Transcript What is mobility?

ICMP: Internet Control Message
Protocol
• used by hosts, routers,
gateways to communication
network-level information
– error reporting:
unreachable host, network,
port, protocol
– echo request/reply (used
by ping)
• network-layer “above” IP:
– ICMP msgs carried in IP
datagrams
• ICMP message: type, code
plus first 8 bytes of IP
datagram causing error
Type
0
3
3
3
3
3
3
4
Code
0
0
1
2
3
6
7
0
8
9
10
11
12
0
0
0
0
0
description
echo reply (ping)
dest. network unreachable
dest host unreachable
dest protocol unreachable
dest port unreachable
dest network unknown
dest host unknown
source quench (congestion
control - not used)
echo request (ping)
route advertisement
router discovery
TTL expired
bad IP header
DHCP: Dynamic Host Configuration
Protocol
Goal: allow host to dynamically obtain its IP
address from network server when it joins
network
Can renew its lease on address in use
Allows reuse of addresses (only hold address while
connected an “on”
Support for mobile users who want to join network
(more shortly)
DHCP overview:
– host broadcasts “DHCP discover” msg
– DHCP server responds with “DHCP offer”
DHCP client-server scenario
A
B
223.1.2.1
DHCP
server
223.1.1.1
223.1.1.2
223.1.1.4
223.1.2.9
223.1.2.2
223.1.1.3
223.1.3.1
223.1.3.27
223.1.3.2
E
arriving DHCP
client needs
address in this
network
DHCP client-server scenario
DHCP server: 223.1.2.5
DHCP discover
src : 0.0.0.0, 68
dest.: 255.255.255.255,67
yiaddr: 0.0.0.0
transaction ID: 654
DHCP offer
src: 223.1.2.5, 67
dest: 255.255.255.255, 68
yiaddrr: 223.1.2.4
transaction ID: 654
Lifetime: 3600 secs
DHCP request
time
src: 0.0.0.0, 68
dest:: 255.255.255.255, 67
yiaddrr: 223.1.2.4
transaction ID: 655
Lifetime: 3600 secs
DHCP ACK
src: 223.1.2.5, 67
dest: 255.255.255.255, 68
yiaddrr: 223.1.2.4
transaction ID: 655
Lifetime: 3600 secs
arriving
client
What is mobility?
• spectrum of mobility, from the network
perspective:
no mobility
mobile user, using
same access point
high mobility
mobile user,
connecting/
disconnecting
from network
using DHCP.
mobile user, passing
through multiple
access point while
maintaining ongoing
connections (like cell
phone)
Mobility: Vocabulary
home network: permanent
“home” of mobile
(e.g., 128.119.40/24)
Permanent address:
address in home
network, can always be
used to reach mobile
e.g., 128.119.40.186
home agent: entity that will
perform mobility functions on
behalf of mobile, when mobile
is remote
wide area
network
correspondent
Mobility: more vocabulary
Permanent address: remains
constant (e.g., 128.119.40.186)
visited network: network
in which mobile currently
resides (e.g., 79.129.13/24)
Care-of-address: address
in visited network.
(e.g., 79,129.13.2)
wide area
network
correspondent: wants
to communicate with
mobile
home agent: entity in
visited network that
performs mobility
functions on behalf
of mobile.
How do you contact a mobile friend:
Consider friend frequently
changing addresses, how do
• you
search
phone
findall
her?
books?
• call her parents?
• expect her to let you
know where he/she
is?
I wonder where
Alice moved to?
Mobility: approaches
• Let routing handle it: routers advertise
permanent address of mobile-nodes-inresidence via usual routing table exchange.
