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Chapter 6
Wireless and
Mobile Networks
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Computer
Networking: A Top
Down Approach
6th edition
Jim Kurose, Keith Ross
Addison-Wesley
March 2012
Thanks and enjoy! JFK/KWR
All material copyright 1996-2012
J.F Kurose and K.W. Ross, All Rights Reserved
Wireless, Mobile Networks
6-1
Chapter 6 outline
6.1 Introduction
Mobility
Wireless
6.5 Principles: addressing and
routing to mobile users
6.6 Mobile IP
6.7 Handling mobility in
cellular networks
6.8 Mobility and higher-layer
protocols
6.2 Wireless links,
characteristics
 CDMA
6.3 IEEE 802.11 wireless
LANs (“Wi-Fi”)
6.4 Cellular Internet Access
 architecture
 standards (e.g., GSM)
6.9 Summary
Wireless, Mobile Networks
6-2
Ch. 6: Wireless and Mobile Networks
Background:

# wireless (mobile) phone subscribers now exceeds #
wired phone subscribers (>5-to-1)!
 41% of homes in U.S. do not have a land-line telephone (2014)

# wireless Internet-connected devices now exceeds #
wire line Internet-connected devices
 laptops, Internet-enabled phones promise anytime untethered
Internet access

two important (but different) challenges
 wireless connectivity: communication over wireless link
 mobility: handling the mobile user who changes point of
attachment to network
Wireless, Mobile Networks
6-3
Elements of a wireless network
network
infrastructure
Wireless, Mobile Networks
6-4
Elements of a wireless network
wireless hosts



network
infrastructure
laptop, smartphone, tablet
run applications
may be stationary (nonmobile) or mobile
 wireless does not always
mean mobility
Wireless, Mobile Networks
6-5
Elements of a wireless network
base station


network
infrastructure
typically connected to
wired network
relay - responsible for
sending packets between
wired network and
wireless host(s) in its
“area”
 e.g., cell towers,
802.11 access points
Wireless, Mobile Networks
6-6
Elements of a wireless network
wireless link


network
infrastructure


typically used to connect
mobile(s) to base station
also used as backbone
link
multiple access protocol
coordinates link access
various data rates &
transmission ranges
Wireless, Mobile Networks
6-7
Characteristics of selected wireless links
Data rate (Mbps)
200
802.11n
54
802.11a,g
5-11
802.11b
4G: LTE
802.11a, g point-to-point
Enhanced 3G: HSPA
4
1
802.15
.384
2.5G: UMTS/WCDMA, CDMA2000
.056
2G: IS-95, CDMA, GSM
Indoor
Outdoor
10-30m
50-200m
Mid-range
outdoor
Long-range
outdoor
200m – 4 Km
5Km – 20 Km
Wireless, Mobile Networks
6-8
Elements of a wireless network
infrastructure mode


network
infrastructure
base station connects
mobiles into wired
network
handoff: mobile changes
the base station that is
providing its connection
to the wired network
Wireless, Mobile Networks
6-9
Elements of a wireless network
ad hoc mode
 no base stations
 nodes can only
transmit to other
nodes within link
coverage
 nodes organize
themselves into a
network: route
among themselves
Wireless, Mobile Networks 6-10
Wireless network taxonomy
single hop
infrastructure
(e.g., APs)
no
infrastructure
host connects to
base station (WiFi,
3G cellular)
which connects to
larger Internet
no base station, no
connection to larger
Internet (Bluetooth,
WiFi ad hoc nets)
multiple hops
host may have to
relay through several
wireless nodes to
connect to larger
Internet: mesh net
no base station, no
connection to larger
Internet. May have to
relay to reach other
a given wireless node
MANET, VANET
Wireless, Mobile Networks 6-11
Chapter 6 outline
6.1 Introduction
Mobility
Wireless
6.5 Principles: addressing and
routing to mobile users
6.6 Mobile IP
6.7 Handling mobility in
cellular networks
6.8 Mobility and higher-layer
protocols
6.2 Wireless links,
characteristics and
technical challenges
 CDMA
6.3 IEEE 802.11 wireless
LANs (“Wi-Fi”)
6.4 Cellular Internet Access
 architecture
 standards (e.g., GSM)
6.9 Summary
Wireless, Mobile Networks 6-12
Wireless Link Characteristics (1)
important differences from wired link ….
 decreased signal strength: radio signal attenuates as it
propagates through matter (path loss)
 interference from other sources: standardized
(unlicensed) wireless network frequencies (e.g., 2.4
GHz) shared by other devices (e.g., portable phone,
EGDOs); devices (motors) interfere as well
 multipath propagation: radio signal reflects off objects
ground, arriving at destination at slightly different
times, phases & intensities (signal diffusion)
…. make communication across wireless link (even pointto-point) much more “difficult” than over a wired link
Wireless, Mobile Networks 6-13
Wireless Link Characteristics (2)

