DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING STAFF NAtdE: S.PRASANNA &
R.MOIIAN
CLASS: IV/CSE
SEM: VII
SU&ItrCT CODE: CS24O2 SUBJDCT NAME: MoBILE AND PERVASryE COMPI-ITING 2 lVlarks
l, How thedata is transferred? hansrer are circuit swirchins .","n,ff,T1',1"",1[T?,:flL?l"J.':l ror,data & Packer circuir is firsr esrabtished across a sequence orii*. ulra tr,.rli" ;;;i;,:;"#..is",:3,ed rs allocated lo a single
lhe
call.
user for the rhole duraiion
2. Why is ptysical
of
layer in IEEf,802.ll subdivided? What are its sub layers?
raverhas ro be dependenr on .Il"J,Y".,'fr:3il:;,?:ltl';l*::-tl''t:qbecauseasub *d lhe other has lo be medium dependanr. The r"o.rL ruy,i ur. n#.iy'"" """'ou,''
F > d.)hat
Physical layer convergence protocol Physical rnedium dependarisub layer
are the elements
in core protocols irr Bluetooth?
in core_ prorocols in Btuetoorh are, 11.:!T"1. > (adto Base band
> LiDk Manager protocol ) Logical Link control and adaptatioo prctocol . F Service discovery protocol. r.'.
:,.rt :rrrrhd advantages
i ! !
F 5.
iJeh flexibilitv Simple Design Easy planning
\\ iAN?,11
Low-cost
Whai are the benefits
) > !
of
;f
using infrared for transmission? It is simple and extremely cheap sencleG and receivers.
Il defines higher data mtes The electrical devices do not interilre with the infrar.ed transmission 5, What ar. ed hoc neh?orks? Adhoc networks do not need ,Dy_ infrastrucfurc to work and each node communj-care wirh orher nodes can direcrty. so rr,u, ,r," u""o ooi",'.l,rlrJilr"li,o,,l. ,. ,", l]ecessary.
PREPARED
By: ,t
r
s.PRASANNA A.p-CsE a rilr A.^IOHAN A.p_csE
\ DEPARTMENT OF COMPATER SCIENCE AND ENGINEERING 7,
What are tbe disadvatrtages oI WLAI{? > Lower quality ofservjce ) Slow standardizalion procedues ), frequencyreslriction
>
Less safety and secudty.
\ryhar is IEEE 802.11standard? Tbe IEEE 802.1I standard snecifis5 thg physical and mediun access layer adapted to the. special requirements or *;..r".. ut r". i.t TJ*o.o *o asyrchronous services. The dara rate of this sra"dard is 8.
i"-;d;';;;,##:
a;;;it;; ;a#.
*'
What is ESS and ESSID? A distdbution system is used to connect a several BSS via the access Doint to form 9.
and rhereby "-:,,Tf extendedl"]11 service set anct it Lrate
11.
different Detworks_
*,"t".; ;o,";;;,;;. ilil"",;il,. ;;i;;;i"S"ti."ii"';'a"r'tB;."i:J
exrends rhe has own identifie;
Define SIFS and pIFS.
called the short interftame is 8 microssec. The wailins
r
12.
interframe spacinA.
What are the services provided by the MAC layer?
> >
Asynchronous data service Time bounded services
tr/"nl-"_!I"u*o*. ilil:"Jffi i*In;:H"J]"H*AH,#1'j;:j,: [f.:ii[,]::]"?ryd$,xffi r, in"rua". ,oipoiogf .f 1o.9._t-oootoet".. d-i;;Ji."l ?".;',1i,ir,tl'1,r"1ffi]ry,n, encr,?lton, power conservotion mechaorsu.
"r",
*X
List the phases in Ey_NpMAThe hean of channel access r prioriLies is eliminalion yield preemptive priorily multiple non ..' - access. r, u'Hdes oi'.olidlg --' Lhe medium access ofdillerent competing '! nodes into three phase.. 14,
) > ,
pr.ioritizationphase
Contention phase I ransmrsslon phase
PREPARED
By: , r S.PRASANNA A.p_CsE & M. R.IIOHAN
A_P_CSE
DEPARTMENT OF COMPATER SCIENCE AND ENGINEERING 15.
Wiat
>
> ! > 15.
are tbe dilferent chatrnels used in IIIPERLAN2? . Broadcast channel Long tmrspoit channel Random channel Access leedback chaDnel Short transpod ehannel Fmme channel
lyhat are t[e features of IIIpERLAN2?
) > > >
High tlroughput transmission Connection orienled Security support
Quality ofservice suppod
17.
What are the functiorls of link manager protocol? > Authenljcation. paging and encrlpiion Ccpabilily negotiation > power control Synchronizarion LinJ< supervision
18.
What is Bluetooth?
The.Bluetooih technology also called as adhoc piconets. It is a local area network .., wrm aver rlmrted covemge
and does not need for an infrastructue. It is used to connect g:ry*_ in cJose proximity ab",t 10,h" flccq tor wlreless I n trastrucfure. ",
j:*::,::11
;il;;i;;,""-#,,ij"g
Whar are the advatrtages of Bluetoofb technologJ,? Bluetooth provides a range of about 100 meies. It is also low power and low processing with an overhead protocol. The applicatiorc rlitfl tf," nfr"i."If, 19,
endless. 20. Write somc
.
"r,
,imffy
WATM serviee? WATM is mainly designed for transferring voice, classical data, video, multimedia
data.
! ! ! ! >
Office envircnment Uliversities Schools Hospital
Indust
es.
21. Di-fferetrtiale p-savers aDd p_supporterc.
a node may have a specific ,".-*,11"I]i!jl^ oerennines at what 1, ftItle l_he node is read to receive,
wake up pattem. His panern so that other timis, the node can fum offits receiver^and save the energy. These types ofnodes are called p_;;r;;..--The information about the wake-up palems of all the p savers are in p supporters. When the p saver is awake. it forwards thi dau to p a saver. What is scattemet? ofpiconels are called as scaflernels. A scaler net may have .in whichGroup two piconets, one device panicipares in two different piconers. 22.
PREPARED
8y: ,l.ir S.PRASANNA A.p-CsE &
r{r
R.A,IOHAN A.p_csE
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING 23. Define Frequency hopping spread spectrum?
hopping spread specmm (FHSS) is ..,. I:Cr"l"y wtuch, ailows fbr the coexislence
of mLrltiple netrvo*s
diferent networks using different hopping sequences
a spread
spectrum technique
in the same area
by
separating
24. What is direct sequetrat spread spectrum?
Lllrcct sequence spread specuum (DSSS) is the altemative sprcad specfum
method sepamting by code and
noiby frequency
25, Defiue Mobile quality ofservice? Quality o I service (OoS ) eua ran rqs5 a].s ons oflhe main advanlages envisxged lor WATM networks co.pa.ed to,-e.g., ,o worting p""n"i,"Of"'r",*_tr. -otife While the inremet protocol Ip does n'ot guarantee eos. ATM nerworks do
;r;.
26. Dislinguish between infraslructure and ad hoc
Infrastructure Netwoi[i it Communication rokes pla- rlroughiccess
iii)
Cannot be
is
- J fr1
Ad hoc Networks i) No access point cont-tting;"diu. is
pornt
ii) The design ofnetworks
nctwork
simpler
ii) Complexity ofeach node is lr'gh.r iii) Used for disaster relief
use7foriisiter reliel
,/lWhat are the lhree Loy porver
,.
yv '/
Slales provided by Bluerooth? : Ir,has rhe highesr porver consumplion of rhe low power stcres :,1,T::1. Hoid state : The deyice does not release irs AMA but srops ACL rransmission Park state The device has-fie lowest a*y ani rf,"*l"*"" powct/-) consumption "y"i""
:
t
28.In *hat situation can collisions occur in IEEE 802.11? For 802. t I collisions on ttre va^C. tayer is nott in-g'uru"rut. The MAC algorithm wilh bacl-olTsolves this problem. ln g02.ll networks MAC collisions are also collisions 'rt rhe pHy. Iayer. tmportanr packers shorter waiting tjmes rSIFS, PIFS).
i
"
sor.ii
h; ;;;.";;ffi :".s.;il1;"0 r,"
29. What is adaptive modulttionl i. a term used in v-lglq55lofiuunications to denote , ]! the matching modulatjo4 " coding and other sisnal ,.0. p-to"ot pu-rn-"r""'i"
*
radiO
.ut"t,
link. A&ptive modrlationlr..t.-. Imprcve
rate of transmission' and /or
uv it p*senr.at "*proiiiog-,rr";#;i';ij[;i over tbding channels which ..d.t '].11.1111
-"d,r"il";'.;
*.'."r1g,fo,i
of
the
,1. bit",e,or
rhe lransmitler' Especiclll
;;;;;, ft;",' ;:,',.hH'J:Trl'ffi Hl'::d}:;"ffii,,:Jl;:l';:
not exptott channel knowledge ct the lransmilter. PREPARED
By: ttr s.pRAsANNA A.p_csE 6 r[r R.I^OHAN A.p-csE
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING J0. Metrtion the featureq ot
HtpERl-AN
i) Integiation of time se$itive data transfer services Standardization efforts bad lot of impact on .ii) eOS supporting wireless broadband iirfhe current focus is on HTpERLANI a t"rn ETSI'S BRAN and wireless ATM activities "r"il"r"
st-dil
31, DiIIer
d'";;fi";;.ii
Infiared Vs radio transmissior
i) Rased on the tranimissior of infra red light
ii) Bas.d on th. rrarsmission of *dio *aves
ii) Adv: Simple and ext.emety clleap iii) Dis-adv : Low bandwidth
ii)Adv: Il cover iii) Dis-adv :
(900 tun lensth)
large
arda&
peneh"Ie *all-s
16 Marks
i. !a\lijriii the advrntages,
disadyantages and Design goals of Wireless
LAN
IVIRELESS LAN The global goal
of WLANs
is to replace
office cabling, to enable
teLher less access
to the
intemet and to introduce a higher flexibility for ad-hoc communication in, e.g., group meetings.
ADVANTAGES
t
Flexibilityl within radio coverage, nodes can communicate without firther reshiction.
Radio waves can penetmte walls, senden and receivers can be placed. Sometimes wrring
is difficult
if firewalls
buildings. peretratior of a firewall is only pemitted at certain points to prcvent fiIe from spreadi[g too fast.
.
Pla,ni,g: Only
separate
wireless ad-hoc networks allow for cormrmication without previous
planning, any wired network needs wiring plans. As long as devices follow the same slandard, they can commudcate. For wited netwotks, additioflal cabling with the right plugs and probably inter \rotking ur ts have to be provided.
