Resource Management and QoS Control in Mobile Communication Networks. Zhisheng NIU. State Key Lab on Microwave and Digital Communication

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1 Resource Management and QoS Control in Mobile Communication Networks Zhisheng NIU State Key Lab on Microwave and Digital Communication Tsinghua University, Beijing , China Zhisheng Tsinghua University 1 Content Introduction to mobile communication networks Cellular networks (2G/3G/4G) and Wireless LAN The trend toward mobile Internet The need for resource management and QoS control Resource management of wireless links (wireless QoS) Characteristics of wireless radio links End-to-end TCP performance enhancement Power allocation and rate control Resource management during handovers (mobile QoS) Handovers in TDMA-based cellular networks (hard handovers) Handovers in CDMA-based cellular networks (soft handovers) Standardization in IMT2000/UMTS working group Summary Zhisheng Tsinghua University 2

Introduction to Wireless/Mobile Networks Cellular networks: Firstly proposed in 1960 s and commercialized in 1980 s (frequency reuse) One-hop access to BS s which are connected to wired backbone

2 Introduction to Wireless/Mobile Networks Cellular networks: Firstly proposed in 1960 s and commercialized in 1980 s (frequency reuse) One-hop access to BS s which are connected to wired backbone TDMA-based multiple access Wide coverage (1-10km) and hard handovers Have over 1 billion users by the end of Zhisheng Tsinghua University 3 Introduction to Wireless/Mobile Networks 3G Firstly proposed in 1980 s and was expected to be commercialized in 2000 CDMA-based multiple access Interference-limited channels and soft handovers Air interface has not yet been (will never be?) unified (WCDMA, CDMA200, TDS- CDMA) Firstly commercialized in Japan (Oct 2001) and hold several hundred thousand users only Low speed wireless data service Start to move toward beyond 3G or 4G Zhisheng Tsinghua University 4

Introduction to Wireless/Mobile Networks WLAN and WPAN High speed wireless data service (>2Mbps) Local

11a,b,g (CSMA/CA) Widely available now WLAN Access Cellular access Bluetooth within PAN PAN IP internet

3 Introduction to Wireless/Mobile Networks WLAN and WPAN High speed wireless data service (>2Mbps) Local coverage and quasistationary (hot spot) De facto standards: IEEE a,b,g (CSMA/CA) Widely available now WLAN Access Cellular access Bluetooth within PAN PAN IP internet Iu-ps UTRAN/GERAN BS IP-RNC 3G SGSN Zhisheng Tsinghua University 5 3G 3G vs WLAN Up to 2 Mbps (HSDPA 10.8 Mbps) Wide area coverage (384 kbps) Licensed spectrum Anytime, Anywhere WLAN Up to 11/50Mbps data rate Local area coverage (up to 500/50m) Unlicensed spectrum Sometimes, Somewhere Zhisheng Tsinghua University 6

Current Status: Current Status and New Trends of Mobile Communication Networks Over 1B mobile phone users by end of 2002 Several millions of users of Internet enabled palm devices Packet based

(RAN), and core network, traffic management, quality of service Need for reliable and distributed servers and databases control infrastructure Evolution toward all IP solution (3G to 4G) Design

connectivity complement mobile operators' GPRS and 3G services offering high speed indoor solution Mobile operator network Public Wireless LAN network LAN SIM authentication & billing Secure VPN data

4 Current Status: Current Status and New Trends of Mobile Communication Networks Over 1B mobile phone users by end of 2002 Several millions of users of Internet enabled palm devices Packet based multimedia services, including IP telephony, to account for over 50% of all wireless traffic New Trends: Need for more capacity in mobile network, higher bandwidth in radio link, radio access network (RAN), and core network, traffic management, quality of service Need for reliable and distributed servers and databases control infrastructure Evolution toward all IP solution (3G to 4G) Design networks, including wireless, for the dominant traffic type - data Zhisheng Tsinghua University 7 WLAN Integrates with Cellular Networks fast and secure wireless indoor laptop connectivity complement mobile operators' GPRS and 3G services offering high speed indoor solution Mobile operator network Public Wireless LAN network LAN SIM authentication & billing Secure VPN data connection Internet Virtual Private Network Encrypted Tunnel Corporate Intranet 11 Mbps WLAN connection Authentication and charging is performed using the GSM SIM (Smart) Card Zhisheng Tsinghua University 8

