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 Work in 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 Incoming traffic 6 m/s Service rate 6 m/s Non-guaranteed service: 90% m/s

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

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 managers 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