WN notes

1. EC 8004-WIRELESS
NETWORKS
1)Jochen Schiller, ”Mobile Communications”, Second
Edition, Pearson Education 2012.(Unit I,II,III)
2)Vijay Garg , “Wireless Communications and networking”,
First Edition, Elsevier 2007.(Unit IV,V)
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2. UNIT I - WIRELESS LAN
Introduction-WLAN technologies: - IEEE802.11: System
architecture, protocol architecture, 802.11b, 802.11a – Hiper
LAN: WATM, BRAN, HiperLAN2 – Bluetooth: Architecture, WPAN
– IEEE 802.15.4, Wireless USB, Zigbee, 6LoWPAN,
WirelessHART
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3. Why Wireless?
• Benefits
– Mobility Ability to communicate anywhere!!
– Easier configuration, set up and lower installation cost
– Easier to maintain.
– Solution in areas where cables are impossible to install (e.g.
hazardous areas, long distances etc.)
Difficulties
– Communication medium: Free space
• Noisy and unpredictable channel
• Broadcast channel, more user ->less BW per user
– Equipment cost is high
– limited BW
– Wireless comm. is influenced by physical obstructions, climatic
conditions, interference from other wireless devices
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4. The Electromagnetic Spectrum
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5. The Electromagnetic Spectrum
Extremely Low Frequencies
(ELF) Power transmission
30–300 Hz.
Voice Frequencies (VF)
Audio applications
300Hz–3KHz.
Very Low Frequencies (VLF)
Navy,Military applications
3KHz-30KHz
Low Frequencies (LF)
Aeronautical,Marine
30KHz–300 KHz.
Medium Frequencies (MF)
AM radio broadcasting
300–3MHz
AM radio 535–1605 kHz.
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6. The Electromagnetic Spectrum
High Frequencies (HF)
(short waves; BBC broadcasts;
government and military two-way
communication; amateur radio,
CB.
3–30 MHz
Very High Frequencies (VHF)
FM radio broadcasting (88–108
MHz), television channels 2–13.
30–300 MHz
Ultra High Frequencies (UHF)
TV channels 14–67, cellular
phones, military communication.
300–3GHz
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7. The Electromagnetic Spectrum
Microwaves and Super High
Frequencies (SHF)
Satellite communication, radar,
wireless LANs, microwave ovens
1–30 GHz
Extremely High Frequencies
(EHF)
Satellite communication,
computer data, radar
30–300 GHz
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8. The Electromagnetic Spectrum
Optical Spectrum
– The optical spectrum exists directly above the millimeter
wave region.
– Three types of light waves are:
• Infrared
• Visible spectrum
• Ultraviolet
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9. WIRELESS TRANSMISSION-Introduction
• Provide excellent high speed and reliable data communications in building or
campus environment.
• Wireless devices transmit using one of the following signals such as IR and
RF.
1. INFRARED Txlight based Txn using 900nm wavelength.
It use LASER as a Txr and photodiode as a Rxr.
Requires direct LOS for good Tx
cannot penetrate through walls
No electrical interferences occurs
Requires low BW,no need for license
2.UHF Narrowband TxIt support both unlicensed band(430-450MHz) and
licensed (450-470MHz)
power level is about 2W
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10. electrical interference
light
Comparison: infrared vs. radio Tx
Infrared Radio
 uses IR diodes, diffuse light,  typically using the license free
multiple reflections (walls, ISM band at 2.4 GHz
furniture etc.) Advantages
Advantages  experience from wireless WAN
 simple, cheap, available in and mobile phones can be used
many mobile devices  coverage of larger areas
 no licenses needed possible (radio can penetrate
 simple shielding possible walls, furniture etc.)
Disadvantages Disadvantages
 interference by sunlight, heat  limited license free frequency sources etc.
bands
 many things shield or absorb IR  shielding more difficult,
 low bandwidth Example
Example  Many different products
 IrDA (Infrared Data Association)
interface available everywhere
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11. Spread Spectrum Systems
• Spread spectrum techniques spread information over a very large bandwidth –
specifically, a bandwidth that is much larger than the inverse of the data rate.
• Different users can be spread across the spectrum in different ways.
• This allows multiple users to transmit in the same frequency band
simultaneously..
• The receiver can determine which part of the total contribution comes from a
specific user by looking only at signals with a specific spreading pattern.
Types
• FREQUENCY HOPPING SPREAD SPECTRUM(FHSS)
• DIRECT SEQUENCE-SPREAD SPECTRUM(DSSS)
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12. IEEE 802.11-WLAN
• Connect single MS to public landline system..
• Connect fixed-location computers to internet.
• Very flexible within reception area
• Ad-hoc networks do not need planning
• No wiring difficulties (e.g. historic buildings, firewalls)
• More robust against disasters like, e.g., earthquakes, fire
• Coverage area upto 100m.
• Data rate from 700kbps-55Mbps
• Operating Frequency 2.4-2.5GHz
Classifications
1. Infrastructure network
2. Ad-hoc network
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13. AP
AP
Comparison: infrastructure vs. ad-hoc networks
infrastructure network
AP: Access Point
AP wired network
ad-hoc network
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14. 802.11 LAN terminal with access mechanisms

802.x LAN
BSS1
group of stations using the same

ESS Portal
Point
802.11 - Architecture of an infrastructure network
Station (STA)
to the wireless medium and radio
contact to the access point
STA1 Basic Service Set (BSS)
Access Portal radio frequency
Point Access Point
Distribution System  station integrated into the wireless
Access LAN and the distribution system
 bridge to other (wired) networks
BSS2 Distribution System
 interconnection network to form
one logical network (ESS:
Extended Service Set) based
STA2 802.11 LAN STA3 on several BSS
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15. • Basic Service Set (BSS) consists of some number of stations
executing the same MAC protocol and competing for access
to the same shared wireless medium.
• A BSS may be isolated or it may connect to a backbone
distribution system (DS) through an access point (AP)
• The AP functions as a bridge and a relay point
• In a BSS, client stations do not communicate directly with
one another.
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16. • If one station in the BSS wants to communicate with another
station in the same BSS, the MAC frame is first sent from
originating station to the AP,
destination station.
and then from the AP to the
• A MAC frame from a station in the BSS to a remote station is
sent from the local station to the AP and then relayed by the
AP over the DS on its way to the destination station
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17. • An Extended service set (ESS) consists of two or more basic
service sets(BSS) interconnected by a distribution system.
• Typically, the distribution system is a wired backbone LAN but
can be any communications network
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18. WLAN Services
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19. mobile terminal
IEEE 802.11 –Protocol/Layered Architecture
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20. 1) PHY or Physical LayerEncoding –decoding , modulation-demodulation.
MAC layer
2) MAC Sub LayerFragmentation and reassembly of packets
3) MAC Management Sub LayerRoaming,power management,Registration and
connection management.
IEEE 802.11LAYERS
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21. 1) Physical layer is further subdivided into sub layers
1)PLCP Carrier sensing and
convert data-frame and carry mgt
information.
2) PMD define modulation and
coding techniques for signaling.
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22. Physical media for WLANs
1.3) Diffused infrared (baseband)
1.2) DSSS PHY (Direct sequence spread spectrum)
1.1) FHSS PHY (Frequency-hopping spread spectrum)
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23. 1.1) Frequency Hopping Spread Spectrum
• Two data rates for transmission at 1 and 2Mbps.
• Available channel 78 with a BW of 1GHz.
• Modulation technique is GFSK.
• Each BSS select one of the three patterns of 26 hops with the 3 groups..
• Group1(0,3,6,….75),Group2(1,4,…76) and Group3(2,5,…77)
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24. 00111001
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25. FHSS PHY
• In FHSS PHY, data transmission over media is controlled by the
FHSS PMD sublayer as directed by the FHSS PLCP sublayer.
• Binary information bits converts them into RF signals by
using carrier modulation and FHSS techniques.
• Data whitening is used for the PSDU before transmission to
minimize DC bias on the data if long strings of 1s or 0s are
contained in the PSDU. The PHY stuffs a special symbol every
4 octets of the PSDU in a PPDU frame
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26. FHSS PHY PPDU
• The sync field contains a string of alternating0s and 1s pattern
and is used by the receiver to synchronize the receiver’s
packet timing and correct for frequency offsets.
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27. • The SFD field contains information marking the start of a PSDU
frame.
• The PLCP length word (PLW) field specifies the length of the
PSDU in octets and is used by the MAC layer to detect the end
of a PPDU frame.
• The PLCP signaling field (PSF) identifies the data rate of the
whitened PSDU ranging from 1 to 4.5 Mbps in increments of
0.5 Mbps
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28. • The header error check field contains the results of a
calculated frame check sequence from the sending station.
• The FHSS PMD uses two-level Gaussian frequency shift key
(GMSK) modulation to transmit the PSDU at the basic rate of
1Mbps.
• Four-level GFSK is an optimal modulation scheme enables the
whitened PSDU to be transmitted at a higher rate
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29. •The encoding scheme that is used is DBPSK (differential binary
phase shift keying) send 1 or 2 bits per symbol.
•Total BW 2.4GHz is divided in to 11 channels with spaced by 5MHz.
•DSSS communicates non overlapping pulses at the chip rate of
11Mcps,which occupy 26 MHz.
1.2)DSSS PHY
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30. DSSS Transmitter & Receiver
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31. • An 11-bit Barker code (1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) is used for
spreading
In the transmitter, the 11-bit Barker code is applied to a modulo-2
adder together with each of the information bits in the PPDU.
•
• The
rate
the
output of the modulo-2 adder results in a signal with a data
that is 10 times higher than the information rate. The result
in
frequency domain is a signal that is spread over a wide
bandwidth at a reduced
power level.
• At the receiver, the DSSS signal is convolved with the same 11-bit
Barker code and correlated
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32. Frame Format
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33. • The SYNC field is 128 bits (symbols) in length and contains a
string of 1s .The receiver uses this field to acquire the
incoming signal and to synchronize the receiver’s carrier
tracking and timing prior to receiving the SFD
• The SFD field contains information to mark the start of the
PPDU frame.
