Ethereal Protocol Analyzer:
http://www.ethereal.comOpen H.323 Open source Freeware VoIP Implementations:
http://www.openh323.orgFree SIP Proxy service:
http://www.freeworldialup.comFree SIP Client X-Lite:
http://www.xten.comPartysip - Open Source SIP Proxy:
http://www.nongnu.org/partysip/Internet Traffic Report:
http://www.internettrafficreport.comLondon Internet Exchange Public Traffic Statistics:
http://www.linx.net/tools/stats/index.thtmlTechnology Frequency Allocations for Europe:
http://www.ero.dk/doc98/official/pdf/Rep025.pdfRFCs and IETF documents
: http://www.rfc-editor.org/