SNR: signal-to-noise ratio
10-1
 larger SNR – easier to
extract signal from noise (a
“good thing”)
SNR versus BER tradeoffs
 for given physical layer modulation:
increase power -> increase
SNR->decrease BER
 for given SNR: choose physical
layer that meets BER
requirement, giving highest
throughput
• SNR may change with mobility:
dynamically adapt physical layer
(modulation technique, rate)
10-3
BER

10-2
10-4
10-5
10-6
10-7
10
20
30
40
SNR(dB)
QAM256 (8 Mbps)
QAM16 (4 Mbps)
BPSK (1 Mbps)
Wireless, Mobile Networks 6-14
Wireless network characteristics
Multiple wireless senders and receivers create additional
problems (beyond multiple access):
B
A
C
C
B
C’s signal
strength
A’s signal
strength
A
Hidden terminal problem



B, A hear each other
B, C hear each other
A, C can not hear each other
means A, C unaware of their
interference at B
space
Signal attenuation:



B, A hear each other
B, C hear each other
A, C can not hear each other
interfering at B
Wireless, Mobile Networks 6-15
Code Division Multiple Access (CDMA)

unique “code” assigned to each user; i.e., code set
partitioning
 all users share same frequency, but each user has own
“chipping” sequence (i.e., code) to encode data
 allows multiple users to coexist and transmit
simultaneously in the same physical media with minimal
interference (if codes are “pairwise orthogonal”)
encoded signal = (original data) X (chipping
sequence)
 decoding: inner-product of encoded signal and
chipping sequence

Wireless, Mobile Networks 6-16
CDMA encode/decode
sender
d0 = 1
data
bits
code
Zi,m= di.cm
-1 -1 -1
1
-1
1 1 1
-1 -1 -1
slot 1
-1
slot 1
channel
output
1
-1
1 1 1 1 1 1
1
d1 = -1
1 1 1
channel output Zi,m
-1 -1 -1
slot 0
1
-1
-1 -1 -1
slot 0
channel
output
M
Di = S Zi,m.cm
m=1
received
input
code
receiver
1 1 1 1 1 1
1
-1 -1 -1
-1
1 1 1
1
-1
-1 -1 -1
-1
1 1 1
-1 -1 -1
slot 1
M
1
1
-1
-1 -1 -1
slot 0
d0 = 1
d1 = -1
slot 1
channel
output
slot 0
channel
output
Wireless, Mobile Networks 6-17
CDMA: two-sender interference
Sender 1
channel sums together
transmissions by sender 1
and 2
Sender 2
using same code as
sender 1, receiver recovers
sender 1’s original data
from summed channel
data!
Wireless, Mobile Networks 6-18
Chapter 6 outline
6.1 Introduction
Mobility
Wireless
6.5 Principles: addressing and
routing to mobile users
6.6 Mobile IP
6.7 Handling mobility in
cellular networks
6.8 Mobility and higher-layer
protocols
6.2 Wireless links,
characteristics
 CDMA
6.3 IEEE 802.11 wireless
LANs (“Wi-Fi”)
6.4 Cellular Internet Access
 architecture
 standards (e.g., GSM)
6.9 Summary
Wireless, Mobile Networks 6-19
IEEE 802.11 Wireless LAN
802.11a
 5-6 GHz range
 up to 54 Mbps
802.11b
 2.4-2.5 GHz
 up to 11 Mbps
802.11g
 2.4-2.5 GHz range
 up to 54 Mbps
802.11n:
 Multiple antennae: MIMO
• 4 spatial streams
 2.4 or 5 GHz range
 up to 200 Mbps
802.11 ac (MIMO)
 Multiple antennae: MIMO
• 8 spatial streams
 5 GHz range
 up to 867 Mbps (theoretical to
1.37 Gbps)
 limited range, but…
Wireless, Mobile Networks 6-20
IEEE 802.11 Wireless LAN
Modulation/multiplexing
 802.11b: direct sequence spread spectrum (DSSS)
in physical layer
 80211a/g: orthogonal frequency division
multiplexing (OFDM)
 802.11n: spatial division multiplexing (SDM)
 802.11ac: spatial division multiplexing (SDM) with
QAM 256 per channel, and beamforming


