Performance Issues of TCP and MPEG-4 4 over UMTS

Transcription

1 Performance Issues of TCP and MPEG-4 4 over UMTS Anthony Lo [email protected] 1 Wiskunde end Informatica Outline UMTS Overview TCP and MPEG-4 Performance Summary 2 1

2 Universal Mobile Telecommunications System (UMTS) Radio interface is based on Wideband Code Division Multiple Access (WCDMA) Support of variable bit rates: up to 384 kb/s in wide area coverage, up to 2 Mb/s in indoor/short-range range outdoor Support four Quality of Service traffic classes: Conversational: low delay voice Streaming: : low delay video streaming Interactive: moderate delay web browsing Background: : no delay requirement FTP, 3 IMT-2000 Family of 3G Systems IMT-2000 Core Network Technologies ITU-T UMTS Network-to-Network Interfaces (3G Inter Family Roaming) GSM (MAP) ANSI-41 (IS-634) Flexible connection between radio access and core networks Future -based Networks IMT-2000 Radio Access Technologies ITU-R IMT-DS (Direct Spread) UTRA FDD (WCDMA) 3GPP IMT-TC (Time Code) UTRA TDD (TD-SCDMA) 3GPP IMT-MC (Multi Carrier) cdma2000 3GPP2 IMT-SC (Single Carrier) GERAN 3GPP IMT-FT (Freq. Time) DECT ETSI 4 2

3 IMT-2000 Frequency Spectrum ITU/RR IMT-2000 Reg.2 IMT-2000 Reg.2 Europe GSM 1800 DECT UMTS TDD UMTS UMTS UMTS Japan PHS uplink IMT-2000 downlink IMT-2000 China IMT-2000 IMT-2000 USA uplink PCS downlink Frequency in MHz 5 Frequency Spectrum The Netherlands Vodafone KPN Mobile Orange Telfort T-Mobile f 1 f 2 f 3 f 1 f 2 f 3 f 1 f 1 f 2 f 1 f 2 f 2 5 MHz 1920 MHz Uplink Frequency 1980 MHz 2110 MHz Downlink Frequency 2170 MHz 6 3

4 UMTS Wideband CDMA (WCDMA) FDMA POWER TIME FREQUENCY TDMA POWER TIME FREQUENCY CDMA POWER TIME FREQUENCY 7 FDD TDD FDD (Frequency Division Duplex) separated frequency bands for Up- and Downlink most suited for symmetrical services, e.g. voice, video telephony paired frequency bands needed used for WCDMA UL DL t TDD (Time Division Duplex) Up- and Downlink signal within the same frequency band, but separated in time also suited for asymmetrical services, e.g web browsing DL flexible allocation in unpaired frequency band possible Time synchronization needed 5 MHz will be used for private indoor services 5 MHz 5 MHz UL 8 t 4

5 UMTS WCDMA Spreading Operation The operation of spreading in a WCDMA system is divided into two separate parts: Spreading code = Channelization code + Scrambling code Data R bit Channelization code Chip rate R chip 3.84 Mc/s Scrambling code Chip rate R chip 3.84 Mc/s Chip rate 3.84 Mc/s Spreading factor (Processing gain) G = R chip R bit 9 Wireless Internet Access via UMTS UE Node B UTRAN RNC SGSN GGSN Core Network Network App App TCP TCP PDCP PDCP GTP-U GTP-U GTP-U RLC RLC UDP UDP UDP UDP MAC PHY UE Legend: Uu PHY UMTS Node B FP MAC FP RNC Iub SGSN GGSN IuPS Gn Gi UMTS Transport Network Internet Other 10 Host 5

6 Packet Data Transmission over UMTS Radio Interface packets can be carried using different types of UMTS/WCDMA Transport Channels: Dedicated Channel (DCH): power control resources allocated to a UE high channel bits rates => high volume of data Common Channel (CCH): no power control shared resources low channel bit rates => low volume of data Random Access Channel (RACH) uplink Forward Access Channel (FACH) downlink 11 Transmission Control Protocol The main Transport protocol in the Internet protocol suite Functionality: provide end-to to-end reliability on top of unreliable network, provide in-sequence packet delivery, detect and prevent network congestion TCP uses complex mechanisms: Slow start and Congestion avoidance Fast retransmit and recovery 12 6

7 TCP Vegas TCP Vegas vs. Reno TCP Reno Better performance than Reno Proactive network congestion algorithms Reactive network congestion algorithms Slow Start Window (WND) is increased for every other RTT Slow Start Window (WND) is increased for every RTT = (expected actual) RTT < α (α =1), WND linearly increases > β (β =3), WND linearly decreases expected = WND/RTT actual = WND/RTT RTT base RTT base Packet losses signal congestion Timeout WND = 1 Duplicate ACKs (Fast Retransmit) WND = WND/2 13 Simulation Model DPCH Node UE1 RNC SGSN B GGSN 622 Mb/s, 0.2 ms UE2 DPCH Internet Model Loss = 0% Delay 0s Assumptions: analyze the impact of the radio interface UMTS Core Network and Internet: loss = 0% propagation delay 0s ns - UMTS Nodes Host ns - traditional Nodes 14 7

8 Simulation Parameters Application TCP PDCP RLC MAC PHY File Transfer Protocol (FTP) TCP Variants Window Size (Segments) Maximum Segment Size (Bytes) TCP Header Size (Bytes) Header Size (Bytes) Packet Loss Rate in the Internet TCP/ Header compression RLC Mode Window Size (Blocks) Payload Size (Bits) RLC Header (Bits) MAC Header (Bits) MAC Multiplexing Physical Channel Type Transport Block Size (Bits) Transport BLER Error Model Vegas and Reno % No Acknowledged Mode with In-sequence delivery Not required for DPCH Bit Rate (kb/s) % Uplink TTI (ms) 20 Uniform Distribution DPCH Bit Rate (kb/s) Downlink TTI (ms) Packet Transfer Scenario Header (20 Bytes) TCP Header (20 Bytes) TCP Payload (512 Bytes) PDCP RLC PDCP Header (1 Byte) RLC Payload (40 Bytes) RLC Header (2 Bytes) MAC MAC Header 0 bit for DCH 3 Bytes for FACH/RACH PHY CRC (2 Bytes) 16 8

9 Throughput vs. BLER (FTP Traffic) Reno Vegas 17 TCP Vegas and Reno Congestion Window 384 kb/s, 5% TBLER Reno Vegas 18 9

10 TCP Vegas Round-Trip Time Variability 384 kb/s, 5% TBLER 19 Mobile Video Streaming Streaming: multimedia content is played out without downloading a complete file Traffic characteristics: video video time-sensitive tolerate lost/erroneous packets data delay-insensitive error-free packets 20 10

11 Streaming Video Model Video Clips (Raw) MPEG-4 Encoder Trace File Encoded Video (Original) Network Simulator (ns-2) Post- Simulation Processing Log File Encoded Video (Received) Video Clips (Reconstructed) MPEG-4 Decoder 21 Demo Music clip Container clip 22 11

12 Summary UMTS/WCDMA radio interface gives large round-trip time variations RLC retransmission Transmission time interval Vegas congestion control is very sensitive to the large round-trip time variations: throughput degradation sender window shrinks (but no congestion!) spurious timeout Reno s congestion control is insensitive to the large round-trip time variations Performance as expected MPEG-4 video streaming RLC retransmission achieves better quality Adaptive and fast RLC ARQ scheme for video 23 12