Networking and protocols for real-time signal transmissionskom.aau.dk/project/sipcom/SIPCom04/sites/sipcom9/courses/... · Networking and protocols for real-time signal transmissions

Page 1 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall04

Networking and protocols for real-time signal transmissionsby Hans-Peter Schwefel & Søren Vang Andersen

• Mm1 Introduction & simple performance models (HPS)

• Mm2 Real-time Support in Wireless Technologies (HPS)

• Mm3 Transport Layer Aspects and Header Compression (HPS)

• Mm4 IP Quality of Service: Advanced Concepts (HPS)

• Mm5 Session Signalling and Application Layer/Codecs (SVA)

[email protected] [email protected]

http://www.kom.auc.dk/~hps http://www.kom.auc.dk/~sva

Note: Slide-set contains more material than covered in the lectures!


Wireless Communication Technologies

20 155

Indoor

Pedestrian

High SpeedVehicular

Rural

Mobility & Range

Personal Area

VehicularUrban

0.5 2

UMTS

GSM

DECT

Fixed urban

Total data rate per cell10

WLAN/ BRAN

B-PANWPANBluetooth

1000 Mb/s

Different Requirements on Wireless Communication:•Range, Mobility Support

•Throughput (interference/medium sharing), availability/reliability, QoS support

•Scalability/Number of Nodes

•Power consumption

•Cost, simplicity

•Voice / data support

•Security


Intro: Cellular systems

• Geographic region subdivided in radio cells

• Base Station provides radio connectivity to Mobile Station within cell

• Handover to neighbouring base station when necessary

• Base Stations connected by some networking infrastructure


Content1. Introduction

• Cellular Concepts & Technologies2. Cellular Technologies

• GSM: Architecture, Air Interface, IP Data Transmission, HSCSD• GPRS: Architecture, Air Interface Properties, EDGE• UMTS: architecture & domains• QoS Support in PS domain

3. Wireless LAN: IEEE 802.11• Architecture, Modes, PHY, MAC• QoS Support: 802.11e

4. Wireless PAN: IEEE 802.15• Architecture (Piconets, Scatternets), PHY, MAC• SCO transmissions• High data-rate: 802.15.3

5. Summary/Conclusions/Outlook

Exercise


GSM: Global System for Mobile Communication

• 2nd Generation of Mobile Telephony Networks• 1982: Groupe Spèciale Mobile (GSM) founded• 1987: First Standards defined• 1991: Global System for Mobile Communication,

Standardisation by ETSI (European Telecommunications Standardisation Institute) - First European Standard

• 1995: Fully in Operation

• Deployed in more than 184 countries in Asia, Africa, Europe, Australia, America)

• more than 747 million subscribers• more than 70% of all digital mobile phones use GSM• over 10 billion SMS per month in Germany, > 360 billion/year

worldwide

History:

Today:


GSM – Architecture

Components:• BTS: Base Transceiver Station• BSC: Base Station Controller• MSC: Mobile Switching Center• HLR/VLR: Home/Visitor Location

Register• AuC: Authentication Center• EIR: Equipment Identity Register• OMC: Operation and

Maintenance Center

Transmission: • Circuit switched transfer• Radio link capacity: 9.6 kb/s

(FDMA/TDMA)• Duration based charging

BSC

BSC

MS

BTS

BTS

BTS

MS

MS

MSC

HLR

VLR

OMC

EIR

AuC

O

Abis AUm

Radio Link

Base StationSubsystem

Network andSwitchung Subsystem

OperationSubsystem

Connection toISDN, PDNPSTN

Radio Subsystem (RSS)


GSM Services‘Traditional’ voice services

– voice telephonyprimary goal of GSM was to enable mobile telephony offering the traditional bandwidth of 3.1 kHz

– emergency numbercommon number throughout Europe (112); mandatory for all service providers; free of charge; connection with the highest priority (preemption of other connections possible)

– Multinumberingseveral ISDN phone numbers per user possible

– voice mailbox (implemented in the fixed network supporting the mobile terminals)– Supplementary services, e.g.: identification, call forwarding, number suppression,

conferencing

‘Non-Voice’ Services (examples)• Fax Transmissions• electronic mail (MHS, Message Handling System, implemented in the fixed network)• Short Message Service (SMS)

alphanumeric data transmission to/from the mobile terminal using the signaling channel, thus allowing simultaneous use of basic services and SMS