PREPARED
By: l,tr S.mASANNA A.P-CSE a rrlr R.A{OHAN ,4.p_CsE
DEPARTI'TENT OF COMPATER SCIENCE AND ENGINEERING
.
De.$igr: Wireless networks allow for
tle
design ofsmall, independent devices which can for exarnple be put into a pocket. cables not onry rcstdct use,, but also designers of small PDAs, notepads etc. Wireless senders and receivers can be hidden in historic buildings, i.e., current networking technology can be introduced without being visible. o Robusfoess: Wireless networks can survive disasteG, e.g., earthquakes or users a plug. Iftte wireless devices survive, people can still conu[unicate. a wired inFastructue
.
Networks requiring
will usually
breakdown completeiy.
Cost: Afler Foviding wireless acce
.nrst
user, adding
pulling
addi,,",",,,".,,.
i;ii"::i:#iTffiffi,::;'i"r":1" "
t'
""
DISADVANTAGES: :
Quality of service: wLaNs tlpicatty offer rower quality than their wired counter parts. The main reasons for this are the iorver bandwiclth due to limitations in radio transmission (e.g., only l_10 Mbit/s user data rate inshad of l0O_1,000 Mbit/s), higher etor ratcs due to interference (e.g., lo_4instead of lG_12 for fiber optics), and higher
'
delay/delay variation due to extensive ellor correction and detection mechanisms.
.
Propriet ry solutions: Due to slow sl come up wirh proprietary .",,,,",,
#illl'11fl}li,iJTil#"
:Ii.#;
enhancedleafures.However,lheseaddition,lf".h-." litional features only work in a homogeneous
environmefi.
o Restrictioas: All \ /ircless products have to comply with natt'onal regulations. Seveml govemment ald non-governmenf hstitutions woddwide regulate the operation and restrict Aequencies to minimize interference. Consequently, it takes a yery long time to establish global solutions. WLANS are limited to low-power s€trdeN and certaio license_free frequenry bands, which are not the same
worldwide.
PREPARED
8y:
l,1,.
s.pRAsANNA A.p-csE &
i& R.,uoHAN A.p_csE
DEPARTMENT' OF COMPUTER SCIENCE AND ENGINEER]NG safety a,d security: using radio waves for data transmission might interfere with other high-hch equipment in, e.g., hospitals. speciar precautions have to be t,ken to preve[t safsty hazards.
'
DESIGN GOALS
.
Global oper.tion: The infrastructue of tvireless \yANs, LAN equipment may be
carried from one country into another
r
-
the operation should still be legal in this case.
Low poper: The LAI.I design should take this into account and implement
special
power-saving modes and power matagement functions.
.
License-free operation: LAN operators do not want to apply for a special license to be able to use the product. The equipment must operate in a ricense-free band, such as the 2.4 cHz ISMbond.
.
RobIst transDission techtrolos/: Compared to their wired counterparts, WLANS operate under difficult conditions. If they use radio transmission, many other electrical devices can interfere with them WLAN transceiveN cannot be adjusted for perfect transmission h
a
standard office or production environmenl.
o Simplified spontaneous coopemtion: To be usefirl in practice, WLANS should not
,
rcquire complicated setup routines but should opemte spontaneously after power-up. Easy to us. In conhast to huge and comprex wireless wANs, wireless LAN. are made for simple use. They should not require complex management, but mther work on a plug_ and-play basis.
'
.
Protection ofitrvestment: A lot ofmoney has already been invested into wired LANS. The new WLANs should protect this investment by being interoperable with the existing networks.
6 TransparcnrJ for applications: Existing appricatiors should continue to run over WLANs, the only difference being higher delay and lower bandwidth.
2. Explair
the System
Architecture ofIEEE g02,11 TANDAIDS
The IEEE standard 802,11 oEEE, 1999) specifies the most famous f.amily of wLANs in which many products are avairabre. As the slandard,s number indicates, this
PREPARED
8y: l,1r S.PRASANNA A.p-csE & r R. oHAN A.p_csE ^
t-
DEPARTMENT OF COMPTTTER SCIENCE AND ENGINEERkNG standard belongs
to the group of g02.x LAN standards, e.g., g02.i Ethemet or
802.5
Token Ring.
This means that the standad specifies the physical and medjum access layer adapted to the special requirements ofwireless LANS, but offerc the same interface as the
otheis to higher layers to maintain interoperability. The primary goal
the specification
of a simple
and robust
ofthe
standard was
,LAN
which offers time-bounded and asyncluonous services. The MAC layer slDuld be able to opemte with multiple physical layers, each ofwhich exhibits a different medium sense aad transmission characteristicSYSTEM ARCIIITECTURE 'Wireless
. . '
networks can exhibit tuo dilferent basic system architectues ate Inl"raslrucntre_based
Ad-hoc.
Figure shows
fi"
aornporarr, ofun infrastructure and a wireless parl as specified for IEEE 802.1l. Several irodes, called stations (STAi), are connected to access points (AP). Stations are teminals with access mechanisms to the wireless Dedium and radio contact to the Ap.
f
+-b-r
.'
The
,
PPEPARED BY: /i,tr
5.pp454*"o
A.p_csE &
/ur
R.A4OHAN A.P-CSE
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEEMNG Stations and the
Ap which are within
the same
(BSSi). The example shows two BSSS
-
radio coverage forma basic service set
BSSI anrt BSS2
Distribution system.
A distribution
system connects seveEl BSSS via t}]e
-
which are connected via
Ap to form a single network
and thereby extends the wiieless coverage area
This network is now calred a,, extetrded service set (ESS) and has its own identifi% the ESSID. The ESSID is the ,name, of a network and is used to separate dillerent networks. Without knowing the ESSID it should not be possible to participate in the
WLAN.
The distributiorr system connects the wireless networks via the Aps wifi a portal, which forms the intei working unit to other LANS. The architecture of the distribution system is nor specified furrher in IEEE802.1 IEEE LANS, wireless links, or any other net\lorks.
l. It could consist of bridged
Flowever, distribution system services are defined in the standard Stations can selod an AP and associate with ii. me Aps suppo roaming the distribution system handles data transfer betweelt the different Aps. APs provide synchronization r.Xithin a BSS, suppon power management, and can control medium access to support time_bounded service
In addition to
infrastructure-based rctworks, IEEE g02.1
I
allows the building
[etworks between stations, thus fomitrg one or morc independent BSSs (itsSs) shown in Figure 7.4. In this case, an IBSS comprises group a ofstations using ad-hoc
of as
the sarne
mdio frequency. Stations STAI, STA2, and STA3 are
in IBSSI,STA4 and S.tA5 in
IBSS2. This means for example thar STA3 cao communicate d;rectly with STA2 but nor
with STA5.
PREPARED Byr Atr S.PRASANNA A.p-CsE & ,,1r R.r,loHAN A.P-csE
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERTNG
-
{*'*p3
c-\\to
Several IBSSS can eitier be formed via the distance between the IBSSS (see Figure 7.4) or by using different canier frequcncies.
J.
Explain the protocol Archileclure of
I
EE E 8t 2.t
I STANDARDS
The IEEE standard 802.11 (IEEE, 1999) specifies the most famous l.amily of wLANs in which many prcducts are availabre. As the standad,s munber i.dicates, this standard belongs to the grow of g02.x LAN standards, e.g., go2.3Erhemet
or 802.5
Token Ring.
This means that the stada.d specifies the physical and medium accass layer adapted to the special requirements ofwireress LANS, but offers the sa,e inte ace
tre
as
others to higher layers to maintain inreropembility.
The primary goal of 0le standard was the specificarjon WLAN which offers time_bounded and asynchronous
ofa
simple and robust
services.
The MAC layer should be able to operate wilh mulriple physical layers, each which exhibis a different mgdium sense and transmission characteristic.
PREPARED
By:
ltr
s-pR^sANNA A.p_CsE a rrlr R./[OHAN
A.p-csE
of
lO
DEPARTMENT OF COMPUTER SCIENCE AI]ID ENGINEERING
Fgure 7.6 telaitei, JE€E aO2.11 P.otoeol architectx.e 3nd m$agement
Figure shows the most common scenario: an IEEE connected lo a swilched IEEE 802.3 Ethemel via a briJge.
g02.ll wireless LAN
Applications should notnotice any difference apart from the lower bandwidth alrd perhaps higher access time from. the wireless LAN. The WLAN behaves like a slow
wired LAN. Consequently, rr ireless nodes as
for wired
the higher layers (application,
TCp, lp) Iook the same fb.
nodes.
The upper part of.the jata link controJ layer, the logicai ljnk conrrol (LLC), cove6 lhe diflerences of the medium access control layers needed for the different media.
The IEEE 802.11 standa.d only covers the physical layer pHy and medium access layer MAC like the other 802.x LANs do. The physical layer is suMivided. into the physical layer convergencc protocol
(PLCP) and the ph.ysical medium
depend
(see Figure 7.6). The basic
tasks of the MAC layer comprise medium access, fragmentation of user data, and encr\ otiolt.
--:/-
.. The PLCP sub layer provides
d I- rP
a carriei
sense signal, called clear channel
assessmell (CCA), and provides a common pHy service access point (Sap) indepeident cf the transmission technologl..
Finally, the PMD sub layer hdndles modulation and encoding/decoding of signals. The PHY layer (conprising pMD and pLCp) and the MAC layer will be explained in more detail in the following sections.
to an
The MAC management supports the association ard rc_associatiotr of a station access point and roaming between dErlrrt u""".,
poiillliTJ
"o.,t.ot. tion, synchronization of a station with regard to an
L---"->
PREPARED
By: /vir s.pRlsANNA A.p-csE d
l{r
R.^,iOHAN
A.p-CsE
II
DEPARTMENT OF COMPT]TER SCIENCE AND ENGINEEKING access point, and power maiiagement
to save battery power. MAC malagement also
mainraiis the U4g-Eas4g949g! q&g3&Lb,4!e (MrB). The main tasks of the plry manacemeDt
include channel tuning and
maintenance
Fi*lly,
s?:lryryelc4r,teracts
pHyMIB
wilh both management layers and is
responsible for additional higher layer functions.
4. Dircuss the archilccture
ofBluetooth in detail.
Like IEEE 802.11b, Bluetooth operates MAC, physical layer and the offered
in
the 2.4
GHz ISM band. However,
services are completely
differeot. Aftei presenting the overall architectue ofBluetooth and its specialty, the piconets, the following sections explain all protocol layers and components in more detail.
Nefsorking
-
To understand the netlyo*ing ofBluetooth device.s
a
quick introduction to its key
features is necessary. Bluetooth operates oll Zgrhannels in lhe 2.4 GHz band with
caliertins::ach
device performs
tqg?_!9!!ln&with
random fashion. Blueloorh applies FHSS fo, irrt".f"."n"" separation of rEtworks).
