A Dynamic Buffer Management Scheme for End-to-end QoS Enhancement of Multi-flow Services in HSDPA

1. A Dynamic Buffer Management Scheme for End-to-end QoS Enhancement of Multi-flow Services in HSDPA Suleiman Y. Yerima, Khalid Al-Begain Integrated Communications Research Centre Faculty of Advanced Technology University of Glamorgan

2. Outline • HSDPA overview • TSP queuing and BM schemes • Time-space priority BM • Dynamic Time-space priority BM • Simulation model • Results • Conclusions 2NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

3. External Network Core Network User Equipments Iub interface Radio Network Controller Node B HSDPA CELL HSDPA Overview • High Speed Downlink Packet Access (HSDPA): • 3GPP Enhancements to UMTS (3G) RAN • Higher Peak data rate: up to 14Mbps • Lower connection and response times • 3-5 X capacity increase Three interacting domains: • Core Network • Radio Access Network (RAN) • User Equipment (UE) 3NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

4. External Network Core Network User Equipments Iub interface Radio Network Controller Node B HSDPA CELL HSDPA Overview • New PHY & MAC enhancements in Node B: • New MAC-hs layer in Node B • High-Speed downlink Shared Channel • Link adaptation (AMC) • Packet Scheduling (PS) • L1 retransmissions (HARQ) • Shorter Transmission interval (2ms) 4NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

5. motivation: • Emergence of multiple flow traffic profile per user/connection • Existing HSDPA QoS mechanisms single flow based • E.g. MAC-hs Packet Scheduling (PS) • Node B buffering • No BM schemes in standards- open issue 5NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

6. motivation (contd.) • The most challenging multiple flow scenario is connections with RT and NRT flows (conflicting QoS requirements) e.g. Voice + file download • RT flow -> delay, jitter sensitive & loss tolerance • NRT flow-> loss sensitivity & delay, jitter tolerance • Hence our proposed MAC-hs BM schemes based on Time-Space Priority (TSP) queuing model 6NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

7. TSP threshold RTC flow Service process NRTC flow Transmission to user terminal TSP queuing model • Typical priority queuing models are either loss or delay differentiated • Our Time-space priority queuing model (TSP): • Single queue with hybrid differentiation • Loss differentiated • delay differentiated • RTC packets: • High priority delay • Low priority loss • NRTC packets • High priority loss • low priority delay • Hence RTC => preferential transmission • NRTC =>preferential buffer admission 7NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

8. TSP advantages • Efficient buffer utilization • Most viable for joint RTC and NRTC QoS control compared to typical priority queuing approaches • Hence we designed an efficient TSP-based BM scheme for HSDPA • Exploiting existing mechanisms in HSDPA specs. 8NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

9. TCP Source UE Node B CN & EXTERNAL IP RNC HARQ ARQ TCP Air interface Iub interface RNC UE1 MAC-hs buffer UE1 N H Iub flow control L UE2 R Packet Scheduling UE1 RT flow UE1 NRT flow UE3 RNC Node B Capacity Request {Priority, User Buffer Size (UBS)} Capacity Allocation {Priority, Credits} HS-DSCH Frame {Priority, UBS, PDU size, #PDUs} TSP-based Buffer Mgt. in HSDPA Enhanced TSP with flow control thresholds • RNC sends MAC PDUs over Iub interface • Employs Iub signalling with credit allocation algorithm to mitigate buffer overflow • Employs Discard Timer for RTC • Higher layer protocol (ARQ, TCP) performance improvement 9NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

10. TSP-based BM in HSDPA Credit based FC algorithm: CTotal = CNRT + CRT CRT = (λRT / PDU_size) ∙ TTI CNRT = min { CNRTmax , RNCNRT } CNRTmax = (λ’NRT /PDU_size) ∙ TTI , N’T < L β ∙ (λ’NRT /PDU_size) ∙ TTI , L ≤ N’T ≤ H, 0 < β < 1 0 , N’T > H Where λ'NRT = α ∙ λ'NRT-1 + (1- α) ∙ λNRT is EWMA of Scheduler NRT data rate and N’T = θ ∙ NT-1 + θ ∙NT is an EWMA of total queue size 10NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

