Fire-Lite IPDACT-2UD Technical Reference - Manual (Page 7)

IPDACT-UD - Introduction
I-4
Doc.DM385-I
Rev. 2.0
VisorALARM, to which it will now try and send the alarms, polls, etc. In
cases where communication with this second device also fails, the telephone
line access is returned to the control panel as if the IPDACT-UD was not
present. From this point on, the IPDACT-UD will try to re-establish
communications both with the main Teldat VisorALARM and the backup,
communication with the main device taking priority. The moment
communications are reestablished with either of the two ARC devices, the
IPDACT-UD intercepts the telephone line once more.
The supervision traffic is encrypted UDP. The Ethernet frame size does not
exceed 70 bytes. The monitoring interval, the number of retries and time
between retries are all configurable, and are values that must be carefully
considered. Normally the monitoring interval in the control panel is high as
this implies a telephone call. However, in the case of IPDACT-UD, this cost is
irrelevant as it is dealing with traffic which in all likeliness is running over a flat
rate connection. In addition, a high value here is not advisable in cases where
the IPDACT-UD connects to Internet through a router executing NAT, a very
probable situation. This is because traffic coming from the ARC towards the
IPDACT-UD reaches this thanks to the router maintaining the entry in the NAT
table active during a period of time, the entry being refreshed with supervision
traffic. If the supervision interval is greater than the residence time for the
entry in the NAT table, communications from the ARC will not be possible.
There is no rule to say how long an entry in the NAT table must last for. In
cases of the TELDAT devices, this is around 5 minutes. A low value has the
problem that the traffic the VisorALARM must process is high, the same as
the bandwidth requirements. If ARC Internet access is ADSL, you need to
consider that the upstream channel is smaller than the downstream one and
that supervision traffic returned to the IPDACT-UDs is slighter larger than the
incoming.
The incoming traffic to the ARC is:
mips ALIVE KEEP
N T C * * 528
−
=
The minimum supervision time can be 1 second and a VisorALARM can have
3000 IPDACT-UDs registered that give an input traffic of 1,58 Mbps. The
return traffic is approximately 6% larger.
The Teldat VisorALARM received monitoring messages from the IPDACT-
UDs. If these are registered, they are assumed alive and an
acknowledgement response is sent to them; if the IPDACT-UDs are not
registered, they are ignored. Periodically the status of all the registered
IPDACT-UDs is checked and all those which have not notified their availability
(i.e. those which have not responded since the last check) an alarm is
generated. This is a 350 code alarm from the Contact-ID protocol
(Communication trouble) which is received in SwAut.
In order to prevent the Teldat VisorALARM from sending hundreds or
thousands of communication failure alarms when faced with a situation of
general failure of IP traffic reception, the device itself monitors the network