
13
SIP–DNS interaction
extended email-like domain resolution ➠ try until success:
1. try SRV DNS record for “
sip. udp” and “ sip. tcp” in domain, with
priority and weights for randomized load balancing
2. DNS CNAME or A record
3. may try SMTP EXPN command to get new address; goto (1)
4. if all else fails, send SIP request via MIME
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