all use CSMA/CA for multiple access
all support infrastructure and ad-hoc network operation
Wireless, Mobile Networks 6-21
IEEE 802.11 Wireless LAN
Physical layer modulation/multiplexing

DSSS modulation (802.11b)
 CDMA-like physical transmission with 8-bit chipping sequence
 14 overlapping frequency bands (11 useable channels)

OFDM modulation (802.11a/g)
 FDM-like modulation with all frequencies pairwise-orthogonal
 Reverts to DSSS (11 MBPS) for 802.11b compatibility

SDM modulation (802.11n & 802.11ac)
 Complex OFDM schema using QAM modulation across 4 or 8
spatial streams with multiple antennae and frame aggregation
Wireless, Mobile Networks 6-22
802.11 LAN architecture

Internet
Wireless Host
communicates with base
station
 base station = access point
(AP)
hub, switch
or router
BSS 1

Basic Service Set (BSS) (aka
a WiFi “cell”) in
infrastructure mode
contains:
 wireless host(s)
 access point (AP): base
station (ad hoc mode has
hosts only)
BSS 2
Wireless, Mobile Networks 6-23
802.11: Channels, association

802.11b/g: 2.401GHz-2.485GHz spectrum divided into 11
channels at different frequencies
 wireless network admin chooses frequency for AP
 interference possible: channel can be same as that used by a
neighboring AP!

SDM used in 802.11n & ac with 4 & 8 MIMO streams
reduces cross channel interference

host: must associate with an AP
 scans channels, listening for beacon frames containing AP’s name
(SSID) and MAC address
 selects AP to associate with
 may perform authentication [Chapter 8]
 will typically run DHCP to get IP address in AP’s subnet (note:
AP device may also serve as local router)
Wireless, Mobile Networks 6-24
802.11: association via passive/
active scanning
BBS 1
BBS 1
BBS 2
BBS 2
1
AP 1
1
1
2
AP 2
AP 1
2
3
2
3
AP 2
4
H1
H1
passive scanning (typical):
active scanning:
(1) beacon frames sent from APs
(2) association Request frame sent: H1 to
selected AP
(3) association Response frame sent from
selected AP to H1
(1) Probe Request frame broadcast
from H1
(2) Probe Response frames sent
from APs
(3) Association Request frame sent:
H1 to selected AP
(4) Association Response frame sent
from selected AP to H1
Wireless, Mobile Networks 6-25
IEEE 802.11: multiple access


avoid collisions: 2+ nodes transmitting at same time
802.11: CSMA - sense before transmitting
 don’t collide with ongoing transmission by another node

802.11: does not use collision detection!
 difficult/expensive to receive (sense collisions) when transmitting due
to weak received signals (fading)
 can’t sense all collisions in any case: hidden terminal, fading
 goal: avoid collisions: CSMA/CA(Collision Avoidance)
B
A
C
C
A
B
C’s signal
strength
A’s signal
strength
space
Wireless, Mobile Networks 6-26
IEEE 802.11 MAC Timing
duration depends
on MAC load type
duration depends
on network condition
MAC frame: Control,
management , data + headers
(size depends on frame load and type)
Reference: W.
Stallings: Data
and Computer
Communications,
7th ed
DIFS: Distributed Inter-Frame Space (minimum delay for asynchronous
frame access)
SIFS: Short Inter-Frame Space (minimum timing for high priority frame
access as ACK, CTS, MSDU…)
10
IEEE 802.11 MAC Protocol: CSMA
802.11 sender
1. if sense channel idle for DIFS then
transmit entire frame (no CD)
2. if sense channel busy then
start random back-off time
timer counts down while channel idle
transmit when timer expires
if no ACK, increase random back-off
interval, repeat 2
802.11 receiver
- if frame received OK
sender
receiver
DIFS
data
SIFS
ACK
return ACK after SIFS (ACK needed due to
hidden terminal problem)
Wireless, Mobile Networks 6-28
Avoiding collisions (CSMA/CA)
concept: allow a sender to “reserve” channel rather than
random access of data frames: avoid collisions of long
data frames
 sender first transmits small request-to-send (RTS) packets
to AP using CSMA
 RTSs may still collide with each other (but they’re short)


