Transcript Location management

Location management
Components of cellular network architecture
MSC
cell
 connects cells to wide area net
 manages call setup (more later!)
 handles mobility (more later!)
 covers geographical
region
 base station (BS)
analogous to 802.11 AP
 mobile users attach
to network through BS
 air-interface:
physical and link layer
protocol between
mobile and BS
Mobile
Switching
Center
Public telephone
network, and
Internet
Mobile
Switching
Center
wired network
Location management(1)
Location management (2)
Steps in mobility management
Location update procedure
Mobility in IP networks
• 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)
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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
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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.
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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
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– 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
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– 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
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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
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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
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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
Care-of address:
79.129.13.2
packet sent by
correspondent
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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
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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
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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?
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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
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Mobile IP: agent discovery
• agent advertisement: foreign/home agents
advertise service by broadcasting ICMP
16
0
8= 9)
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messages (typefield
type = 9
H,F bits: home
and/or foreign agent
R bit: registration
required
checksum
=9
code = 0
=9
router address
type = 16
length
registration lifetime
standard
ICMPfields
sequence #
RBHFMGV
reserved
bits
0 or more care-ofaddresses
mobility agent
advertisement
extension
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Mobile IP: registration example
hom
eagent
H
A
: 128.119.40.7
foreignagent
CO
A
: 79.129.13.2
visitednetw
ork: 79.129.13/24
ICM
Pagentadv.
C
O
A: 79.129.13.2
…
.
registrationreq.
C
O
A: 79.129.13.2
H
A: 128.119.40.7
M
A: 128.119.40.186
Lifetim
e: 9999
identification: 714
encapsulationform
at
…
.
M
obileagent
M
A
: 128.119.40.186
registrationreq.
C
O
A: 79.129.13.2
H
A: 128.119.40.7
M
A: 128.119.40.186
Lifetim
e: 9999
identification:714
…
.
registrationreply
tim
e
H
A: 128.119.40.7
M
A: 128.119.40.186
Lifetim
e: 4999
Identification: 714
encapsulationform
at
…
.
registrationreply
H
A: 128.119.40.7
M
A: 128.119.40.186
Lifetim
e: 4999
Identification: 714
…
.
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