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34. • Signal Field - Specifies the data rate at which the MPDU
portion of the frame is transmitted.
• Length: Indicates the length of the MPDU field by specifying
the number of microseconds necessary to transmit theMPDU
• CRC fields are used for error checking and correction.
• PPDU – PHY Protocol Data Units
• PSDU - PLCP Service Data Unit
• MPDU - MAC protocol data unit
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35. 1.3)Diffused IR
• The PMD of DFIR operates based on transmission of 250ns pulses.
• These pulses are generated by switching the transmitter LEDs on and off duration
of pulse.
• Peak power of pulse is 2W and wavelength is 850nm to 950nm.
• 16-PPM and 4-PPM modulation techniques at the data rate of 1and 2Mbps.
• 16-PPMblocks of 4-bits of information are coded occupy by the 16 slots of
length of 16 bit sequence..
• In this 16x250ns=4000ns carries 4 bit of information that supports 1Mbps.
• 4-PPM 4x250ns=1000ns carries 2 bit of information that supports 2Mbps.
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36. PLCP frame format for DFIR
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37. 1.5) IEEE 802.3 Carrier Sensing
• The receiver reads the peak voltage of wire of cable and compares it
against a threshold.
• The PHY sensing is through the CCA signal produced by PLCP..
• The real sensing mechanism done by two methods.(detects bits in air ,
checking RSS)
• Detection method is reliable than RSS because of interference..
• Virtual carrier sensing based on Network Allocation Vector (NAV)
supported by the RTS/CTS and PCF mechanisms.
• A length field in the MAC layer is used to specify the amount of time that
must elapse before the medium can be freed..
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38. 2) IEEE 802.11 MAC LAYER
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39. 802.11Layers
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40. Layer 2 Functions
• Medium Access Control (MAC)
– On transmission, assemble data into a frame with address and error
detection fields.
– On reception, disassemble frame, and perform address recognition and
error detection.
– Govern access to the LAN transmission medium.
• Logical Link Control (LLC)
– Provide an interface to higher layers and perform flow and
error control
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41. • The lower sublayer of the MAC layer is the distributed
coordination function (DCF). DCF uses a contention algorithm
to provide access to all traffic.
• The point coordination function (PCF) is a centralized MAC
algorithm used to provide contention-free service. PCF is built
on top of DCF.
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42. Distributed Coordination Function(DCF)
• DCF uses interframe space (IFS) & CSMA
• Steps
1. A station with a frame to transmit senses the medium. If the medium
is idle, it waits to see if the medium remains idle for a time equal to
IFS. If so, the station may transmit immediately.
2. If the medium is busy, the station defers transmission and continues
to monitor the medium until the current transmission is over.
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43. 3. Once the current transmission is over, the station delays another IFS.
the medium remains idle for this period, then the station backs off
random amount of time and again senses the medium. If the medium
If
a
is
still idle, the station may transmit. During the backoff time, if the medium
becomes busy, the backoff timer is halted and resumes when the medium
becomes idle
4. If the transmission is unsuccessful, which is determined by the absence of
an acknowledgement, then it is assumed that a collision has occurred
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44. Point Coordination Function (PCF)
PCF is an alternative access method implemented on top of the DCF. The
operation consists of polling by the centralized polling master (point
coordinator).
•
• The point coordinator makes use of PIFS when issuing polls.
• During the first part of this interval, the point coordinator issues polls in a
round-robin fashion to all stations configured for polling.
• When a poll is issued, the polled station may respond using SIFS. If the
point coordinator receives a response, it issues another poll using PIFS
• The point coordinator then idles for the remainder of the superframe,
allowing a contention period for asynchronous access
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45. 2.1)MAC SUB LAYER define the access mechanism and
packet formats
2.2)MAC MANAGEMENT SUBLAYER Roaming support, power
management, security
MAC LAYER
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46. 2.1) MAC Sub Layer-Accessing Mechanism
• Contention methods CSMA/CA
• Contention-free Access
1)RTS/CTS(avoid hidden terminal-Exposed terminal problems)
2)PCF(assign a priority for packet transmission,based on polling)Time bounded
applications
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47. 2.1.1)CSMA/CA Operation-DCF
• Case1Station transmit a packet immediately, by sensing the channel is free.
• Case2if the channel is busy,then NAV is turned ON,By setting backoff time and
wait the DIFS period..
• SIFSShort Interframe Spacinghighest priority packet such as ACK,CTS.
• PIFSPCF-IFS2nd priority,duration between SIFS-DIFS..
• DIFSDCF-IFSLowest priority and longest duration.
• After completion of transmission each station has to wait based on its priority..
• This method reduces collision but can’t eliminate it.
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48. Implementation of CSMA-CA/ACK
• When AP receive a packet of data, it
waits for SIFS and send ACK..
• Because SIFS<DIFS.
• All other terminals must wait until
the tx of ACK to MS is completed.
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49. 2.1.2)Implementation of RTS/CTS Mechanism
• If a channel freesend
RTS(20bytes),which carry
source,destination address and data.
• Destination station reply CTS(16
byte),after SIFS period.
• The source terminal send data after SIFS
period.
• Finally destination reply ACK after
receiving data.
• STATION3 It hear RTS/CTS
communication for the entire period,by
setting their NAV signal ON.
• After completion of transmission,NAV is
terminated,opening the contention for
other users.
STATION 3
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50. 2.1.3) PCF Operation
• AP organizes periodical contention free period for the time bounded information.
• Data to be transmitted at the beginning of each CFP, during that period it arrange
NAV for other terminals.
• Length of the PCF is occupied by CFP + DCF packets.
• If DCF packet occupies the channel,and doesnot complete before the start of the
next CFP.
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51. MAC frame Format
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52. • Frame Control: Indicates the type of frame and provides control
information
Duration/Connection ID: indicates the time (in microseconds) the
channel will be allocated for successful transmission of a MAC
frame. In some control frames, this field contains an association,
or connection identifier.
Sequence Control: Contains a 4-bit fragment number subfield
usedfor fragmentation and reassembly, and a 12-bit sequence-No
•
•
used to number frames sent between a given transmitter and
receiver.
Frame Check Sequence: A 32-bit cyclic redundancy check.
•
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53. Frame Control Field
Sleep mode
Power-save mode
Encryption
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54. • Type: Identifies the frame as control, management, or data.
• Subtype: Further identifies the function of frame.
• To DS: The MAC coordination sets this bit to 1 in a frame
distribution system.
destined to the
• From DS: The MAC coordination sets this bit to 1 in a frame leaving
distribution system.
the
• More Fragments: Set to 1 if more fragments follow this one.
• Retry: Set to 1 if this is a retransmission of a previous frame.
• Protocol version00 ,reserved for fututre.
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55. 2.2)MAC Management Sub layer
• Establish a connection between stations and AP.
• It provide a accessing mechanism for mobile station
Functions
1. Registration
2. Handoff
3. Power management
4. Security
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56. 1)Registration
• AP periodically send Beacon frame to MS for
timing synchronization.
• It contains BSS-ID, RSS, Roaming, time
stamp.
• Beacon used to identify the AP and N/W.
• Association REQMS send this request to
AP.
• Association RESAP grant permission MS.
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57. 2)Handoff
Mobility Environment
• No Transition MS is static or moving but inside BSA.
• BSS Transition MS moves from one BSS to another BSS but in same ESS.
• ESS Transition  MS moves from one BSS to another BSS but in new ESS.
Connection Registration
• Re-Association service MS moves from one BSS to another BSS but in same
ESS.Hence MS send request to distributed system via AP.
• Diassociation service used to terminate the association, for MS when it leave
from BSS.
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58. Handoff Procedure
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59. MS moves from AccessPoint1 to AccessPoint1
• Step1)Send Becon signal from APMS
• Step2)MS lock AP1 who has strong RSS.
• STEP 3)MS lies in border between two AP, hence it send probe signal to all
AP’s
• Step4) All AP reply Probe via RSS to MS.
• Step5)MS select AP by a strongest signal
• Step6)MS send reassociation req to AP3
• Step7)AP reply reassociation response to MS
• Step8) Handoff message infromed to old AP1,AP2 via Inter Access Point
Protocol
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60. Role of IAPP in Handoff
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61. 3)Power Management
• When a station is idledominates
LAN adaptor power consumption.
• It is important to put MS in
sleeping mode , buffer the data in
AP,send to MS is awakened.
• MS uses the power management
bit in the frame control field to
announce its active/sleep mode.
• With every beacon TIM sent list of
stations has buffered data.
• MS check the TIM and change its
mode to active.
• Now AP send the data to MS.
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62. 4)Security
1)Open system authentication/secret keyRequested user
send ID to open system, then the response station send the result of request.
2) Shared key authentication
• Request Station send authentication ID using 40-bit secret code that is shared
between itself-AP.
• The second station sends a challenge text 128bytes.
• The first station sends the encrypted challenged text as a response.
• The second station send the authentication results.
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63. IEEE 802.11a
• The PHY layer of IEEE 802.11a is based on OFDM transmission
which operates 5GHz.
• MAC layer same as like as IEEE 802.11.
• Supporting data rate Min 6Mbps -Max 54Mbps.
• Use 52 sub carriers for BPSK,QPSK,16QAM modulation methods.
• Use convolution encoder (1/2,2/3,3/4) for error correction.
• OFDM used to reduce the symbol rate by distributing bits over
numerous subcarriers.
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64. IEEE 802.11a – PHY Layer frame format
rate service payload
variable bits
6 Mbit/s
PLCP preamble signal data
symbols
12 1 variable
reserved length tail
parity tail pad
6
16
6
1
12
1
4 variable
6, 9, 12, 18, 24, 36, 48, 54 Mbit/s
PLCP header
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65. • PLCP preambleconsists of 12 symbols and is used for
frequency acquisition, channel estimation, and synchronization.
The duration of the preamble is 16 μs.