AP broadcasts clear-to-send CTS in response to RTS
CTS heard by all nodes
 sender transmits data frame
 other stations defer transmissions
avoid data frame collisions completely
using small reservation packets!
Wireless, Mobile Networks 6-29
Collision Avoidance: RTS-CTS exchange
A
B
AP
reservation collision
DATA (A)
defer
time
Wireless, Mobile Networks 6-30
802.11 frame: addressing
2
2
6
6
6
frame
address address address
duration
control
1
2
3
Address 1: MAC address
of wireless host or AP
to receive this frame
(receiver)
2
6
seq address
4
control
0 - 2312
4
payload
CRC
Address 4: used only in
ad hoc mode
Address 3: MAC address
of router interface to
which AP is attached
Address 2: MAC address
of wireless host or AP
transmitting this frame
(sender)
Wireless, Mobile Networks 6-31
802.11 frame: addressing
Internet
R1 router
H1
R1 MAC addr H1 MAC addr
dest. address
source address
802.3 frame
AP MAC addr H1 MAC addr R1 MAC addr
address 1
address 2
address 3
802.11 frame
Wireless, Mobile Networks 6-32
802.11 frame: more
frame seq #
(for RDT)
duration of reserved
transmission time (RTS/CTS)
2
2
6
6
6
frame
address address address
duration
control
1
2
3
2
Protocol
version
2
4
1
Type
Subtype
To
AP
6
2
1
seq address
4
control
1
From More
AP
frag
1
Retry
1
0 - 2312
4
payload
CRC
1
Power More
mgt
data
1
1
WEP
Rsvd
frame type
(RTS, CTS, ACK, data)
Wireless, Mobile Networks 6-33
802.11: mobility within same subnet
H1 remains in same
IP subnet: IP address
can remain same
 switch: which AP is
associated with H1?

 self-learning (Ch. 5):
switch will see frame
from H1 and
“remember” which
switch port can be
used to reach H1
BBS 1
H1
BBS 2
Wireless, Mobile Networks 6-34
802.11: advanced capabilities
Rate adaptation
base station, mobile
dynamically change
transmission rate
(physical layer modulation
technique) as mobile
moves, SNR varies
QAM256 (8 Mbps)
QAM16 (4 Mbps)
BPSK (1 Mbps)
operating point
10-2
10-3
BER

10-1
10-4
10-5
10-6
10-7
10
20
30
SNR(dB)
40
1. SNR decreases, BER
increase as node moves
away from base station
2. When BER becomes too
high, switch to lower
transmission rate but with
lower BER
Wireless, Mobile Networks 6-35
802.11: advanced capabilities
power management
 node-to-AP: “I am going to sleep until next
beacon frame”
 AP knows not to transmit frames to this node
 node wakes up before next beacon frame

beacon frame: contains list of mobiles with APto-mobile frames waiting to be sent
 node will stay awake if AP-to-mobile frames to be
sent; otherwise sleep again until next beacon frame
Wireless, Mobile Networks 6-36
802.15.1: personal area network




less than 10 m diameter
replacement for cables (mouse,
keyboard, headphones)
ad hoc: no infrastructure
master/slaves:
 slaves request permission to send
(to master)
 master grants requests

802.15.1: evolved from
Bluetooth specification
 2.4-2.5 GHz radio band
 TDM, 625µsec channels
 FHSS, up to 4 Mbps
P
S
P
radius of
coverage
M
S
P
S
P
M Master device
S Slave device
P Parked device (inactive)
Wireless, Mobile Networks 6-37
Chapter 6 outline
6.1 Introduction
Wireless
6.2 Wireless links,
characteristics
 CDMA
6.3 IEEE 802.11 wireless
LANs (“Wi-Fi”)
6.4 Cellular Internet access
 architecture
 standards (e.g., GSM)
Mobility
6.5 Principles: addressing and
routing to mobile users
6.6 Mobile IP
6.7 Handling mobility in
cellular networks
6.8 Mobility and higher-layer
protocols
6.9 Summary
Wireless, Mobile Networks 6-38
Components of cellular network architecture
MSC
connects cells to wired tel. net.
 manages call setup (more later!)
 handles mobility (more later!)

