Technical Overview
42
DNS SRV
The phone supports the use of DNS SRV record lookups to allow SIP serv-
ers to be located. This mechanism is described in detail in RFC 3263 - Lo-
cating SIP Servers.
If the location to which a SIP message is to be sent is defined as a name
as opposed to an IP address a DNS SRV lookup will be performed. An ex-
ample query being:
_sip._tcp.example.com.
This indicates a query for a SIP server supporting the TCP transport proto-
col. The transport used in this query is determined by the SIP transport
menu setting
Æ
page 217. The DNS server may return an IP address for
the requested SIP server or may return a single name or list of names
which require further A or AAAA record lookups to determine an IP ad-
dress. The response to a DNS SRV query will also contain information re-
garding the Time To Live for the information returned, the port address to
which requests should be sent and weighting information relating to load
balancing of requests.
DNS SRV and failover
Lists of candidate SIP server names are often returned in response to DNS
SRV queries to allow failover mechanisms to be implemented which in-
crease overall system availability.
If the phone sends a request to the first address in the list but fails to re-
ceive a response (currently the failover time is 6 seconds, this is not con-
figurable) the address is placed in a "penalty box" which means that it will
not be tried again until a specific time interval has past (currently pre-set to
1 minute). The request is sent to the next SIP server in the list and the pro-
cess continues. The penalty box mechanism ensures that the responsive-
ness of the phone is maintained by not continually retrying SIP servers that
are failing to respond.
For example the request to the first SIP server in the list fails, a call to an-
other user hosted on the SIP server will result in the user experiencing a 6
second delay before the failover to the secondary occurs. This means the
"Calling.." status will remain on the display until the second SIP server is
contacted. All subsequent messages for this call will go to the second SIP
server until the first SIP server is removed from the penalty box and it can
be tried once again to see if it is back in service. Note this mechanism is
independent of call setup. The first SIP server will not be retried necessar-
ily when the next call is established, only when it is removed from the pen-
alty box.
Summary of Contents for HiPath 8000
Page 1: ...HiPath 8000 optiPoint 410 S V7 0 optiPoint 420 S V7 0 Administrator Manual ...
Page 114: ...Web Interface 114 Network IP and routing Network Addresses Æ page 57 ...
Page 115: ...Web Interface 115 SIP environment Configure System Information Æ page 61 ...
Page 116: ...Web Interface 116 SIP features SIP Features Æ page 64 Transfer on Ringing ...
Page 117: ...Web Interface 117 Quality of Service Quality of Service QoS Æ page 58 ...
Page 120: ...Web Interface 120 Time and date Configuring Date and Time Æ page 67 ...
Page 121: ...Web Interface 121 SNMP Use SNMP Æ page 92 Speech Change Speech Parameters Æ page 93 ...
Page 122: ...Web Interface 122 Ringer settings Configure Ringer Settings Æ page 94 ...
Page 124: ...Web Interface 124 Function keys Function Key assignments Æ page 74 ...
Page 126: ...Web Interface 126 Function key Select a function optiPoint 410 420 economy economy plus ...
Page 137: ...Web Interface 137 Address Book Address Book Æ page 162 WAP WAP Settings Æ page 81 ...
Page 141: ...Web Interface 141 RTP Statistics These parameters are used for development only ...
Page 142: ...Web Interface 142 QoS Data Collection These parameters are used for development only ...
Page 146: ...Web Interface 146 FPN Port Settings Only available in Web Interface ...