• signal contains the following fields and is BPSK-modulated.
rate determines the data rate
length indicates the number of bytes in the payload field.
tail bits are set to zero, also used to reset the encoder
• data field is sent with the rate determined in the rate field .
• service field which is used to synchronize the descrambler of the
receiver
• payload contains the MAC PDU (1-4095 byte).
• pad ensures that the number of bits in the PDU maps to an
integer number of OFDM symbols.
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66. IEEE 802.11b
• Data ratemin 1Mbps- max 6 Mbps
• Transmission range300m outdoor, 30m indoor
• Frequency 2.4 GHz ISM-band
• SecurityLimited, WEP insecure, SSID
• At 2.4 GHzIEEE 802.11b specify a new PHY layer called Clear
Channel Assignment (CCK) to support data rate of max 11Mbps.
• It uses Walsh code with the complementary codes for M-ary
orthogonal data tx.
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67. Implementation of CCA Transmitter
•Serial data is multiplied by into 8-bit address.
•6 of 8 bits are used to select one of 64 orthogonal codes.
•2-bits are directly modulated and txed.
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68. Implementation of CCK Receiver
•The receiver comprised two parts Barker and correlator code
•By checking the PLCP data rate,the receiver knows which decoder
employed for the rx packets.
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69. IEEE 802.11b – PHY frame formats
synchronization SFD signal service HEC payload
PLCP preamble PLCP header
128 16 8 8 16 variable bits
length
16
192 µs at 1 Mbit/s DBPSK 1, 2, 5.5 or 11 Mbit/s
short synch. SFD signal service HEC payload
PLCP preamble
(1 Mbit/s, DBPSK)
PLCP header
(2 Mbit/s, DQPSK)
56 16 8 8 16 variable bits
length
16
96 µs 2, 5.5 or 11 Mbit/s
Long PLCP PPDU format
Short PLCP PPDU format (optional)
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70. w
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71. HIPERLAN
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72. • HIPERLAN -High Performance Radio Local Area Network
• It is a European alternative for the IEEE 802.11 standards.
• It is defined by the European Telecommunications Standards
Institute (ETSI)
• The goal of the HiperLAN was to have data rate higher than
802.11
• HiperLAN/1 was planned in 1991 and implemented in
1997
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73. HIPERLAN Family
1.
2.
3.
HiperLAN/123Mbps
HiperLAN/254Mbps
HiperLAN/3-
HIPERACCESS
– provides up to 100 Mbps in the 40.5–43.5 GHz band
4. HiperLAN/4- HIPERMAN
– designed for a WMAN in 2 GHz and 11 GHz bands (155
Mbps)
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74. Hiperlan/1features
•
•
•
Data rate 23.529Mbps.
Coverage 100m,frequency 5.2GHZ.
Supports asynchronous and synchronous
•Support power saving
traffic
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75. HIPERLAN-1 Architecture Ad-hoc model
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76. • Each HIPERLAN node is either forwarder (F) or non-forwarder.
• Forwarder Node receive packet and retransmit it to the other node.
• Non-forwarder Node Simply it accept a packet intended for it.
• Each non forwarder node select at least one forwarder node as a neighbor.
• Both nodes periodically update the routing database.
From Architecture
• Node 1,4,6 are forwarder node, having peer-peer connections
• Node 4 act as a bridge between HIPERLAN A-HIPERLAN B
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77. PHY-MAC Layer
1)PHY Layer
• Bandwidth 5.15-5.35GHZ.Total channel is 5 with 40MHZ spacing
• Transmission power 1W
• GMSK modulation methods, support data rate 23Mbps.
• CSMA/CA used for channel access.
2) MAC Layer
• Handles encryption and power conservation.
• MAC address size is 48 bits.(source, destination and neighbor hop)
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78. Channel Access Methods
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79. • If a terminal senses the medium to be free at least 1700bit durations, it
immediately transmit.
• If the channel is busy the terminal access has three phases .
• Prioritization phaseit has the highest priority. If a MS has a highest priority
survive for the next phase and others are eliminated from the contention.
• Contention phaseit consists of elimination period and yield period.
• elimination period Each terminal run a random number generator to select one
of the available 12 slots in which it sends continuous burst of 256bits.
• After sending burst MS listen the channel, if it doesn’t hear any other burst, then
send another burst after 12 slots for survival..
• If a node hear any burst during this period,then eliminate itself.
• yield periodIf an MS senses the medium free for the entire yield period,then
start the tx immediately..
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80. HiperLAN--2
• HiperLAN/2
2000.
functional specification was accomplished Feb
• HiperLAN/2
data rate.
uses the 5.15–5.25 GHz band and up to 54 Mbps
• Provide high data rate and supports mobility
• The physical layer of HiperLAN/2 is very similar to IEEE
802.11a wireless local area networks.
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81. ARCHITECTURE
 Connection between the MS
and AP is similar to WLAN.
 But communication between
APs are different.
 It allows handover in a subnet
and IP based handover for
non homogeneous network.
 It support seamless
interoperation Ethernet and
point-point connection.
Access point
Access point controller
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82. Protocol stack of HIPERLAN/2
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83. 1) Physical layerOFDM ,52 Sub carriers(48 for data+4 sync)
– to provide several modulation and coding schemes
according to current radio link quality and meet the
requirements for different physical layer
by transport channels within DLC.
modes as defined
2)DLC layer
– The DLC layer constitutes the logical link between an
access point (AP) and mobile terminals (MTs)
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84. The DLC layer consists of
• Medium Access Control (MAC),
• Error control (EC),
• Radio link control (RLC),
• DLC connection control (DCC),
• Radio resource control (RRC) and
• Association control function (ACF)
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85. 2.2)MAC-Layer
•
•
•
Medium access in HIPERLAN/2 is based on the TDD/TDMA
It uses a MAC frame of 2 ms duration.
An AP provides centralized control and informs the mobile
terminals at which point in time in the MAC frame they are
allowed to transmit their data.
Time slots are allocated dynamically depending on the need
for transmission resources.
HIPERLAN/2 operates as a connection-oriented wireless link
•
•
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86. • Down Link Data,
MAC FRAME
•
•
Uplink Data, and
•
•
•
Broadcast control (BCH),
Frame Control (FCH),
Access control (ACH),
Random Access (RCH)
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87. • The BCH
the MTs.
network
contains broadcast control information
It provides for general information such
and AP identifiers, transmission power
for all
as the
levels,
and FCH and RCH length and wake-up indicator.
• The FCH contains details of distribution of resources
among the fields of each packet.
• The ACH conveys information on previous access
attempts made in the RCH
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88. • The RCH is commonly shared among all MTs
for random access and contention. If collisions
occur the results from RCH access are re-
ported back to the MTs in ACH
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89. 3)Convergence layer
– it maps the service requirements of the higher layer to
service offered by the data link control layer
the
– converts packets to frame and frame to packets
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90. Relation between logic-transport channels
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91. SBCHIt carry the information about handover,security,association and
radio link control functions.
DCCHConveys RLC sublayer signals between MS-AP.
UDCHCarry DLC PDU for convergence layer data
ASCHcarry Assoiation req and Association reply messages
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92. Security
• Comprehensive security mechanisms are seen in the
HIPERLAN-
standards.
2 system compared with other wireless
• When contacted by an MT, the AP will respond initiating a
selected authentication and encryption procedure.
• As always, there is an option not to use any authentication
or encryption.
• Diffie-Hellman encryption is used for
authentication
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93. w
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94. WIRELESS
ATM
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95. ATM Forum Wireless ATM Working Group
 compatibility to existing ATM Forum standards important and easily
upgrade existing ATM networks with mobility functions.
characteristics
• Location management able to locate a wireless terminal or a
mobile user.
• Mobile routingto route the traffic through the network to the
access point currently responsible for the wireless terminal. Each
time a user moves to a new access point, the system must reroute
traffic.
• Handover signalingThe network must provide mechanisms to set
up new connections between intermediate systems.
• QoS and traffic controlWATM should be able to offer many QoS
parameters.
• Network management to control the network To ensure wireless
access
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96. WATM-Architecture
WMT
WMT
EMAS-E
EMAS-N
EMAS-N
M-NNI
RAS
RAS
LS
AUS
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97. Wireless ATM Protocol Architecture
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98. Radio Access LayerTo support wireless communication,new
wireless channel specific medium access.
Medium Access Controlprovide point to point link for the
higher protocol.
Data link controlprovide service to ATM layer.used to control
reduce channel error detection/correction
Radio resource controlneeded for support of control plane
functions related to the radio access layer
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99. WATM components
• T(Terminal)-A standard ATM terminal offering ATM services defined
for fixed ATM networks
• MT(Mobile Terminal)-MT can be moved between different access
points within a certain domain
• WT(wireless Terminal)-This terminal is accessed through a wireless
link
• WMT (Wireless Mobile ATM Terminal)-Combination of a wireless
and a mobile terminal results in the WMT
• RAS (Radio Access System)-Point of access to a network through a
radio link
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100. • EMAS-E (End-user Mobility-supporting ATM Switch - Edge)-
Switches with the support of end user mobility
• EMAS-N (End-user Mobility-supporting ATM Switch -
Network)-A whole network can be mobile not just terminals
• MS(Mobile ATM Switch)-ATM switches can also be mobile and
can use wireless access to another part of ATM network
• ACT(Adhoc controller terminal)-These terminal control wireless
access without aan RAS
• M-NNI (Network-to-Network Interface with Mobility support)
• LS (Location Server)
• AUS (Authentication Server)
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101. BLUETOOTH
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102. Bluetooth
• Basic idea
– Universal radio interface for ad-hoc wireless connectivity
– Interconnecting computer and peripherals, handheld devices, PDAs,
cell phones – replacement of IrDA
– Embedded in other devices, goal: 5€/device (already < 1€)
– Short range (10 m), low power consumption, license-free 2.45 GHz ISM
– Voice and data transmission, approx. 1 Mbit/s gross data rate
One of the first modules (Ericsson).
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103. History and hi-tech…
1999:
Ericsson mobile
communications AB
reste denna sten till
minne av Harald
Blåtand, som fick ge
sitt namn åt en ny
teknologi för trådlös,
mobil
kommunikation.
