\begin{thebibliography}{1}

\bibitem{rfc3261}
J.~Rosenberg, H.~Schulzrinne, G.~Camarillo, A.~Johnston, J.~Peterson,
  R.~Sparks, M.~Handley, and E.~Schooler, \htmladdnormallink{``{SIP:} session
  initiation protocol,''}{http://www.rfc-editor.org/rfc/rfc3261.txt} RFC 3261,
  Internet Engineering Task Force, June 2002.

\bibitem{rfc2119}
S.~Bradner, \htmladdnormallink{``Key words for use in {RFCs} to indicate
  requirement levels,''}{http://www.rfc-editor.org/rfc/rfc2119.txt} RFC 2119,
  Internet Engineering Task Force, Mar. 1997.

\bibitem{rfc3264}
J.~Rosenberg and H.~Schulzrinne, \htmladdnormallink{``An offer/answer model
  with session description protocol
  {(SDP)},''}{http://www.rfc-editor.org/rfc/rfc3264.txt} RFC 3264, Internet
  Engineering Task Force, June 2002.

\end{thebibliography}