1,600 hops/s in a
I MHz
ffi
,nitigutjoriffiH_CDMA for
A
very importalt term in the context of Bluetootl is a picolet. A piconet is a collection of Bluetooth devices which are synchronized to the same hopping sequence. Figure 7.41 shows a collection ofdevices with different roles. One device in the piconet can act as master (M), all other devices cormected to the
O..- f.-^,'l.,-', Lo:+ 3 LcuJ-r-\
PREPARED
8y: Atr s.pRAsANNA A.p-CsE a ,'1r R.,I{OHAN A.p-6sE
12
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING master must act as slaves (S). The master determines the hoppi[g pattem in the piconet and the slaves have to synchronize to this pattem. Each piconet has a unique hopping
pattem,
Ifa
device wants to participate it hhs to synchronize to this.
Two additional types idevices are shown: parked devices (p) can not actively partioipate in the piconet (i.e., they do not have a connection), but are known and can be reactivated within some c
milliseconds.
Devic6s in stand.by (SB) do not padcipate in the piconet. Each piconet has exactly one master and up to seven simultaneous sraves. Morp than 200 devices can be parked. The reason for the upper limit ofeight active devices, is the 3.bit addrcss used in Bluetoolh. If a parked device wants to communicate and there are already seven active slaves, one slaye has to switch to park mode to allow ttre parked device to switch to active mode. Fig\ne 7.42 gives an overview of the formation of a piconet. As all active devices have to use the same hopping sequarce lhey must be synchronized.
The first step iivolves a master sending its clock and device ID. All Bluetooth devices have the same networking capabilitier, i."., th"y aun b" ,*"t"r or slave. There is no dittinction betweefl terminals and base stations, any two or more devices can fblm a
piconet. The unit establishi[g the piconet automatically becomes the master, all other devices
will
be slaves,
The hopping pattem is detemined by the device ID, a 48-bit worldwide unique identifier. The ptase in the hopping pattem is determined by the master,s clock. Aller adjusting the internai clock accordirg lo the master a device may participate in the
piconet.
AII
active devices are assigned a 3-bit active menber address (AMA). An parked devices usc an 8"bit parked m€mber eddress (pMA). Devices in stand_by do rot nced an address, All users within one piconer have the same hopping sequencc and share the same I MHz channel. As morc users join thd piconet, the throughput per user drcps quickly (a single piconet offers less thar I Mbit/s gross data mte). (Only havlng one piconet available within the 80 MHz in total is not very efficient.)
This is called to the idea of forming goups of piconets called scattenret (see Fipre 7.43). Only those units that really must exchange data share the piconet, same
so
that ritany piconeh with overlapping coverage can exist simultaneously, PRE?ARED Sy: ,t'lr S.PRASANNA A.p_CsE
& ,,^r R.ltoHAN
A.p_csE
tl
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
ln the example, the scat emet consists of two
piconets,
in which one
device
participates
in two differcnt piconeb. Both picorets use a different hopping sequence, alnays determined by the master of the piconet. Bluetooth applies FH-CDMA fbr separation
of piconets. In an average sensq all piconets
"-
sh.e th"
bandwidth available. Adding rnore piconets leads to a graceful
miuffl ,iH,
p"rfo_un.. d"g.iutin...-
ofa single piconet because more and more collisions may occur. A collision occurs ift\yo or more piconets use the same carrier frequency at the same time.
'ta
CI(63J
%%.
rh
el
CI\9
cq-Isl n-'@ \-l\
\ ,)
This
will probably happen
as the hopping sequences are not coordinated.
device wants to participate in more than one picom!
ofthe piconet it wants to take part itr.Ifa device acts as slave in simply starts to synchronize with the hopping sequence of the picoret
it
acts as a slave
a
it has to synchronize to the hopping
sequerce
Aflcr s).nchronization, it
If
one piconet,
it
wants to jojn.
in rhis piconer and no longer panicipites in its
fomerpiconet.
To enable synchronizalion, a slave has to know the identity of the master that determhes the hopping sequence of piconet a Before leaving one piconet. a slave infoms the current master that it will be unavailable for a certain amount of time.
PREPARED
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/',1r
s.pIAsANNA A.p_cS€ & Ivtr R.I OHAN A.p-CsE
t4
DEPARTMENT OF COMPATER SCIENCE AND ENGINEERING The remaining devices in the piconet continue to communicate as usual.
4E
?.{3
\
.-....t......-A master
can also leave
its piconet
and act as
a slave in another piconet. It
is
clearly not possible for a master of one piconet lo act as the master ofanother piconet as this would lead to identical behavior (both would have the same
hopping sequence, which
is detennined by the master per definition). As soon as a master leaves a piconet, all taffic within this piconet is suspended u,,t the master returns. communication between
diff€rent piconets takes place by devices jumping back and
forth between theses nets.
If
this is done periodically, for instance, isochronous data steams can be forwarded trcm one piconet to another. However, scattemets are not yet supported by all devices.
5, Explain
h detail the protocol
$tack ofBluetooai?
As Figure shows, the Bluetooth specification already comprises many protocols and componcnts. Starting as a simpie idea, it now covers over 2,OOO pages dealing with not only the Bluetooth protocols but many adaptation function and enlarcements. The lliuetooth protocol stack can be divided into a core specification (Bluctooth, 2001a),
which describes the protocols from physical layer to the data
link controi together with
management functions, and profile specificatiotr! (Bluetooth, 20Olb).
The latter d€sc bes ma.ny protocols ard functions needed to adapt the wireless Bluetooth technology to legacy and new applications The core
protocoh ofBluetooth
PREPARED,By:
tlr
comprise the
S.PRASANNA A.p-CsE
I
following elements: Mr R.l oHAN
A,p-csE
15
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERLNG
.
Radio: Specification ofthe ai! interface, i.e., frequencies, modulation, and transmit power . Baseband: Description ofbasic connection establishmen! packet fomats, timing, and basic QoS pa.iameters
;igrrs
diElli,cn Es$$.,cs c3ft.li.cr srdr'r€€ TCS BII,]: t .pho.ry cn rrol proiocd spdcifciltrn bins"y Bl{.F: Atuelo€th nealsrt Bn.Ssute$m
Al
SOrt €E viu dilcolE / pdoed RFDOIIH: haque;y,roma 'Edio
trolcco,
.
Link. manager protocol: Link s€t-up and management between devices including
security flDctions and parameter negotiation
.
Logical litrk control and adaptation protocol (L2CAP): Adaptation ofhigher layers
to the base band (connectionless a;d connection-odented services,
.
Service discoyery protocol: Device discovery in close prcximify plus querying of service characteristics On top of I2CAP is the cable replacement protocol RFCOMM that emulates serial line interface following the EIA-232 (formerly RS-232) standards.
This allows for a simple
replacement
of serial iine
cables and enables many legacy
applicatioos and protocols to run over Bluetooth. RFCOMM supports multiple serial ports over a single physical channel.
PREPARED
8y: Mr
S.PRASANNA A.p-CsE & Mr R-,!iOHAN
A.p-CsE
16
7€{
DEPARTMENT OF COMPATER SCIENCE AND ENGINEENNG The lqlqp-hguy cotrtrol prolocol specification
-
binary (TCS
SIN
descrihes_a
5if--
oriented protocol that defines call control si$laling for the estabiishment of voice and a-between Bluetooth devices.
It also
describes mobility and group management
iinctions. The host cortroller interface (HCl) between the base baad and L2CAP provides a command interface to the base band controller and link manager, and access to the hardware status and control registers. The HCI can be seen as the hardware/software boundary.
Many protocols have been adopted in the Bluetooth standard. Classical Intemet applications can still use the standard TCp/p stack running over ppp or use the more
efficient Bluetooth network encq)sulation protocol (BNEP), Telephony applications can use the AT modem connnands i; if they werc using a standard modem. Calendat aad business card objects (vcalendar/vcard) can be exchanged using the object exchange -protocol (OBEX) as common wilh IiDA interfaces. A real difference to other protocol stacks is he support of audio. Audio application may directly use the base band layei after encoding the audio signals.
6.
Explain
WIII
in detail,
WI-FI - Wireless Fidelity - popularly knoDn as Wi-Fi, developed on IEEE 802.11
wi6iy usea-EEotogy advancement in wireless communication. As the name indicates, \\rI-FI provides wireless access to applications and data across a radio standards, is
network WI-FI
sels up numercus ways
and the receiver such a\DSEg FHSS,
to build up a connection between the trar$mitter
IR
Infrared and OFDM. Wi-Fi p.ovides its users
with the liberty ofconnecting to tie Iotemet from any place such
as
their homg office or a
public place wiLhour the hassles ofplugging in the wires.
Wi-Fi is quicker than the conventional modem for accessing information over large network.
a
Mth the help of different amplifiers, ihe users can easily change their
location without disruption in their letwork access. Wi-Fi devices are compliant with each
clher to grant efficient access of iofotmatiol to the user, WlFi location where thc users PREPARED
8y: Mr s.PRrsAM.lA A.P-CSE a i4r R.AioHAN A-p-csE
lj
--r
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING car coftrect to the wireless network is called a the
E-Fi-!9lA9t
user can even enhance their home business
as accessing
Ttrough the
Wi_!i
hotspot,
inforoation thrcugh Wi_Fi is
simple. Accessing a wireless network through a hotspot in some cases is cost_free while in some it may carry additiorBl charyes. Many standard
WlFi
devices such as
pCI, minipCl,
USB, Cardbus and PC card, Exprcsscard make ths Wi-Fi experience convenient and
pleasuable for
the
user.
Distarc€ liom
a
wireless network can lessen the signal strength to quite an extent; some devices such as Erman no Pietrosemoli and EsLaRed of Venezuela Distance are used for amplifying the
signal strength ofthe network. These devices create an embeddcd system that corresponds
with any other node on lhe Intemet.
Wi-Fi
uses
radjgiet!{o*rs to transmit
<
data between its Dodes. Such networks are
of cells that provide covemge across the network. The n0ore the number of cells, the greater and stronger is the covemge on the radio network. The mdio technology $ a made up
complete package deal as it offers a safe and consistent coinectiyity. Radio bands such as
2,4GHz al,ld 5GHz depend on wireless hardrrare such Ethemet protocol aaa CSMa. Initially, Phase Shift Kelng @SK), a oodularion method for conveying dala was used, however now it has been replaaed with CCK. Wi-Fi uses many spectrums such as FHSS and DSSS. The most popular
ryGHzW
Wi-Ii
technology such as goaLl5 opemtes on the mnge
of
to .4835 cHzband.
