AASTRA 6700i series, 9143, 9480i, 9480i CT SIP Administrator Guide EN - Manual (Page 671)

6-44 41-001343-01 Rev 03, Release 3.2.2
1 SRV & A The phone issues requests for “SRV” (Service Location Record)
records from the DNS server to get the port number. Most often,
the IP address is included in the response from the DNS server to
avoid extra queries. If there is no IP address returned in the
response, the phones send out the request for “A” records from the
DNS server to find the IP address.
2 NAPTR & SRV & A First, the phone sends "NAPTR" (Naming Authority Pointer) lookup
to get the “SRV” pointer and service type. For example, if Global
SIP transport protocol on the phone is “UDP”, and Proxy server on
the phone is “test.aastra.com”, then:
1 If the NAPTR record is returned empty, the phone will use the
default value “_sip._udp.test.aastra.com" for the “SRV” lookup.
2 If the NAPTR record is returned "test.aastra.com SIP+D2U ....
_sip._udp.abc.aastra.co m", the phone will use
“_sip._udp.abc.aastra.com" for the “SRV” lookup.
3 If the NAPTR record is returned "test.aastra.com SIP+D2T ....
_sip._tcp.test.aastra.com", where the service type TCP
mismatches the phone configured transport protocol “UDP”,
the phone will ignore this value and use the default value
“_sip._udp.test.aastra.com" for the “SRV” lookup.
Note: The phone does not use the service type sent by the NAPTR
response to switch its transport protocol, nor does it use the
NAPTR response to determine whether to use a secure or
unsecure communication path. The phone will always use a global
sip protocol that is configured on the phone via configuration files
or the web user interface.
After performing NAPTR, the phone sends “SRV” lookup to get the
IP address and port number. If there is no IP address in the “SRV”
response, then it sends out an “A” lookup to get it.
Note: On the phone side, if you configure the phone with a Fully-
Qualified Domain Name (FQDN) proxy and specified port, the phone
always sends “A only” lookups to find the Host IP Address of the proxy.
Configuration
File Value DNS Server
Method Used
Description