Chapter 6 Wireless and Mobile Networks - Computer … Wireless Technologies...6: Wireless and Mobile Networks 6-3. Chapter 6 outline. 6.1 Introduction Wireless 6.2 Wireless links,

6: Wireless and Mobile Networks 6-1

Chapter 6Wireless and Mobile Networks

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Thanks and enjoy! JFK/KWR

All material copyright 1996-2007J.F Kurose and K.W. Ross, All Rights Reserved

Computer Networking: A Top Down Approach 4th edition. Jim Kurose, Keith RossAddison-Wesley, July 2007.

Adapted by Andreas Pitsillides for class EPL324, Computer Science department, University of Cyprus, from Kurose and Ross slides: see below


Chapter 6: Wireless and Mobile Networks

Background: # wireless (mobile) phone subscribers now

exceeds # wired phone subscribers! See trends

computer nets: laptops, palmtops, PDAs, Internet-enabled phone promise anytime untethered Internet access

two important (but different) challenges wireless: communication over wireless link mobility: handling the mobile user who changes point

of attachment to network


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


Elements of a wireless network: wireless host

network infrastructure

wireless hosts laptop, PDA, IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility


Elements of a wireless network : base station


base station 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

Base Station (BS) is also known as Access Point (AP)


Elements of a wireless network : wireless link


wireless link typically used to

connect mobile(s) to base station

may also used as backbone link

multiple access protocol coordinates link access

various data rates, transmission distance


Characteristics of selected wireless link standards

Indoor10-30m

Outdoor50-200m

Mid-rangeoutdoor

200m – 4 Km

Long-rangeoutdoor

5Km – 20 Km

.056

.384

1

4

5-11

54

IS-95, CDMA, GSM 2G

UMTS/WCDMA, CDMA2000 3G

802.15

802.11b

802.11a,g

UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 3G cellularenhanced

802.16 (WiMAX), LTE, LTE enhanced

802.11a,g point-to-point

200 802.11n

Dat

a ra

te (M

bps) data

A recent call for papers (CFPs):A new generation of Wireless Local Area Networks (WLANs) is going to make its appearance in the upcoming years, with the IEEE 802.11aa (Robust Audio Video Transport Streaming), IEEE 802.11ac (Very-high throughput < 6GHz), IEEE 802.11af (TV White Spaces) and IEEE 802.11ad (Very-high throughput ~60 GHz), as examples of the most expected ones. Nevertheless, all next-generation standards will consider some of the most significant advances on the wireless communication and networking area in the last decade, developed by a highly active community, in both academia and industry.

This special issue requests papers that advance the state-of-the-art of the recent and on-going IEEE 802.11 standards (i.e., IEEE 802.11p, IEEE 802.11s, IEEE 802.11aa, IEEE 802.11ac, IEEE 802.11ad, IEEE 802.11ae, IEEE 802.11ah, IEEE 802.11af, IEEE 802.11ai, etc.), as well as present mechanisms and solutions, from MAC or above layers, that could be readily transferred to the not-yet finished standards or their future amendments.

Recent IEEE 802 standardisation efforts

8


Elements of a wireless network : infrastructure


infrastructure mode base station connects

mobiles into wired network

handoff: mobile changes base station providing connection into wired network


Elements of a wireless network : ad-hoc

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

Examples include: MANETSSensor NetworksVANETS


Wireless network taxonomy

single hop multiple hops

infrastructure(e.g., APs)

noinfrastructure

host connects to base station (WiFi,WiMAX, cellular) which connects to

larger Internet

no base station, noconnection to larger Internet (Bluetooth,

ad hoc nets)

host may have torelay through several

wireless nodes to connect to larger

Internet: mesh net

no base station, noconnection to larger

Internet. May have torelay to reach other a given wireless node

MANET, VANET


Wireless Link Characteristics (1)Differences from wired link ….

decreased signal strength: radio signal attenuates as it propagates through matter (path loss)

interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well

multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times

…. make communication across (even a point to point) wireless link much more “difficult”

Known problems with WLANs Wireless link characteristics: media is error prone

and the bit error rate (BER) is very high compared to the BER of wired networks.

Carrier Sensing/collision detection is difficult in wireless networks because a station is incapable of listening to its own transmissions in order to detect a collision (more later).

The Hidden Terminal problem also decreases the performance of a WLAN (more later).

Mobility (variation in link reliability, seamless connections required, battery limitations) (more later)

13

Wireless Link CharacteristicsDifferences from wired link ….

decreased signal strength: radio signal attenuates as it propagates through matter (path loss)

interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); also devices (e.g. motors) interfere as well (noise)

multipath propagation: radio signal reflects off objects, arriving at destination at slightly different times (channel quality varies over time)

shared with other technologies and spectrum users more difficult security (shared medium)

…. make communication across (even a point to point) wireless link much more “difficult”

14

Signal quality Two commonly used metrics are signal level

and signal to noise ratio (SNR) Signal level is the strength of your Wi-Fi signal.

Signal levels above -40 dBm are considered good and of concern and lower than -80 dBm are considered critical.