1 2 3 124

890 915Uplink Downlink

MHz 935 960

Kanäle:

200 kHz

Frequenzband derMobilstation

Frequenzband derBasisstation

GSM: Air Interface IFrequency Division Multiple Access (FDMA)• Separate up-link (MT BTS) and down-link (BTS MT) traffic

– Two 25MHZ bands • Distinguish 124 adjacent channels within each band

– Each channel 200kHz

Radio Network Planning:• Determine location of BTS• Determine number of TRX per BTS

– Multiple transceivers (TRX) per BTS (e.g. 1,4 ,or 12)simultaneous use of different FDMA channels

• Assign subsets of 124 channels to BTSs


1 2 3 4 5 6 7 8

higher GSM frame structures

935-960 MHz124 channels (200 kHz)downlink

890-915 MHz124 channels (200 kHz)uplink

frequ

ency

time

GSM TDMA frame

GSM time-slot (normal burst)

4.615 ms

546.5 µs577 µs

tail user data TrainingSguardspace S user data tail

guardspace

3 bits 57 bits 26 bits 57 bits1 1 3

GSM Air Interface: Combination of TDMA & FDMA


Overview: GSM protocol layers for signaling

CM

MM

RR

MM

LAPDm

radio

LAPDm

radio

LAPD

PCM

RR’ BTSM

CM

LAPD

PCM

RR’BTSM

16/64 kbit/s

Um Abis A

SS7

PCM

SS7

PCM

64 kbit/s /2.048 Mbit/s

MS BTS BSC MSC

BSSAP BSSAP

• Layer 1, Um: Radio– Creation & multiplexing of bursts, synchronisation,

modulation, en/decryption, channel coding, error detection/correction

• LAPDm: variant ofLink Access Procedure for the D-Channel• RR: Radio Resource Management• BTSM: BTS Management

• MM: Mobility Management• CM: Call Management:

– Call control– Short Message Service (SDCCH, SACCH)– Supplementary service

• PCM: Pulse Code Modulation


0

200

400

600

800

1000

1200

1400

1600

1800

1995 2000 2005 2010

Subscriptions worldwide (millions)

Mobile InternetSubscribers

MobileSubscribersMobile

FixedMobile InternetFixed Internet

• The future Internet will mainly be accessed by mobile devices

Mobile Communication & Data Traffic


Data services in GSM & HSCSD• Data transmission standardized with only 9.6 kbit/s

– advanced coding allows 14,4 kbit/s– not enough for Internet and multimedia applications

• HSCSD (High-Speed Circuit Switched Data)– mainly software update– bundling of several time-slots to get higher

AIUR (Air Interface User Rate)(e.g., 57.6 kbit/s using 4 slots, 14.4 each)

– advantage: ready to use, constant quality, simple– disadvantage: channels blocked for voice transmission

AIUR [kbit/s] TCH/F4.8 TCH/F9.6 TCH/F14.44.8 19.6 2 1

14.4 3 119.2 4 228.8 3 238.4 443.2 357.6 4


GPRS: General Packet Radio Service

• Packet Switched Extension of GSM• 1996: new standard developed by ETSI• Components integrated in GSM architecture• Improvements:

– Packet-switched transmission– Higher transmission rates on radio link (multiple

time-slots)– Volume based charging ‚Always ON‘ mode

possible• Operation started in 2001 (Germany)


GPRS - Architecture

PDN

Other

PLMN

GSM GPRS

BTS

CCU

MSC

BSC

PCU

HLR GR

GGSN

Components

A Abis Gb Gp

Gs

Gn

G Gr

Gi

UmBSS

SGSN

MS

Components:• CCU: Channel Coding Unit• PCU: Packet Control Unit• SGSN: Serving GPRS Support Node • GGSN: Gateway GPRS Support Node• GR: GPRS Register

Transmission: • Packet Based Transmission• Radio link:

– Radio transmission identical to GSM– Different coding schemes (CS1-4)– Use of Multiple Time Slots – On-demand allocation of time-slots

• Volume Based Charging


GPRS: Channel Coding and Multiplexing

9,05 kbit/s

.....