5 Seamless Broadband IP Mobility Networks Mobility Vehicular Pedestrian Stationary WCDMA Rel -00 Cdma2000 1X, EDGE = Evolved 2G 1XEV E.g. Narrow Beams HSP DA WCDMA Rel 01 Seamless IP Broadband Networks WLAN Seamless services in all radio environments Air interface optimized based on service, cost and radio conditions Multimode terminals combining EDGE, WCDMA, WLAN and BT air interfaces IPv6 network connecting different types of radios in a seamless way Synchronization of information and security Data Rate (Mbps) Zhisheng Tsinghua University 9 Within the next 5 years Internet access will happen mainly via mobile devices Subscriptions worldwide (millions) Mobile Fixed Mobile Internet Fixed Internet Mobile subscribers Mobile Internet subscribers Zhisheng Tsinghua University 10

6 Vision of Wireless Communications beyond 3G Seamless network of complementary access systems Services and applications download channel return channel e.g. cellular Digital Broadcast Cellular 2nd gen. New Radio Interface Wireline IP based xdsl Core Network IMT-2000 WLAN type Short Range Connectivity other entities Source: ITU-R WP8F 7th Meeting, Queenstown, February 27 March 5, 2002, TEMP 251r1e Zhisheng Tsinghua University 11 Layered system structure beyond third generation Distribution Layer Digital Broadcast Possible Return Channels?full coverage?global access?full mobility?not necessarily individual links Cellular Layer Pre-IMT-2000 IMT-2000?full coverage and "hot spots"?global roaming?full mobility?individual links "Hot Spot" Layer?local coverage?"hot spots"?global roaming?local mobility?individual links Personal Network Layer Fixed (Wired) Layer X X X X X X X X horizontal: handover within a system X X X X X X X vertical: handover between systems?short range communication?global roaming?individual links?no mobility?global roaming?individual links Source: ITU-R WP8F 7th Meeting, Queenstown, February 27 March 5, 2002, TEMP 251r1e Zhisheng Tsinghua University 12

7 Moving towards Mobile Internet In the past 5 years, Internet and mobile/wireless communications are two most successful technologies in communication field The convergence of Internet and mobile/wireless communications has been emerging (e.g., imode in Japan) The future Internet will be much more mobile and wireless than today, especially with the wireless mobile geolocation technology Zhisheng Tsinghua University 13 Convergence of Mobile and Internet Worlds Mobile NW s Internet Packet transmission Increasing mobility Mobile Internet Zhisheng Tsinghua University 14

8 The Need for IPv6 The great success of Internet creates new problems: IPv4 is running out of global IP addresses due to unpredictably fast growth and biased address allocation The strong needs for QoS-guarantee and security due to commercialization of Internet more and more multimedia applications rather than data only Internet is evolving into an information infrastructure The strong needs for mobility enhancement Mobile Internet needs IPv6 because Tremendous mobile terminals need much more IP addresses NAT has extended the life of IPv4, but Breaks IP end-to-end model Inhibits new applications and QoS guarantee Barrier to mobile IP communication IPv6 provides the framework of QoS guarantee, mobility enhancement, security system, as well as enough IP addresses Zhisheng Tsinghua University 15 Global Address 1 billion billion / mm 2 Features of IPv6 Auto-configuration for plug&play Hierarchical address and auto-routing High Security IPsec QoS provisioning IPqos Mobility support Mobile IPv4 and mobile IPv6 Cellular IP and Hawaii LMM (local mobility management) Zhisheng Tsinghua University 16

9 Key Issues of IPv6-based Mobile Internet Architecture for a HUGE-scale network! HUGE-scale creates new problems (e.g., routing table explosion) Flat networking paradigm is no more efficient Fast and scalable (re)routing algorithms are needed Quality of Services QoS guarantee is essential for multimedia applications Difficulties from the best-effort nature of IP Much more challenges in HUGE-scale networks with global roaming and frequent handovers Mobility management Mobile hosts will be the main part of IPv6-based Internet Fast and seamless handover as well as global roaming in HUGEscale Internet is the key Power-limited nature of mobile terminals is another bottleneck Zhisheng Tsinghua University 17 No: QoS: is it really necessary? QoS guarantee by traffic control and resource management is too complicated to be practical Over-provision of bandwidth will provide QoS Yes: ( Concepts without intuitions are empty; intuitions without concepts are blind ) Traffic growth is always faster than bandwidth growth; over provision can not solve the congestion completely Bandwidth available can not be infinite, especially at the edge (including wireless access) QoS control should be end-to-end, otherwise you just move the problem elsewhere Seamless handover and roaming of mobile hosts need strict QoS QoS differentiation and tariff need QoS guarantee Zhisheng Tsinghua University 18