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104. …and the real rune stone
Located in Jelling, Denmark,
erected by King Harald “Blåtand”
in memory of his parents.
The stone has three sides – one side
showing a picture of Christ.
This could be the “original”
colors of the stone.
Inscription:
“auk tani karthi kristna” (and
made the Danes Christians)
Inscription:
"Harald king executes these sepulchral
monuments after Gorm, his father and
Thyra, his mother. The Harald who won
the whole of Denmark and Norway and
turned the Danes to Christianity."
Btw: Blåtand means “of dark complexion”
(not having a blue tooth…)
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105. Bluetooth
• Bluetooth is the most successful WPAN technology
commercially available.
• It was originally conceived as a wireless alternative to
RS-232 data cables
• Bluetooth uses frequency-hopping spread spectrum
• Frequency range from 2402 to 2480 MHz(2.4GHz)
• A typical Bluetooth device has a range of about 10 meters
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106. Piconet
• Collection of devices connected in an ad hoc
fashion
• One unit acts as master and the others as slaves for
the lifetime of the piconet
• Master determines hopping pattern, slaves have to
synchronize
• Each piconet has a unique hopping pattern
• Participation in a piconet = synchronization to
hopping sequence
• Each piconet has one master and up to 7
simultaneous slaves (> 200 could be parked)
M=Master
S=Slave
P=Parked
SB=Standby
M
S
P
SB
S
S
P
P
SB
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107. Scatternet
• Linking of multiple co-located piconets through the sharing of
common master or slave devices
– Devices can be slave in one piconet and master of another
• Communication between piconets
– Devices jumping back and forth between the piconets
M=Master
S=Slave
P=Parked
SB=Standby
M
S
P
SB
S
S
P
P
SB
M
S
S
P
SB
Piconets
(each with a
capacity of
720 kbit/s)
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108. Bluetooth protocol stack
Radio
Baseband
Link Manager
Control
Host
Controller
Interface
Logical Link Control and Adaptation Protocol (L2CAP)
Audio
TCS BIN SDP
OBEX
vCal/vCard
IP
NW apps.
TCP/UDP
BNEP
RFCOMM (serial line interface)
AT modem
commands
telephony apps.
audio apps. mgmnt. apps.
AT: attention sequence
OBEX: object exchange
TCS BIN: telephony control protocol specification – binary
BNEP: Bluetooth network encapsulation protocol
SDP: service discovery protocol
RFCOMM: radio frequency comm.
PPP
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109. Radio: Specification of the air interface, i.e., frequencies, modulation,
and transmit power
● Baseband: Description of basic connection establishment, packet
formats,timing, and basic QoS parameters
Link manager protocol: Link set-up and management between devices
including security functions and parameter negotiation
● Logical link control and adaptation protocol (L2CAP): Adaptation
of higher layers to the baseband (connectionless and connection-
oriented services
● Service discovery protocol: Device discovery in close proximity plus
querying of service characteristics
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110. •Radio: Specifies details of the air interface, including.
frequency, the use of frequency hopping, modulation scheme,
and transmit power
•The baseband and link control layer enables the physical
between Bluetooth units forming a piconet- addressing,
format, timing, and power control.
RF link
packet
• It provides two different kinds of physical links
1.
2.
SCO – Synchronous Connection Oriented Link
ACL- Asynchronous Connectionless Link
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111. SCO link
• The SCO link
voice traffic.
is symmetric and typically supports time-bounded
• The master maintains the SCO link by using reserved slots
• Once the connection is established, both master and slave units
may send SCO packet continuously.
• A fixed bandwidth is allocated for a point-to-point connection.
• SCO packets are never retransmitted.
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112. SCO payload types
payload (30)
audio (30)
audio (10)
audio (10)
HV3
HV2
HV1
DV
FEC (20)
audio (20) FEC (10)
header (1) payload (0-9) 2/3 FEC CRC (2)
(bytes)
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113. ACL link
• The
and
ACL link is packet oriented and supports both symmetric
asymmetric traffic.
• The master unit controls the link bandwidth and decides how
the
much piconet bandwidth is given to each slave and
symmetry of the traffic.
• Slaves must be polled before they can transmit data.
• The ACL link also supports broadcast messages from the master
to all slaves in the piconet
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114. ACL Payload types
payload (0-343)
header (1/2) payload (0-339) CRC (2)
header (1) payload (0-17) 2/3 FEC
header (1) payload (0-27)
header (2) payload (0-121) 2/3 FEC
header (2) payload (0-183)
header (2) payload (0-224) 2/3 FEC
header (2) payload (0-339)
DH5
DM5
DH3
DM3
DH1
DM1
header (1) payload (0-29)
AUX1
CRC (2)
CRC (2)
CRC (2)
CRC (2)
CRC (2)
CRC (2)
(bytes)
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115. Link Management Protocol(LMP)
standby
inquiry page
connected
AMA
transmit
AMA
park
PMA
hold
AMA
sniff
AMA
unconnected
connecting
active
low power
Standby: do nothing
Inquire: search for other devices
Page: connect to a specific device
Connected: participate in a piconet
detach
Park: release AMA, get PMA
Sniff: listen periodically, not each slot
Hold: stop ACL, SCO still possible, possibly
participate in another piconet
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116. L2CAP - Logical Link Control and
Adaptation Protocol
• Simple data link protocol on top of baseband
• Connection oriented, connectionless, and signaling channels
• Protocol multiplexing
– RFCOMM, SDP, telephony control
• Segmentation & reassembly
– Up to 64kbyte user data, 16 bit CRC used from baseband
• QoS flow specification per channel
– Follows RFC 1363, specifies delay, jitter, bursts, bandwidth
• Group abstraction
– Create/close group, add/remove member
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117. L2CAP logical channels
baseband
L2CAP
baseband
L2CAP
baseband
L2CAP
Slave Slave
Master
ACL
2 d 1 d d 1 1 d 2
1
signalling connectionless connection-oriented
d d d
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118. L2CAP packet formats
length
2 bytes
CID=2
2
PSM
≥2
payload
0-65533
length
2 bytes
CID
2
payload
0-65535
length
2 bytes
CID=1
2
One or more commands
Connectionless PDU
Connection-oriented PDU
Signalling command PDU
code ID length data
1 1 2 ≥0
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119. Security
E3
E2
link key (128 bit)
encryption key (128 bit)
payload key
Keystream generator
Data Data
Cipher data
Authentication key
generation
(possibly permanent
storage)
Encryption key
generation
(temporary storage)
PIN (1-16 byte)
User input
(initialization)
Pairing
Authentication
Encryption
Ciphering
E3
E2
link key (128 bit)
encryption key (128 bit)
payload key
Keystream generator
PIN (1-16 byte)
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120. SDP – Service Discovery Protocol
• Inquiry/response protocol for discovering services
– Searching for and browsing services in radio proximity
– Adapted to the highly dynamic environment
– Can be complemented by others like SLP, Jini, Salutation, …
– Defines discovery only, not the usage of services
– Caching of discovered services
– Gradual discovery
• Service record format
– Information about services provided by attributes
– Attributes are composed of an 16 bit ID (name) and a value
– values may be derived from 128 bit Universally Unique Identifiers
(UUID)
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121. WiMAX
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122. WIMAX/IEEE802.16
Introduction
• Worldwide Interoperability for Microwave Access (WiMAX) is a wireless
communications standard for Metropolitan Area Networks..
• Networks covering whole cities or even whole countries.
• It is a IEEE 802.16d.. originally intended for data communications.
• For voice communication( is enabled by Voice over Internet Protocol (VoIP)).
• The modulation format MIMO/OFDM/OFDMA…
• This uses licensed worldwide spectrum 2.3 GHz, 2.5GHz, 3.3 GHz, and 3.5 GHz
frequency bands
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123. w
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124. 1. Fixed WIMAX (IEEE 802.16d — 2004)
2. Mobile WIMAX (IEEE 802.16e — 2005)
• Fixed WiMAX is a point-to- multipoint technology,
where the base station is fixed.
• Mobile WiMAX is a multipoint-to-multipoint
technology.
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125. • It supports communication between subscriber stations with
one another(Mesh connection)
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126. Physical Layer (PHY)
The 802.16 PHY supports TDD and full and half duplex
FDD operations.
•
• PHY features include adaptive modulation and coding (AMC),
hybrid automatic repeat request (HARQ) and fast channel
feedback to enhance coverage and capacity of WiMAX in
mobile applications.
• WiMAX provides signaling to allow fully asynchronous
operation.
This gives more flexibility to the
system
•
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127. MAC layer overview
• The MAC layer consists (i) the MAC Convergence Sublayer (CS), (ii) the MAC
Common Part Sublayer, and (iii) the MAC Security Sublayer.
1) Convergence Sublayer receives data packets from higher layers and modify the
suitable format for sending via air medium by suppressing redundant information in
their headers..
2) Common Part Sublayerprovides the essential support functions for the over the-
air transmission of the information.
• It includes such functions as signaling,modulation/coding scheme, feedback and
bandwidth allocation.
• It also provides fragmentation and packing…
3) Security Sublayer assign service flow identifier (ID), Connection Identifier (CID),
provisioned QoS parameters and the authorization module.
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128. • The station’s concurrent transmission and reception is
possible through time division duplex (TDD)
division duplex (FDD).
and frequency
• In TDD, a station transmits then receives (or
not at the same time.
vice versa) but
• In FDD, a station transmits and receives simultaneously on
different channels.
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129. • The 802.16 MAC protocol is connection-oriented and
performs link adaptation and ARQ functions to maintain
target bit error rate while maximizing the data throughput
• It supports different transport technologies such as IPv4, IPv6,
Ethernet, and ATM.
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130. Wi-MAX Network Structure
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131. • A main goal of this architecture is to separate the over-the-air access (the Access
Service Network (ASN) from the Internet access (Connectivity Service Network
(CSN).