Signal-to-Noise Ratio The signal-to-noise ratio (SNR) compares the level of the Wi-Fι

signal to the level of background noise. Sources of noise can include microwave ovens, cordless phones, Bluetooth devices, wireless video cameras, wireless game controllers, fluorescent lights, and more. Note that “noise” does not include co-channel interference from other radio transmitters — that is shown in the signal-to-interference ratio.

A ratio of 10-15dB is the accepted minimum to establish an unreliable connection; 16-24dB (decibels) is usually considered poor; 25-40dB is good and a ratio of 41dB or higher is considered excellent.

http://help.netspotapp.com/what-is-the-signal-to-noise/ 15

http://help.netspotapp.com/noise-level/

http://help.netspotapp.com/signal-to-interference-ratio/


Wireless Link Characteristics (2) SNR: signal-to-noise ratio

larger SNR – easier to extract signal from noise (a “good thing”)

SNR versus BER tradeoffs given physical layer:

increase power -> increase SNR->decrease BER

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 20 30 40

QAM256 (8 Mbps)

QAM16 (4 Mbps)

BPSK (1 Mbps)

SNR(dB)BE

R

10-1

10-2

10-3

10-5

10-6

10-7

10-4


Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access):

AB

C

Hidden terminal problem B, A hear each other B, C hear each other A, C can not hear each othermeans A, C unaware of their

interference at B

A B C

A’s signalstrength

space

C’s signalstrength

Signal attenuation: B, A hear each other B, C hear each other A, C can not hear each other

interfering at B


Code Division Multiple Access (CDMA)

used in several wireless broadcast channels (cellular, satellite, etc) standards

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

encoded signal = (original data) X (chipping sequence)

decoding: inner-product of encoded signal and chipping sequence

allows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)


CDMA Encode/Decode

slot 1 slot 0

d1 = -1

1 1 1 1

1- 1- 1- 1-

Zi,m= di.cm

d0 = 1

1 1 1 1

1- 1- 1- 1-

1 1 1 1

1- 1- 1- 1-

1 1 11

1-1- 1- 1-

slot 0channeloutput

slot 1channeloutput

channel output Zi,m

sendercode

databits

slot 1 slot 0

d1 = -1d0 = 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 1 11

1-1- 1- 1-

slot 0channeloutput

slot 1channeloutputreceiver

code

receivedinput

Di = Σ Zi,m.cmm=1

M

M


CDMA: two-sender interference


Chapter 6 outline

6.1 Introduction




6.4 cellular Internet access architecture standards (e.g., GSM)





layer protocols

6.9 Summary


IEEE 802.11 Wireless LAN 802.11b

2.4-5 GHz unlicensed spectrum up to 11 Mbps direct sequence spread

spectrum (DSSS) in physical layer

• all hosts use same chipping code

802.11a 5-6 GHz range up to 54 Mbps

802.11g 2.4-5 GHz range up to 54 Mbps

802.11n: multiple antennae 2.4-5 GHz range up to 200 Mbps, and more

with MIMO all use CSMA/CA for multiple access all have base-station and ad-hoc network

versions

NEW STANDARD: 802.11ac MORE LATER


802.11 LAN architecture

wireless host communicates with base station base station = access

point (AP) Basic Service Set (BSS)

(aka “cell”) in infrastructure mode contains: wireless hosts access point (AP): base

station ad hoc mode: hosts only

BSS 1

BSS 2

Internet

hub, switchor routerAP

AP

IEEE 802.11 terminologyBasic Service Set (BSS)

– group of stations using same radio frequency

Access Point (AP)– station integrated into the wireless LAN

and the distribution systemStation (STA)

– terminal with access mechanisms to wireless medium and radio contact to access point

Portal– bridge to other (wired) networks

Distribution System (DS)– interconnection network to form one

logical network Extended Service Set (EES)

– based on several BSS

Distribution System

Portal

802.x LAN

AccessPoint

802.11 LAN

BSS2

802.11 LAN

BSS1

AccessPoint

STA1

STA2 STA3

ESS

System Architecture of an infrastructure network

24

IEEE standard 802.11

mobile terminal

access point

fixedterminal

application

TCP

802.11 PHY

802.11 MAC

IP

802.3 MAC

802.3 PHY

application

TCP

802.3 PHY

802.3 MAC

IP

802.11 MAC

802.11 PHY

LLC

infrastructurenetwork

LLC LLC

25


802.11: Channels, association

802.11b: 2.4GHz - 2.485GHz spectrum divided into 11 physical channels at different frequencies AP admin chooses frequency for AP interference possible: channel can be same as

that chosen by neighboring AP! host: must associate with an AP

scans channels, listening for beacon framescontaining AP’s name (SSID) and MAC address

selects AP to associate withmay perform authentication [Chapter 8] will typically run DHCP to get IP address in AP’s

subnet

WLAN physical channels



802.11: passive/active scanning

AP 2AP 1

H1

BBS 2BBS 1

122

3 4

Active Scanning: (1) Probe Request frame broadcast

from H1(2) Probes response frame sent from

APs(3) Association Request frame sent:

H1 to selected AP (4) Association Response frame

sent: H1 to selected AP

AP 2AP 1

H1

BBS 2BBS 1

12 3

1

Passive Scanning:(1) beacon frames sent from APs(2) association Request frame sent:

