Modeling and simulation of SIP tandem server with finite buffer

Abstract

Recent collapses of SIP servers (e.g., Skype outage) indicate that the built-in SIP overload control mechanism cannot mitigate overload effectively. We introduce our analytical approach by investigating an overloaded tandem server scenario. Our analytical model: (1) considers a general case that both arrival rate and service rate for signaling messages are generic random processes; (2) makes a detailed analysis of departure processes; (3) allows us to run fluid-based simulations to observe and analyze SIP system performance under some specific scenarios. This approach is much faster than event-driven simulation which needs to track thousands of retransmission timers for outstanding messages and may crash a simulator due to limited computing resources. Our numerical results help us reach a counterintuitive conclusion: A SIP system with a large buffer size may continuously exhibit overload and long queuing delay after experiencing a short period of demand burst or a temporary server slowdown. Small buffer size, on the other hand, can mitigate overload quickly by rejecting a large portion of the requests from a demand burst, and then resume normal operation after a short period of time. Furthermore, numerical results demonstrate that overload at a downstream server may propagate or migrate to its upstream servers and therefore cause widespread server crashes in a real SIP network. ACM Reference Format:Hong, Y., Huang, C., and Yan, J. 2011. Modeling and simulation of SIP tandem server with finite buffer. ACM Trans. Model.

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“…-Retransmission rate variation: These methods review retransmission mechanism of SIP by studying servers' buffer size [8,20]. By limiting the dedicated memory of the server, admitting over-capacity calls can be avoided.…”

“…The setback of such methods is scalability and high delay. Further, congestion in TCP occurs due to limited bandwidth, whereas overload in SIP happens due to limited processing capacity of servers' CPU [8].…”

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“…To this end, it needs to provide reliability by retransmission of the messages with unconfirmed delivery [5]. In this state, a large set of retransmission timers are employed [2,4]. Although this mechanism is useful in case of unreliable links, under the overload conditions, it imposes high loads to the server and decreases its efficiency [4] 1 .…”

Overload Control in SIP Networks: A Heuristic Approach Based on Mathematical Optimization

“…However, problems such as scalability and high delay hinder use of this protocol. Furthermore, the congestion designed for TCP control mechanism occurs due to limited bandwidth, whereas the overload in SIP is caused by the limited processing capacity of servers' CPU [4].…”