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

Content What is GPRS ? What is QoS? Characteristics of proposed protocols. Conclusion. Questions ?

GPRS- General Packet Radio Service GPRS is a Global System for Mobile communications (GSM) service that provides mobile subscribers with performance guaranteed packet data services over GSM radio channels and external packet data networks. Base Station (BS) Mobile Station (MS 1 ) MS 2 Uplink Downlink Uplink MS 3 MS 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, )

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

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.

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

GQ-MAC – Slotted Aloha Send request on first available time slot. If collision then send on the next slot with probability P a.. 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) =R n e -R / n! ; Pr(0) = Pr[no collision] = e -R => P a = e -R ● Total throughput is therefore: T = Re -R = t λ e - tz

GQ-MAC –Tree Limited Contention Protocol e  Collision, 0  Idle, 1  Success Maximum Contention Resolution Period = TDMA_FRAME_LENGTH * (2 (log 2 j + 1) – 1) j=no. of conversational MS’s contending for access simultaneously Success LRRR Success LRRL Success LRL Success LL Idle R Collison S Collision L Collision LR Collision LRR SlotTransmitWaitingFeedback 1S-e 2LRe 3LLLR,R1 4LRRe 5LRLLRR,R1 6LRRRe 7LRRLLRRR, R1 8LRRRR1 9R-0

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.

GQ-MAC –Modified Slotted Aloha  L U is a fixed upper threshold   proportional to ADR/RDR 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

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.

GQ-MAC - Conversational and Interactive packet dropping probability

GQ-MAC - Conversational and Interactive access time Conversational and Interactive average packet delay depicted trend similar to above

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.

PH-CAC- What does it do? Supports handoff’s from multiple traffic classes. Guard channel concept is 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.

PH-CAC H2H1, H2H1, H2, N N G1 NTNT N G2 0 Number of Free Channels 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 N G2 N-New calls --- (lowest priority) : admitted only when the number of free channels exceeds N G1 N G2, N G1 - Guard Channels ; N T – Total number of channels

PH-CAC BNBN B H2 B H1 H1 H2 N H1, H2H1, H2, N N G1 NTNT N G2 0 µ Arrival rates: H2, H1, N ; Depature rate: µ Blocking probabilities: B H2, B H1, B N B H1 =Σ P j, j= N T -N G2 to j =N T ; B N =Σ P j, j= N T -N G1 to j =N T ; B H2 =P N T P j is poisson probability distribution

PH-CAC Simulation: To test how the guard channels (N G1 and N G2 ) are adaptively varied to satisfy targeted values of B H1 and B H2 under stationary traffic Hard target is set for B H2 (≤ 0.003) Calculate min (N G1, N G2 ), which can achieve this target Effect on blocking probabilities B H1, B N for different values of H2, H1, N. N T =50, 1/ µ =120s

PH-CAC (B H2  0.003) λ N = 0.05, λ H1 = 0.02 λ N = 0.05, λ H1 = 0.05 λ N = 0.05, λ H1 = 0.08 λ N = 0.1, λ H1 = 0.02λ N = 0.1, λ H1 = 0.05λ N = 0.1, λ H1 = 0.08 B H2 A B It can be seen that for an increase in lamdaH2 from 0.16 at ’A’(green circle) to 0.17 at ‘B’(red circle), the PH-CAC module adapts to this change by increasing the guard threshold, N G2, thus reducing B H2 from 2.75x10 -3 to 2.3x10 -3.

PH-CAC (B H2  0.003) λ N = 0.05, λ H1 = 0.02 λ N = 0.05, λ H1 = 0.05 λ N = 0.05, λ H1 = 0.08 λ N = 0.1, λ H1 = 0.02λ N = 0.1, λ H1 = 0.05λ N = 0.1, λ H1 = 0.08 BNBN BH1BH1 A B A B The increase in N G2 has only minimal effect on B N and B H1, which increased slightly from their original values. Degradation at higher values of lamdaH2 -- saturation

Conclusion Performance analysis of the GQ-MAC protocol shows that it is capable of providing guaranteed QoS performances for streaming, conversational, interactive and background traffic classes over GPRS wireless links while optimizing channel resource utilization. Performance analysis of the PH-CAC protocol shows that it is capable of maintaining QoS performance guarantees under the effect of mobile handoffs by providing dynamic adaptive prioritized admission control for multiple traffic classes via the multiple dynamic guard channel scheme

QUESTIONS ?