att_abstract={{A back-to-back user agent (B2BUA) is a powerful mechanism for realizing
complex SIP applications. The ability to create, terminate, and modify SIP
dialogs allows the creation of arbitrarily complex services. However, B2BUAs
must be designed with care so as not to disrupt service interoperability. A
commonly-stated goal is for B2BUAs to be as {it transparent} as possible
while achieving its design goals. Though the notion of transparency is
intuitively appealing, it is difficult to define. To address this issue,
this paper proposes a definition of transparency and
presents a formal model of a transparent B2BUA to serve as the
specification of transparency.  From this specification, we identify issues
with both the realizability and desirability of this behavior, and suggest
modifications to the original model.  We evaluate the behavior of a number of
public B2BUA implementations via testing, using some novel techniques to
create test cases based on the formal models.}},
	att_authors={gb2191, ec1916, ts2732, pz2728},
	att_copyright_notice={{(c) ACM, 2010. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution.
The definitive version was published in Proc. of the 4th International Conference on Principles, Systems, and Applications of IP {{, 2010-08-02}}.	}},
	author={Gregory Bond and Eric Cheung and Thomas Smith and Pamela Zave},
	institution={{4th International Conference on Principles, Systems and Applications of IP Telecommunications}},
	title={{Specification and evaluation of transparent behavior for SIP back-to-back user agents}},