QoS Guaranteed Provisioning over GPRS Wireless Mobile Links

1. QoS Guaranteed Provisioning over GPRS Wireless Mobile Links Benjamin ESHUN MSc CCN INT France

2. Content • What is GPRS ? • What is QoS? • Characteristics of proposed protocols. • Conclusion. • Questions ? ben@benjamineshun.de

3. GPRS- General Packet Radio Service GPRS is a Global Systemfor Mobile communications (GSM) service that providesmobile subscribers with performance guaranteed packet dataservices over GSM radio channels and external packet datanetworks. Mobile Station (MS1) Downlink Uplink MS2 Uplink MS4 Uplink MS3 Base Station (BS) ben@benjamineshun.de

4. Quality of Service (QoS) • QoS is a mechanism that provides a level of assurance • that ensures that a service or application can be delivered to the end-user in a satisfactory time frame • Qos Profile is defined in terms of precidence, delay, reliability, mean and peak throughput. These are classified into; • Streaming traffic – (e.g. Video, Music) • Conversational traffic – (e.g. Voice) • Interactive traffic – (e.g. Telnet, rlogin) • Background traffic – (e.g. FTP, Email) ben@benjamineshun.de

5. Problem • Demand – Assignment mechanism? • GQ-MAC (Guaranteed QoS Media Access Control) protocol(enables performance guarantees for the four defined QoS classes ) • How to handle Hand-off’s with multiple classes? • PH-CAC (Prioritized Handoff Call Admission Control) protocol(differentiates handoff requests with diffrent higher admission priorities over new calls via a multiple guard channels scheme) • A MAC protocol distributes packet transmission over a shared medium among all users • CAC protocol aims to maximize the number of admitted traffic sources while guaranteeing their QoS requirements ben@benjamineshun.de

6. GQ-MAC – What does it do? • Supports multiple traffic classes like: Streaming, Conversational, Interactive, Background (Best Effort). • Guaranteed bandwidth and bounded jitter for streaming traffic type. • Guaranteed bounded channel access delay for delay sensitive conversational traffic. • Average throughput guarantees for Interactive traffic. • Support for background traffic. • Bounded packet loss probability for loss sensitive traffic. ben@benjamineshun.de

7. In-Session calls (Tree Protocol& Modified Slotted Aloha) New & Handoff calls (Slotted Aloha) GQ-MAC – Channel Division and MAC Downlink Channels Uplink Channels Control Channel (Acknowledgement & Resource Allocation) Control Channel (Random Access) Traffic Channels (Payload) Traffic Channels (Payload) ben@benjamineshun.de

8. GQ-MAC – Slotted Aloha • Send request on first available time slot. • If collision then send on the next slot with probability Pa.. • Higher probability allocated to handoff calls. What is the efficiency of this approach? ● Assume fixed packet transmission time t ● Assume Poisson packet transmissions at rate of λ packets/sec ● Channel utilization R = t λ Total Throughput is calculated as: ● the time interval during which a collision might occur is t ●Probability of n packets being generated during an interval of t is: Pr(n) =Rn e -R / n! ; Pr(0) = Pr[no collision] = e-R => Pa= e-R ●Total throughput is therefore: T = Re-R = t λ e - tz ben@benjamineshun.de

9. GQ-MAC –Tree Limited Contention Protocol Maximum Contention Resolution Period = TDMA_FRAME_LENGTH * (2(log2j + 1) – 1)j=no. of conversational MS’s contending for access simultaneously e  Collision, 0  Idle, 1  Success SuccessLRRL SuccessLRRR SuccessLRL CollisionLRR SuccessLL CollisionLR Idle R CollisionL Collison S ben@benjamineshun.de

10. GQ-MAC – Conversational • Demand channel on activity, and relinquish when inactive. • Channel demands are sent on the random access channel using tree limited contention protocol. • If no channels are available • Check if any interactive source is using the channel and reallocate this to the current conversational user. • If all channels are occupied by conversational users then drop a packet and restart channel access procedure. ben@benjamineshun.de

11. GQ-MAC –Modified Slotted Aloha • Similar to Slotted Aloha except when collision occurs Pa =P(x) • P(x) reduces Pa by 0.5 in the next slot for every 8 maximum retries • Pa = P(x) = 0 if there is contention resolution cycle in progress – ie interractive MS’s does not parcipate in the cycle • Higher priority is given to MS’s that have not been able to achieved RDR to send RRP • LU is a fixed upper threshold • proportional to ADR/RDR ben@benjamineshun.de