cell
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
Mobile
Switching
Center
wired network
GSM: Global System for
Mobile Communications
Wireless, Mobile Networks 6-39
Cellular networks: the first hop
Two primary techniques for
sharing mobile-to-BS radio
spectrum
 combined FDMA/TDMA: divide
spectrum in frequency
channels, divide each channel
into time slots (2G)
 CDMA: code division multiple
access (3G – used in addition
to FDMA/TDMA)
frequency
 DS-WCDMA

time slots
bands
4G and variants: more later
Wireless, Mobile Networks 6-40
2G (voice) network architecture
Base station system (BSS)
MSC
BTS
G
BSC
Public
telephone
network
Gateway
MSC
Legend
Base transceiver station (BTS)
Base station controller (BSC)
Mobile Switching Center (MSC)
Mobile subscribers
Wireless, Mobile Networks 6-41
3G (voice+data) network architecture
MSC
G
radio
network
controller
Gateway
MSC
G
SGSN
Key insight: new cellular data
network operates in parallel
(except at edge) with existing
cellular voice network
 voice network unchanged in core
 data network operates in parallel
Public
telephone
network
Public
Internet
GGSN
Serving GPRS Support Node (SGSN)
Gateway GPRS Support Node (GGSN)
Wireless, Mobile Networks 6-42
3G (voice+data) network architecture
MSC
G
radio
network
controller
Public
telephone
network
Gateway
MSC
G
SGSN
Public
Internet
GGSN
radio interface
(WCDMA, HSPA)
radio access network
Universal Terrestrial Radio
Access Network (UTRAN)
core network
General Packet Radio Service
(GPRS) Core Network
public
Internet
Wireless, Mobile Networks 6-43
Evolution to 4G


Promises advanced features and data rates of 100s of Mbps
Evolved Packet Core (EPC)
 unifies circuit-switched cellular voice and packet-switched data
networks into “all-IP” approach (e.g., packetized voice and data)
 can support 2G and 3G access networks

Long-Term Evolution (LTE) Radio Network
 radio network utilizes ODFM in combination with
FDMA/TDMA for downstream data
 each active node allocated one or more 0.5ms time slots in one
or more frequency bands
 dynamic slot allocation/reallocation and modulation schema

WiMAX
 evolving 802.16 standard
Wireless, Mobile Networks 6-44
Chapter 6 outline
6.1 Introduction
Wireless
6.2 Wireless links,
characteristics
 CDMA
6.3 IEEE 802.11 wireless
LANs (“Wi-Fi”)
6.4 Cellular Internet Access
 architecture
 standards (e.g., GSM)
Mobility
6.5 Principles: addressing and
routing to mobile users
6.6 Mobile IP
6.7 Handling mobility in
cellular networks
6.8 Mobility and higher-layer
protocols
6.9 Summary
Wireless, Mobile Networks 6-45
What is mobility?

spectrum of mobility, from the network perspective:
no mobility
mobile wireless user,
using same access
point
high mobility
mobile user,
connecting/
disconnecting from
network using
DHCP.
mobile user, passing
through multiple
access points while
maintaining ongoing
connections (like cell
phone)
Wireless, Mobile Networks 6-46
Mobility: vocabulary
home network: permanent
“home” of mobile
(e.g., 128.119.40/24)
home agent: entity that will
perform mobility functions on
behalf of mobile, when mobile is
remote
wide area
network
permanent address:
address in home
network, can always be
used to reach mobile
(e.g., 128.119.40.186)
Wireless, Mobile Networks 6-47
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
foreign agent: entity in
visited network that
performs mobility
functions on behalf of
mobile.
Wireless, Mobile Networks 6-48
How do you contact a mobile friend:
Consider friend frequently changing
addresses, how do you find her?