H1 to selected AP (3) association Response frame sent:

H1 to selected AP

IEEE 802.11: MAC overview Two basic access mechanisms have been defined

for IEEE 802.11 CSMA/CA (mandatory) summarized as distributed

coordination function (DCF)• Optional method (RTS/CTS) avoiding the hidden terminal

problem A contention-free polling method for time-bounded

service called point coordination function (PCF)• access point polls terminals according to a list

DCF only offers asynchronous service, while PCF offers both asynchronous and time-bounded service, but needs the access point to control medium access and to avoid contention.

only asynchronous data service in ad-hoc network mode29

IEEE 802.11: MAC overviewWithin the MAC layer, Distributed

Coordination Function (DCF) (asynchronous service) is used as a fundamental access method, while Point Coordination Function (PCF) (synchronous service) is optional. – DCF is also known as Carrier Sense Multiple

Access with Collision Avoidance (CSMA/CA) protocol. It is an asynchronous access method based on the contention for the usage of shared channels. A contention-free access mechanism is provided through the RTS/CTS (Request to Send/Clear to Send) exchange.

– PCF is used for time-bounded transfer of data

30


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 other node 802.11: no collision detection!

difficult to receive (sense collisions) when transmitting due to weak received signals (fading) + single Rx/Tx

can’t sense all collisions in any case: hidden terminal, fading goal: avoid collisions: CSMA/C(ollision)A(voidance)

AB

CA B C

A’s signalstrength

space

C’s signalstrength

IEEE 802.11: CSMA/CA Collision Avoidance

idea is to prevent collisions at the moment they are most likely to occur , i.e. when the bus is released (since many stations may compete then).

In the event medium is sensed busy, all clients are forced to wait for a random number of timeslots and then sense the medium again, before starting a transmission. (more later)

If the medium is sensed to be busy, the client freezes its timer until it becomes free again. (more later)

Thus, the chance of two clients starting to send simultaneously is reduced.

32

IEEE 802.11: MAC overview CSMA/CA protocol basics:

medium can be busy or idle (detected by the CCAClear Channel Assessment-CCA signal of the physical layer)

• If medium busy this can be due to data frames or other control frames

during a contention phase several nodes try to access medium

optionally, the standard allows for collision free operation through small reservation packets (RTS, CTS)

33


Avoiding collisionsidea: allow 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 BS using CSMA RTSs may still collide with each other (but they’re short)

BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

avoid data frame collisions completely using small reservation packets!


IEEE 802.11 MAC Protocol: CSMA/CA

802.11 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expiresif no ACK, increase random backoff

interval, repeat 2802.11 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

Define (802.11b): slot = 20 µs (9 or 20 µs for 802.11g) Short inter-frame spacing (SIFS) = 10 µs (16 µs for 802.11a)

• shortest waiting time for medium access• defined for short control messages (e.g., ACK of data packets)

DCF inter-frame spacing (DIFS) = 50 µs (28 µs for 802.11g)• longest waiting time used for asynchronous data service within a

contention period DIFS=SIFS + two slot times PCF inter-frame spacing (PIFS)

• an access point polling other nodes only has to wait PIFS for medium access (for a time-bounded service) PIFS=SIFS + one slot time (30 µs for 802.11b)

The standard defines also two control frames: RTS: Request To Send CTS: Clear To Send

IEEE 802.11: MAC overview

36

Interframe Spacing (IFS) and priorities

SIFS (Short IFS) ACK, CTS, Poll Messages, Poll responses, CF-End

PIFS (PCF IFS) PCF operation mode, including Beacon,

Retransmitted poll messages DIFS (DCF IFS)

DCF operation mode, including back-off, RTS EIFS (Extended IFS)

After detection of erroneous frame

High to low priority

Shorter to longer time

37

IEEE 802.11: CSMA/CA • Broadcast data transfer (DCF)

t

medium busy

DIFSDIFS

next frame

contention window(randomized back-offmechanism)

slot timedirect access if medium is free ≥ DIFS

– station ready to send starts sensing the medium (Carrier Sense based on CCA-Clear Channel Assessment)

– if the medium is busy, the station has to wait for a free DIFS, then the station must additionally wait a random back-off time (collision avoidance)

– if another station occupies the medium during the back-off time of the station, the back-off timer stops (fairness – during the next phase this node will continue its timer from where it stopped)

– if the medium is free for the duration of a Distributed Coordination Function Inter-Frame Space (DIFS), then station can start sending

38

IEEE 802.11 : CSMA/CA • E.g. Unicast data transfer

DIFS

data

ACK

otherstations

receiver

sender

t

data

DIFS

waiting time

contention

SIFS

– station has to wait for DIFS before sending data

– receivers acknowledge after waiting for a duration of a Short Inter-Frame Space (SIFS), if the packet was received correctly

Channel sensed busy

39

EE802.11: Exponential backoff mechanism

binary exponential backoff: After k collisions, a random number of slot times between 15 and 2k+5-1 is chosen. So, for the first collision, each sender might wait between 15 or 31 slot times. After the second collision, the senders might wait between 15 and 63 slot times, and so forth.

