Yealink SIP-T48G Administrator's Manual page 409

6. Click Confirm to accept the change.
Note
If the outbound proxy server is required and the transport is set to DNS-NAPTR, you must
set the port of outbound proxy server to 0 for NAPTR, SRV and A queries.
If a domain name is configured for a SIP server, the IP address(es) associated with that
domain name will be resolved through DNS as specified by RFC 3263. The DNS query
involves NAPTR, SRV and A queries, which allows the IP phone to adapt to various
deployment environments. The IP phone performs NAPTR query for the NAPTR pointer
and transport protocol (UDP , TCP and TLS), the SRV query on the record returned from
the NAPTR for the target domain name and the port number, and the A query for the IP
addresses.
If an explicit port (except 0) is specified, A query will be performed only. If a SIP server
port is set to 0 and the transport type is set to DNS-NAPTR, NAPTR and SRV queries will
be tried before falling to A query. If no port is found through the DNS query, 5060 will be
used.
The following details the procedures of DNS query for the IP phone to resolve the
domain name (e.g., yealink.pbx.com) of working server into the IP address, port and
transport protocol.
NAPTR (Naming Authority Pointer)
First, the IP phone sends NAPTR query to get the NAPTR pointer and transport protocol.
Example of NAPTR records:
order
IN NAPTR 90
IN NAPTR 100
Parameters are explained in the following table:
Parameter
order
pref
Flags
service
pref flags service
50 "s" "SIP+D2T"
50 "s" "SIP+D2U"
Specify preferential treatment for the specific record. The order
is from lowest to highest, lower order is more preferred.
Specify the preference for processing multiple NAPTR records
with the same order value. Lower value is more preferred.
The flag "s" means to perform an SRV lookup.
Specify the transport protocols:
SIP+D2U: SIP over UDP
SIP+D2T: SIP over TCP
Configuring Advanced Features
regexp replacement
"" _sip._tcp.yealink.pbx.com
"" _sip._udp.yealink.pbx.com
Description
395