• The ASN provides the over-the-air connectivity corresponding to the PHY and
MAC layer as defined in the IEEE 802.16 (scheduling and resource management)
• It discovers which networks are available and connects the user to the preferred
(permissible) CSN..
• Each BS is connected to an ASN Gateway,which has somewhat similar functionality
as the BS controller in GSM..
• During network discovery, the Mobile Station (MS) discovers both the access
service provider and the available Network Service Provider (NSP).
• The situation is similar to WiFi ,where an access point just provides a wireless link
that can be seen as a “cable replacement” for a wired Internet connection..
• Getting access and making payments to the Internet service provider is
independent of this operation.
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132. w
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133. Introduction - Mobile IP: IP packet delivery, Agent
discovery, tunneling and encapsulation, IPV6-Network layer
in the internet- Mobile IP session initiation protocol -
mobile ad-hoc network: Routing: Destination Sequence
distance vector, IoT: CoAP
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134. Motivation for Mobile IP
Mobile IPis a protocol used to allow internetwork mobility for wireless node
without changing their IP address.
Routing
 based on IP destination address,
 network prefix (e.g. 129.13.42) determines physical subnet
 change of physical subnet => change of IP address to have a topological
correct address (standard IP)
Solution: Temporarily change routing table entries for mobile host
 Problem: does not scale if many mobile hosts or frequent location changes
Solution: Change mobile host IP-address
 adjust the host IP address depending on the current location
 DNS updates take to long time
 Old TCP connections break
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135. Requirements to Mobile IP
Transparency
 mobile end-systems keep IP address
 Continuous service after link interruption
 point of connection to the fixed network can be changed
Compatibility
 No changes to current hosts, OS, routers
 mobile end-systems can communicate with fixed systems
Security
 authentication of all registration messages
Efficiency and scalability
 only few additional messages to mobile system (low bandwidth)
 Global support for large number of mobile systems
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136. Mobile Node (MN)
 Laptop, PDA, etc.. that may move about
Home Agent (HA)
 Router in home network of the MN, helps in forwarding
 registers current MN location, tunnels IP datagrams to COA
Foreign Agent (FA)
 Router in current foreign network of MN
 forwards tunneled datagrams to the MN
Care-of Address (COA)
 address of the current tunnel end-point for the MN (at FA or MN)
 can be chosen, e.g., via DHCP
Correspondent Node (CN)
 Node that wants to communicate with MN
Entities and Terminology
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137. for the MN)
Example network
HA
MN
router
home network mobile end-system
Internet
(physical home network
FA foreign
network
router
(current physical network
for the MN)
CN
end-system router
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138. network
Internet network
home MN
4.
Internet network
CN 2
router
router router
HA
FA
Overview of Packet Delivery (Mobile Node)
COA
home router router
MN
foreign
CN router
3.
network HA
2. FA
foreign
1.
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139. Packet Routing Procedure
1. Sender sends to the IP address of MN, HA intercepts packet
2. HA tunnels packet to COA by encapsulation
3. FA forwards the packet to MN
4. Reverse: Sender sends to IP address of receiver, FA is default router
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140. Packet Routing Process
1. Agent Discovery(agent advertisement, agent solicitation)
2. Registration
3. Tunneling and Encapsulation
4. Routing Optimization
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141. 1.1)Agent Advertisement
• HA and FA advertise their presence periodically using AA
messages.
• These advertisement messages(ICMP) is a beacon broadcast into
the subnet.
Characteristics of agent
1. Bit H and F denotes whether agent offers services on the link
2. Bit Mand G specify the method of encapsulation
3. Mmin;GGeneric
4. Brepresents agent busy
5. Treverse tunneling
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142. Agent Advertisement-message
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143. 1.2)Agent Solicitation(AS)
• If no agent advertisements are present then the MN send AS.
• MN can send out a max of 3 solicitations,1per second.
• Move detection using life time when MN fails to an
advertisement from FN with the specified lifetime.Hence HA
wait for AA or send AS
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144. 2)Registration
• To inform the current location of MN to HA.
Registration process
• Get a COA from FA
• Inform its HA of its current COA
• Renew registration with FA.
• De-register when it back to Home
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145. Registration Request Registration Reply
MN FA HA MN HA
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146. Registration Request message
Registration Reply message
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147. • Type set to 1 for a registration request
• Lifetime denotes the validity of the registration in seconds.
• B bitindicates broadcast packets which have been received by
the HA in the home network.
• D bit indicates this behavior of MN
• M and G denote the use of minimal encapsulation or generic
routing encapsulation
• Tindicates reverse tunneling, r and x are set to zero.
• home address is the fixed IP address of the MN
• home agent is the IP address of the HA
• COA represents the tunnel endpoint. The 64 bit identification is
generated by the MN to identify a request and match it with
registration replies.
• extensions contain parameters for authentication.
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148. 3) Tunneling and Encapsulation
• Tunneling  establishes a virtual pipe for data packets between a tunnel entry
and a tunnel endpoint.
• Encapsulationis the mechanism of taking a packet consisting of packet
header and data and putting it into the data part of a new packet.
• Decapsulation The reverse operation, taking a packet out of the data part of
another packet.
Encapsulation methods
1. IP-in-IP encapsulation
2. Minimal encapsulation
3. Generic routing encapsulation
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149. 3.1) IP-in-IP encapsulation
•Tunnel between HA and COA
• HA takes the original packet with the MN as destination, puts it into the
data part of a new packet and sets the new IP header.
•Then the packet is routed to the COA. The new header is also called the
outer header.
•Inner header which can be identical to the original header
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150. • Ver is 4 for IP version
• Internet header length (IHL)denotes the length of the outer header (32 bit)
• TTL must be high(the packet can reach the tunnel endpoint)
• DS(TOS) is just copied from the inner header.
• IP-in-IP used in the IP payload. (field size set to 4)
• HA tunnel entry as source address
• COA tunnel exit point as destination address
Outer Header
Inner Header
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151. 3.2) Minimal encapsulation
• It avoids duplication of identical fields and is an optional encapsulation
method for mobile IP.
• The inner header is different.
• The tunnel entry point and endpoint are specified.
• The type of the following protocol and the address of the MN are needed.
• If the S bit is 1, the original sender address of the CN is included
Inner Header
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152. 3.3) Generic Routing Encapsulation(GRE)
• IP-in-IP encapsulation and minimal encapsulation work only for IP.
• GRE  supports other network layer protocols in addition to IP.
• It allows the encapsulation of packets of one protocol suite into the payload
portion of a packet of another protocol suite.
• The packet of one protocol suite with the original packet header and data is
taken and a new GRE header is prepended.
• Together this forms the new data part of the new packet.
• Finally, the header of the second protocol suite is put in front.
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153. w
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154. • GRE header uses only 4 bytes.
• C bit indicates if the checksum field is present and contains
valid information.
• R bit indicates if the offset and routing fields are present and
contain valid information.
• Checksum field is valid only if C is set
• Offset field is valid only if R is set
• Key field which may be used for authentication. If this field is
present, the K bit is set.
• Sequence number bit S indicates if the sequence number field is
present, if the s bit is set
• Recursion control field (rec.) is an important field that
additionally distinguishes GRE from IP-in-IP and minimal
encapsulation
• Reserved fields must be zero and are ignored on reception. The
• Version field contains 0 for the GRE version.
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155. 4)Routing Optimization
• Triangular Routing
 sender sends all packets via HA to MN
 Triangular routes longer, higher latency and network load
• “Route optimization”
 CN learn the current location of MN via HA
 forward its pkts directly without HA.
• CN create routing table which has info about MN.(location)
Mobile IP protocol needs 4 messages
• Binding RequestCN send binding request about the Current location of
MN to HA.
• Binding updateIt contains MN-IP address + COA
• Binding AckCN reply to HA
• Binding warningafter decapsulating pkt,if MN is not current location of
FA,then CN send warning msg.
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156. 2
3
1
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157. • Case(1)Routing (Directly)
• CN send request to HA about the current location of MN
• HAsend update msg about MN to CN
• CNsend ACK to HA
• CNSend data directly to FA old,forward data to MN.
• Case(2)Routing (Handover)
• MN changes its location and register under new FA.
• FA(new)informs FA old about the new registration of MN by sending
update.
• FA(old)reply ACK to FA new
• CNDoesn’t know about the new location,still it send data to FA(old).
• FA(old)forward the data to FA (new) and send warning msg to CN.
• Case(3)Routing
• CN send request to HA about the New location of MN
• HAsend update msg about MN to CN
• CNsend ACK to HA
• CNSend data directly to FA new,forward data to MN.
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158. Reverse Tunneling
• MN can directly send its packets to the CN.
• MN can request a reverse tunnel between its FA and its HA.
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159. IPv6
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160. Problems with mobile IP
Security
 FA typically belongs to another organization
 authentication with FA problematic
 patent and export restrictions
Firewalls
 Firewalls filter based on IP addresses
 FA encapsulates packets from MN
 Home firewalls rejects packet from MN (unless reverse tunneling)
 MN can no longer send packets back to home network QoS, etc..
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161. IPV6 Introduction
• IPv6 is the next generation network protocol to restore the
current IP and simplifies the protocol.
• COA can be assigned via auto-configuration (DHCPv6 is one
candidate) by every node
• MN can signal a sender directly the COA, without HA
• MN sends the new COA to its old router
• old router encapsulates all packets for MN, forwards them to
new COA
• authentication is always granted
• IP address size is 128bits
• IPSEC provide solid security for communication
• Checksum field is not available
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162. IPv6 Header format
Traffic class Assign priority for packets by associating different delivery
Flow Label source node assign label to set of pkts belonging same flow.
Next Header identifies the type of header immediately after IPv6 pkt
header.
Hop limit decremented by 1,when each node forwards a pkt.
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163. Mobile IP
• Mobile IP exhibits several problems regarding the duration of
handover and the scalability of the registration procedure. ( large
number of mobile devices changing)
IP Micro-mobility support:
• Efficient local handover inside foreign domain without involving a
HA.