Time Slot (MS-> BTS)

Coding Scheme 1

72.4.......171,2 kbit/s

9,05 kbit/s

13,4 kbit/s

9,05 kbit/s

1 2 8

13,4 kbit/s 13,4 kbit/s

15,6 kbit/s 15,6 kbit/s 15,6 kbit/s

.....

.....21,4 kbit/s .....21,4 kbit/s 21,4 kbit/s

9,05 kbit/s

3

Coding Scheme 2

Coding Scheme 3

Coding Scheme 4

.....

‚optimal‘ radio quality: no interference, etc.

Selection of Codingdepending on qualityof radio connection

Overall transmission rate


GPRS: channel types


Example: Channel Assignment

• 4 TRX 4 FDMA channels32 time slots

• 3 Signalling Channels– 1TS: FCCH, SCH, BCCH (PBCCH),

PAGCH, RACH (PRACH)– 2 TS: SDCCH

• 29 Tracffic Channels (TCH/PDTCH)– GSM calls only– GPRS calls only– Common channels


GPRS: Protocol Stack

• RLC: Radio Link Control– Acknowledged mode (reliable) or unacked

• LLC: Logical Link Control– Acknowledged mode (reliable) or unacked

• BSSGRP: BSS GPRS Protocol

• SNDCP: Sub-Network Dependent Convergence Protocol

• GTP: GPRS Tunneling Protocol– Mobility Support– GTP-C and GTP-U


Data Units in GPRS


Coding Schemes

• USF = Uplink State Flag– ‘owner’ of time-slot in next uplink TDMA frame– Allows multiplexing of up to 8 MS on one time-slot

• Block header contains Temporary Flow Identifier (TFI)– TFI and direction identifies Temporary Block Flow (TBF)


BSS

SGSN

Um GbGr

Insert Subscriber Data Ack(NSAPI,TI,PDP Type)

Insert Subscriber Data(NSAPI,TI,PDP Type)

Attach Request(NSAPI,TI,PDP Type)

Attach Accept(NSAPI,TI,PDP Type)

Attach Complete(NSAPI,TI,PDP Type)

HLR

Authentication/Ciphering Authentication/Ciphering

GPRS: Obtaining IP Connectivity• GPRS attach

– Authentication of MS

– Establishment/Initialization of security functions

• PDP Context Setup– Obtain IP

address– Connect to

‚external‘ network[see later]


Enhanced Data rates for the GSM Evolution (EDGE)

Time Slot (MS-> BTS) Transmission Rate

48.......384 kbit/s

1 2 8

48 kbit/s ....48 kbit/s 48 kbit/s8 PSK

....New Modulation

Scheme

• Advantages– Increased Data Rate– No Modificatíons in Core Network (SGSN/GGSN) required

• Disadvantages– New Modulationscheme(8 PSK), not compatible to GSMK– HW Changes in the BTS required


3rd Generation Systems: IMT-2000• Proposals for IMT-2000 (International Mobile Telecommunications)

– UWC-136, cdma2000, WP-CDMA– UMTS (Universal Mobile Telecommunications System) from ETSI

• Frequencies

IMT-2000

1850 1900 1950 2000 2050 2100 2150 2200 MHz

MSS↑

ITU allocation(WRC 1992) IMT-2000 MSS

↓

Europe

China

Japan

NorthAmerica

UTRAFDD ↑

UTRAFDD ↓

TDD

TDD

MSS↑

MSS↓

DECT

GSM1800

1850 1900 1950 2000 2050 2100 2150 2200 MHz

IMT-2000 MSS↑

IMT-2000 MSS↓

GSM1800

cdma2000W-CDMA

MSS↓

MSS↓

MSS↑

MSS↑

cdma2000W-CDMAPHS

PCS rsv.


Universal Mobile Telecommunication System (UMTS)• Currently standardized by 3rd Generation Partnership Project (3GPP),

see http://www.3GPP.org[North America: 3GPP2]

• So far, four releases: R’99, R4, R5, R6

Modifications:• New methods & protocols on radio link increased access bandwidth• Coexistence of two domains in the core network

– Packets Switched (PS)– Circuit Switched (CS)

• New Services• IP Service Infrastructure: IP Based Multimedia Subsystems (IMS) (R5)


UMTS Domains

B S C

B T S

B T S

B S S (R A N /G E R A N )

R N C

N o d e B

N o d e B

U T R A N

M E

S IM

U S IM

M S

S G S N

P S D o m a in

G G S N

C S M G W

C S D o m a in

H S S /A u C

R N C

M S C -S e rv ./V L RA b is

S IM - M E

Iu b is C u

U m

U u

Iu C s G b

A

Iu P S

CD

Iu r

G n

G r G c

G s

C S M G W M S C -S e rv ./V L R

C S M G W

G M S C -S e rv .