As the number of retransmission attempts increases, the number of possibilities for delay increases .

Note that the suggested minimum window is normally set at 15 (or 31) at start, so as to have some initial non-zero random delay and there is a max number prior to declaring the transmission not possible

40

Contention window (CW) for 802.11b

If transmission of a frame was unsuccessful and the frame is allowed to be retransmitted, before each retransmission the Contention Window (CW) from which bn is chosen (at random, starting from 15 or 31) is increased.

DIFS … CW = 25-1 = 31 slots(slot = 20 µs)

Initial attempt

DIFS …CW = 26-1 = 63 slots1st retransm.

DIFSCW = 210-1 = 1023 slots

5th (and further) retransmissions

:…

CW802.11b


:

41

Contention window (CW) for 802.11g

In the case of 802.11g operation, the initial CW length is 15 slots. The slot duration is 9 µs. The backoff operation of 802.11g is substantially faster than that of 802.11b.

DIFS … CW = 24-1 = 15 slots(slot = 9 µs)

Initial attempt

DIFS …CW = 25-1 = 31 slots1st retransm.

DIFSCW = 210-1 = 1023 slots

6th (and further) retransmissions

:…

CW802.11g


:

42

Selection of random backoffFrom the number CW (= 15 / 31 … 2k+5-1 slots) the random backoff bn (in terms of slots) is chosen in such a way that bn is uniformly distributed between 0 … CW.

Since it is unlikely that several stations will choose the same value of bn, collisions are rare.

The next slides show wireless medium access in action. The example involves four stations: A, B, C and D. ”Sending a packet” means ”Data+SIFS+ACK” sequence. Note how the backoff time may be split into several parts.


43

Wireless medium access example

Station A

Station B

Station C

Station D

DIFS

Defer

Defer

Contention Window

Backoff

1) While station A is sending a packet, stations B and C also wish to send packets, but have to wait (defer + backoff)

2) Station C is ”winner” (backoff time expires first) and starts sending packet

21

ACK

Data+SIFS+ACK


44


Station A

Station B

Station C

Station D

DIFS DIFS

Defer

3) Station D also wishes to send a packet

4) When medium becomes idle plus DIFS elapses,

station B continues to count down and station D draws a CW number D(bn)

station B is ”winner” After its CW counts down to zero it starts sending packet

3

4

ACK


45


Station A

Station B

Station C

Station D

DIFS

5) Station D counts down to 0 and then starts sending packet. Now there is no competition.

DIFS

5

ACK


46

No shortcuts for any station…

DIFS SIFS DIFS

ACK (B=>A)

Transmitted frame

(A=>B)

Next frame

(A=>B)

Backoff

When a station wants to send more than one frame, it has to use the backoff mechanism like any other station (of course it can ”capture” the channel by sending a long frame, for instance using fragmentation).


47

Avoiding collisions (using extra signalling). How?idea: allow 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 BS

using CSMA RTS packets may still collide with each other (but they are very

short) BS broadcasts clear-to-send CTS in response to RTS CTS heard by all nodes

sender transmits data frame other stations defer transmissions. For how long?

avoid data frame collisions completely using small reservation packets!

IEEE 802.11: MAC overview

48

Network Allocation Vector (NAV)

Each RTS frame includes the duration of the time it needs to occupy the channel.

NAV: a timer on other stations which have to wait NAV before checking if the channel/medium is free.

When a station (WS1) sends RTS (or CTS), other stations on the system start NAV (WS2 and WS3 in example below)

RTSRTS

WS3 WS1 WS2

49

Hidden Station Problem (Solution)

B CA

RTS/NAV RTS/NAV

CTS

Data CTS/NAV

B accepts RTS from A and rejects RTS from C.

CTS from B (actually BS) to A is also received on C which starts the NAV timer in CTS.

A and C want to send to B B can hear A and CA and C cannot hear each other

50

Busy Medium

Physically busy: a station senses the wireless medium to determine if it is busy.

Virtually busy: a station receives a control message (RTS or CTS) which indicates the wireless medium is busy for the duration of the NAV timer. All stations must monitor the headers of all frames

they receive and store the NAV value in a counter. The counter decrements in steps of one

microsecond. When the counter reaches zero, the channel is available again.

51

IEEE 802.11 • Sending unicast packets with RTS/CTS control frames

SIFS

DIFS

data

ACK

totherstations

receiver

sender data

DIFS

defer access contention

RTS

CTSSIFS SIFS

NAV (RTS)=3SIFS+CTS+data+ACKNAV (CTS)=2SIFS+data+ACK

– station can send RTS with reservation parameter after waiting for DIFS (reservation determines amount of time the data packet needs the medium and the ACK related to it).