I wonder where
Alice moved to?
search all phone books?
call her parents?
expect her to let you
know where he/she is?
Wireless, Mobile Networks 6-49
Mobility: approaches


let routing handle it: routers advertise permanent address of
mobile-nodes-in-residence 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 address of
mobile, sends directly to mobile
Wireless, Mobile Networks 6-50
Mobility: approaches


let routing handle it: routers advertise permanent address of
not via usual routing table exchange.
mobile-nodes-in-residence
scalable
 routing tables indicate
where each mobile located
to millions of
 no changes to end-systems
mobiles
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 address of
mobile, sends directly to mobile
Wireless, Mobile Networks 6-51
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
Wireless, Mobile Networks 6-52
Mobility via indirect routing
home agent intercepts
packets, forwards (via
tunneling) to foreign agent
foreign agent
receives packets,
forwards to mobile
visited
network
home
network
3
1
correspondent
addresses packets
using home address of
mobile
wide area
network
2
4
mobile replies
directly to
correspondent
Wireless, Mobile Networks 6-53
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
correspondent, mobile
are in same network
Wireless, Mobile Networks 6-54
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!

Wireless, Mobile Networks 6-55
Mobility via direct routing
correspondent forwards
to foreign agent
foreign agent
receives packets,
forwards to mobile
visited
network
home
network
3
1
correspondent
requests, receives
foreign address of
mobile
2
4
mobile replies
directly to
correspondent
Wireless, Mobile Networks 6-56
Mobility via direct routing: comments
overcome triangle routing problem
 non-transparent to correspondent: correspondent
must get care-of-address from home agent

 what if mobile changes visited network?
3
1
2
4
Wireless, Mobile Networks 6-57
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
data forwarded from old FA (chaining)

foreign net visited
at session start
wide area
network
anchor
foreign
agent
1
2
4
5
correspondent
agent
correspondent
3
new foreign
agent
new
foreign
network
Wireless, Mobile Networks 6-58
Chapter 6 outline
6.1 Introduction
Wireless
6.2 Wireless links,
characteristics
 CDMA
6.3 IEEE 802.11 wireless
LANs (“Wi-Fi”)
6.4 Cellular Internet Access
 architecture
 standards (e.g., GSM)
Mobility
6.5 Principles: addressing and
routing to mobile users
6.6 Mobile IP
6.7 Handling mobility in
cellular networks
6.8 Mobility and higher-layer
protocols
6.9 Summary
Wireless, Mobile Networks 6-59
Mobile IP
RFC 5944 (November 2010)
 has many features we’ve seen:

 home agents, foreign agents, foreign-agent registration,
care-of-addresses, encapsulation (tunneling: packetwithin-a-packet)

three components to standard:
 agent discovery
 registration with home agent
 indirect routing of datagrams
Wireless, Mobile Networks 6-60
Mobile IP

RFC 5944 Protocol Requirements
 A mobile node must be able to communicate with
other nodes after changing its link-layer point of
attachment to the Internet, yet without changing its IP
address.
 A mobile node must be able to communicate with
other nodes that do not implement these mobility functions.
No protocol enhancements are required in hosts or
routers that are not acting as any of the new
architectural entities introduced in this RFC.
 All messages used to update another node as to the
location of a mobile node must be authenticated in
order to protect against remote redirection attacks.
Wireless, Mobile Networks 6-61
Mobile IP: indirect routing
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
Wireless, Mobile Networks 6-62
Mobile IP: agent discovery

agent advertisement: foreign/home agents advertise
service by broadcasting ICMP messages (typefield = 9)
type = 9
24
checksum
=9
code = 0
=9
H,F bits: home and/or
foreign agent
R bit: registration
required
16
8
0
standard
ICMP fields
router address
type = 16
length
registration lifetime
sequence #
RBHFMGV
bits
reserved
1 or more care-ofaddresses
mobility agent
advertisement
extension
Wireless, Mobile Networks 6-63
Mobile IP: registration example
home agent
HA: 128.119.40.7
foreign agent
COA: 79.129.13.2
mobile agent
MA: 128.119.40.186
(Also: agent solicitation via
ICMP Type 10 message)
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 reply
HA: 128.119.40.7
MA: 128.119.40.186
Lifetime: 4999
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
HA: 128.119.40.7
MA: 128.119.40.186
Lifetime: 4999
Identification: 714
….
time
Internet
visited network: 79.129.13/24
Wireless, Mobile Networks 6-64