IM S D o m a in (R e le a s e 5 )

M b /G i

C x

M c

N b

N b

G /E /N c

N c

M c

U s e r E q u ip m e n t D o m a in

A c c e s s N e tw o rk D o m a in

C o re N e tw o rk D o m a in

In f ra s tru c tu r e D o m a in


User EquipmentDomain

User EquipmentDomain Access

NetworkDomain

AccessNetworkDomain

CoreNetworkDomain

CoreNetworkDomain

Service and ApplicationDomain

Service and ApplicationDomain

Charging/ Lawful Interception/ OAMCharging/ Lawful Interception/ OAM

Other Networks (IP/ ISDN)

Other Networks (IP/ ISDN)

• Radio Access Network– Node B (Base station)– Radio Network Controller (RNC)

• Mobile Core Network– Serving GPRS Support Node (SGSN)– Gateway GPRS Support Node (GGSN)– Mobile Switching Center (MSC)– Home/Visited Location Register (HLR/VLR)– Routers/Switches, DNS Server, DHCP Server,

Radius Server, NTP Server, Firewalls/VPN Gateways

• Application/Services• IP-Based Multimedia Subsystem (IMS)

– [see 9th Semester]• Operation, Administration & Maintenance (OAM)• Charging Network • [Legal Interception]

UMTS Network Domains


UMTS Radio Access Network (UTRAN): architecture

• CDMA (Code Division Multiple Access) on Radio Link

• transmission rate theoretically up to 2Mbit/s (realistic up to ≈300kb/s)


Transport of IP packets

ApplicationServerGGSNTerminal SGSNUTRAN

GTP-UGTP-U

User IP (v4 or v6)

Radio Bearer

IP tackets are tunnelled through the UMTS/GPRS network(GTP – GPRS tunneling protocol)

L1

RLC

PDCP

MAC

IPv4 or v6

Application

L1

RLC

PDCP

MAC

ATM

UDP/IPv4 or v6

GTP-U

AAL5

Relay

L1

UDP/IPv4 or v6

L2

GTP-U

IPv4 or v6

Iu-PSUu Gn Gi

ATM

UDP/IPv4 or v6

GTP-U

AAL5

L1

UDP/IPv4 or v6

GTP-U

L2

Relay

L1

L2

IPv4 or v6

[Source: 3GPP]


GGSN

IP Transport: PDP Context & APNs

Terminal SGSNGGSN

PDP Context X2 (APN X, IP address X, QoS2)

PDP Context X1 (APN X, IP address X, QoS1)

ISP X

ISP Z

ISP Y

PDP Context Z (APN Z, IP address Z, QoS)

PDP Context Y (APN Y, IP address Y, QoS)

APN

YA

PN Z

APN

X

Same PDP (IP) address and APN

PDP Context selectionbased on TFT (downstream)

[Source: 3GPP]


IP Transport: Concepts• PDP contexts (Packet Data Protocol) activation

• done by UE before data transmission• specification of APN and traffic parameters• GGSN delivers IP address to UE• set-up of bearers and mobility contexts in SGSN and GGSN• activation of multiple PDP contexts possible

•Access Point Names (APN)• APNs identify external networks (logical Gi interfaces of GGSN)• At PDP context activation, the SGSN performs a DNS query to find out the GGSN(s) serving the APN requested by the terminal.• The DNS response contains a list of GGSN addresses from which the SGSN selects one address in a round-robin fashion (for this APN).

•Traffic Flow Templates (TFTs)• set of packet filters (source address, subnet mask, destination port range, source port range, SPI, TOS (IPv4), Traffic Class (v6), Flow Label (v6)• used by GGSN to assign IP packets from external networks to proper PDP context

• GPRS tunneling protocol (GTP)•For every UE, one GTP-C tunnel is established for signalling and a number of GTP-U tunnels, one per PDP context (i.e. session), are established for user traffic.


