void
rrToWire(DNSOutput out, Compression c, boolean canonical) {
	host.toWire(out, c, canonical);
	admin.toWire(out, c, canonical);
	out.writeU32(serial);
	out.writeU32(refresh);
	out.writeU32(retry);
	out.writeU32(expire);
	out.writeU32(minimum);
}
Returns the minimum TTL for records in the zone
src/main/java/core/org/xbill/DNS/SOARecord.java