PREPARED
8y: rt{r S.PRASANNA 7.p-csE
I
rrir R.l4oHAN
A.p-csE
l8
DEPARTMDNT OF COMPATER SCIENCE AND ENGINEER]NG This provides a comprehensive
platfom for operating Bluetoolh shategy, cellular phones, and other scientific equipmeds. While 802.1I a technology has the ranee of 5.725 cIIz to GIIz and provides up to 54 Mbps;-speea, tOU.t lg rechnotogy i, .";m;; ; '-overs thrce nonovedapping channels and allows pBCC. go2.lle technology takes a fair lead by providing excellent streaming quarity ofvideo, audi;roi6ihanaels etc. No matrer 5.850
wheae you are, you can access the
world ofweb through your handsets and your laptops
and your iPads. You might not have noticed what
it is but
the terhnology that enables you
to plug in intemet
;ithout any wires whether you arc in a cafe, a library, a shopping mall or an airport is M-Fi - tlre wircless [etwork a]so known as g02.1 L The circumference where wireless technology is present and available to the users is kno\rn as Hotspot. The inexpensive, lser_fiendly WiFi nehvo*s arc also obtrusive; ifyou do not need one you would not know there exists any. wi-Fi courd be also installed in home or offices in oder to transmit information over the air without thb aid near future you would find wireless netvrorking avajlable
of wires. In
in every nook cnd comer For
those whose laptops and
could purchase
a
cel phones do not have a bu t-in
wireless adaptor
wireless transmitter then you
and inject it into USB
port.
A WiFi
hotspot is automatically discovered and coDected by the hansmitters. The presence of Wi-Fi in public places makes it convenient to stay connected to your ofticial tasks or 1o the sociar nehrorking. wi-Fi communication devices a.re extended lb,.s of
for cell phones and walkietalkies: they simultaneously bansmit and receive mdio waves and convert ls to 0s into the radio waves along with reconverting the radio mdios. used
waves into
,:.
ls and
0s, however the
Wi-Fi radios enjoy some exceptional features
iixplain the architecture of WIMAX in rletail.
WI-MAX
Wi-MAX (Worldwide Interoperability for Microx,ave Access) unites technologies
of
the
wireless and broadband to provide high_speed intemet access ac.oss long
distances. The name was cMstened by
PREPARED By:
itr
WiMAX Fomm that
promotes interoperability and
s.pR4sANNA A.p-esE & Mr R.llo}l^N
A.p-CsE
t9
I
DEPARTMENT- OF COMPUTER SCIENCE AND ENGINEERING conformity
of the
standard. The forum defines lhe technology as ,,a standards_based technolos/ enabling the delivery oflast mire wireres broadband access as an altemative to cable and DsL". with the guarantee of v/iMAx rorum the vendo$ are authodzed to se their WiMAX certified products so they can enjoy operabiliry with other products
of same
O?e. It is a telecommunication p.otocol capable ofproviding intemet access to fixed and mobile users. For an outstanding performance like Wi_Fi nete/o.ks along with eOS (Quality of Service) and covemge this Wireless Broadband Access (BAS) technology is around (irtemet protocol).
assembled
IP
Cunently it offers 40 Mbit/s but expected to offer I Gbit/s speed for fixed users.
WI-MAX ARCHITECTURE There are three
mail
components
of
WiMax network architecture, The first
component is the mobile stations which are used as a source
ofnetwork connection for end
user. The second network is an access service nefwork which is
three base stations.
It also
fomed ofmore
lan two or
contains ASN gate\^ays which build the mdio access at the en.t
The third component is cormectivity service network which is responsible for providing '
Ip
fimctions. _
The base station provides the air
inteface for fie mobire stations. The
base stations
also provide mobiie management functions, triggering and tunnel establishmeit, mdio rcsource management, dynamiC host control protocol proxy, quality of service enforcement and mullicast group management. ASN is responsible for mdio .esource managemeni, encry?tion keys, routing to the selected network and ciient funcronality. connectivity service relwork is responsible for intemet connectior& corporate and public networks and
mary
other user services.
StaDdard WMax Architecture
Let us analyze a standard WiMax network. As explained earlier the WiMax network is based on thrce four basic components like AS gateway, CSN aod MS. The basic network has a central IP core which is surorulded by an ASN gateway, which is connected to service network or CSN.The main Ip core is attached to the intemet backbone lbr help PREPARED
BY: I,1r 5.PAASANNA A.P-CsE A Alr R.A4OHAN
A.P.CsE
20
DEPARTMENT OF COMPT]TER SCIENCE AND ENGINEERING and coverage. The access s$yice
wiMax network which is arso part of the ISp network is known as
gateway.
lP€a30d t?&f Ax Hotrorr(&cillBelure
E1
l'--l F8r{ I
io
9*"t"
l
This ASN handles the micro and macro base stations, which provide WiMax aocess end usem. The connectivity seryice network or CSN
is an importcnt part of WiMax
architecture which provides the authentication to the user devices. CSN is also rcsponsible
for providing roaming among the network service povide6. It is csN which is responsible for user security and quality for service for this pupose it uses several protocois. The IP address management is also handled by CSN.
Ip core is in th! middle of
CSN and ASN. CSN provides the intemet ard hlecommunications connectivity. ASp conununicates to the base stations and the mobile stations. At the users end the WMax architectue may further contain firewall for secudty. WiMax architectute provides discretion at user end to make possible aruerifolents.
Two Dimensiorx of WiMax Network WiMax network is composed of two parts the WiMa,.( tower and the WiMax receiver. WiMax tower is connected directly to ihe intemet
backbone
using
a
wired
connection
as opticai flber. It can be connected to the WiMax tower usi.g a line of sight link or a non line of sight link The line of site communication involves the use of fixed antenna oi dish. This antenna is fixed or deployed on the roof top or the tower of youl building. Line of sight such
connection is considercd as more stong and stable connection. PREPARED
By: .lit. S.PRASANNA A.p_csE
i,ur
R.^.IOHAN
A.p_csE
21
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEENNG Therefore it sends lot ofenor fue data over the network. It uses a frequency range of 66Ghz. Higher frequency decreases the chance ofsignar weakness and interference and provides more bandwidth. On the other hand the non line ofsight connection provides you connectivity rvith the installation of snall aDteDna in your pC. Thjs mod provides lower ftequency range fiom 2 GHz to GHz. The lower band signals are not prone to obstructions like trees and walls. Hence the signal stength is more and the user rcceives the quality ofservice. For every WiMax conoectivity and architectue it is important
ll
to corulect
to an intemet backbone via swift wiied connection.
8.
Explaitr HIPERLAN in dctait
In 1996, the ETSI standardized HIPERLAN
I
as a
WlANallowing for
node mobility
and supporting ad-hoc and infrastructure_based topologies (ETSI, 1996). (rUPERLAN stands for high performance local area Defwork.) HIPERLAN I was originally one out of four HIPERLANS envisaged, as ETSI decided to have different types of networks for different purposes. The key feature of alr four networks is theii iltegation of time_
sensitive data tmnsfer services. Over time, names have changed and &e former HIPERLANs 2, 3, and 4 are now caled HiperLAN2, HIPERACCESS, and HIpERLINK. currelt focus is on HiperLAN2, a standard that comprises many elements from 1,.._ .....................Jh" ETSI'S BRAN (broadband mdio access networks) and wireress ATM activities. Neither
wireless
ATM nor HIPERLAN 1 were a
standardizatjon efforts had
a lot of
commercial success. However,
impact on
eos
the
supporting wireless broadband
networks such as HiperLAN2. Before desc bing HiperLAN2 in more detajl, the foilo$ring three sections exprain key fealues of, and the motivation behind, HIPERLAN 1, wireless ATM, and BRAN.
Historic.l: HIPERLAN
1
ETSI (1998b) describes HIpERLAN I as a wireless LAN supporting piorities and packet life time for data tmnsfer at 23.5 Mbivs, including forwarding mechanisms,
lopology discoverl user data e.cryption, network identification and power conservation
PREPARED By: AIIr S.PRASANNA A.P-C5E
t
&,tAr i.MoHAN
A.P-C5E
2.)
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERLNG mechanisms. HIPERLAN 1 should operate at 5.1_5.3 GHz with a range
buildings at
1
of50 m in
W transmit power.
The service offeied by a HIPERLAN 1 is compatible with the standard MAC serviccs known from IEEE 802-x I-ANs. Addressing is based on staodard 4g bit MAC Sddresses.
of two
A special HIPERLAN I identification scheme allows the concurrent operation or morc physicaliy overlapping HIPERLANS without mingling their
communication. Confidentiality is ensured by an requires the identical keys and initialization ve
"llryprioddeclet,oq
for successful decryprion of a dala
An jnnovative featurc of HIPERLAN l, which many other wireless networks do nor off"r. is irs ability ro forward data paclers using several relays Relays can e\lend the
.:-
'.-" o P"*
commroication on the MAC layer beyond the radio range. Fo! power conservation, a node may set up a specific wake-up pattem. This pattern determines at what time the
- \ o!r, O
r+*I-!iJ * rkJP6.' {"'.-f
node is ready to receive. so that at other times, the node cari tum
offits receiver
and save
energy. These nodes are called p-saverc and need so-called p-supForteis that contain
infomation about tle
s]ry9{er or
y:l:]!-!3ry8_of
aJI the p-savers rhey are responsible for.
Ap:_
y forwards data to a q-saver at the momenr the p-saver is awake. This action
also requires buffering mechanisms for packets on p_suppofiing fonvarders.
'
The following describes only the medium access scheme of HIPERLAN 1,
scheme that provides QoS and a po$,erful pdoritization scheme. However,
a
it tumed out
that priorilies and Q6S in general are not that importaDt for standa.d LAN appiicalions today. IEEE 802,1.1 in its standard versions does not ofler priorities, the optional pCF is
typically not implemented in products yet 802.1I is very popular. Elimination-yield non-prcemptive priority multiple access (Ey-NpMA) is not only a complex auonlm, but also the heart ofthe channel acc€ss providing priorities and different access schemes. EY-NPMA divides the medium access of.lifforent competing nodes into three phases .-
.