Message Flow: PDP Context Setup

…

…


UMTS Data Transport: Bearer Hierarchy

TE MT UTRAN/GERAN

CN IuEDGENODE

CNGateway

TE/AS

End-to-End Service(IP Bearer Service)

TE/MT LocalBearer Service

UMTS BearerService

External BearerService

UMTS Bearer Service

Radio Access BearerService

CN BearerService

BackboneBearer Service

Iu BearerService

Radio BearerService

PhysicalRadio

Service

PhysicalBearer Service

Air Interface

3G GGSN3G SGSNRAN

User Equipment


UMTS Bearer: Traffic Classes (Source TS23.107, V5.2.0)

UMTS Bearer: Selected Traffic/QoS Parameters• Maximum Bitrate (kb/s)• Guaranteed Bitrate (kb/s)• Source statistics descriptor (`speech´, `unknown´)

• Transfer delay (ms)• SDU error ratio• Maximum SDU size (bytes)


GPRS/UMTS QoS ProvisioningAt PDP context setup

• decision about acceptance of QoS parameters (CAC), based on•subscriber status •available resources

• possibly downgrade of QoS classes/parameters (in RAN/SGSN/GGSN)• initialisation of appropriate data structures, e.g. separate queues

During user data transmission: Provisioning of QoS via• Adequate Radio Resource Management (RRM)

• time-slot allocation (TDMA/GPRS) and selection of coding/FEC• transmission power and rate allocation (CDMA)• scheduling in the RAN (e.g. for TBF multiplexing in GPRS)

• scheduling in UMTS/GPRS Network Elements• Use of adequate IP/ATM transport mechanisms

• within RAN• between SGSN and GGSN• in IP networks connected to GGSN


Exercises: see MM1








Exercise


WLAN: IEEE 802.11 standard• 802.3 Ethernet• 802.5 Token ring• 802.11 WLAN• 802.15 WPAN• Standards specify PHY and MAC, but offers the same interface to higher

layers to maintain interoperability

access pointapplication

TCP

802.11 PHY

802.11 MAC

IP

802.3 MAC

802.3 PHY

application

TCP

802.3 PHY

802.3 MAC

IP

802.11 MAC

802.11 PHY

LLCLLC LLC

IEEE=Institute of Electrical and Electronics Engineers


802.11 - Architecture of an infrastructure network

•Station (STA)– terminal with access mechanisms

to the wireless medium and radio contact to the access point

•Basic Service Set (BSS)– group of stations using the same

radio frequency•Access Point

– station integrated into the wireless LAN and the distribution system

•Portal– bridge to other (wired) networks

•Distribution System– interconnection network to form one

logical network (EES: Extended Service Set) based on several BSS

Distribution System

Portal

802.x LAN

AccessPoint

802.11 LAN

BSS2

802.11 LAN

BSS1

AccessPoint

STA1

STA2 STA3

ESS

System architecture


802.11 - Architecture of an ad-hoc network

• Direct communication within a limited range–Station (STA):terminal with access mechanisms to the wireless medium

• Independent Basic Service Set (IBSS):group of stations using the same radio frequency

802.11 LAN

IBSS2

802.11 LAN

IBSS1

STA1

STA4

STA5

STA2

STA3


802.11 - Physical layer• 3 versions: 2 radio (2.4 GHz), 1 IR

– data rates 1 or 2 Mbit/s• FHSS (Frequency Hopping Spread Spectrum)

– separate different networks by using different hopping sequences– 79 hopping channels; 3 different sets with 26 hopping sequences per set

• DSSS (Direct Sequence Spread Spectrum)– method using separation by code– preamble and header of a frame is always transmitted with 1 Mbit/s, rest of

transmission 1 or 2 Mbit/s– chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code)– max. radiated power 1 W (USA), 100 mW (EU), min. 1mW

• Infrared– 850-950 nm, diffuse light, typ. 10 m range, indoor– Low cost: laser diodes and photodiodes as a receiver


IEEE 802.11 MAC802.11 supports 2 different fundamental MAC schemes:

– Distributed Coordination Function (DCF): all users have to contend for accessing the channel ad-hoc or infrastructure mode

– Point Coordination Function (PCF), optional: based on polling by an AP inside the BSS infrastructure mode

• PCF is required to coexist with the DCF: when the PCF is available in a network, there still is a portion of the time allocated to the DCF.