– Every node receiving this RTS now has to set its net allocation vector – it specifies the earliest point at which the node can try to access the medium again

– acknowledgement via CTS after SIFS by receiver (if ready to receive)– sender can now send data at once, acknowledgement via ACK– Other stations store medium reservations distributed via RTS and CTS

52

Collision Avoidance: RTS-CTS exchange

APA B

time

DATA (A)

reservation collision

defer

53


framecontrol duration address

1address

2address

4address

3 payload CRC

2 2 6 6 6 2 6 0 - 2312 4seq

control

802.11 frame: addressing

Address 2: MAC addressof wireless host or AP transmitting this frame

Address 1: MAC addressof wireless host or AP to receive this frame

Address 3: MAC addressof router interface to which AP is attached

Address 4: used only in ad hoc mode


Internetrouter

AP

H1 R1

AP MAC addr H1 MAC addr R1 MAC addraddress 1 address 2 address 3

802.11 frame

R1 MAC addr AP MAC addr dest. address source address

802.3 frame

802.11 frame: addressing


framecontrol duration address

1address

2address

4address

3 payload CRC

2 2 6 6 6 2 6 0 - 2312 4seq

control

Type FromAPSubtype To

APMore frag WEPMore

dataPower

mgtRetry RsvdProtocolversion

2 2 4 1 1 1 1 1 11 1

802.11 frame: moreduration of reserved transmission time (RTS/CTS)

frame seq #(for reliable ARQ)

frame type(RTS, CTS, ACK, data)


hub or switch

AP 2

AP 1

H1 BBS 2

BBS 1

802.11: mobility within same subnet

router 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


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)

10 20 30 40SNR(dB)

BER

10-1

10-2

10-3

10-5

10-6

10-7

10-4

operating point

1. SNR decreases, BER increase as node moves away from base station2. When BER becomes too high, switch to lower transmission rate but with lower BER


802.11: advanced capabilitiesPower Management node-to-AP: “I am going to sleep until next

beacon frame”AP knows not to transmit frames to this

nodenode wakes up before next beacon frame

beacon frame: contains list of mobiles with AP-to-mobile frames waiting to be sentnode will stay awake if AP-to-mobile frames

to be sent; otherwise sleep again until next beacon frame


M radius ofcoverage

S

SS

P

P

P

P

M

S

Master device

Slave device

Parked device (inactive)P

802.15: 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: evolved from

Bluetooth specification 2.4-2.5 GHz radio band up to 721 kbps


802.16: WiMAX like 802.11 & cellular:

base station model transmissions to/from

base station by hosts with omnidirectional antenna

base station-to-base station backhaul with point-to-point antenna

unlike 802.11: range ~ 10 Km (“city

rather than coffee shop”)

~14 Mbps

point-to-multipoint

point-to-point


802.16: WiMAX: downlink, uplink scheduling

transmission frame down-link subframe: base station to node uplink subframe: node to base station

prea

m.

DL-MAP

UL-MAP

DLburst 1 SS #1DL

burst 2DL

burst nInitialmaint.

requestconn.

downlink subframe

SS #2 SS #k

uplink subframe

…

…

…

…

base station tells nodes who will get to receive (DL map) and who will get to send (UL map), and when

WiMAX standard provide mechanism for scheduling, but not scheduling algorithm


Chapter 6 outline

6.1 Introduction









layer protocols

6.9 Summary


Mobile Switching

Center

Public telephonenetwork, andInternet

Mobile Switching

Center

Components of cellular network architecture (GSM)

connects cells to wide area net manages call setup (more later!) handles mobility (more later!)

MSC

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

cell

wired networkWhy use cells? To reuse frequency spectrum. Recall signal power diminishes as an inverse power law with distance (1/dα) a>=2

3G (UMTS) Network Architecture

Radio Network Subsystem (RNS)

Core Network (CN)

UE – User EquipmentRNC – Radio Network ControllerSGSN – Serving GPRS Support NodeGGSN – Gateway GPRS Support Node

65


Cellular networks: the first hopTwo techniques for sharing

mobile-to-BS radio spectrum

combined FDMA/TDMA:divide spectrum in frequency channels, divide each channel into time slots

CDMA: code division multiple access

frequencybands

time slots


Cellular standards: brief survey

2G systems: voice channels IS-136 TDMA: combined FDMA/TDMA (north

america) GSM (global system for mobile communications):

combined FDMA/TDMA most widely deployed

IS-95 CDMA: code division multiple access

GSMDon’t drown in a bowlof alphabet soup: use thisfor reference only


Cellular standards: brief survey

2.5 G systems: voice and data channels for those who can’t wait for 3G service: 2G extensions general packet radio service (GPRS)

evolved from GSM data sent on multiple channels (if available)

enhanced data rates for global evolution (EDGE) also evolved from GSM, using enhanced modulation data rates up to 384K

CDMA-2000 (phase 1) data rates up to 144K evolved from IS-95


Cellular standards: brief survey3G systems: voice/data Universal Mobile Telecommunications Service (UMTS)

data service: High Speed Uplink/Downlink packet Access (HSDPA/HSUPA): 3 Mbps

CDMA-2000: CDMA in TDMA slots data service: 1xEvlution Data Optimized (1xEVDO)

up to 14 Mbps

4G LTE, LTE enhanced, …

IMT and IMT-Advanced Technologies

LTE, LTE Advanced and Wireless MAN-Advanced, are designed to enable high speed Internet/Broadband at anytime, anywhere, with higher level of user-level customization.