Prioritization: Determine the highest prio ty of a data
packet ready to be sent by competing nodes. . Contention: Eliminate all but one of the contenders, if more than one sender has the highest cunenr priority. o Transmission: Finally, transmit the packet ofthe remaining node. PREPARED
By: ,'1r S.PRASANM A.p-csE & r,ir R.i,toHAN
a
algoithm that
Stream encrypted by a sender.
f.J'$,'i(--
d l\
A.p_csE
23
k v
a
Y
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
flgue 7.27 IIIPEiLAII 1 EY NPMA
9. Explain in detail the WATM 1)
Motivation for WATM
2) Wireless ATM working group
y'
/ '/ r' ,/
Location management
Mobile routing Handover signaling QoS and
ta{fic
control
Network management
3) WATM services '
4) Generic reference model
WATM services WATM can be used liom a user,s perspective. These examples show that the idea behind WATM goc-s '-:yond the mere provision of wircless access or the conslmction of a wireless
LAN. The
servicas offered cover many aspects
communications. '.WATM
of today's witeless and mobile
t
systems had to be designed for transfeffing voice, classical data, video
(from low quality to piofessional quality), multimedia data, short messages etc. Several service scenarios could be identified (Rauhal4 1998), (Bartoi, 1998), such as for example:
PR€PARED BY: A,h 5.PRASANNA
A.P.CsE A
illr B. 4OI1AN
^.P-CSE
24
DEPAR'IMENT OF COMPATER SCIENCE AND ENGINEERING
.
Oflice etrvironments: This includes all kinds ofextensions for existing fixed networks
offedng a broad range of Intemet/lntranet access, multimedia conferencing, oDline multi.media database access, and telecommuting. Using WATM technology, the office iLr,i be
t
virtually expanded to the actual location ofan employee,
Universities, schools, training centresi The main foci in this scenario are distance
lcaming, wireless and mobile aqcess to databases, intemet acc€ss, or teaching in the area of mobile multi-media computing.
.
Itrdustryr WATM may offer an extension of the Intanet supporting
database
connection, information rehieval, surveillance, but also rcal-time data transmission and
frctory management.
t
Hospitals: Due to the quality of service offered for d.ata trarrsmission, WATM was
thought of being the prime candidate for reliable, high-bandwidth mobile and wireless networks. Applications could include the tansfer of medical images, rcmote access to patient records, rcmote monitoritg ofpatients, remote diagnosis ofpatients at home or in
an ambulance, as well as tcle-medicine. The latter needs highly reliable networks with guaranteed quality ofservice to enable, e.g., remote surgery.
.
Home: Many electronic devices at home (e.g., TV, radio equipment, CD-player, PC
with intemet access) could be connected using WATM technology. Here, WATM would permit various wireless connections, e.g., a PDA with TV access.
i
Nehyorked vehicles: All vehicles used for the transportation of pople or goods will
have a local network and n€twork access in the future. Currently, vehicles such as trucks,
aircraft, buses, or cars only have very
limited qommunication capabilities (e.g,, via
CSM, UTMS), WATM could provide them with a high-quality
acQess
to thc intemet,
company databases, multimedia conferencing etc, On another l€vel, local networks
ixrong the vehicles within a certain area are of increasing impottaice, e.g,, to prevent accidents or incrcase road capacity by platooning (i.e., forming a train ofcars or trucks on the road Mth very low safety distance between single vehicles).
Generic ref€rcnce model Figure 7.28 shows a generic reference model for wireless mobile access to an
r\TM network. A mobiie ATM (MATM) terminal PAEPARED
uses a
WATM terminal adaplcr to girin
Byr Mr S.PRASANNA A.P-CSE A Ur R.A4OHAN
A,P-CSE
25
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING wireless access to a WATM RAS (Radio Access Sysrem). reprcsented by, e.g., laptops using an ATM adapter for
MATM terminals coutd
be
wired access plus sofrware for
mobility. The WATM teminal adapter enables wireless access, i.e., it includes the transceiver etc., but it does not support mobilify. The RAS with the radio transceivers is connect€d to a mobility enhanced ATM switch (EMAS-E), which in tum connects to the
ATM
with mobility aware swirches (EMAS_N) and other standard ATM switches. Finally, a wired, non-mobility aware ATM end system may be the netryork
communication partner
in this example. The radio
segment spans
from the terminal and
the terminal adapter to the access point, whereas the fixed network segment spans from the access point to the frxed end system, The fixed mobility support network, comp smg
all mobility aware switches EMAS-E and EMAS_N, can be distingui6hed from the standaid ATM network with its non-mobility aware switches and end svstems.
+t
------
do$gmenl+nxed.ehrqks.OfrEnt_+.
alC$.1.2A.
l0:-Discuss the lnyared model of BRAN The broadband
adio
access networks (BRAN), which have been standardized by
the European Telecommunications Standards Institute (ETSI), could have been an for WATM @TSI, 2002b).
llAL
The main motivation behind
BRAN is the de,egulation and privatization of the telecommunication sector in Europe, Many new providers experience problems getting access to cuslomers becruse lhe lelephone infraslruclurE belongs to a [ew big companies.
One possible technology advantages
to
provide network access
for cuslomers js
radio_ The
ofjadio access are hjgh flexibiljty and quick installation. Different types of
traffic are supported, one calr multip]ex t.alIc for higher efficiency, and the connection can be asymmetrical (as, e.g., in the typical
www
scenario where many customeE
pull
a
lot ofdata liom servers but only put very small amounts ofdata onto them). Radio access allows for ecooomical grou4h of access bandwidth- If more bandwidth is needed, PREPARED
BYI /vlr S.PRASANNA A.P.csE & Ir{r R.MoHAN A:P-csE
26
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING additional transceiver systems can be installed easjly. For wired transmission this would involve the installation of additional wires. The primary market for BI(AN includes p vate customers and small to medium_sized companies with Internet applications, tnulti-media conferencing, and virtual private networks. The BRAN standard and IEEE 802.16 (Bmadband wireless access, IEEE, 2002b) have similar goals.
BRAN staldardization has a rathet large scope including indoor and campus mobility, transfer rates of 25-155 Mbit/s, and a tansmissior range of 50 m_5 km. Standardization efforts are coordinated with the ATM Forum; the IETF, other groups
from ETSI, the IEEE etc. BRAN has specified four different network types (ETSI, 1998a):
.
This high-speed WLAN supports mobility at data 'rates above 20 Mbit/s. Range is 50 m. connections are multi-point-lo-m ulli-point ,,irg1d_hoi- in-[rrr*",rr"
HIPERLAN
l:
networks (see sectior 7.4.1 and ETSI, l99gb).
'
II'IPERLANi2: this techlology can be used for wireless access to ATM or Ip netwo s and suppods up to 25 Mbit/s user data rate in a point-to_multi_point configuration Transmission mnge is 50 m with suppori of slow (< I O r/s) mobility (ETSI, I 997). This standaxd has been modified over time and p
'
.
eos
is
presented
in sectior
7.4.4 as a high
support.
HIPERACCESS: This technorogy could be used to cover .rast the mire, to a customer via an fixed radio link, so could be an alteinative to cable modems or XDSL technologies (ETSI 1998c). Transmission range is up to 5 km, dara mtes of up to 25 Mbit/s are supported. However, many proprietary products already offe. 155 Mbirs and more, plus
eos. HIPERLINK: To connect differenr HIpERLAN acccss points or HIpERACCESS nodes with a high-speed link, HIPERLINK technology can be chosen. HIpERLINK provides a fixed point-to-point comection with
Common chamcterisrics
of HIPERLAN/2, HIPERACCESS, and HIPERLINK include their support of the ATM service classes CB& VBR_(, VBR-n( UBR, and ABR. It is clear that only HiperLAN2 can be a candidate for the RAL of WAIM. This
PREPiqREo
By: M. S.PRASANNA A.p-CSE d
R.,IOHAN
^lr
A.p_CsE
27
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING technology fulfills the requirements ofATM eoS support, mobility, wircless access, and high bandwidth.
I;**";
Flgl,,e ?,30 Lar€red
mo&tor8fiAlt
LI
akdess aacess neirorks
I
M@l As an access network, BRAN technology is independent from the protocols ofthe fixed network. BRAN can be used for ATM and TCp,{p netlvorks as illustrated iir Figure 7.30. Based on possibly different ?hysical layers, the DLC layer of BRAN offers a common interface to higher layers. To cover special cha.acteristics of wireless links and.
to adapt directly to different higher laygr network technoiogies, BRAN provides
a
network convergence sublayer. This is the layer which can be used by a wireless ATM network, Ethernet, Firewire, or an Ip network. In the case of BRAN as the ML for
WATM, the core ATM network would
use services
of the BRAN letwork
converpence
suDIayer,
11.
f,xplain HIPERLAN2 basic structure and protocol stack
While HIPERLAN 1 did not
succeed
HiperLAN2 might have a berter
chance.
(This is also wdtten as HIPERLAN/2, HiperLAN/2, t1/2; official name: FIIpERLAN TWe 2.) Staodardized by ETSI (2000a) this wireless netwrirk works at 5 GHz (Europe: 5.15-5.35 GHz and 5.47-5.'725 GHz license exempt bands; US: license free U-NII bands,
section 7.3.7) and offeis data rates of up to 54 Mbit/s including eoS support and enlanced security fqetures. In comparison with basic IEEE 802.11 LANS, HiperLAN2 offels more l'eatures in the mandatory parts ofihe staldard (HiperLAN2,2OO2). see
Iligh-throughput transmission: Using OFDM in the physical layer and a
dynamic
TDMA/TDD-based MAC protocol, HiperLAN2 not only offers up to 54 Mbit/s at the PREPARED BY: A.tI S.PRASANNA A.P-csE &
Mr A.MoHAN
A.P-csE
28
DEPAR?MENT OF COMPUTER SCIENCE AND ENGINEER]NG physical layer but also about 35 Mbit/s at the network layer. The overheads intoduced by the layers (medium access, packet headers etc.) remains almost constant over a wide rage ofuser packet sizes and data rates. HiperLAN2 uses MAC Aames with a coNtanl length of 2 ms.
t
Connection-oriented: prior
to
data hansmission HiperLAN2 networks establish
logical connections betweel a sender and a receiver (e.g., mobile device and access point). connection set-up is used to negotiate eos parameteE. A connections me timedivision-multiplexed over the air interface (mMA with TDD
for
sepamtion
of
up/downlink). Bidirectional point-topoint as well as unidiectional pointto_multipoint coinections are offered. Additionally, a broadcast channel is available
to rcach ail mobile
devices in the tuansmission range of an access point.
.
Qualify of service support: With the help of connections, support:f eos is much simpler. Each connection has ils own set ofeoS parameters (bandwidth, delay, jilEr bit eror rate etc.). A more simpJistic scheme using priorities only is available. .'
.
Dytramic frequency selection: HiperLAN2 does not rcquirc frequency planning of cellular networks or standard IEEE 802.11 networks. All access points have built_in
support which automatically selects an appropriate frequency within their covetage area.
All APs listen to neighbodng Aps
as well as
to other radio souces in the environmeni
The best fiequency is chosen depending ort the cu.rent interference level and usage of mdio channels.
.
Securily support: Authentication
as
will
as
encryption are supponed by HiperLAN2.
