cellular internet access

7/30/2019 Cellular internet access

1/21

Cellular Internet Access


2/21

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


3/21

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


4/21

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


5/21

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


6/21

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


7/21

Addressing and routing to

mobile users


8/21

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.


9/21

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


10/21

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


11/21

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?


12/21

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


13/21

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


14/21

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


15/21

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


16/21

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


17/21

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!


18/21

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


19/21

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?


20/21

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)


21/21

Recall : How to incorporate mobilityw.r.t short range communication model

cellular internet access

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