The format of DNS SRV queries for sip (RFC 3263) and H.323 used by Expressway are: _sips._tcp.<fully.qualified.domain> _sip._tcp.<fully.qualified.domain> _sip._udp.<fully.qualified.domain> - not recommended for video calls, only use for audio-only calls _h323ls._udp.<fully.qualified.domain> - for UDP location (RAS) signaling, such as LRQ _h323cs._tcp.<fully.qualified.domain> - for H.323 call signaling The format of DNS SRV queries for sip (RFC 3263) and H.323 typically used by an endpoint are: _sips._tcp.<fully.qualified.domain> _sip._tcp.<fully.qualified.domain> _sip._udp.<fully.qualified.domain> - not recommended for video calls, only use for audio-only calls _h323ls._udp.<fully.qualified.domain> - for UDP location (RAS) signaling, such as LRQ _h323cs._tcp.<fully.qualified.domain> - for H.323 call signaling _h323rs._udp.<fully.qualified.domain> - for H.323 registrations