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1
Chapter 7 outline7.1 Introduction
Mobility 7 5 Principles:Wireless
7.2 Wireless links, characteristics
7.5 Principles: addressing and routing to mobile users7 6 M bil IPcharacteristics
CDMA 7.3 IEEE 802.11
wireless LANs (“wi fi”)
7.6 Mobile IP 7.7 Handling mobility in
cellular networkswireless LANs ( wi-fi ) 7.4 Cellular Internet
Characteristics of selected i l ss li k st d dswireless link standards450 802.11n
802.11ac
5-11
54
802.11b
802.11a, g4G: LTE
802.11a, g point-to-point
bps)
1
4
802.15
Enhanced 3G: HSPA
a ra
te (M
b
056
.384
2G: GSM CDMA
3G: UMTS/WCDMA, CDMA2000
Dat
a
Indoor10-30m
Outdoor50-200m
Mid-rangeoutdoor
Long-rangeoutdoor
.056 2G: GSM, CDMA
12/5/2017Wireless and Mobile Networks (SSL) 7-2
200m – 4 Km 5Km – 20 Km
3
Elements of a wireless network
wireless hosts laptops, phones, sensors run applications may be stationary or
b lnetwork
infrastructure
mobile wireless does not always
mean mobility
Wireless and Mobile Networks (SSL) 7-312/5/2017
4
Elements of a wireless networkf d
base station typically connected to
Infrastructure mode
yp ywired network
forwards packets between wired
t k d i lnetwork
infrastructure
network and wireless hosts in its “area” e.g., 802.11 access
point (AP)point (AP)
Wireless and Mobile Networks (SSL) 7-412/5/2017
5
802.11: mobility within same subnet it h hi h AP i
switch
router switch: which AP is associated with H1? self-learning (Ch. 6) - switchg ( )
switch will see frame from H1 and “remember” which switch port can be
d h H1
AP 2
AP 1
used to reach H1 H1 moves but remains
in same IP subnet - IP AP 2
H1
in same IP subnet IP address can remain the same (See subsection 7.3.4, page 546 of textbook)page 546 of textbook)
Suppose the two APs are connected directly to a router instead of to a switch. Mobility ?
Not covered in this class:
Wireless and Mobile Networks (SSL) 7-512/5/2017
Not covered in this class: mobile IP (section 7.6) and mobility in cellular networks (section 7.7)
6
Elements of a wireless network
ad hoc mode no base stations no base stations nodes can only transmit
to other nodes within link coveragelink coverage
nodes organize themselves into a network: need protocol pto route packets among themselves
Wireless and Mobile Networks (SSL) 7-612/5/2017
7
Wireless network taxonomy
single hop multiple hops
lots of research on routing protocols
single hop mult ple hops
infrastructuremode (e g APs)
hosts connect to base station (WiFi,
ll l WiMAX)
wireless nodes serve as relays towards
Internet e gmode (e.g., APs) cellular, WiMAX) which connects to
Internet
Internet, e.g.,community mesh net
no base station, no
noinfrastructure
no base station, noconnection to Internet
(Bluetooth 802 11
,connection to Internet;
wireless nodes serve as relays to
(Bluetooth, 802.11ad hoc mode)
reach some nodes:MANET, VANET
Wireless and Mobile Networks (SSL) 7-712/5/2017
8
Wireless Link Characteristics (1)W L ( )Differences from wired link ….
decreased signal strength: radio signal attenuates more as it propagates (path loss)
int f n f m th s u s: i l ss n t k interference from other sources: wireless network frequencies (e.g., 2.4 GHz) shared by cordless phones, sensors, etc.; devices (motors) interfere as well
multipath propagation: radio signal reflects off objects multipath propagation: radio signal reflects off objects, reaching destination at slightly different times
…. make communication across a wireless link more “difficult” – may need link layer protocol to provide reliable delivery
Wireless and Mobile Networks (SSL) 7-8
y
12/5/2017
9
Wireless Link Characteristics (2) SNR (signal-to-noise ratio) tradeoffs
for a given modulation technique:increase power or reduce noise ->
10-1
10-2
increase power or reduce noise increase SNR
-> decrease BER for a fixed bit error rate (BER): R
10-3
10-4
for a fixed bit error rate (BER): larger SNR –> higher bit rate for the same bandwidth
for a given SNR: choose
BER 10-5
10-6
for a given SNR: choose modulation technique that meets BER requirement to get highest bit rate QAM256 (8 Mbps)
10 20 30 40SNR(dB)
10-7
SNR may change with mobility dynamically adapt modulation
technique (rate)
QAM16 (4 Mbps)
BPSK (1 Mbps)
Wireless and Mobile Networks (SSL) 7-9
technique (rate) 12/5/2017
10
Wireless network characteristics Multiple wireless senders and receivers create
additional problems (carrier sensing is unreliable):
CA B C
A’ i l C’s signal
AB
dd l bl
A’s signalstrength
C s signalstrength
Hidden terminal problem B, A hear each other B, C hear each other
space
Signal attenuation (fading): B, A hear each other
A, C cannot hear each other-> A, C unaware of interference at receiver B
B, C hear each other A, C cannot hear each other,
unaware of interference at B
Wireless and Mobile Networks (SSL) 7-1012/5/2017
11
IEEE 802.11: multiple accessb f CSMA - sense before transmitting
can’t sense all transmissions: hidden terminal, fading llisi d t ti is diffi lt l collision detection is difficult – strong transmit signal,