Both, mobile termioal and access point can authenticate each other. This 3utlorized access to the network as well as a valid network operator. However,
ensures
additional
firnctions (directory services, key exchange schenles etc.) are needed to support authentication, All user traffic can be encrypted using DES, Triple,DES, or AES to protect against eavesdropping or man-in-the_middle attacks.
t Mobilifi aupport: Mobile terminals place
betwee! the teminal alrd the
can move
access
around whiie transmission arways takes
point with the best radio signal. Handover
between access points is performed autoEatically. connections including their QoS parameters handover.
Ilowevel
will
If
enough resources arc available, al]
be supported by a new access point after
some data packets oay be lost during handover.
PREPARED By:
,tr s.pRAsANM
A.p_CsE & r,1r
R_l,toHAttA_p_csE
2s
DEPARTTYTENT OF COMPUTER SCIENCE AND ENGINEERING i
.
Application atrd network independence: HiperLAN2 was not designed with a certain goup of applications or networks in mind. Access points can connect to LANS running ethemet as welr as IEEE 1394 (Firewire) systems used to connect home audio/video devices. Interoperatio! with jG rletwo*s is also supported, so not only best effofi data is
supported but also the wireless connection of, e.g., a digital camera with a slreaming of video da!a.
TV set lbr live
.
Power saye: Mobile terminals can negotiate certain wake-up paltems to save power. Depending on the sleep pe ods either short latency requirements or Iow power requirements can be supported. The folowing seclions show the reference moder of HiperLAN2 and illustrate sollle mote features. Reierence model and configurations
Figurc 7.31 shows the standard architecture of an infrastructure-based HiperLAN2 network. In the example, two access points (Ap) are aftached to a core network. Core networks might be Ethemet LANs, Firewire (IEEE 1394) connections between audio and video equipment, ATM networks, UMTS 3G cellular phone networks etc. Each AP consists ofan access point controller (ApC) and one or more access
point
Aj.APT can comprise orle or more sectoN (show,n as cell here). Finally' four mobire termiour* (MT) are arso shown. MTs can move around in the cerl
.1,r-,1-r!9,9i_"9ry_(4PT):,
area as shown The system automaticalry assigns the
quality. No frequency pranaing
is
Apr/Ap with
the best transmission
necessary as the
Aps automaticaly select the appropriate frequency via dynamic lrequency selection (DFS, compare with IEEE 802.1 th, section 7.3.8). Three handover situations may occur:
Sector handover (Inter sectot): Ifsector antennas are used for an Ap, whioh is optional in the standard, the Ap shall supporr sector handover. This type ofhaadover is handled inside the DLC layer so is not visible outside the Ap (as long as enough resources are
available in the ne\y sector).
.
Radio hardover (lnrer-ApT/Intra_Ap): As this handover type, too, is handted wirhii) the AP, no extemal interaction is needed. In the example of Figure 7.31 the teminal PREPARED
By; l,tr s.mlsANNA A.p_csE A,!tr" R.MoHAN
A.p_CsE
30
DDPARTMENT oF coMPaTER SCIEI\IoE AND ENGINEERING MT3, moves from one APT to another of the same Ap. All context data for the connections are already in the Ap (encry?tion keys, authenticatioq arld connection parameters) and does not have to be renegotiated.
r
Network handover (lnter-Ap/lntra-network)t This is the most complex sjtuation: MT2 moves fiom one AP to another. In this case, the core network and higher layers are also involved. This handover might be supported by the core network (similar to the lApp, IEEE 802.1lf). otherwise, the MT must provide the required information sim ar to the situation during a new association.
o
r&s!
l+ 6. ''
7.3r,
I.
HircrlA,f2 brsic slru.lue and tisl{,orer
HiperLAN2 networks can operate
in two different modes (which may be used
simultaneously in the same n€twork):
Centralized mode (CM): This infrastructue-based mode is shown again in a more abstract way in Figure 7.32 (left side). All Aps are connected to a core network and MTs are associated
with APs.
Even
the AP. In this mandatory mode
if two MTs share the
same
cell, all
data is transferred
via
tie Ap takes complete control ofeverything.
.
Direct mode (DM): The optional ad-hoc mode ofHiperlAN2 is illustrated on the right side of Figue 7.32. Data is directly exchanged between MTs if they can receive each other, but the network still has to be controlled. This can be done via an Ap that contains a central conholler (CC) anlway or via an PREPARED
By:
MT tlat contains the CC fuactionality. There
, r S.PIASANNA A.P-CSE & l.tr R.I OHAN A.P_C5E 3t
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING is no real diference between an Ap and a CC besides the fact that Aps are always connected to an infrasAucture but here only the CC firnctionality is needed. This is why the standad coircd two different names. IEEE go2.l l, too, offers an ad-hoc mode, but aot the CC fimctionality for eos support.
tbr!
7Jz
Hiperl4.i2 cent ald \,s diied nnde
FigLrre 7.J3 shows
Prctocol sra.ks
lhe HiperLAN2 prolocol stack as used in access point:. iii.iiiiibiG i6iiiii;;l;.differ with re!-pect ro the number of MAC and RLC
instinces (only one of each). The lowest layer, the physicat layer, handles as usual all
functions reiated
to
modulation, forward error correction, signal
detection,
synchronizatio! etc. Section 7.4.4.2 describes the physical layer in more detaii. The data link control (DLC) layer contains th contrcr runctions. rran instance. The MAC
o.
"..0n"".,;"fo1ffi:::"lHTr}:":rJ* J::
ofan Ap assigos
each MT a certain capacity to guamntee connection quality depending on available resources. Above the MAC DLC is divided into a control and a user paat. This separation is cbnmon in classical as
cellularphones
orpsrN. The user HiperLAN2 oflers relirble
rehansmissions. For broadcast
increased reriabirity PREPARED
t{r
parr cootains
error coltror mechanisms.
Jat
transmissl-:1tl*:*
by repeatirs
gy:
connection_oriented systems such
using acknowledgements and
;T:il:"T;,:H;H:T#r:::::
S.PRASANNA A.P_CSE & lylr R,fiOHAN
A.p-CsE
32
DEPARTI,IENT OF COMPATER SCIENCE AND ENGINEERING transmission is available. The radio fink control (RLC) sublayer compdses most conlro] functions in the DLC layer (the CC part of an Ap). The association
control function
(ACF) cortrols association and authentication of new MTs
as well as synchronizatlon of il:e mCio cell via beacons. The DLC user connection confrol (DCC or DUCC) service controls connection setup, modification, and release. Finally, the radio resourcc control (RRC) handles handover between Aps and within an Ap. These funclions control the dynamic frequency selection and power save mechanisms ofthe MTs.
On top of the DLC layer lhere is the convergence layer. This highest layer of HiperLAN2 standardization may comprise segme[tation and reassembly functions and adaptatioN to fixed LANS, 3G networks etc. The following sections give some more insight into the 3 HiperLAN2 layers. neaure 7.33
Hiperltltz potocol
Dlocoold
A--"" .,...9
Con!€.Eence ta\€r
olc
stack
rsr
SAP
tudto [nt oont ot sut,layer
?*u*
@@@
12. Discuss
MAC layer and its seryices
The MAC laye. has to but
fuifill
several tasks. First of all, it has to control mediumaccess,
it
can also offer tupp'ort fo. roarning, authentication, and porver conservation. The basic services provided by the MAC layer are the maldatory
/ '/
asynchrutrous data service and an optional time-boundeal service
PREPARED BY: ,,1r
S.PRA5ANNA A.P-csE &
A.1r
p.IloHAN A.P.csE
.33
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING The following thrce basic access mechanisns have been defined for IEEE g02.1 I: the mandatory basic method based on a versioo of CSMA,iCA, arr optional method avoiding the hidden terminal problem, and finally a contention_ free polling method for time-
bouoded service. The
fust two
methods
are also summarized as distributed
coordination functior @cF), the third method is calred point coordination function @cF) DCF only offers asynchrcnous se ice, wh e pcF olrers both asynchrcnous and time-bounded service but needs an access point to control medium access and to avoid coDtention. The MAC mechanisms are also called distributed foundation wirelcss mcdium access cotrtrol (DFWMAC).
For all access methods, sevemi parameters for controlling the waiting timc before medium access are importa.nt. Figure 7.9 shows the three differcnt parameters that
define t[e priorities ofmedium access. The values ofthe parameters depeld on the pHy ald are defmed in relation to a slot time. Slot time is derived from the medium propagatjol delay, transmittq delay, and other pHy dependent parametets. Slot time is 50 ls for IHSS and 20 ps for DSSS. The medium, as shown, can be busy oridle (which is detected by the CCA).
medium
is busy this can be due to
data frames
Ifthe
or otlier control frames. During
a
contention phase several nodes try to access the medium.
rcdium
ts frEe
:
Or
s
short inter-frame spacing (srFS)r The shortest waiting time for medirm access (so the highest priority) is defined for short contrcl messages, such as acknowredgements ofdata packets orpolling responses. For DSSS - 28 rs rhe use or ,ris pammeter wi, be exp,r.". ,, ."",, 's ' PcF inter-frame spacitrg (pIFs): A waiting time berween DIFS and sIFs (and rhus a medium priority) is used for a time-bounded service. An access point polring
jj.:;l:;:ffif;i:::
other nodes
only has
to wait PIFS for medium
access (see secrion
7.j.4.1). plFS is delined as SllS
plus one slot time. PREPARED
By; ,ttr S.PRASANNA A.P-CSE &
ttr
R.IIOHAN
A.P_CSE
34
DEPARTMENT OF COMPATER SCIENCE AND ENGINEERING
.
DCF inter-frame spacing (DIFS): This pa!.ameter denotes the longest waiting time and has the lowest priority for medium access. This waiting time is used for asynclnorous data service within a contentiotr period (this parameter and the basic access nethod are explained in section 7.3.4.1). DIFS is defined as SIFS plus two slot times. Dasir DFWMAC-DCF using CSMA/CA
The mandatory access mechanism of IEEE g02.ll is based on crrrier sense multiple access with collision avoidance (CSMA/CA), which is a mndom access scheme with caEier sense and collision avoidance through random backotl. The basic CSMA./CA mechanism is shown in Figure 7.10.
If the medium is idle for at least rhe
duration of DIFS (with the help of the CCA signal of the physical layer), a node can access the medium at once. This allows fo. short access delay under light load. But as more aod morc nodes ty to access the medium, additional mechanisms arc needed.
-
If the medium is busy,
L/l -1\
FIE|'e 7.1o
"-*,.n,,,*, lrardomlzed b&[ of
nodes have to wait for the duation of DIFS, entering a
contention phase afterwards. Each node now chooses contentioD
window
a random backolf time withiD
and delays medium access for this iauldom amount of time.
f
a
he node
conti[ues to sense the medium. As sooll as a node senses the channel is busy, it has ]ost this cycle and has to wait for the next chance, i.e., until the medirun is idle again for at least
DIFS. But
if
the mndomized additional waiting time for a node is over and rhe medium is still idle, the node car access the medium immediately (i.e., no other node has a shorter waiting time). The additional waiting time is measured in mulriples of the above-mentioned slots. This additional randomly distributed delay helps to avoid collisions otherwise all stations would try to transmit data after waiting for the medium becoming idle again plus DIFS.