10 What s QoS: Perception is Reality QoS is a measure of the satisfaction experienced by users while receiving a service User perception Technically, we usually transfer the QoS level into (from users point of view) blocking probability; packet loss rate maximum delay time; delay variation, and etc But, from network point of view, QoS depends also on Connectivity (e.g., handoff) Resource utilization ratio Flexibility, Survivability, and Security Zhisheng Tsinghua University 19 QoS: It s not Free QoS is not only bandwidth, but more traffic control and management Traffic control and management is not cheap QoS is not only in the core, but more on the edges End-end QoS is expensive Cost of Wireless Bandwidth C = N user x B user x x A service x f(q) f(q) Where N user = number of users; B user = bandwidth/user; = bandwidth utilization ratio A service = service area (coverage); f(q)=qos guarantee level Q Zhisheng Tsinghua University 20

11 Various Aspects of QoS QoS depends on Diverse user requirements Heterogeneous user perception Different compression and coding techniques Communication protocols Pricing and charging policy Data users are greedy to their QoS Services with more stringent QoS requirements are generally more expensive to provide; users tolerate reduced quality only if the price is substantially less Typically, realtime services require resource reservation based charging, while networks may charge for non-realtime services at a flat rate on an actual usage basis Zhisheng Tsinghua University 21 QoS for Different Media Voice users is Unpredictable user demands Unpredictable network load Unpredictable propagation Data users are greedy to their QoS Unpredictable user demands Unpredictable network load Unpredictable propagation Unpredictable available bit rate Wireless data users have additional problems: Unpredictable user demands Unpredictable network load Unpredictable propagation Unpredictable competition for spectrum resource Unpredictable interference Zhisheng Tsinghua University 22

12 Defining QoS Hard (strict, deterministic) QoS Guaranteed bandwidth (bps): [CLR > or Delay > Dmax] Reject any connections or packets if the QoS is not guaranteed Soft (statistical) QoS P [CLR > ] < or P [Delay > Dmax]< Policy-based QoS (QoS Differentiation) QoS 1 > QoS 2 > QoS 3 > >QoS 8 Perceptual QoS Consistent, predictable transmission Utility-based QoS dimensioning! Zhisheng Tsinghua University 23 QoS for Data Applications For realtime applications, specifying QoS is straightforward by, for examples, throughput, packet delay and loss probability But, for data applications, QoS-defining is not straight-forward because it can be affected by many elements include the physical distance (from source to destination) processing for DNS the transmission capacity of links packet switching and forwarding at routers protocol processing at sender and receiver, and application processing Even the simplest bandwidth-guarantee is not so easy in the Internet Zhisheng Tsinghua University 24

13 Dimensioning of QoS Erlang loss formula has been a successful dimensioning method for telephone network due to its robustness However, QoS dimensioning in data network (e.g., IP) is not easy, because we do not have an adequate performance metric to determine the required amount of network resources; the network provider has no means to measure the performance metric even if it is known; only the users can perceive the performance (e.g., the end-to-end delay time) where the network operator can only know a part of them A rapid growth of data traffic makes it difficult to predict the future traffic demand Zhisheng Tsinghua University 25 Delivering QoS via Traffic Control Traffic Control in tradition networks Circuit-switching (call-blocking, alternative routing, trunk reservation, ) Packet-switching (Window-flow control) Frame-relay (Flow control, selective discarding, ) Local Area Network (contention-reservation, polling, ) ATM was the first networking technology designed with QoS in mind from the outset Connection Admission Control Usage Parameter Control Selective Cell Discarding Control Policing and shaping Buffer Management Flow Control Zhisheng Tsinghua University 26

