Policy-based Congestion Management for an SMS Gateway

1. Policy-based Congestion Management for an SMS Gateway Alberto Gonzalez (KTH) Roberto Cosenza (Infoflex) Rolf Stadler (KTH) June 8, 2004, Policy Workshop

2. Outline • Intro to SMS • Congestion Management in SMSG • Policy-based Approach • System Behavior • Future Work

3. The Short Message Service (SMS) • SMS is based on out-of-band message delivery. It permits users to send and receive text messages to/from their mobile phones • Relevance • By the end of 2002, 30 billion messages exchanged monthly • Growing at 0.5 billions per month. • SMS represents 10% of the revenue of mobile operators • We consider two classes of SMS services • Guaranteed service (zero losses) • Non-guarateed service • Bulk messages, information services

4. SMS Architecture

5. SMS Gateway Model

6. Congestion in a SMS Gateway • Congestion can be caused by a persistent performance degradation of an outgoing port • Why do we need congestion management ? • long buffers suppose a risk. The longer the queue, the higher the cost of a system crash • The focus of this work is to provide the EMG with congestion management capabilities that permit us to adapt dynamically to congestion

7. Related Workin Congestion Management • Congestion management in routing engines has been extensively studied in the context of IP routers • Our work differs from that field in • Problem space: congestion management for IP routers considers physical networks. In contrast, an SMSG is a node in an overlay network, where the service rate of outgoing ports can vary, depending on the state of neighboring SMSGs • Solution space: approaches to congestion management in IP networks often focus on flows. In contrast, flow-based mechanisms are not relevant in the SMS context, since an SMS message fits into a single packet

8. Addressing congestion in the EMG • Two low-level mechanisms for reducing the load on a congested port • reducing the acceptance rate • this reduction affects the loads on all outgoing ports. Therefore the overall throughput of the EMG is compromised • dropping non-guaranteed messages that are routed to its associated queue • They present a trade-off • Throughput vs losses • The EMG manager has to choose between giving priority to: • having low losses • having high throughput.

9. Functional Architecture for Realizing Congestion Control Policies

10. System behavior: unbalanced load m/s • Incoming traffic 6 m/s • Service rate 6 m/s • Non-guaranteed service: 90%

11. System behavior: balanced load m/s • Incoming traffic 6 m/s • Service rate 6 m/s • Non-guaranteed service: 90%

12. Summary • Our architecture permits the EMG manager to control the tradeoff between high throughput of the EMG and low loss rate of the non-guaranteed service class • In situations of congestion and changes in load pattern, the system dynamically re-configures, following the manager’s selected policy • Our proposal does not need other SMSGs/SMSCs to include any type of congestion management

13. Future Work • Service differentiation based on message sender, message content, etc • Different algorithms for parameter estimation • Prototype evaluation using real traces