PREPAPED
By: ,,1r s.pAAsANNA A.p-CsE &,U. R_lloHAN A-p_csE
35,
DEPARTMENT OF CAMPUTER SCIENCE AND ENGINEERING
Obviously, the basic CSMA./CA mechanism is not fair. Independent ofthe overall time a node has already waited for transmission; each node has the same chances for trairsmitting data in the rext cycle. To provide faimess, IEEE g02.ll adds a backoff tiher. Again, each node selects a random waiting time within the range of the contention window. Ifa certain station does not get access to the medium ii1 the fiIst cycie, it stops its backoff timer, waits for the chaDnel to be idle again for DIFS and starts the counter again. As soon as the co'nter expircs, the node accesses the medium. This means that deferred stations do not choose a mndomized backoff time again, but conlinue to count down. Stations that have waited longer have the advantage over stations that have just enlered, in that they only haye to wait for the remainder oftheir backofftimer from the previous cycle(s). Figurc 7.1 I explains the basic access mechanism of IEEE g02.1 I for five stations trying to send a packet at the marked points in time. Station3 has the fi.st rcquest Aom a higher layer to send a packet (packet arrivar at the MAC SAp). The station senses the medium, waits for DIFS and accesses the medium, i.e., sends the packet.
stationl,
station2, and stations have to wait at least until the medium is idle ior DIFS again after station3 has rropp"d .:.lg_1:_g:...I_9y_-g.1..-t1r- e€. !1,a1!9.rls choose a backoff rime wirhin rhe conlenlion nindow and srart counting down their backoff!imers Figure 7.1I shows the random backofftime ofstatiorl as sum ofboe (theelapsed backoff time) and bor (the residuar backoff time). The same is shown for srarions Station2 has a total backoff time ofonly boe and gets access to the medium first. No residual backoff time for station2 is shown. The backoff timers of statiorl aDd stations stop, and the stations store their residual backofftimes. While a new station has to choose its backofftime from the whole contention window, the two old stations have statisticallv smaller backoffvalues. The older values are on average lower than the new ones. Now slation4 wants to send a packet as w8ll, so aller DIFS waiting time, three stations try to get access. It can now happen, as shown in the figure, that two stations
accidentally have the same backofftime, no matter whether remaining or newly chosen. This results in a collision on the medium as shown, i.e., the transmitted frarncs are destroyed. Stationl stores its residual backoff time again_ In the )ast cycle shown stationl PREPARED
By: Mr S.PRASANNA A.p_CsE &,r
r
R.^,IOHAN
A.p-aSE
36
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING finally gets triggers
a
access
to the
medium, while station4 and statio[s have to wait.
retransmission with
a new
modom selection
of
A collision
the backofl time
Retansmissiotrs are not pdvileged.
ffi
$
n"on
rl,-",un,-ne4serc)
roter arrra
IEI
&pssd b3.ror teie
ar r,,rac
while this process describes the comprete access mechanism for
broadcast frames, an additional feature is provided by fhe standard for rmicast data transfer. Figure 7.12 shows a...ry!!qg19.99-e,-s-s-!!&Ih9 rae_djrrm and sending its data. But now, the receiver answers-directly with an acknowredgement (ACK). The receiver accesses tle medium
after waiting for a dumtion of SIFS so no other station c.u access the medium in the meantime afrd cause a col]ision. The other stations have to wait for DIFS plus their backoff time. This acknowledgement ensures the corect reception (corr€.t
checksurn CRC at the recaiver) of a frame on the MAC layer, which is especially impo ant ill eror prone envircnments such as wireless courections. If no ACK is retumed, the sender automatically retmnsmits the frame_ But now the sender has to wait again and compete for the access right. There are no special rules for retransmissions. The number
of
retransmissions is limited, and final
PREPARED
failur! is reported to
the higher layer.
By: i\,tr S.PMSANNA A.p_csE & l.tr R.T OHAN
A.p_CsE
3-l
DEPARTLTENT OF COMPATER SCIENCE AND ENGINEERING
IEEE
802,11
!n,En
DFWMAC-DCF with RTS/CTS extension Section 3.1 discussed the problem ofhidden terminals, a situation that can also occur in IEEE g02.u networks This problem occurs ir one station can receive two others, but those stations cannot receive each other. The two stations may sense the channel is idle, send a frame, and cause a collision at the receiver in the middle. To deal with this problem, the standard cl packets,
Rrs
and
crs. rhe,""
"."1::*-rI:::: il::fffi:,:"X ;'].il
node has to implement the functions to react properly upon reception
packets.
ofRTS/CTS control
Figure 7.13 illushates the use :fllland 9Tq. After waiting for DIFS (plus a random backoff time if the miilu,* turyf. tf," ."ra", ca-o issue a requcs( to send (RTS) contrcl packet Th; RTS packet thus is not given any higher priority other data packets. The RTS packet includes the receiver and the duration of the whole data
comparcd to
ofthe
data
transmis.jon to come
transmission. This duration specifies the tjme iotgrval necessary to tmnsmit the whole data frame and the acknowledgement related to it. Every node receiving this RTS now has to set its net allocation vector (NAV) in accordance rvith tlle duration field. The NAV then specifies the earliest point at which the station can try to access the medium again.
If the
receiver of the data transmission receives
tlit RTS, it answers with a clear to send (CTS) message after waiting for SIFS. This CTS packet contains the duraiion field again and a[ stations receiving this packet from the receiver of the intended dafa transmission have to adjust their NAV. The latter set ofreceivers need not be the same as the first set receiving lhe RTs packet. Now aI nodes within receiving distance around PREPARED By:
tlr
s.pRAsANNd A.p_csE & tut R.I4OHAN
A.P-CSE
i8
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING sgnder and receiver are
infomed that they have to wait
more
lime before accessing the
medium. Basically, this mechanism res€rvgs ihe medium for one sender exclusively (this is why it is soDetimes ca.lled a virtual ieservation scheme). Finally, the selder can send the data after SIFS. The rE@iver waits for SIFS after rcceiving the data packet and then acknowredges whether the hansfer was co,,ect. .rhe tmnsmission has now bee[ completed, the NAV in each node marks the medium as liee and the standard cycle can stafi again.
€aEa02.11nidth
Within this scenario (i.e., using RTS and CTS to avoid the hidden
rerminal problem), collisions can only occur at the beginning while the RTS is sent. Two or more stations may start se.di!,g,g! Jhg...s,q.$s !i111g-.G.rs or other dara packets). Using RTS/crs can result in aron-negligible overhead causing a waste of bandwidth and higher delay. An RTS threshold can determine when to use the additional mechanism (basically at
larger frame sizes) and when to disable (1997) give an overview
it (short frarnes). Chlcya (1996) rnd Chlaya of the as),nchrcnous services irt g02.l l and discuss performance
under different load scenarios.
Wireless LANS have
bit error
mtes
in transmission t[at are t]?ically
several
orders ofmagnitude higher than, e.g., fiber optics. The probability of an enoneous tiame is much higher for wireless links assuming the same frame lergth.
One way to decrcase
the enor probability offrames is to use shorter
frlmes. In this
bit el.ror rate is the same, but now only short frames are destroyed and, the frame eror rate decreases. case, the
However, the mechanism of fragmenting a user data packet jnto seveml smaller pats should be transparent for a user. The MAC layer should have the possibilily of PREPARED By:
Mr S.PRASANNA A.p-CsE & M. R.I4OHAN
A.p_csE
39
DEPARTMENT OF COMPUT:ER SCIENCE AND ENGINEERTNG adjuslhg thg traosmission ftame size to the curent enor mte on the medium. The IEEE 802,11 statdard specifies a fragmetrtation mode (see Figure 7.14). Again, a sender can send an RTS control packet to reserve the medium aller a waiting time of DIFS. This RTS packet now includes the duation for the hansmission of the first fragment and the corrsponding acknowledgement. A certain set of nodes may rcceive this RTS and set their NAV according to the dumtion field. The receiver answers with a CTS, again including the duation of the transmission up to the acknowledgement. A (possibly differed) set ofreceivers gets this CTS message and sets the NAV.
neu.114 tEat 80?,11
'r3gng)tatin
oa
*erdi.
As shorm
in Figure 7.13, the sender
can now send the
first data frame, frag l, afler wailjDg only for SIFS. The new asperr o,f ihis-iagmell1ation. r.node is that it includes anothq duration value in the frame fragl. This dumtion field reserves the medium 1br the
dumtioa
of the transmission following,
the second Aagment ancl its acknowledgement. Again, seveml nodes may receive this reservation and adjust their NAV, Ifall nodes are static and hansmission conditions have not clanged, then fie set of nodes ieceiving the duration fierd in frag r should be the same as the set that has received the initial reservation in the RTS control packet. However, due to ihe mobility of nodes and chaiges in the envi.onment, this could also be a differelt set ofnodes comprising
DF!9MAC.PCF rvith polling The tlvo access mechanisms presented so far cannot guarantee a maximum access
delay or minimum transmissioa banclwidth. To pmvide a timc_bounded service, the standald specifies a poi[t coordination furction @CF) on top of the standard DCF mechaniss' using PcF requires an access point thal controls medium access and pols PREPARED
8y:
r'ylr
S.pMSANNA A.p_csE d
itr
R.lrtOHAN
A.p_csE
40
DEPARTMENT OF COMPT]TER SCIENCE AND ENGINEERING the single nodes. Ad-hoc Detworks cannot use lhis
fimction so, provide no eos but .best efort'in IEEE 802.11 WLANs. The poiot co-orditrator in the access poinr splits the time into super frame periods as sho\rn in Figure 7.15. A super frame comprises a c0ntentiotrfree period and a contention period. The contention period can be used for the two access mechanisms presented above, The figure also shows several wireless stations (all on the same line) and the stations,NAV (again on one line). access
i*i'-'_ slFs
conlelbo.r fres ped,
At
time t0 the contention-free period
another station
also defers
of the super f.ame should theoretically start, -!.-+i
is still transmitting data (i.e.,
to DCF, and the start of the
the medium
until tl,
the
but
is busy). This means that pCF
may be postponed. .fhe only any contention pe od at alr. After the
super frame
possibility of avoiding variations is not to have medium has been idre
I
point coordinalor has to wait for prFS before accessing
the medium. As PIFS is smaller than DIFS, no other station can start sending earlier. The
poilt coordinator
Dow sends data
Dl do\rnsheam to the first
rdireless station.