• PCF used for time-bounded services!


t

medium busy

DIFSDIFS

next frame

contention window(randomized back-offmechanism)

802.11 - CSMA/CA basic access method

station ready to send starts sensing the medium (Carrier Sense)– if the medium is free for the duration of an Inter-Frame Space (IFS,

depends on service type)• the station starts sending

– if the medium is busy• the station has to wait for a free IFS• the station must additionally wait a random back-off time (collision

avoidance, multiple of slot-time) • if another station occupies the medium during the back-off time of the

station, the back-off timer stops (fairness)

slot timedirect access if medium is free ≥ DIFS


Random back-off• If multiple stations are waiting for the medium to become available

potential for repeated collisions• To break symmetry: randomization

– Each station randomly choses integer counter value in [0,CW] (Contention Window)

– when medium was idle for a slot-time back-off counter is decreased– Transmission only started when counter=0 and medium idle

• Congestion Window Size– Initial setting: CW=7– When Collisions detected (missing ACKs)

CW is doubled– After successful transmission

CW set back to initial value


Example: Impact of Maximum Congestion Window

• m=0 corresponds to CW_max=32

• m=5 corresponds to CW_max=1024

Scenario: • 802.11b WLAN with 11Mb/s raw

throughput• Infrastructure setting: one AP, n

stations

See Master Thesis of Rui Martins


Priorities• Priority access to the channel is controlled through the use of interframe space -

mandatory periods of idle time.– SIFS (Short Inter Frame Spacing)

• highest priority, for ACK, CTS, polling response– PIFS (PCF IFS)

• medium priority, for time-bounded service using PCF– DIFS (DCF, Distributed Coordination Function IFS, longest duration)

• lowest priority, for asynchronous data service

t

medium busy SIFSPIFSDIFSDIFS

next framecontention

direct access if medium is free ≥ DIFS


Access methods: variations– DCF CSMA/CA (mandatory) – basic access method

• collision avoidance via randomized „back-off“ mechanism• minimum distance between consecutive packets• ACK packet for acknowledgements (not for broadcasts)

– DCF w/ RTS/CTS (optional) – handshaking access method• avoids hidden terminal problem

– PCF (optional)• access point polls terminals according to a list


• Hidden terminals– A sends to B, C cannot receive A – C wants to send to B, C senses a “free” medium (CS fails)– collision at B, A cannot receive the collision (CD fails)– A is “hidden” for C

• Exposed terminals– B sends to A, C wants to send to another terminal (not A or B)– C has to wait, CS signals a medium in use– but A is outside the radio range of C, therefore waiting is not necessary– C is “exposed” to B

Hidden and exposed terminals (optional)

BA C


802.11 MAC: PCF

PIFS

stations‘NAV

wirelessstations

point coordinator

D1

U1

SIFS

NAV

SIFSD2

U2

SIFS

SIFS

SuperFramet0

medium busy

t1

• Beginning of super frame is indicated by a beacon transmitted by AP (synchronization)

• Minimum duration of PCF period: time required to send 2 frames +overhead + PCF-end-frame

• Maximum duration: at least one frame to be transmitted during DCF period


DFWMAC-PCF (cntd.)

tstations‘NAV

wirelessstations

point coordinator

D3

NAV

PIFSD4

U4

SIFS

SIFSCFend

contentionperiod

contention free period

t2 t3 t4


Enhanced DCF (EDCF): IEEE 802.11e • Each terminal has multiple queues for different traffic type• Each traffic type has different Inter Frame Space (IFS) and contention window (CW)• These different IFS and CW enable service differentiation by giving different priorities for accessing the channel to each traffic• Small CW and IFS can be given to traffic with strict delay constraints

IFS: Time to be sensed “carrier-free” by each terminal before decreasingCW

CW: Counter to be reducedto 0 before contending thechannel








Exercise


WPAN: Bluetooth & IEEE 802.15Bluetooth:• Specification created in 1998• Short-Range, low-power consumption, low cost• Master Slave Principle (Piconets)