• Reduces control traffic on backbone
• Especially needed for route optimization
Example approaches:
1. Cellular IP
2. HAWAII
3. Hierarchical Mobile IP (HMIP)
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164. 1)Cellular IP
• It provides local handovers without renewed registration by installing a single
cellular IP gateway (CIPGW) for each domain.
• In cellular IP domain, all nodes collect routing information from CIPGW.
• Soft handovers are achieved by allowing simultaneous forwarding of packets
destined for a mobile node along multiple paths.
• A mobile node moving between adjacent cells temporarily be able to receive
packets via both old and new base stations (BS)
• Cellular IP requires changes to the basic mobile IP protocol and is not
transparent to existing systems.
• The foreign network’s routing tables are changed based on messages sent by
mobile nodes.
• These should not be trusted blindly even if they have been authenticated. This
could be exploited by systems in the foreign network
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165. on update packets sent by MN data/control
BS
BS
BS
CIP Gateway
1)Cellular IP
Operation:
 „CIP Nodes“ maintain routing Internet
entries (soft state) for MNs
 Multiple entries possible Mobile IP
 Routing entries updated based
CIP Gateway: packets
 Mobile IP tunnel endpoint from MN 1
 Initial registration processing
packets from
MN2 to MN 1
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166. Advantages
• Manageability: Cellular IP is mostly self-configuring.
• Integration with firewalls.
• All control messages by MN are authenticated
Disadvantages
• MN can directly influence routing entries.
• Multipath forwardingmay cause BW
• Efficiency: Additional network load is induced by forwarding
packets on multiple paths.
• Transparency: Changes to MNs are required.
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167. 2)HAWAII(Handoff-Aware Wireless Access
Internet Infrastructure)
• Keep micro-mobility support as transparent as possible for both
HA and MN.
• It doesn’t replace IP but works better than IP.
• Each station maintains routing cache to deal with mobility and
hop-hop tx of pkts.
• It support 2types of Handover.
• Page request reach all stations (multicast group)
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168. • step 1MN obtains a COA
• step 2 MN registers with the HA
MN moving to foreign domain
• step 3MN sends a registration request
to the new base station as to a FA
• step 4 New BS intercepts the registration
request.
• Also it sends out a handoff message, and
routers paths from the old and new BS.
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169. Advantages
•Security: In contrast to Cellular IP, routing changes are always
initiated by the foreign domain’s infrastructure.
•Transparency: mostly transparent to mobile nodes.
Disadvantages
•Security: There are no provisions regarding the setup of IPSec
tunnels.
• Implementation: No private address support is possible
because of co-located COAs.
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170. 3)Hierarchical Mobile IP (HMIP)
• provides micro-mobility support by installing a mobility
anchor point (MAP).
• MAPresponsible for a certain domain and acts as a local
HA within this domain for visiting MNs.
• The MAP receives all packets on behalf of the MN, encapsulates
and forwards them directly to the MN’s current address.
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171. •MAP domain’s boundaries are defined by the access
routers (AR) advertising the MAP information to the
attached MNs
•MNs register their RCOA with the HA using a
binding update.
• When a MN moves locally it must only register its
new LCOA with its MAP.
•The RCOA stays unchanged. To support smooth
handovers between MAP domains, an MN can send a
binding update to its former MAP.
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172. Advantages
• Security: MNs can have (limited) location privacy because
LCOAs can be hidden.
• Efficiency: Direct routing between CNs sharing the same link is
possible
Disadvantages
• Transparency: Additional infrastructure component (MAP).
• Security: Routing tables are changed based on messages sent by
mobile nodes. This requires strong authentication and
protection against denial of service attacks. Additional security
functions might be necessary in MAPs
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173. Dynamic Host Configuration
Protocol(DHCP)
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174. Dynamic Host Configuration Protocol(DHCP)
• used to simplify the installation and maintenance of networked computers.
• Capability to automatically allocate reusable network address
• supplies systems with all necessary information, such as IP address, DNS
server address, domain name, subnet mask, default router etc
• enables automatic integration of systems into an Intranet or the Internet, can
be used to acquire a COA for Mobile IP
Basic configuration in DHCP
• DHCP clients send a DHCPDISCOVER request to a server via MAC
broadcasts to reach all devices in the LAN.
• A DHCP relay might be needed to forward requests across inter-working units
to a DHCP server.
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175. Client Initialization via DHCP
1 2
v
ii
iii
i
iv
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176. • Step(i) DHCP Discover client broadcasts a DHCPDISCOVER into the
subnet.(asking IP address)
• Step(ii) DHCP Offer  Two servers receive the broadcast and checking of
available IP addresses and choosing one for the client.
Servers reply to the client’s request with DHCPOFFER by a list of
configuration parameters.
• Step(iii) DHCP Request  client choose one of the configurations offered by
servers.
• client reply( accepting one server/rejecting the others)
• Step(iv) DHCP Ack server-2 with the configuration accepted by the client
confirms the configuration with DHCPACK.
• This completes the initialization phase.
• Step(v) DHCP Release If a client leaves a subnet, it should release the
configuration received by the server using DHCPRELEASE
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177. Session Initiation Protocol(SIP)
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178. Mobile IP Session Initiation Protocol(SIP)
• It is an application layer protocol for creating, modifying and
terminating sessions with one or more participants.
• Sessions may be text,voice,video,internet telephony and
multimedia
• Communication may be unicast or multicast.
• It provides a mechanism for call management
• It is a very simple protocol has limited set of commands can read.
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179. SIP Entities
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180. SIP Entities
• User AgentIt is an applicants contains both user agent
client(UAC) and user agent server(UAS)
• User Agent ServerIt will response(accept,reject,reidrect) to UA
after receiving SIP request.
• Proxy Serverit act as both client and server.It accept request
from other clients either responding or forward them to server.
• Redirect serverIt accept request from clients and returns 0. It
doesn’t initiate any request or call.
• Registration serveraccept reg request from UA.
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181. SIP Request-Response
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182. SIP Request-Response
• INVITEInitiate session between 2 participants
• ACKclient acknowledges receiving the final msg an INVITE.
• BYETerminate the connection
• CANCELcancel the pending actions
• OPTIONSqueries the server
• REGISTERregister the UAC address with server
• 1XX:PROVISIONALrequest received and continuing to process
• 2XX Success(Action was Successfully received and accepted)
• 3xxRedirection(further action needs to be taken to complete the req)
• 4xxclient error
• 5xxserver error
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183. Mobile Ad-hoc Networks(MANET)
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184. MANET-Introduction
• Infrastructure-less dynamic multihop network
• It does not have a definite Topology.
• No central router required. Each node
itself.
will act as a router
• Data takes multiple hops before reaching destination.
• each node communicates with other nodes directly or
indirectly through intermediate nodes.
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185. MANET
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186. • MANETs are basically peer-to-peer wireless networks in
which information packets are transmitted in a store-and-
forward manner from a source to an arbitrary
intermediate nodes
destination, via
• The network topology keeps changing when
leave the network.
devices join or
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187. • Dynamic topologies: Network topology may
change dynamically as the nodes are free to
move.
• Bandwidth-constrained, variable capacity links:
Realized throughput of wireless communication
is less than the radio’s maximum transmission
rate. Collision occurs frequently.
• Energy-constrained operation: Some nodes in
the ad hoc network may rely on batteries or
other exhaustible means for their energy.
• Limited physical security: More prone to
physical security threats than fixed cable
networks.
Characteristics of MANETs
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188. Applications
1. Defense applications:
– MANETs can be formed among soldiers on the ground or fighter
planes in the air, while sensors can be deployed to monitor
activities in the area of interest
2. Crisis-management applications:
–These arise as a result of natural disasters in which the entire
communication infrastructure is in disarray.
– Restoring communications quickly is essential
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189. 3)Tele-medicine: Conference assistance from a surgeon for an
emergency intervention.
4)Tele-Geo processing: Queries regarding location
information of the users.
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190. 5. Vehicular area network:
– This is a growing and very useful application of ad hoc
network in providing emergency services and other
information
6. Virtual navigation:
– A remote database contains the graphical
representation of streets, buildings, etc of places.
– Blocks of this database are transmitted in rapid
sequence to a vehicle, where a rendering program
permits the occupants to visualize the needed
environment ahead of time
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191. • Routing in a MANET depends on many factors, including
modeling of the topology, selection of routers, initiation of a
route request, and specific underlying characteristics that
could serve as heuristics in finding the path efficiently.
• Routing is facilitated by routing tables, which has the list of
most appropriate neighbor for any given packet destination
Routing
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192. Example Ad-hoc network
Time t1
• Five nodes, N1 to N5, are connected
• In this N4 can receive N1 over a good link, but N1 receives N4 only via a weak link.
• N1 cannot receive N2 at all, N2 receives a signal from N1.
• This situation can change quite fast at t2.
Time t2
• N1 cannot receive N4 any longer.
• N4 receives N1 only via a weak link. But now N1 has an asymmetric but bi-directional
link to N2 that did not exist before.
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193. Requirement of routing protocol
1. Provide the maximum possible reliability by selecting
alternative routes if a node connectivity fails.
2. Route network traffic through the path with least cost by
minimizing
destination
the actual length between the source
number
and
of
through use of the lowest
intermediate nodes.
3. Give the nodes the best possible response time and
throughput. This is especially important for interactive
sessions between user applications.
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194. Routing Classification
The existing routing protocols can be classified as,
– Proactive: when a packet needs to be forwarded,
the route is already known.
– Reactive: Determine a route only when there is data
to send.
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195. Routing Classification
1.
1.1
1.2
Destination-Sequenced Distance-Vector Routing-DSDV
Cluster Head Gateway Switch Routing-CGSR
2. Reactive or on-demand routing protocols.
2.1
2.2
2.3
2.4
Ad Hoc On-Demand Distance Vector Routing-AODV
Dynamic Source Routing-DSR
Temporarily Ordered Routing Algorithm-TORA
Associativity-Based Routing-ABR
Proactive or table-driven routing protocols
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196. 1)Table-driven routing protocols
• Table-driven routing protocols maintain up-to-date routing
information
network.
from each node to every other node in the
• The routing information is kept in different routing tables.
