Page 1 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
Networking and protocols for real-time signal transmissionsby Hans-Peter Schwefel
• Mm1 Introduction & simple performance models
• Mm2 Real-time Support in Wireless Technologies
• Mm3 Transport Layer Aspects and Header Compression
• Mm4 IP Quality of Service: Advanced Concepts
• Mm5 Session Signalling and Application Layer/Codecs
http://www.kom.auc.dk/~hps
Note: Slide-set contains more material than covered in the lectures!
Page 2 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 3 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 4 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 5 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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:
Page 6 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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)
Page 7 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 8 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 9 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 10 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 11 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 12 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 13 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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)
Page 14 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 15 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 16 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
GPRS: channel types
Page 17 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 18 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 19 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
Data Units in GPRS
Page 20 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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)
Page 21 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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]
Page 22 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 23 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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.
Page 24 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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)
Page 25 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 26 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 27 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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)
Page 28 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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]
Page 29 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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]
Page 30 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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.
Page 31 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
Message Flow: PDP Context Setup
…
…
Page 32 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 33 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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)
Page 34 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 35 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
Exercises: (see MM1 Exercise 1)1. GPRS modeling: Traffic measurements in a GPRS radio cell result in the following traffic
model: voice calls arrive at Poisson rate 1call/min and have an average duration of 1.5 min. GPRS data sessions start at rate 1session/5min, have an average duration of 20min, and generate traffic with an averate rate of 10kb/sec using IP packets of 1500 byte size and CS-II.
a) How many time-slots would have to be reserved for GSM voice calls to keep the call blocking probability below 1e-6?
b) Compute the average RLC block delay, if 4 GPRS time-slots are used for the data traffic (as simplification: use an M/M/1 queue on RLC layer, RLC block size for CS-II is 247 bits, TDMA frame duration is 4.615ms; neglect header overhead as well as the overhead of TBF assignments).
Page 36 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 37 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 38 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 39 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 40 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 41 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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!
Page 42 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 43 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 44 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 45 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 46 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 47 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
• 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
Page 48 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 49 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
DFWMAC-PCF (cntd.)
tstations‘NAV
wirelessstations
point coordinator
D3
NAV
PIFSD4
U4
SIFS
SIFSCFend
contentionperiod
contention free period
t2 t3 t4
Page 50 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 51 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 52 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 53 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 54 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 55 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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)
Page 56 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 57 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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»
Page 58 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 59 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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!
Page 60 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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]
Page 61 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 62 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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)
Page 63 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 64 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 65 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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
Page 66 Hans Peter SchwefelSIPCom9-3: RT Networking Lecture 2, Fall05
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