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Cellular Internet Access
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MobileSwitching
Center
Public telephonenetwork, andInternet
MobileSwitching
Center
Components of cellular network architecture
connects cells to wide area net manages call setup handles mobility
MSC
covers geographicalregion base station(BS)analogous to 802.11 AP mobile usersattachto network through BS air-interface:physical and link layerprotocol between
mobile and BS
cell
wired network
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Cellular networks: the first hopTwo techniques for sharing
mobile-to-BS radiospectrum
combined FDMA/TDMA:divide spectrum in
frequency channels, divideeach channel into timeslots
CDMA: code divisionmultiple access
frequencybands
time slots
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Cellular standards: brief survey2G systems: voice channels
IS-136 TDMA: combined FDMA/TDMA (northamerica)
GSM (global system for mobile communications):
combined FDMA/TDMAH most widely deployed
IS-95 CDMA: code division multiple access
GSM
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Cellular standards: brief survey2.5 G systems: voice and data channels
general packet radio service (GPRS)H evolved from GSM
H data sent on multiple channels (if available)
enhanced data rates for global evolution (EDGE)H also evolved from GSM, using enhanced modulation
H Date rates up to 384K
CDMA-2000 (phase 1)H data rates up to 144KH evolved from IS-95
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Cellular standards: brief survey3G systems: voice/data
Universal Mobile Telecommunications Service (UMTS)H GSM next step, but using CDMA
CDMA-2000
and more 4G
5G
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Addressing and routing to
mobile users
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What is mobility? spectrum of mobility, from the networkperspective:
no mobility high mobility
mobile wireless user,using same access
point
mobile user, passingthrough multiple
access point whilemaintaining ongoingconnections (like cellphone)
mobile user,connecting/
disconnectingfrom networkusing DHCP.
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Mobility: Vocabularyhome network:permanenthome of mobile(e.g., 128.119.40/24)
Permanent address:address in home
network, can alwaysbeused to reach mobilee.g., 128.119.40.186
home agent:entity that willperform mobility functions on
behalf of mobile, when mobileis remote
wide areanetwork
correspondent
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Mobility: more vocabulary
Care-of-address:addressin visited network.(e.g., 79,129.13.2)
wide areanetwork
visited network:networkin which mobile currentlyresides (e.g., 79.129.13/24)
Permanent address:remains
constant (e.g., 128.119.40.186)
foreign agent:entityin visited networkthat performsmobility functions onbehalf of mobile.
correspondent:wantsto communicate with
mobile
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How do youcontact a mobile friend:
search all phonebooks?
call her parents? expect her to let you
know where he/she is?
I wonder where
Alice moved to?
Consider friend frequently changing
addresses, how do you find?
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Mobility: approaches Let routing handle it:routers advertise permanent
address of mobile-nodes-in-residence via usualrouting table exchange.
H routing tables indicate where each mobile located
H no changes to end-systems
Let end-systems handle it:
H indirect routing:communication fromcorrespondent to mobile goes through home
agent, then forwarded to remoteH direct routing:correspondent gets foreign
address of mobile, sends directly to mobile
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Mobility: approaches Let routing handle it:routers advertise permanent
address of mobile-nodes-in-residence via usualrouting table exchange.
H routing tables indicate where each mobile located
H no changes to end-systems
let end-systems handle it:
H indirect routing:communication fromcorrespondent to mobile goes through home
agent, then forwarded to remoteH direct routing:correspondent gets foreign
address of mobile, sends directly to mobile
notscalableto millions of
mobiles
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Mobility: registration
End result:
Foreign agent knows about mobile
Home agent knows location of mobile
wide areanetwork
home networkvisited network
1
mobile contactsforeign agent onentering visitednetwork
2
foreign agent contacts homeagent home: this mobile isresident in my network
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Mobility via Indirect Routing
wide areanetwork
homenetwork
visitednetwork
3
2
41
correspondent
addresses packetsusing home addressof mobile
home agent intercepts
packets, forwards toforeign agent
foreign agentreceives packets,forwards to mobile
mobile repliesdirectly tocorrespondent
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Indirect Routing: comments Mobile uses two addresses:
H permanent address: used by correspondent (hence
mobile location is transparentto correspondent)H 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-network-
mobile
H
inefficient whencorrespondent, mobile
are in same network
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Indirect Routing: moving between networks suppose mobile user moves to another
networkH registers with new foreign agent
H new foreign agent registers with home agent
H home agent update care-of-address for mobile
H packets continue to be forwarded to mobile (butwith new care-of-address)
mobility, changing foreign networks
transparent: on going connections can bemaintained!
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Mobility via Direct Routing
wide areanetwork
homenetwork
visitednetwork
4
2
51correspondent
requests, receivesforeign address ofmobile
correspondent forwards
to foreign agent
foreign agentreceives packets,forwards to mobile
mobile repliesdirectly tocorrespondent
3
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Mobility via Direct Routing: comments overcome triangle routing problem
non-transparent to correspondent:correspondent must get care-of-addressfrom home agentH what if mobile changes visited network?
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wide areanetwork
1
foreign net visitedat session start
anchorforeignagent
2
4
new foreignagent
35
correspondentagent
correspondent
newforeignnetwork
Accommodating mobility with direct routing anchor foreign agent: FA in first visited network data always routed first to anchor FA
when mobile moves: new FA arranges to have dataforwarded from old FA (chaining)
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Recall : How to incorporate mobilityw.r.t short range communication model