M. Ohta (Japan)
SIP, IP Telephony, Simulation and Modeling, Traffic management, Communication Protocol
Performance of Session Initiation Protocol (SIP), which is used for IP telephony or multimedia conferences, is studied using the network simulator (ns-2). In order to evaluate SIP, we have developed new types of agents which act as SIP user agents and SIP proxies in ns-2. The paper shows traffic characteristics of SIP signaling in an overload condition. Usually, throughput of SIP signaling increases in pro portion to offered load. However, once offered load ex ceeds a threshold, throughput shows catastrophic degrada tion. Finally, throughput becomes almost 0. This degrada tion comes from the retransmission strategy of SIP. Accord ing to RFC3261, a request in SIP should be retransmitted when an agent does not receive any response within a pre determined interval. This retransmission increases rate of sending packets, and stimulates another retransmissions in a network. Finally, the network falls in a congestion. To prevent the congestion, we introduce a silent in terval in which user agents are inhibited from transmitting any SIP request. The simulation results show that the silent interval improves the performance in overload conditions
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