14 Wireless QoS and Mobile QoS QoS delivery in wireless/mobile Internet should be quite different from that in the fixed Internet because much more realtime voice beside non-realtime data high bit-error-rate and location-dependent errors statistical characteristics of channel condition (fading, shadowing, ) limited bandwidth and low-end terminals packet loss and QoS degradation during handoff QoS delivery in wireless/mobile Internet is also quite different from that in mobile telephone NW because wireless data is much more sensitive to errors/losses traffic characteristics and QoS measures of data users are also quite different from voice Zhisheng Tsinghua University 27 Resource Management in Wireless/Mobile Networks Zhisheng Tsinghua University 28

15 Characteristics of Wireless Channels Cellular station Cn α n V Zhisheng Tsinghua University 29 Characterization of Wireless Channels L T = L + A ( f, d ) H ( h, d ) H ( h, f ) K fs m b b m m T 2 λ 4πd f h b d h m Zhisheng Tsinghua University 30

16 A New QoS Dimensioning Approach Utility-based QoS dimensioning and optimization Utility function in economic science Different utility functions among voice, data, and video Zhisheng Tsinghua University 31 (time-variant) location-dependent Zhisheng Tsinghua University 32

17 smart antenna ARQ/FEC and Hybrid ARQ MAC CAC Wireless TCP Fast and seamless handovers Rerouting and bandwidth reallocation Zhisheng Tsinghua University 33 Bandwidth (management) Limited and time-variant Reallocation is needed during handovers Buffer/memory (management) Limited and slow Crucial to wireless data service Power (management) Limited and sensitive Crucial to CDMA systems (interference-limited) Zhisheng Tsinghua University 34

18 (location-dependent error) Location-dependent error Zhisheng Tsinghua University 35 J. Kim, M.Krunz, Bandwidth allocation in wireless Network with guaranteed packet-loss performance, IEEE/ACM transactions on networking, vol 8, No.3, June, Zhisheng Tsinghua University 36

19 Zhisheng Tsinghua University 37 Power Control for Multimedia CDMA Networks Sufficient condition for optimal power allocation A closed-form approximation solution (QOPA) CAC under imperfect power control Capacity optimization under other imperfect interference management techniques (imperfect interference cancellation, etc) Joint power and rate allocation by using utility function Zhisheng Tsinghua University 38

20 TCP/IP Zhisheng Tsinghua University 39 Some Conclusions: TCP Performance Experiments show that Internet packet loss rate will be around 2% WaveLAN suffers from a frame error rate of 1.55% when transmitting 1400-byte frames over an 85 ft distance with clustered losses [3] Reducing the frame size by 300 bytes halves FER, but increases framing overhead In shared medium WLANs, collisions of forward data pkts and reverse ACKs increase FER dramatically [4] Mobility also increases FER for WaveLAN by about 30% [5] Zhisheng Tsinghua University 40

21 Some Conclusions: TCP Performance When e2e paths include multiple wireless links, the accumulated losses further reduce throughput, also causing underutilization of wireless links Long RTT in CC links have great impact on TCP performance, specially its deviation Appropriate frame size is also very important to TCP throughput Spurious timeouts reduce TCP performance dramatically, especially timeouts due to handoffs in CC links Spurious fast retransmissions due to handoff Higher-speed links are affected more by losses, since TCP takes longer to reach its peak throughput after each loss Zhisheng Tsinghua University 41 TCP Performance Enhancements Transport Layer Solutions (e2e solutions) Idea: distinguish losses due to congestion from the losses due to channel errors, also from the losses due to handoffs Fast retransmissions (fast TCP) (e.g., TCP Reno Multiple copy retransmission (MCR) and Delayed MCR TCP-aware and TCP-unaware Link Layer Solutions (local recovery) Idea: hiding wireless losses from TCP layer e.g., Snoop TCP: Split TCP: TCP connection split can shorten the end-to-end retransmission delay, but of course this violate TCP semantics since acks may reach the sender before data packets reach their destination. To preserve TCP semantics, acks must be delayed, thus reducing throughput Zhisheng Tsinghua University 42

22 T 1 T 3 T 2 T 3 T=1 T=2 T 1 T=3 T=2 T=1,L=1 T=3,L=2 T=2,L=3 T=3,L=4 T TCP A TCP ML L L T=2,L=3 T=3,L=2 T=2,L=3 T=2,L=2 T=1,L=1 T=3,L=2 T=3,L=1 T=3,L=4 T=1,L=1 T=3,L=2 T=2,L=3 T=3,L=4 A=2, A=3, ML=1 ML=3 A=2, A=3, ML=1 ML=3 T=1,L=1 T=3,L=2 T=2,L=3 T=3,L=4 A=2, A=3, ML=1 ML=3 T=3 T=2 T=1 TCP Aware Zhisheng Tsinghua University 43 Inhomogeneous traffic, capacity, data rate requirement Traffic, capacity and data rate requirements Requires scalable system, which can be adapted to different local traffic and capacity demands Zhisheng Tsinghua University 44

