  Having facilities such as being in text form, end-to-end connection
establishment, and being independence from the type of transmitted data, SIP
protocol is a good choice for signaling protocol in order to set up a
connection between two users of an IP network. Although utilization of SIP
protocol in a wide range of applications has made various vulnerabilities in
this protocol, amongst which overload could make serious problems in SIP
servers. A SIP is overloaded when it does not have sufficient resources
(majorly CPU processing power and memory) to process all messages. In this
paper the window-based overload control mechanism which does not require
explicit feedback is developed and implemented on Asterisk open source proxy
and evaluated. The results of implementation show that this method could
practically maintain throughput in case of overload. As we know this is the
only overload control method which is implemented on a real platform without
using explicit feedback. The results show that the under load server maintains
its throughput at the maximum capacity.