• These tables were updated regularly with respect to the
changes in network topology
• It is proactive in the sense that when a packet needs to be
forwarded, a route will be already available and can be
immediately used.
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197. 1.1)Destination-Sequenced Distance Vector
Routing-DSDV
• Each mobile node maintains a routing table with a route
every possible destination in the network and the number
hops to the destination
to
of
• Each such entry in the table is marked with a sequence
number assigned by the
The sequence numbers
destination node.
allow the mobile node to distinguish
•
stale routes from
routing loops
new ones, and help avoid formation of
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198. w
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199. • A new route broadcast contains:
– The destination address.
– The number of hops required to reach the destination
– The sequence number of the information received about
the destination and a new sequence number unique to
the broadcast
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200. • If multiple routes are available for the same destination the
route with the smaller hops is used.
Any updates in the routing tables are periodically broadcast
in the network to maintain table consistency
The amount of traffic generated by these updates can be
huge
To alleviate this problem, the updates are made through two
types of packets (a) Full Dump (b) Incremental dump
•
•
•
• A full dump packet carries all the available routing
information and can require multiple network protocol data
units (NPDUs).
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201. • When there is only occasional movement, smaller
incremental packets are used to relay only the change in
information since the last full dump.
• The incremental packets fit into a standard NPDU and
hence decrease the amount of traffic generated.
• The nodes maintain a separate table in which they
maintain all the information sent in the incremental
routing information packets
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202. 2)On-demand routing protocols.
• This maintains information only for active routes
• Only when a node requires a route to a destination, a route
discovery process is initiated
• Once a route has been established the searching process will
be halted
1. Ad hoc On-Demand Distance Vector (AODV).
2. Dynamic Source Routing (DSR)
3. Temporary Ordered Routing Algorithm (TORA)
4. Associativity Based Routing (ABR)
5. Signal Stability Routing (SSR)
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203. 2.1)Dynamic Source Routing
 The protocol consists of two major phases: Route Discovery,
Route Maintenance.
 When a mobile node has a packet to send to some
destination, it first consults its route cache to check whether
it has a route to that destination.
 If it is an un-expired route, it will use this route.
 If the node does not have a route, it initiates route
discovery by broadcasting a Route Request packet.
 This Route Request contains the address of the destination,
along with the source address.
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204. Dynamic Source Request (Cont’d)
 Each node receiving the packet checks to see whether it has
a route to the destination. If it does not, it adds its own
address to the route record of the packet and forwards it.
 A route reply is generated when the request reaches either
the destination itself or an intermediate node that contains
in its route cache an un-expired route to that destination.
 If the node generating the route reply is the destination, it
places the route record contained in the route request into
the route reply.
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205. Dynamic source routing (DSR)
• Reactive routing protocol
• 2 phases, operating both on demand:
– Route discovery
• Used only when source S attempts to to send a packet to destination D
• Based on flooding of Route Requests (RREQ)
– Route maintenance
• makes S able to detect, while using a source route to D, if it can no longer
use its route (because a link along that route no longer works)
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206. DSR: Route discovery (1)
E G
M
H
R
F
A
B
C
I
D
S
K
N
L
P
J
Q
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207. DSR: Route discovery (2)
E G
M
H
R
F
A
B
C
I
D
S
K
N
L
P
J
Q
(S)
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208. DSR: Route discovery (3)
E G
M
H
R
F
A
B
C
I
D
S
K
N
L
P
J
Q
(S,A)
(S,E)
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209. DSR: Route discovery (4)
E G
M
H
R
F
A
B
C
I
D
S
K
N
L
P
J
Q
(S,E,G)
(S,B,C)
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210. DSR: Route discovery (5)
E G
M
H
R
F
A
B
C
I
D
S
K
N
L
P
J
Q
(S,E,G,J)
(S,A,F,H)
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211. DSR: Route discovery (6)
E G
M
H
R
F
A
B
C
I
D
S
K
N
L
P
J
Q
(S,A,F,H,K)
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212. DSR: Route discovery (7)
E G
M
H
R
F
A
B
C
I
D
S
K
N
L
P
J
Q
(S,A,F,H,K,P)
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213. DSR: Route discovery (8)
E G
M
H
R
F
A
B
C
I
D
S
K
N
L
P
J
Q
RREP(S,E,G,J,D)
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214. DSR: Route Discovery (9)
• Route reply by reversing the route (as illustrated)
works only if all the links along the route are
bidirectional
• If unidirectional links are allowed, then RREP may
need a route discovery from D to S
• Note: IEEE 802.11 assumes that links are
bidirectional
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215. DSR: Data delivery
E G
M
H
R
F
A
B
C
I
D
S
K
N
L
P
J
Q
DATA(S,E,G,J,D)
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216. DSR: Route maintenance (1)
E G
M
H
R
F
A
B
C
I
D
S
K
N
L
P
J
Q
DATA(S,E,G,J,D)
X
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217. DSR: Route maintenance (2)
E G
M
H
R
F
A
B
C
I
D
S
K
N
L
P
J
Q
X
RERR(G-J)
When receiving the Route Error message (RERR),
S removes the broken link from its cache.
It then tries another route stored in its cache; if none,
it initializes a new route discovery
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218. Overview of UTMS Terrestrial Radio access network-UMTS
Core network Architecture: 3GPP Architecture, User
equipment, CDMA2000 overview- Radio and Network
components, Network structure, Radio Network, TD-CDMA,
TD – SCDMA.
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219. TRANSMISSION CONTROL
PROTOCOL(TCP)
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220. Traditional TCP
• Guarantees or Reliable message delivery
• It support connection oriented data/voice services
• Delivers messages in the same order they were sent
• Delivers at most one copy of each message
• Supports arbitrarily large messages
• Supports synchronization between the sender and the receiver
• It provide end to end flow control mechanism.
• It incorporates congestion control mechanism
• It uses sliding window mechanism for data transmission
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221. Flow control VS Congestion control
• Flow control involves preventing senders from
overrunning the capacity of the receivers
• Congestion control involves preventing too much
data from being injected into the network, thereby
causing switches or links to become overloaded
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222. TCP Header
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223. TCP Header
• The SrcPort and DstPort fields identify the source and destination ports,
respectively.
• SequenceNum field contains the sequence number for the first byte of data
carried in that segment.
• The 6-bit Flags field is used to relay control information between TCP peers.
• The possible flags include SYN, FIN, RESET, PUSH, URG, and ACK.
• The SYN and FIN flags are used when establishing and terminating a TCP
connection, respectively.
• The ACK flag is set any time the Acknowledgment field is valid, implying that
the receiver should pay attention to it.
• The URG flag signifies that this segment contains urgent data.
• The PUSH flag signifies that the sender invoked the push operation, which
indicates to the receiving side of TCP that it should notify the receiving
process of this fact.
• Finally, the RESET flag signifies that the receiver has become confused
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224. Connection Establishment/Termination in TCP
Timeline for three-way handshake algorithm
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225. TCP Congestion Control
• Congestiontemporary overload some point in the transfer path.
Controlling mechanism
• Additive Increase Multiplicative Decrease
• Slow start or exponential start
• Fast Retransmit/Recovery
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226. 1) Additive Increase Multiplicative Decrease
At start CWND=1
New Congestion Window(CWND) = CWND+1
segment
ACK
CWND=1+1+1
CWND=1
CWND=1+1
CWND=1+1+1+1
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227. Additive Increase Multiplicative Decrease
– TCP does not wait for an entire window’s worth of ACKs to add 1
packet’s worth to the congestion window, but instead increments
Congestion Window by a little for each ACK that arrives.
– Specifically, the congestion window is incremented as follows each
time an ACK arrives:
• Increment = MSS × (MSS/Congestion Window)
• Congestion Window+= Increment
• That is, rather than incrementing Congestion Window by an entire MSS
bytes each RTT, we increment it by a fraction of MSS every time an ACK is
received.
• Assuming that each ACK acknowledges the receipt of MSS bytes, then that
fraction is MSS/Congestion Window.
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228. 2)Slow start or exponential start
• Slow start effectively increases the congestion window
exponentially, rather than linearly.
• source starts out by setting Congestion Window to one packet.
• When the ACK for this packet arrives, TCP adds 1 to Congestion
Window and then sends two packets.
• Upon receiving the corresponding two ACKs, TCP increments
Congestion Window by 2—one for each ACK—and next sends
four packets.
• The end result is that TCP effectively doubles the number of
packets it has in transit every RTT.
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229. TCP Congestion Control-Mechanism
• Slow Start
At start CWND=1
Congestion Window(CWND) = 2n
segment
ACK
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22
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230. • Slow Start
– There are actually two different situations in which
slow start runs.
• The first is at the very beginning of a connection, at which time
the source has no idea how many packets it is going to be able to
have in transit at a given time.
• In this situation, slow start continues to double Congestion
Window each RTT until there is a loss, at which time a
timeout causes multiplicative decrease to divide Congestion
Window by 2.
• The second situation in which slow start is used is a bit more
subtle; it occurs when the connection goes dead while
waiting for a timeout to occur.
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231. 2)Fast Retransmit and Fast Recovery
– Every time a data packet arrives at the receiving side, the receiver responds
with an acknowledgment.
– when a packet arrives out of order TCP resends the same acknowledgment
it sent the last time.
– This second transmission of the same acknowledgment is called a
duplicate ACK.
– When the sender sees a duplicate ACK, it knows that the other side must
have received a packet out of order, which suggests the earlier packet
might have been lost or delayed
– TCP waits until it has seen three duplicate ACKs before retransmitting the
missing packet
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232. – When the fast retransmit mechanism signals congestion,
rather than drop the congestion window all the way back to
one packet and run slow start, it is possible to use the ACKs
that are still in the pipe to clock the sending of packets.
– This mechanism, which is called fast recovery, effectively
removes the slow start phase that happens between when fast
retransmit detects a lost packet and additive increase begins.
