Measurements of SIP signaling over 802.11b links

Abstract

The Session Initiation Protocol (SIP) is a popular application-level signaling protocol that is used for a wide variety of applications such as session control and mobility handling. In some of these applications, the exchange of SIP messages is time-critical, for instance when SIP is used to handle mobility for voice over IP sessions. SIP may however introduce significant delays when it runs on top of UDP over lossy (wireless) links. These delays are the result of the exponential back-off retransmission scheme that SIP uses to recover from packet loss, which has a default back-off time of half a second.In this paper, we empirically investigate the delay introduced by SIP when it runs on top of UDP over IEEE 802.11b links. We focus on the operation of SIP at the edge of an 802.11b cell (e.g., to update a mobile host's IP address after a handoff) as this is where SIP's retransmissions scheme is most likely to come into play. We experiment with a few 802.11 parameters that influence packet loss on the wireless link, specifically with different link-level retransmission thresholds, signal-to-noise-ratios (SNRs), and amounts of background traffic. We conduct these experiments in a controlled environment that is free from interfering 802.11 sources.Our results indicate that (1) SIP usually introduces little delay except for an SNR range of a few dBs at the very edge of an 802.11 cell in which the delay increases sharply, and (2) that a maximum of four 802.11 retransmissions suffices to limit the delay introduced by SIP retransmissions. The first result is of interest to developers of SIP applications who have to decide at which SNR to initiate a handoff to another network. The second result allows network providers to optimize their 802.11b networks for delay sensitive SIP applications.

Benchmark of middleware protocols for application and service interaction

“…The average latency of SIP transactions over UDP was reported as 25-90 ms between a SIP client and a SIP server [3]. The gap could be explained by the different link technologies used, and the presence of background traffic in [3]. IMS seems to produce more overhead to SIP [5], when compared to our results based on standard SIP.…”

“…The SI P MESSA GE has been defined, for carrying MIME-based content in instant messages between SIP User Agents (SIP UA) and SIP Servers. The earlier SIP performance studies have mostly concentrated on the latency of call/video session setup over 802.11b WLAN [3], on Javaplatform [4] and in the Internet Multimedia Subsystem (IMS) enabled 3G network [5].…”

“…However, the call setup in [4] is probably composed of 1.5 RTTs (INVITE, 200 OK, ACK) as opposed to one RTT in our study. The average latency of SIP transactions over UDP was reported as 25-90 ms between a SIP client and a SIP server [3]. The gap could be explained by the different link technologies used, and the presence of background traffic in [3].…”

Security study of voice communication over wireless local area network

“…QoS issues of WVoIP have been widely studied [6][7][8][9], and security issues are rarely addressed. Among WVoIP security issues, DoS attack is the worst one.…”

A reality check on sip-based streaming applications on the next generation mobile test network

“…There are various related-work where the measurements are made on a controlled test bed setup or in a simulated environment [3], [4], [5]. Unlike the above mentioned work, the experiments presented in the paper are conducted in an uncontrolled environment with the test network connected to the live mobile operator network.…”