http://windowsbtpro.blogspot.com/2010/12/sip-trunking-between-avaya-ipo500-and.html

http://www.tek-tips.com/faqs.cfm?fid=7248

http://www.valcom.com/techsupport/config-docs/Avaya%20IPOffice%20SIP%20Trunk%20Configuration%20Guide.pdf