– Star Topology (1 Master up to 7 active slaves)– MAC scheme: polling by Master– Frequency Hopping: 79 channels, 1600 hops/s

• Support of voice (Synchronous Connection Oriented) & data (Asynchronous ConnectionLess)

• Co-located Piconets can form Scatternets (with bridging)

IEEE 802.15:• IEEE WPAN standard based on Bluetooth specification

– 802.15.1 – WPAN based on Bluetooth– 802.15.2 – Coexistence– 802.15.3 – High Rate (HR) WPAN– 802.15.4 – Low Data Rate WPAN


Characteristics• Unlincensed 2.4 GHz Industrial-Scientific-Medical (ISM) band• 79 (23) RF channels, 1 MHz carrier spacing

– Channel 0: 2402 MHz … channel 78: 2480 MHz– G-FSK modulation, 1-100 mW transmit power

• FHSS and TDD– Frequency hopping with 1600 hops/s– Hopping sequence in a pseudo random fashion, determined by a master– Time division duplex for send/receive separation

• Voice link – SCO (Synchronous Connection Oriented)– FEC (forward error correction), no retransmission, 64 kbit/s duplex, point-to-point,

circuit switched• Data link – ACL (Asynchronous ConnectionLess)

– Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9 kbit/s symmetric or 723.2/57.6 kbit/s asymmetric, packet switched

• Topology– Overlapping piconets (stars) forming a scatternet


Piconet: details• 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 may only contain 1 master and up to 7 simultaneous/ active slaves (> 200 could be parked)

• 7 slaves in order to keep high-capacity links between all the units + to limit the addressing overhead

M

SS

S

SB

P

P

M=MasterS=Slave

P=ParkedSB=Standby


Piconets: details (cntd.)• All devices in a piconet hop together

– Master gives slaves its clock and device ID• Hopping pattern: determined by device ID (48 bit, unique

worldwide)• Phase in hopping pattern determined by clock

• Addressing– Active Member Address (AMA, 3 bit)– Parked Member Address (PMA, 8 bit)


Communication in a piconet• Communication only between Master and Slave (no direct Slave to Slave)

• Polling-based TDD packet transmission– 625µs slots– master polls slaves according to a polling scheme. – Slave transmits only after it has been polled (NULL packet

Master schedules the traffic in both the uplink and downlink completely contention-free access intelligent scheduling algorithms are needed


Multislot packets• 3-slot and 5-slot packets• Multi-slot packets are sent on a single-hop carrier

• Independ piconets can interfere when they occasionaly use the same hop carrier «no listen-before-talk»


Details: Format of packets• Access code is used as a direct-sequence code in certain access

operations. It includes the ID of a piconet master. • Packet header contains link control information:

• 3-bit slave ADR• 4-bit packet type code to define 16 different payload types• 8-bit header error check

Access code Packet header payload

72 54 0-2745 bits


Link types• SCO (Synchronous Connection Oriented) – Voice

– Periodic single slot packet assignment, 64 kbit/s full-duplex, point-to-point• ACL (Asynchronous ConnectionLess) – Data

– Variable packet size (1,3,5 slots), asymmetric bandwidth, point-to-multipoint– Different amount of FEC– Reliable transmission in unicast (lLLC retransmissions)

• SCO has priority over ACL!


IEEE 802.15.3: High-Data Rate WPAN• Target: High Rate (up to 20 Mbps) and QoS support• Master-Slave based TDMA/TDD• A superframe is prepared, which consists of Contention Access Period (CAP) and Contention-Free

period called Guaranteed Time Slots (GTS)• CAP

– Non-QoS data frames can be sent based on CSMA/CA– Channel Access Requests for getting GTS are also transmitted

• The rest of superframe is reserved for GTS, which supports QoS provisions

• The boundary betweenCAP and GTS isvariable

• Beacon is used forachieving superframesynchronizationamong terminals

[Source: CNTK]








Exercise


Comparison of technologiesUTRA 802.11

a b g Bluetooth 802.15.1 .3 .4

Standard Availability

1999 2001 1999 2003 1999 2002 (2004) (2004)

Frequency Band /

Licences

2GHzYes

5 GHz 2.4GHz 2.4GHzNo No No

2.4 GHzNo

2.4 2.4 2.4/.915/.868No No No

Cell Radius 30 m – 20 km 50 - 300 m 0,1 - 10 m 10m...100m

Modulation W/TD-CDMA OFDM DSSS DSSS FHSS FHSS FHSS DSSS

MAC Mechanism

Polling CSMA/CA & Polling Polling Polling Poll. CSMA/CA

MobilitySupport

High (Soft handover)

Limited (802.11f) Limited Limited

QoS Support Reservation Polling (PCF) & Priorities (802.11e, HCF)

SCO SCO enhanced Prio.

