram
is delivered to the care-of address. After the
readdressing function is performed, the foreign
agent delivers the resulting datagram to the mobile
node.
Mobile IP Protocol Overview
• Mobile IP is, in essence, a way of doing
three relatively separate functions:
– Agent discovery
– Registration
– IP-to-IP tunneling
Agent Discovery
• Home agents and foreign agents may
advertise their availability on each link for
which they provide service. A newly arrived
mobile node can send a solicitation on the
link to learn if any prospective agents are
present.
Agent Registration
• Before it can receive datagram at a foreign
location, a mobile host must register.
• The procedure allows a host to:
– Register with an agent on the foreign network
– Register directly with its home agent to request
forwarding
– Renew a registration that is due to expire
– Deregister after returning home
Registration Message Format
Datagram Routing
• Once it has registered, a mobile host can
communicate with an arbitrary host. To do so, the
mobile creates a datagram with the destination
address in the destination field and the mobile’s
home address as the source.
• The datagram will travel along the shortest path
from the foreign network to the destination.
• However, a reply will not follow the shortest path
directly to the mobile node. Instead, it travels to
the mobile node’s home network.
IP-to-IP Tunneling
• The home agent, which has learned the
current location from the registration,
intercepts the datagram and uses IP-in-IP
encapsulation to tunnel the datagram to the
care-of address.
The Two-Crossing Problem
• Major problem of mobile IP: inefficiency.
• Because a mobile node uses its home
addresses, a datagram sent to the mobile
will be forwarded to the mobile’s home
network first and then to the mobile.
• The problem is especially severe because
computer communication often exhibits
special locality of reference.
Also referred to as Triangle Routing
Route Optimization
• Update binding cache
• Managing smooth handoffs between foreign
agents
• Acquiring registration keys for smooth
handoffs
• Using special tunnels
Wireless LAN Issues
• Medium access – Carrier Sense Multiple
Access/Collision Avoidance
• IEEE 802.11-Wireless LAN (WLAN)
specification
Suggested Reading
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Perkins: RFC 2002
Perkins: RFC 2004
Hanks et. al.: RFC 1701(IP-to-IP tunneling)
Montenegro: RFC 2344(reverse tunneling)
Perkins and Johnson: optimization for
mobile IP