Connecting two Asterisk box via SIP


I managed to connect two Asterisk box via SIP. My problem is when I login using Realtime SIP, I will get

chan_sip.c:8373 check_auth: username mismatch, have <100778208>, digest has <hk_asterisk>

Failed to authenticate user “unknown” sip:100778208@x.x.x.x;tag=as47a2c05a

when trying to send call to the 2nd server.

but when I login using sip.conf setting I managed to send call to the 2nd server with no errors. Any ideas?