11. Enhanced TSP improves e2e NRTC throughput without compromising RT QoS • Problem: TSP has static delay prioritization • Potential NRTC bandwidth starvation • Non optimal ARQ and TCP performance • A possible solution: • Exploit possible RTC delay tolerance Hence we extend the TSP BM with Dynamic Time priority switching 11NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

12. RNC UE1 MAC-hs buffer UE1 N H Iub flow control L RT R NRT Packet Scheduling Priority switching D-TSP Incorporates delay Priority switching to TSP DTSP priority switching algorithm: IFRT packets < k AND RT HOL delay< MAX_delay AND NRT packets > 0 Time Priority = NRT flow Generate Transport Block from NRT PDUs ELSE Time Priority = RT flow Generate Transport Block from RT PDUs MAX_delay = Max e2e delay – other queuing and propagation delays k= Delay budget / RTC inter-arrival time Delay budget ≤ MAX_delay Discard timer (DT) setting = MAX_delay 12NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

13. User Equipments voice + data connection HSDPA CELL Core Network External Network Node B RNC 70ms 2ms 20ms HSPDA modelling • Detailed custom modelling with OPNET: • Multi-flowconnection: VoIP source, NRT source with TCP • Fixed external and Core Network delay assumed • RNC: Packet segmentation, RLC modes • Node B: AMC Link adaptation, HARQ, MAC-hs buffers, Packet scheduler • Receiver: SINR, HARQ, RLC modes, re-assembly queues, TCP 13NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

14. RNC Node B 70ms 2ms 20ms simulation set up • Concurrent VoIP + FTP for 180s • MAX_delay = 250 –( 70 – 20) = 160ms • BM config: R = 10, L =100, H= 150, N= 200 PDUs • DTSP params: k = 2, 4, 6, 8 • channel load: 1, 5, 10, 20, 30, 50 users • Performance metrics in test UE: • End-to-end NRTC throughput • Voice PDU discard ratio (Discard timer) • % HSDPA channel utilization 14NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

15. Results: UE1 Data download throughput (1 user) • Throughput at UE1 • DTSP and TSP show similar performance • Increased DB settings has marginal effect on throughput • very low HS-DSCH load hence no DTSP gain 15NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

16. Results: UE1 Data download throughput (5 users) • Throughput at UE1 • More load on HSDPA channel • Increased DB settings show noticeable improvement • DTSP performs better than TSP 16NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

17. Results: UE1 Data download throughput (10 users) • Throughput at UE1 • Higher load on HSDPA channel • Increased DB settings show noticeable improvement • DTSP performs better than TSP 17NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

18. Results: UE1 Data download throughput (20 users) • Throughput at UE1 • Higher load on HSDPA channel • Increased DB settings show noticeable improvement • DTSP performs better than TSP 18NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

19. Results: UE1 Data download throughput (30 users) • Throughput at UE1 • Higher load on HSDPA channel • Increased DB settings show noticeable improvement • DTSP performs better than TSP 19NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

20. Results: UE1 Data download throughput (50 users) • Throughput at UE1 • Higher load on HSDPA channel • Increased DB settings show noticeable improvement • DTSP performs better than TSP • performance peaks at k = 6 20NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

21. Results: Voice pdu discard ratio vs DB settings • Voice pdu discard loss • assuming max DR= 2% • In 1, 5, and 10 user scenarios VoIP QoS satisfied • Optimum k for 20 users = 6 • optimum k for 30 users = 4 • Optimum k for 50 users = 2 21NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

22. Results: HSDPA channel utilization vs DB settings • UE1 HSDPA channel utilization • Utilization constant in DTSP regardless of DB setting in 1 user scenario • channel utilization improves with higher load due to pdu bundling • DTSP has better channel utilization than TSP except at very low load ( e.g. 1 user scenario) 22NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

23. Conclusions and Summary • Conclusions: • DTSP achieves e-2-e throughput improvement for the multi-flow NRTC traffic • Better channel utilization is achieved with DTS P over TSP • Acceptable VoIP performance within QoS constraints Further work • Investigate with other Packet Scheduling • Investigate other possible multi-flow scenarios 23NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

24. Thank You!!! 24NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008