2N PRI Gateways - User Manual - Manual (Page 10)

8
Example of call cost reduction with using of PRIGW with Thin VoIP card
- BlueTower with Thin VoIP card you handle with 2xPRI ISDN interfaces, 4xVoIP-SIP
interface and up to 4xGSM interface.
Selection of GSM module use – the PRIGW allows you to select one of three available
ways of GSM module occupation: 1. Any outgoing call is set up via a GSM module according to
the B channel used. This option helps transfer routing functions to a connected PBX router. 2.
This mode allows to occupy GSM modules in groups cyclically, and 3. the last option helps
select GSM modules in a group according to the number of minutes called (the counting mode
can be predefined of course).
GSM network friendly – the PRIGW allows activating the automatic GSM module log-out
in certain time intervals. Using this function you can log out and disable automatically unused
GSM modules at defined time intervals. Since the time between the GSM module activation and
readiness for work is roughly 10-25 seconds, a user-defined hot reserve is maintained, i.e.
some GSM modules keep logged in. This means that any increase in the 2N PRIGW load result
in an automatic activation of other GSM modules so that the hot reserve be maintained. This
feature also reduces the capacity of the GSM network to detect a unit and disconnect it from the
mains.
High connection rate – since GSM networks are not quite reliable and show lack of
capacity occasionally, the PRIGW is equipped with the automatic call forwarding to other GSM
networks or call rejection (without call loss). This function uses the ISDN signaling protocol
where a call SETUP message is sent to the PRIGW first. This message contains the called
number and CLIP if necessary. Having received this message, the 2N PRIGW can either: reject
the call (the other party will route it to another device), REJECT message including reasoning
(CAUSE), or receive and connect the call – SETUP.ACK message.
The device on the other side awaits one of the above mentioned responses for 2 seconds.
During this time, PRIGW has to decide whether it is able to set up the call, tries to find a free
GSM module and establish connection. If the selected GSM module is busy, it must find other
free GSM modules. If it fails to find a free route, it rejects the call request. The CAUSE number
is user-defined. If it succeeds, it receives and sets up the call.
A (Madrid)
PBX
A (Paris)
PBX
Company A
Headquaters
(Prague)
SIP
proxy
BlueTower
BlueTower
BlueTower
ISDN
PRI
ISDN
PRI
ISDN
PRI
GSM
networks
GSM
networks
GSM
networks
PSTN
network
PSTN
network
PSTN
network
ISDN
PRI
ISDN
PRI
SPAIN FRANCE
CZECH REP.
Internet