Fast Recovery
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233. TCP Congestion control
Slow start
Additive Increase
Multiplicative decrease
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234. Classical TCP Solutions
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235. Methods
1. Indirect TCP
2. Snooping TCP
3. Mobile TCP
4. Fast Retransmit/fast recovery
5. Transmission/time out freezing
6. Selective retransmission
7. Transaction –oriented TCP
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236. 1)Indirect TCP (I-TCP)
•TCP performs poorly together with wireless links
•TCP within the fixed network cannot be changed.
•mobile host connected via a wireless link and an access point to the ‘wired’ internet where the
correspondent host resides
mobile host
access point
(foreign agent) „wired“ Internet
„wireless“ TCP standard TCP
CN
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237. • Standard TCP is used between the fixed computer and the access point.
• Instead of the mobile host, the access point now terminates the standard TCP
connection, acting as a proxy.
• This means that the access point is now seen as the mobile host for the fixed host and
as the fixed host for the mobile host.
• If the correspondent host sends a packet,the foreign agent acknowledges this packet
and tries to forward the packet to the mobile host.
• If a packet is lost on the wireless link due to a transmission error, the correspondent
host would not notice this. In this case, the foreign agent tries to retransmit this packet
locally to maintain reliable data transport
• If the packet is lost on the wired link, the mobile hosts notice this much faster due to
the lower round trip time and can directly retransmit the packet
• Packet loss in the wired network is now handled by the foreign agent.
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238. I-TCP socket and state migration after handover
access point1
socket migration
and state transfer Internet
access point2
mobile host
new
old
CN
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239. • Access point acts as a proxy buffering packets for retransmission.
• After the handover, the old proxy must forward buffered data to
the new proxy because it has already acknowledged the data.
• After registration with the new foreign agent, this new foreign
agent can inform the old one about its location to enable packet
forwarding.
• The sockets of the proxy, must migrate to the new foreign agent
located in the access point.
• The socket reflects the current state of the TCP connection, i.e.,
sequence number, addresses, ports etc.
• No new connection may be established for the mobile host, and
the correspondent host must not see any changes in connection
state.
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240. Advantages
 No changes in the fixed network necessary, no changes for the hosts
(TCP protocol) necessary, all current optimizations to TCP still work
 Wireless link transmission errors isolated from those in fixed network
 simple to control, mobile TCP is used only for one hop between, e.g.,
a foreign agent and mobile host
 therefore, a very fast retransmission of packets is possible, the short
delay on the mobile hop is known
Disadvantages
 loss of end-to-end semantics, an acknowledgement to a sender does
now not any longer mean that a receiver really got a packet, foreign
agents might crash
 higher latency possible due to buffering of data within the foreign
agent and forwarding to a new foreign agent
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241. foreign host
mobile
end-to-end TCP connection
2)Snooping TCP I
„Transparent“ extension of TCP within the foreign agent
 buffering of packets sent to the mobile host
 lost packets on the wireless link (both directions!) will be
retransmitted immediately by the mobile host or foreign agent,
respectively (so called “local” retransmission)
 the foreign agent therefore “snoops” the packet flow and recognizes
acknowledgements in both directions, it also filters ACKs
 changes of TCP only within the foreign agent
local retransmission correspondent
agent
„wired“ Internet
snooping of ACKs buffering of data
host
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242. Snooping TCP II
Data transfer to the mobile host
 FA buffers data until it receives ACK of the MH, FA detects packet
loss via duplicated ACKs or time-out
 fast retransmission possible, transparent for the fixed network
Data transfer from the mobile host
 FA detects packet loss on the wireless link via sequence numbers,
FA answers directly with a NACK to the MH
 MH can now retransmit data with only a very short delay
Integration with MAC layer
 MAC layer often has similar mechanisms to those of TCP
 thus, the MAC layer can already detect duplicated packets due to
retransmissions and discard them
Problems
 snooping TCP does not isolate the wireless link as good as I-TCP
 snooping might be tough if packets are encrypted
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243. 3) Mobile TCP
Special handling of lengthy and/or frequent disconnections
M-TCP splits as I-TCP does
 unmodified TCP fixed network to supervisory host (SH)
 optimized TCP SH to MH
Supervisory host
 no caching, no retransmission
 monitors all packets, if disconnection detected
set sender window size to 0
 sender automatically goes into persistent mode
 old or new SH reopen the window
Advantages
 maintains semantics, supports disconnection, no buffer forwarding
Disadvantages
 loss on wireless link propagated into fixed network
 adapted TCP on wireless link
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244. 4)Fast retransmit/fast recovery
 TCP reacts with slow-start although there is no congestion
Forced fast retransmit
 as soon as the mobile host has registered with a new foreign agent,
the MH sends duplicated acknowledgements on purpose
 this forces the fast retransmit mode at the communication partners
 additionally, the TCP on the MH is forced to continue sending with
the actual window size and not to go into slow -start after
registration
Advantage
 simple changes result in significant higher performance
Disadvantage
 Cooperation required between IP and TCP, no transparent
approach
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245. 5)Transmission/time-out freezing
Mobile hosts can be disconnected for a longer time
 no packet exchange possible, e.g., in a tunnel, disconnection due
to overloaded cells or mux. with higher priority traffic
 TCP disconnects after time-out completely
TCP freezing
 MAC layer is often able to detect interruption in advance
 MAC can inform TCP layer of upcoming loss of connection
 TCP stops sending, but does now not assume a congested link
 MAC layer signals again if reconnected
Advantage
 scheme is independent of data
Disadvantage
 TCP on mobile host has to be changed, mechanism depends on
MAC layer
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246. 6)Selective retransmission
TCP acknowledgements are often cumulative
 ACK n acknowledges correct and in-sequence receipt of packets
up to n
 if single packets are missing quite often a whole packet sequence
beginning at the gap has to be retransmitted (go-back-n), thus
wasting bandwidth
Selective retransmission as one solution
 RFC2018 allows for acknowledgements of single packets, not only
acknowledgements of in-sequence packet streams without gaps
 sender can now retransmit only the missing packets
Advantage
 much higher efficiency
Disadvantage
 more complex software in a receiver, more buffer needed at the
receiver
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247. 7)Transaction oriented TCP
TCP phases
 connection setup, data transmission, connection release
 using 3-way-handshake needs 3 packets for setup and release,
respectively
 thus, even short messages need a minimum of 7 packets!
Transaction oriented TCP
 RFC1644, T-TCP, describes a TCP version to avoid this overhead
 connection setup, data transfer and connection release can be
combined
 thus, only 2 or 3 packets are needed
Advantage
 efficiency
Disadvantage
 requires changed TCP
 mobility not longer transparent
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248. Example TCP connection
setup overhead
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249. Comparison of different approaches for a
“mobile” TCP
Approach Mechanism Advantages Disadvantages
Indirect TCP splits TCP connection
into two connections
isolation of wireless
link, simple
loss of TCP semantics,
higher latency at
handover
Snooping TCP “snoops” data and
acknowledgements, local
retransmission
transparent for end-to-
end connection, MAC
integration possible
problematic with
encryption, bad isolation
of wireless link
M-TCP splits TCP connection,
chokes sender via
window size
Maintains end-to-end
semantics, handles
long term and frequent
disconnections
Bad isolation of wireless
link, processing
overhead due to
bandwidth management
Fast retransmit/
fast recovery
avoids slow-start after
roaming
simple and efficient mixed layers, not
transparent
Transmission/
time-out freezing
freezes TCP state at
disconnect, resumes
after reconnection
independent of content
or encryption, works for
longer interrupts
changes in TCP
required, MAC
dependant
Selective
retransmission
retransmit only lost data very efficient slightly more complex
receiver software, more
buffer needed
Transaction
oriented TCP
combine connection
setup/release and data
transmission
Efficient for certain
applications
changes in TCP
required, not transparent
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250. TCP over 2.5/3G wireless networks
• The following characteristics have to be considered
when deploying applications over 2.5G/3G wireless
links:
Data rates:
While typical data rates of today’s 2.5G systems are 10–
20 kbit/s uplink and 20–50 kbit/s downlink, 3G and
future 2.5G systems will initially offer data rates
around 64 kbit/s uplink and 115–384 kbit/s downlink.
Typically, data rates are asymmetric as it is expected that
users will download more data compared to
uploading. Uploading is limited by the limited battery
power
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251. Latency:
• All wireless systems comprise elaborated algorithms
for error correction and protection, such as forward
error correction (FEC), check summing, and
interleaving.
• FEC and interleaving let the round trip time (RTT)
grow to several hundred milliseconds up to some
seconds.
• The current GPRS standard specifies an average delay
of less than two seconds for the transport class with
the highest quality
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252. Jitter:
Wireless systems suffer from large delay variations or
‘delay spikes’. Reasons for sudden increase in the
latency are:
link outages due to temporal loss of radio coverage,
blocking due to high-priority traffic, or handovers
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253. Packet loss:
• Packets might be lost during handovers or due to
corruption.
• Recovery at the link layer appears as jitter to the
higher layers
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254. The following configuration parameters to adapt TCP to
wireless environments:
Large windows:
• TCP should support large enough window sizes based on the
bandwidth delay product experienced in wireless systems.
• With the help of the windows scale option (RFC 1323) and
larger buffer sizes this can be accomplished (typical buffer
size settings of 16 Kbyte are not enough).
Limited transmit:
• It is particularly useful when small amounts of data are to be
transmitted (standard for, e.g., web service requests).
Large MTU:
• The larger the MTU (Maximum Transfer Unit) the faster TCP
increases the congestion window.
• To employ larger segment sizes instead of assuming the small
default MTU.
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255. Selective Acknowledgement (SACK):
SACK (RFC 2018) allows the selective retransmission of
packets and is almost always beneficial compared to the
standard cumulative scheme.
Explicit Congestion Notification (ECN):
• ECN allows a receiver to inform a sender of congestion in
the network by setting the ECN-Echo flag on receiving an
IP packet that has experienced congestion.
• This mechanism makes it easier to distinguish packet
loss due to transmission errors from packet loss due to
congestion.
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