12. GQ-MAC –Interactive • Demand channel on activity, and relinquish when inactive. • Channel demands sent on the random access channels using modified slotted ALOHA protocol. • If no channels are available • Check if any interactive source has achieved the QoS it has requested, and if so reallocate the channel to this user. • If all channels occupied by conversational users then buffer the packet and restart channel access procedure. ben@benjamineshun.de

13. GQ-MAC - Conversational and Interactive packet dropping probability ben@benjamineshun.de

14. GQ-MAC - Conversational and Interactive access time • Conversational and Interactive average packet delay • depicted trend similar to above ben@benjamineshun.de

15. GQ-MAC – Streaming and Background • Streaming is provided as a dedicated service in multiples of quantized data rates. (e.g. - For a streaming rate X ; one full Traffic channel is allocated - For rate 0.5X ; only half of the traffic chanel is allocated by a slot in every alternate frame ) • Similar to a circuit switched service, with flexible bandwidth allocation. • MS sends a request on the random access channel only during Call Initiation. Thus, once admitted it is guaranteed a bounded packet delay, constant inter-packet delay and guaranteed throughput. • Background service provided by allocating unused uplink Traffic channels to users in a round-robin fashion. ben@benjamineshun.de

16. PH-CAC- What does it do? • Supports handoff’s from multiple traffic classes. • Guard channel conceptis used to support multiple admission priorities for handoffs. • Blocking probabilities for different traffic classes can be calculated using poission arrival and departure rates • Why “Adaptive” and “Prioritized”? • “Adaptive” because both over-provisioning and under-provisioning is prevented. • “Prioritized” because handoff are differentiated according to the service requested. ben@benjamineshun.de

17. PH-CAC H2 H1, H2 H1, H2, N 0 NT Number of Free Channels NG2 NG1 • H2-Handoff’s ---Streaming Class (highest priority) : • admitted whenever a free channel is available • H1-Handoff’s ---Conversational, Interactive, Background classes : • admitted only when the number of free channels exceeds NG2 • N-New calls --- (lowest priority) : • admitted only when the number of free channels exceeds NG1 • NG2 , NG1 - Guard Channels;NT– Total number of channels ben@benjamineshun.de

18. PH-CAC H2 BH2 µ H2 H1, H2 H1, H2, N BH1 H1 0 NT NG2 NG1 BN N Arrival rates: H2,H1, N;Depature rate:µBlocking probabilities: BH2, BH1,BN BH1=ΣPj , j=NT-NG2toj=NT ; BN=ΣPj , j=NT-NG1 toj=NT ; BH2=PNT Pjis poisson probability distribution ben@benjamineshun.de

19. PH-CAC Simulation: To test how the guardchannels (NG1 and NG2) are adaptively varied to satisfytargeted values of BH1 andBH2 under stationary traffic • Hard target is set for BH2(≤ 0.003) • Calculate min (NG1, NG2), which can achieve this target • Effect on blocking probabilities BH1, BNfor different values ofH2,H1, N. NT=50, 1/ µ =120s ben@benjamineshun.de

20. λN = 0.05, λH1 = 0.08 λN = 0.05, λH1 = 0.05 λN = 0.05, λH1 = 0.02 λN = 0.1, λH1 = 0.02 λN = 0.1, λH1 = 0.05 λN = 0.1, λH1 = 0.08 PH-CAC (BH2 0.003) BH2 It can be seen that for an increase in lamdaH2 from 0.16 at ’A’(green circle) to0.17 at ‘B’(red circle), the PH-CAC module adapts to this change byincreasing the guard threshold, NG2, thus reducing BH2 from 2.75x10-3 to 2.3x10-3. A B ben@benjamineshun.de

21. λN = 0.05, λH1 = 0.08 λN = 0.05, λH1 = 0.05 λN = 0.05, λH1 = 0.02 λN = 0.1, λH1 = 0.02 λN = 0.1, λH1 = 0.05 λN = 0.1, λH1 = 0.08 • Theincrease in NG2 has only minimal effect on BN and BH1, whichincreased slightly from their original values. • Degradationat higher values of lamdaH2 -- saturation PH-CAC (BH2 0.003) BH1 BN A B A B ben@benjamineshun.de

22. Conclusion • Performance analysis of the GQ-MAC protocol shows thatit is capable of providing guaranteed QoS performances forstreaming, conversational, interactive and background trafficclasses over GPRS wireless links while optimizing channelresource utilization. • Performance analysis of the PH-CACprotocol shows that it is capable of maintaining QoSperformance guarantees under the effect of mobile handoffsby providing dynamic adaptive prioritized admission controlfor multiple traffic classes via the multiple dynamic guardchannel scheme ben@benjamineshun.de

23. QUESTIONS ? ben@benjamineshun.de