Page 1 Hans Peter Schwefel SIPCom9-3: RT Networking Lecture 2, Fall05 Networking and protocols for real-time signal transmissions by 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 [email protected]http://www.kom.auc.dk/~hps Note: Slide-set contains more material than covered in the lectures! Page 2 Hans Peter Schwefel SIPCom9-3: RT Networking Lecture 2, Fall05 Wireless Communication Technologies 20 155 Indoor Pedestrian High Speed Vehicular Rural Mobility & Range Personal Area Vehicular Urban 0.5 2 UMTS GSM DECT Fixed urban Total data rate per cell 10 WLAN/ BRAN B-PAN WPAN Bluetooth 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
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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
• GSM: Architecture, Air Interface, IP Data Transmission, HSCSD• GPRS: Architecture, Air Interface Properties, EDGE• UMTS: architecture & domains• QoS Support in PS domain
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
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
• 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,
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
• 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
• GSM: Architecture, Air Interface, IP Data Transmission, HSCSD• GPRS: Architecture, Air Interface Properties, EDGE• UMTS: architecture & domains• QoS Support in PS domain
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
• collision avoidance via randomized „back-off“ mechanism• minimum distance between consecutive packets• ACK packet for acknowledgements (not for broadcasts)
– 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
• GSM: Architecture, Air Interface, IP Data Transmission, HSCSD• GPRS: Architecture, Air Interface Properties, EDGE• UMTS: architecture & domains• QoS Support in PS domain
• 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
• GSM: Architecture, Air Interface, IP Data Transmission, HSCSD• GPRS: Architecture, Air Interface Properties, EDGE• UMTS: architecture & domains• QoS Support in PS domain
• 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
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