As per ITU for IMT-Advanced technologies, the targeted peak data rates are up to 100 Mbit/s for high mobility and up to 1 Gbit/s for low mobility scenario. Scalable bandwidths up to at least 40 MHz should be provided

key technologies: Orthogonal Frequency Division Multiplex (OFDMA) Multiple Input Multiple Output (MIMO) and System Architecture Evolution (SAE)

70

MIMO Multiple Input Multiple Output

• Uses multiple transmitter and receiver antennas, whichallow independent channels to be created in space.

• Various Approaches for MIMO: Space diversity:- to improve the communication reliability by

decreasing the sensitivity to fading by picking up multiple copiesof the same signal at different locations in space.

Beamforming:- antenna elements are used to adjust the strengthof the transmitted and received signals, based on their direction forfocusing of energy.

Spatial Multiplexing:- Increased capacity, reliability, coverage,reduction in power requirement by introducing additional spatialchannels that are exploited by using space-time coding

71

OFDMA Orthogonal Frequency Division Multiple Access

Based on the idea of dividing a given high-bit-ratedata stream into several parallel lower bit-ratestreams and modulating each stream on separatecarrier – often called sub-carriers or tones. Multi-carrier modulation scheme minimize inter-symbol

interference (ISI) by making the symbol time large enough so thatthe channel-induced delays are an insignificant (<10%) fraction ofthe symbol duration.

OFDM is a spectrally efficient version of multi-carrier modulationwhere sub-carriers are selected such that they are all orthogonal toone another over the symbol duration, thereby avoiding the need tohave non overlapping sub-carrier channels to eliminate inter-carrier interference .

72

OFDMA Orthogonal Frequency Division Multiple Access

• OFDMA can be used as a multi-access scheme, where theavailable sub-carriers may be divided into several groupsof sub-carriers called sub-channels. Different sub channelsmay be allocated to different users as a multiple accessmechanism. This type of multi access scheme is calledOFDMA.

• OFDMA is essentially a hybrid of FDMA and TDMA.Users are dynamically assigned sub-carriers (FDMA) indifferent time slots (TDMA).

• OFDMA is a flexible multiple access technique that canaccommodate many users with widely varyingapplications, data rates and QoS requirements.

73

LTE Specifications and speed

Parameter Details Peak downlink speed with 64QAM in Mbps 100 (SISO), 172 (2x2 MIMO), 326 (4x4 MIMO) Peak uplink speeds(Mbps) 50 (QPSK), 57 (16QAM), 86 (64QAM)

Data type All packet switched data (voice and data). No circuit switched.

Channel bandwidth (MHz) 1.4, 3, 5, 10, 15, 20 Duplex schemes FDD and TDD

Mobility 0 - 15 km/h (optimised), 15 - 120 km/h (high performance)

Latency Idle to active less than 100ms Small packets ~10 ms

Spectral efficiency Downlink: 3 - 4 times Rel 6 HSDPA Uplink: 2 -3 x Rel 6 HSUPA

Access schemes OFDMA (Downlink) SC-FDMA (Uplink)

Modulation types supported QPSK, 16QAM, 64QAM (Uplink and downlink)

74

Cellular Core Network

eNodeB 3 S-GW 2P-GW

S-GW 1

eNodeB 1

eNodeB 2

Internet andOther IP Networks

GTP Tunnels

UE 2

UE 1

LTE Architecture• UE: user equipment• eNodeB: base station• S-GW: serving

gateway• P-GW: packet data

network gateway• MME: mobility

management entity• HSS: home subscriber

server

MME/HSS

enhanced packet core (EPC)

75

Comparison chart

WCDMA (UMTS)

HDPA HSPA+ LTE LTE Advanced

Max downlink speed( bps) 384 k 14 M 28 M 300M 1G

Max uplink speed (bps) 128 k 5.7 M 11 M 75 M 500 M

Latency round trip time(approx)

150 ms 100 ms 50ms (max)

~10 ms less than 5 ms

3GPP releases Rel 99/4 Rel 5 / 6 Rel 7 Rel 8 Rel 10

Access methodology CDMA CDMA CDMA OFDMA SC-FDMA

OFDMA / SC-FDMA

76


Chapter 6 outline

6.1 Introduction









layer protocols

6.9 Summary


What is mobility?

spectrum of mobility, from the network perspective:

no mobility high mobility

mobile wireless user, using same access point

mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone)

mobile user, connecting/ disconnecting from network using DHCP.


Mobility: Vocabularyhome network: permanent “home” of mobile(e.g., 128.119.40/24)

Permanent address:address in home network, can always be used to reach mobilee.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


Mobility: more vocabulary

Care-of-address: address in visited network.(e.g., 79,129.13.2)

wide area network

visited network: network in which mobile currently resides (e.g., 79.129.13/24)

Permanent address: remains constant (e.g., 128.119.40.186)

foreign agent: entity in visited network that performs mobility functions on behalf of mobile.

correspondent: wants to communicate with mobile


How do you contact a mobile friend:

search all phone books?

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 her?


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


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

not scalable

to millions ofmobiles


Mobility: registration

End result: Foreign agent knows about mobile Home agent knows location of mobile

wide area network

home networkvisited network

1

mobile contacts foreign agent on entering visited network

2

foreign agent contacts home agent home: “this mobile is resident in my network”


Mobility via Indirect Routing

wide area network

homenetwork

visitednetwork

3

24

1correspondent addresses packets using home address of mobile

home agent intercepts packets, forwards to foreign agent

foreign agent receives packets, forwards to mobile

mobile replies directly to correspondent


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-network-

mobile inefficient when correspondent, mobile are in same network


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!