This station can answer at once after SIFS (see Figrfre 7.15). After waiting for SIFS agairL lhe point coordinatoi can poll the second station by sending D2. This statron may answer upstream to the coordinator with data U2. pouing continues with the third node. This lime the node has nothing to answer and Ihe
poilt coordinator will not receive
a
packet aner SIFS.
PIEPARED By: /rtr S.PRASANNA A.p-esE &
t
tlr
R.^toHAN
A.p-csE
4t
DEPARTMETYT OF COMPILTER SCIENCE AND ENGINEERING After waiting for PIFS, the coodinator can resume polling the stations. Finally, the point coordinator can issue atr end marker (CFend), indicating that the contention
period may slart again. Using pCF automatically sets the NAV, prcventing other stations from sending. In the example, the contention_free period plarmed initially would have been from t0 to t3. However, the point coordinator finished polling earlief shifting the end of the contention-free pedod to t2. At t4, the cycle starts again with the next super fmme. 13.
Explain l\{AC managehcnt
aDal packet
structure
MAC managemenl MAC management plays
role in an IEEE g02.I I station as it more or Iess controls all fimctions related to system integration, i,e., integration of a wi.eless station into a BSS, formation of al ESS, synchronization of shtions etc. .lhe folJowing functional groups have been identified and will be discussed in more detail in rhe following sections: a centml
.
Synchronizafio[: Frmctions to support finding a wireless LAN, synchronization of internal clocks, generation of beacon signals. . Power managementi Functions to conlrol lransmiller activity for power conservarion, e.g., periodic sleep, buffering, without missing a irame.
r
Roaming: Functions for joining a network (association), changing
access points,
scanning Ior access poinls.
.
ManagemeDt itrformation base (MIB): All parameteN representing the curreu slate ofa rvircless station and an access poin! a-re stored wirhin a MrB for intemar and extemal access. A MIB can be accessed via standardized protocols such as the simple net\,r'ork management protocol (SNMP).
MAC frames
Figrre 7.16 shows the together with the content of the following: PREPAPED
basic structure
of an IEEE 802.1 I MAC
data fmme
frame contiol field. The fields in the figure refer to the
By: ,,tr s.pRAsANNA A.p_csE & r,tr R.i,toHAN A.p_csE
42
DEPARTMENT OF COMPATER SCIENCE AND ENGINEERING
FE'8.716 EEE
4
.
I
1
, -
AO2,11
AC
'l- -. r_
Frame control: The fiIst 2 byes serve several purposes. They contai! several sub-
fields as explained aner the MAC frame. o Duration/ID: Ifthe field value.is less than 32,76g, the duration field contains fte value indicating the period of time in which tle medium is occupied (in ps). This field is used for settilg the NAV for the virtual reservation mechanism using RTS/CTS and cluring fragmentation. Certain values above 32,76g are reserved fo. identifiels.
.
Address I to 4: The four
address fields contain standard IEEE g02
MAC
addresses (48
bit each), as thiy are known from other g02.x LANS. The meaning of each acldress depends on the DS bits in the frame control field and is explained in more detail in a separate paragmph.
.
Sequence conlrol: Due
to the
acknowledgement mechanism faames may be
duplicated. Therefore a sequence number is r.rr.a
t
rl i,fi", Jrpfi.or".
Data: The MAC iame may contain arbitmry data (mar. 2,312
tlansferled transparently from
a sender to the
byte),
which is
receiver(s).
.
Checksum (CRC): Finally, a 32 bit checksum is used to protect the frame as comrllon practice in all 802.x networks.
it
is
The frame conhol field shown in Figure 7.16 contains the following fields:
Protocol versiotr: This 2 bit field indicates the cunent protocOl versior and is fl-\ed to 0 by now If major revisions to the sta[dard make it incampatible with the curent versron, this value will be increased.
PPEPARED
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43
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERTNG
.
Type: The type field determines the fuDction of a llame: managemenr (:00), col1tlol (=01), or data (=10). The value 1l is reserved. Each type has s€veral subq?es as indicared in rhe lollowing field.
.
Subtype: Example subry?es for management frames are: 0000 for association request, 1000 for beacon. RTS is a control frame with subtype l0l l, CTS is coded as I100. User data is tEnsmitted as data frame wirh subtype 0000 All details can be found in IEEE. 1999.
To DSlFrom DS: Explained in the following in more detail.
'
More fmgme.,tsi This fierd is set to
another fragment ofthe cunent
.
Retry:
If
the
I
in ar data or mal,gement Iiames that
have
MSDU to follow.
curle
frame is a retrarsmission of an earlier frame, this bit is set to With the help ofthis bit it may be simpler for receivers to eliminate duplicate
.
l
.
Aames.
Power managemeDt: This field indicates
transmission mode.
ofa
Ifthe field
.
frame. Set
to I the field
tle mode of a station afler
successful
indicates that the station goes into power_save
is set ro 0, the ;tation stays active.
More data: In general, this field is used to indicate a receiver ihat a sender has more data to send than the cultent frame. This can be used by an access point to indicate to a station in power-save mode thar more packets u." !.y,f&I-gg.:..Q!.!-!gl-be.us€d..bJ a slarion
to indicate to an station has
point after being palled that more polling is necessary as the more dala ready lo tmnsmil. accoss
e Wired equivalent privacy (WEl'): This field indicates mechanism of 802
I
that the standard secu ty
is applied. However, due to many weaknesses found in the wEp algorithm higher layer secuity shourd be used to securc an g02.lr network (tsorisov, 2001). o Order:
Ifthis bit is set to I
14. Discuss the
the received Aames must be processed in strict order.
Infrastructure anal ad_hoc networks
Infrastructure Networls
Many WLANS of today need an infrastructure nehrork. Infiastructure PR€PARED By: l,tr s.pRAsANNA A.p_csE
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44
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING networks not only Fovide access
to
other rletworks, but also include forwarding
firnclions, medium access control etc.
In these infrastructure-based wireless Detworks, communication typically
takes
place only between the wireless nodes and the access point (s€e Figurc 7.1), but not directly between the wircless nodes. The access point does [otjust control medium aocess, but also acts as a bddge to other wireless or wired networks. Figure 7.1 shows three access points with their three wireless networks and a wircd network. Seveml wireless networks may folm one logical wireless network, so thg accesspoints together with the fixed network in between can connect several wireless networks to form a larger network beyond achral radio coverage.
Typically, the design
of
infrastructure_based wireless networks
is
simpler
most of the network funationality lies within the access point, whereas the wireless clients can r€main quite simple. This structure is reminiscent of switched because
Ethemet
or
other
slar-based
networks, where
a
central element (e.g,, a switch) contols network flow. This type of network can use different access schemes with or without collision. Collisions may occur if medium access of the wireless nodes and the access point is not coordinated..However, ifonly the access point controls mediurn access, no collisions are possible. Tiis setting may be
useful for quality of service guarantees such as minimum bandwidth for certain nodes. The access point may poll the single wireless nodes to ensue the data rate.
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DEPART:IY{ENT OF COMPUTER SCIENCE AND ENGINEERING
Ad-hoc Networks Ad-hoc wireless networks, however, do not need any infrastructure to work. Each oode can communicate direcuy with other nodes, so no accgss point conholling medium access is necessar).
Figure 7.2 shows two ad-hoc networks
hoc nelwork can only communicate
wit
tuee nodes each. Nodes withrn an acl,
if t::';T,i::H:l
are witrin each other,s radio .",-" Nodes 6om the two networks shown
:::T:i:jT"
:"::::"J
in Figu.e 7.2 cannot, therefore. communicate with each otier ifthey are not \i/ithin the same radio range, In ad_hoc networks, the complexity
of
eacr rcde
is higher
because every node has
to irnprement medium access mechanisms, mechanisms to handle hidden or exposed terminal problems, and perhaps priority mechanisms, to provide a certain quality ofservice.
This type
ofwireless network
for exampre, needed
e
r". rr",,r"I'j"tlj";:::"t;::it'"ffi*:r:
infrastructure or communication scenaios far away fiom any infrastructure
PnEP,{RED
By: /ur S.PRASANNA A.P-CSE a l4r R.^/IOHAN A.P_CSE
ts,
of
46
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING 15, Discuss the c.omparison ofwireless tretworks
#3iffer
lyItrI atrd wIMAx V/IFI
it
Wireless Fidelity
ii)
Coverage is very area
,,-? limited to some small
iiDLAN iv) Low cost
;
Microwave
ii)
Access
a4
Covemge is about 30 miles
iiDMAN
v) NonJine of sight antennas vi)Less QoS vii) CSMA/CA protocol
PREPARED
WIMAX i) Worldwide Interoperability for
'
,-
iv) High cost' v) Line ofsight anteruras vi) More QoSu' ' vii) Connection oriented MAC
By: ,'1r S.PRASANNA A.P-dsE d t4r R_IIoHAN
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r:('
D EPARTTTE NT
OF
",*,O,U
*
M
Upiyersifv questiotrs NovemberlDecember
2012
2 marks
*t*,
J.
l6 marks
1. .Wrj1e
-
and ad hoc networks (page
"',11ffi;ttlt:sjuch&
notes on
tle MAC maragen
w rt te short notes
on tr,"
z.
the IEEE 8o2 l I prot ocol lPare 421 e1 sublayer (page 33)
ccess control "r,-*, #ll-oJ
NlaylJnne 2012
2 marks
i.
4)
ln_what situation can collisions rx urhar rs adaprive moorr"r;or:
rpuilal
IEEE 802.1 I? (Pase 4)
I6 mcrks
I. Compare HiperLAN mode. sotvrng hiddeD r.etaiac chuirn.t
ui{l,u, un
ad-hoc capabililies. po$er saving nrovrdinS reiiabilitv fairnesi problem
t.-r,
"..f,*t"l::.of a;""ii.'firii"r'-'
" 'ft'Pl'n
th. o*.urlo, oior-wMic_ ocF \,tirh a near riming diagram (page ii) Draw the MAC Aame of 802.11 and list lhe use of rhe field,s..(p_age -.a?)_............=............
November/December
2 marks
20ll
l-ear6es of HtpERLAN (page s) Y:.",,".r,*" z, Lrst oLrt lhe various element ofBluetootticore protocol (page
] 16
l)
marks
L Explain tIe architecture and fealures
2. Describe rhe
*'ee
o 802 r I in derail t) -.') iil;;;;:',-r?;i'iEE la dependences in detail u (P age
ith an example
ti May/June
20tl
2 marks
l. 2.
M_ention the advantages
what are
rhe rhree
Low
ofWLAN? (pagc power Stale;
l)
p;id;d
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tr
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