– routing tables indicate where each mobile
located
– no changes to end-systems
• Let end-systems handle it:
– indirect routing: communication from
correspondent to mobile goes through home
agent, then forwarded to remote
– direct routing: correspondent gets foreign
Mobility: approaches
• Let routing handle it: routers advertise
not
permanent address
of mobile-nodes-inscalable
residence via usual
routing
table exchange.
to millions
of
mobiles
– routing tables indicate
where each mobile
located
– no changes to end-systems
• let end-systems handle it:
– indirect routing: communication from
correspondent to mobile goes through home
agent, then forwarded to remote
– direct routing: correspondent gets foreign
Mobility: registration
visited network
home network
2
1
wide area
network
foreign agent contacts home
agent home: “this mobile is
resident in my network”
mobile contacts
foreign agent on
entering visited
network
End result:
• Foreign agent knows about mobile
• Home agent knows location of mobile
Mobility via Indirect Routing
foreign agent
receives packets,
forwards to mobile
home agent intercepts
packets, forwards to
foreign agent
home
network
visited
network
3
wide area
network
correspondent
addresses packets
using home address
of mobile
1
2
4
mobile replies
directly to
correspondent
Indirect Routing: comments
• Mobile uses two addresses:
– permanent address: used by correspondent
(hence mobile location is transparent to
correspondent)
– care-of-address: used by home agent to
forward datagrams to mobile
• foreign agent functions may be done by mobile
itself
• triangle routing: correspondent-home-networkmobile
– inefficient when
Forwarding datagrams to remote
mobile
foreign-agent-to-mobile packet
packet sent by home agent to foreign
agent: a packet within a packet
dest: 79.129.13.2
dest: 128.119.40.186
dest: 128.119.40.186
Permanent address:
128.119.40.186
dest: 128.119.40.186
packet sent by
correspondent
Care-of address:
79.129.13.2
Indirect Routing: moving between
networks
• suppose mobile user moves to another
network
– registers with new foreign agent
– new foreign agent registers with home agent
– home agent update care-of-address for
mobile
– packets continue to be forwarded to mobile
(but with new care-of-address)
• Mobility, changing foreign networks
transparent: on going connections can be
maintained!
Mobility via Direct Routing
correspondent forwards
to foreign agent
foreign agent
receives packets,
forwards to mobile
home
network
4
wide area
network
2
correspondent
requests, receives
foreign address of
mobile
visited
network
1
3
4
mobile replies
directly to
correspondent
Mobility via Direct Routing: comments
• overcome triangle routing problem
• non-transparent to correspondent:
correspondent must get care-of-address
from home agent
– What happens if mobile changes networks?
Mobile IP
• RFC 3220
• has many features we’ve seen:
– home agents, foreign agents, foreign-agent
registration, care-of-addresses, encapsulation
(packet-within-a-packet)
• three components to standard:
– agent discovery
– registration with home agent
– indirect routing of datagrams
Mobile IP: agent discovery
• agent advertisement: foreign/home agents
advertise service by broadcasting ICMP
16
0
8= 9)
24
messages (typefield
type = 9
H,F bits: home
and/or foreign agent
R bit: registration
required
checksum
=9
code = 0
=9
standard
ICMP fields
router address
type = 16
length
registration lifetime
sequence #
RBHFMGV
bits
reserved
0 or more care-ofaddresses
mobility agent
advertisement
extension
Mobile IP: registration example
home agent
HA: 128.119.40.7
foreign agent
COA: 79.129.13.2
visited network: 79.129.13/24
ICMP agent adv.
COA: 79.129.13.2
….
registration req.
COA: 79.129.13.2
HA: 128.119.40.7
MA: 128.119.40.186
Lifetime: 9999
identification: 714
encapsulation format
….
registration req.
COA: 79.129.13.2
HA: 128.119.40.7
MA: 128.119.40.186
Lifetime: 9999
identification:714
….
registration reply
time
HA: 128.119.40.7
MA: 128.119.40.186
Lifetime: 4999
Identification: 714
encapsulation format
….
registration reply
HA: 128.119.40.7
MA: 128.119.40.186
Lifetime: 4999
Identification: 714
….
Mobile agent
MA: 128.119.40.186