Mobility via Direct Routing

wide area network

homenetwork

visitednetwork

4

2

41correspondent requests, receives foreign address of mobile

correspondent forwards to foreign agent

foreign agent receives packets, forwards to mobile

mobile replies directly to correspondent

3


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?


wide area network

1

foreign net visited at session start

anchorforeignagent 2

4

new foreignagent

35

correspondentagent

correspondent

new foreignnetwork

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)


Chapter 6 outline

6.1 Introduction









layer protocols

6.9 Summary


Mobile IP

RFC 3344 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: indirect routing of datagrams agent discovery registration with home agent


Mobile IP: indirect routing

Permanent address: 128.119.40.186

Care-of address: 79.129.13.2

dest: 128.119.40.186

packet sent by correspondent

dest: 79.129.13.2 dest: 128.119.40.186

packet sent by home agent to foreign agent: a packet within a packet

dest: 128.119.40.186

foreign-agent-to-mobile packet


Mobile IP: agent discovery agent advertisement: foreign/home agents advertise

service by broadcasting ICMP messages (typefield = 9)

RBHFMGV bits reserved

type = 16

type = 9 code = 0

checksum

router address standard

ICMP fields

mobility agent advertisement

extension

length sequence #

registration lifetime

0 or more care-of-addresses

0 8 16 24

R bit: registration required

H,F bits: home and/or foreign agent


Mobile IP: registration example

visited network: 79.129.13/24 home agent

HA: 128.119.40.7 foreign agent

COA: 79.129.13.2 COA: 79.129.13.2

….

ICMP agent adv. Mobile agent MA: 128.119.40.186

registration req. COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification:714 ….

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 reply

HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 ….

time


Components of cellular network architecture

correspondent

MSC

MSCMSC MSC

MSC

wired public telephonenetwork

different cellular networks,operated by different providers

recall:


Handling mobility in cellular networks

home network: network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon) home location register (HLR): database in home

network containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network)

visited network: network in which mobile currently resides visitor location register (VLR): database with

entry for each user currently in network could be home network


Public switched telephonenetwork

mobileuser

homeMobile

Switching Center

HLR home network

visitednetwork

correspondent

Mobile Switching

Center

VLR

GSM: indirect routing to mobile

1 call routed to home network

2

home MSC consults HLR,gets roaming number ofmobile in visited network

3

home MSC sets up 2nd leg of callto MSC in visited network

4

MSC in visited network completescall through base station to mobile


Mobile Switching

Center

VLR

old BSSnew BSS

old routing

newrouting

GSM: handoff with common MSC

Handoff goal: route call via new base station (without interruption)

reasons for handoff: stronger signal to/from new

BSS (continuing connectivity, less battery drain)

load balance: free up channel in current BSS

GSM doesn’t mandate why to perform handoff (policy), only how (mechanism)

handoff initiated by old BSS


Mobile Switching

Center

VLR

old BSS

1

3

24

5 6

78

GSM: handoff with common MSC

new BSS

1. old BSS informs MSC of impending handoff, provides list of 1+ new BSSs

2. MSC sets up path (allocates resources) to new BSS

3. new BSS allocates radio channel for use by mobile

4. new BSS signals MSC, old BSS: ready 5. old BSS tells mobile: perform handoff to

new BSS6. mobile, new BSS signal to activate new

channel7. mobile signals via new BSS to MSC:

handoff complete. MSC reroutes call8 MSC-old-BSS resources released


home network

Home MSC

PSTN

correspondent

MSCanchor MSC

MSCMSC

(a) before handoff

GSM: handoff between MSCs

anchor MSC: first MSC visited during cal call remains routed

through anchor MSC new MSCs add on to end

of MSC chain as mobile moves to new MSC

IS-41 allows optional path minimization step to shorten multi-MSC chain


home network

Home MSC

PSTN

correspondent

MSCanchor MSC

MSCMSC

(b) after handoff

GSM: handoff between MSCs

anchor MSC: first MSC visited during cal call remains routed

through anchor MSC new MSCs add on to end

of MSC chain as mobile moves to new MSC

IS-41 allows optional path minimization step to shorten multi-MSC chain


Mobility: GSM versus Mobile IPGSM element Comment on GSM element Mobile IP element

Home system Network to which mobile user’s permanent phone number belongs

Home network

Gateway Mobile Switching Center, or “home MSC”. Home Location Register (HLR)

Home MSC: point of contact to obtain routable address of mobile user. HLR: database in home system containing permanent phone number, profile information, current location of mobile user, subscription information

Home agent

Visited System Network other than home system where mobile user is currently residing

Visited network

Visited Mobile services Switching Center.Visitor Location Record (VLR)

Visited MSC: responsible for setting up calls to/from mobile nodes in cells associated with MSC. VLR: temporary database entry in visited system, containing subscription information for each visiting mobile user

Foreign agent

Mobile Station Roaming Number (MSRN), or “roaming number”

Routable address for telephone call segment between home MSC and visited MSC, visible to neither the mobile nor the correspondent.