23 QoS Guarantee during Handovers TDMA-based cellular networks Hand handovers Trunk reservation and other priority control CDMA-based cellular networks Soft handovers Need to introduce outage probability WLAN-based packet networks Was not initially considered Open issue Zhisheng Tsinghua University 45 QoS Differentiation in UMTS UE RAN SGSN GGSN Traffic Flow Template (TFT) Flow label DS code points Source port Destination port Source address SPI (Security Parameters Index for IPSec) Protocol number PDP address (IP) TFT PDP context, QoS 3 PDP context, QoS 2 PDP context, QoS NSAPI TI TFT PDP type PDP address Access point requested QoS requested PDP configuratio options Zhisheng Tsinghua University 46

24 UMTS QoS (Architecture and Requirements) Main target of UMTS packet service QoS standardization is to enable UMTS to provide data delivery with appropriate end-to-end QoS guarantees. To meet this objective, the standard effort has proposed a layered service architecture describing the following key elements: Mapping of end-to-end service to services provided by the UE, the UTRAN, the CN and external IP networks Traffic classes and associated QoS parameters Location of QoS functions QoS negotiation Multiplexing of flows onto network resources An end-to-end data delivery model From end-to-end connectivity standpoint, UMTS offers CS domain toward the PSTN and ISDN, mainly for voice communications, and IP connectivity provided through the PS domain as a pure network layer service between a UMTS mobile and an Internet host Zhisheng Tsinghua University 47 UMTS QoS Requirements (Bearer Attributes for Each Traffic Class) Traffic class Conversational class Streaming class Interactive class Background class Maximum bitrate X X X X Delivery order X X X X Maximum SDU size X X X X SDU format information Delivery erroneous SDUs of Residual bit error ratio X X X X X X X X X X SDU error ratio X X X X Transfer delay X X Guaranteed bitrate X X Traffic priority handling Allocation/Retention priority X X X X X Zhisheng Tsinghua University 48

25 GPRS rel'97, '98 Precedence class Delay class Reliability class Peak throughput class Mean throughput class QoS Parameters ConversationalStreaming class class Allocation/retention priority 1, 2, 3 1, 2, 3 Traffic handling priority Transfer delay Residual BER SDU error ratio Maximum bitrate <100 ms 5* < 2048 kbps < 2048 kbps Guaranteed bitrate <2048 kbps <2048 kbps Yes/No <250 ms 5* *10-3 6*10-8 4*10-3 6* Yes/No Interactive class 1, 2, 3 1, 2, < 2048 kbps -overhead Maximum SDU size <=1500 octets <=1500 octets <=1500 octets <=1500 octets Delivery order SDU format information Delivery of erroneous SDUs GPRS/UMTS rel'99, '00 Yes/No Background class 1, 2, < 2048 kbps -overhead Yes/No Yes/No/- Yes/No/- Yes/No/- Yes/No/ Zhisheng Tsinghua University 49 UMTS QoS Traffic Classes Traffic class Conversational class conversational RT Streaming class streaming RT Interactive class Interactive best effort Background Background best effort Fundamental characteristic s -Preserve time relation (variation) between info. entities of the stream -Conversational pattern (stringent and low delay ) -Preserve time relation (variation) between information entities of the stream -Request response pattern -Preserve payload content -Destination is not expecting the data within a certain time -Preserve payload content Example of the application -Voice -Video telephony -Streaming video -Streaming audio -Video surveillance -Web browsing -Signaling -Interactive games -Background download of s -Calender update Zhisheng Tsinghua University 50

26 Summary Wireless communications are getting more and more mobile and data (multimedia)-centric Resource management and QoS control are the key to the future of mobile Internet Wireless channels are very complicated compared with wired channels, making the QoS guarantee hard Power-efficient control algorithm is crucial Mobility management and handovers should be paid much more attentions than before This is an active hot area with a lot of open issues Zhisheng Tsinghua University 51 For the published papers in our lab: Zhisheng Tsinghua University 52

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