Security Encryption (data), Integrity

(Signalling)Encryption and Integrity

(WEP, 11i, 11x)

3 levels: no, link level,

service level

3 levels

Hyperlan1 2

1998 2000

5GHz 5GHzNo No

50 - 300 m

GMSK OFDM

Polling

Limited

Scheduling by AP

56\168 DES Encrypt.

(Data+Sgn)

Data Rates(50-60m dist.)

Max. 2 Mbit/s 54Mb/s 11Mb/s 54Mb/s6Mb/s 2Mb/s 2Mb/s

0.72Mb/s0

20Mb/s 55Mb/s 0.25Mb/s20Mb/s 54Mb/s

NO Yes (but throughput degradation)

Yes (Scatternets)

Yes (Scatternets)Support of multi-hop

dynamic Sleep mode Sleep Mode Sleep ModeSleep ModePower Management

Yes (but throughput degradation)


Summary: WLAN / WPAN QoS• QoS Mechanisms for WLAN and WPAN

– Centralized (TDMA/TDD)– Distributed (CSMA/CA with prioritization of channel access)

• Centralized mechanism requires central coordinator while distributed mechanism can work in distributed (flat) network

• Interactions of these mechanisms with QoS support mechanisms in higher layer, e.g. routing and application layers, should be discussed


Topics not treated in this lecture• Security aspects

• GPRS/UMTS: Attach procedure, UMTS AKA, encryption & integrity protection• WLAN: authentication, encryption and integrity protection

• Mobility Support/Hand-over• types of HO, GSM procedures, GPRS cell reselection, UMTS soft handover• WLAN scanning, association• BT: Piconet/Scatternet formation• IP mobility support, ad-hoc routing

• Energy efficiency• cellular systems: Power control• BT: Park/Sniff/hold modes• 802.15.4 standard (sensor networks)

• Radio Resource Management Procedures• time-slot allocation, and scheduling in GPRS/GERAN• power-control, rate-allocation, and scheduling in UMTS/UTRAN

• wireless multi-hop performance issues/problems


Outlook: Future wireless networksServices andapplications

IP based core network

IMT-2000UMTS

WLANtype

cellularGSM

short rangeconnectivity

WirelinexDSL

otherentities

DABDVB

New radiointerface

Properties of future networks (‘4G’):• Heterogeneous access

technologies – 802.11, Bluetooth, cellular, etc.

• IP-based core network– Mobility support on IP layer

(complemented by higher-layer methods)• Mobile IP one major candidate

• wireless multi-hop connections• Personalization (Personal Area Networks,

Personal Networks)• Reconfigurability (Software Defined Radio)• Context Sensitivity


Acknowledgements/References• Lecture notes: Mobile Communciations, Jochen Schiller, www.jochenschiller.de• Lecture: Wireless Networks II, MM1 • Lecture: Wireless Networks III, MM1 (Fall 2003)• Tutorial: IP Technology in 3rd Generation mobile networks, Siemens AG (J. Kross, L. Smith, H.

Schwefel)• Various 3GPP Presentations. www.3gpp.org• J. Schiller: ’Mobile Communications’. Addison-Wesley, 2000.• GPRS books:

– T. Halonen, J. Romero, J. Melero: ‘GSM, GRPS, EDGE Performance: Evolution towards 3G/UMTS’, Wiley, 2003

Bluetooth:• Bluetooth Specification, v.1.1• J.C. Haartsen, «The Bluetooth radio System», IEEE Personal Communications, February 2000• B.A. Miller, C. Bisdikian. Bluetooth Revealed, Prentice Hall, 2001WLAN:• http://grouper.ieee.org/groups/802/11/• B. Crow et al, “IEEE 802.11 Wireless Local Area Networks”, IEEE Comm. Magazine, September

1997

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