Care-of-address


Wireless, mobility: impact on higher layer protocols

logically, impact should be minimal … best effort service model remains unchanged TCP and UDP can (and do) run over wireless, mobile

… but performance-wise: packet loss/delay due to bit-errors (discarded

packets, delays for link-layer retransmissions), and handoff

TCP interprets loss as congestion, will decrease congestion window un-necessarily

delay impairments for real-time traffic limited bandwidth of wireless links


Chapter 6 Summary

Wireless wireless links:

capacity, distance channel impairments CDMA

IEEE 802.11 (“wi-fi”) CSMA/CA reflects

wireless channel characteristics

cellular access architecture standards (e.g., GSM,

CDMA-2000, UMTS)

Mobility principles: addressing,

routing to mobile users home, visited networks direct, indirect routing care-of-addresses

case studies mobile IP mobility in GSM

impact on higher-layer protocols

Supplementary slides



Mobile Communications

Use

rs/m

illion

s

Approximately 7 billion mobile users worldwide

Revenues from the wireless/mobile networks industries exceed revenues from the fixed networks industry

Internet brought communication industry from the office to the home and to the mobile user

It is undoubtedly the largestindustry on a worldwide scale

MANETS In many (not all!) ad hoc network applications,

participants move around • In mobile ad hoc

networks (MANET):• Mobility changes

neighborhood relationship • Must be compensated for• E.g., routes in the network

have to be changed

• Complicated by scale• Large number of such nodes

difficult to support

108

A NETWORK consisting of devices (sensors) that:

… communicate wirelessly… are battery-powered… may have different characteristics… have limited processing capabilities… have limited life… often operate in noisy/adversarial environments… monitor/control physical processes

WHAT’S A SENSOR NETWORK?

May be part of the Internet/Web of ThingsLeading to ambient intelligence / pervasive computing …

UC Berkeley: COTS Dust

UC Berkeley: COTS DustUC Berkeley: Smart DustUCLA: WINS

Rockwell: WINS

JPL: Sensor Webs

Sensor Nodes

Rene Mote

Dot Mote

weC MoteMica node

Sensor Nodes

NETRL Sensor network devices Testbed

Crossbow Mica2 Crossbow MicaZCrossbow Mica2Dot

Parallax BOE-Bot Parallax BOE-Bot Tank

Parallax BOE-Bot with gripper

112

http://images.google.com/imgres?imgurl=http://www.btnode.ethz.ch/pub/uploads/Projects/mica2.jpg&imgrefurl=http://www.btnode.ethz.ch/Projects/Mica2&h=733&w=838&sz=68&hl=en&start=1&um=1&tbnid=BRmx_6OUzBPYYM:&tbnh=126&tbnw=144&prev=/images%3Fq%3DMICA2%26svnum%3D10%26um%3D1%26hl%3Den

http://images.google.com/imgres?imgurl=http://www.btnode.ethz.ch/pub/uploads/Projects/mica2.jpg&imgrefurl=http://www.btnode.ethz.ch/Projects/Mica2&h=733&w=838&sz=68&hl=en&start=1&um=1&tbnid=BRmx_6OUzBPYYM:&tbnh=126&tbnw=144&prev=/images%3Fq%3DMICA2%26svnum%3D10%26um%3D1%26hl%3Den

http://www.eecs.harvard.edu/%7Emdw/course/cs263/pics/mica2dot.jpg

http://www.eecs.harvard.edu/%7Emdw/course/cs263/pics/mica2dot.jpg

http://images.google.com/imgres?imgurl=http://www.electronicproducts.com/images2/F304CROE0105.gif&imgrefurl=http://www.electronicproducts.com/ShowPage.asp%3FFileName%3Dpoy.jan2005.HTML&h=222&w=250&sz=20&hl=en&start=2&um=1&tbnid=TlIg94AKMQrcpM:&tbnh=99&tbnw=111&prev=/images%3Fq%3DMICAz%26svnum%3D10%26um%3D1%26hl%3Den

http://images.google.com/imgres?imgurl=http://www.electronicproducts.com/images2/F304CROE0105.gif&imgrefurl=http://www.electronicproducts.com/ShowPage.asp%3FFileName%3Dpoy.jan2005.HTML&h=222&w=250&sz=20&hl=en&start=2&um=1&tbnid=TlIg94AKMQrcpM:&tbnh=99&tbnw=111&prev=/images%3Fq%3DMICAz%26svnum%3D10%26um%3D1%26hl%3Den

Example: Patient Monitoring(Body Area Networks)

http://www.imec.be/human

another example SENSOR NETWORK

SNETs will consist of thousands of interacting devices!

Example scenario: Setting with VANETs

Unexpected hazard in the freeway with VANETs The vehicle/driver is

informed ‘hopefully’ in a few milliseconds

Post accident• Call emergency services &

Towing services

115

Documents

Chapter 6 Wireless and Mobile Networks - Computer … Wireless Technologies...6: Wireless and Mobile Networks 6-3. Chapter 6 outline. 6.1 Introduction Wireless 6.2 Wireless links,