1) Initial request REGISTER sip:home.mobile.biz SIP/2.0 2) Response containing a challenge SIP/2.0 401 Unauthorized WWW-Authenticate: Digest realm="RoamingUsers@mobile.biz", nonce="CjPk9mRqNuT25eRkajM09uTl9nM09uTl9nMz5OX25PZz==", qop="auth,auth-int", opaque="5ccc069c403ebaf9f0171e9517f40e41", algorithm=AKAv1-MD5 3) Request containing credentials REGISTER sip:home.mobile.biz SIP/2.0 Authorization..