As an IT
manager, interworking between Legacy and New telephony
technologies is one of the top priorities on your agenda.
This includes everything from mission critical applications
like 911/ Emergency Calling to basic applications like
number dialing and Call setup. Most legacy telecom networks
like ISDN or POTS support a feature called Overlap Dialing.
This means the user can pick up his phone and dial digits
afterwards, which are then sent out to the network one by
one.
On the
other hand, Native SIP is designed to use en-block
signaling. En-block signaling consists of sending the
complete number of the dialed party (callee) in the first
signaling message. This is fine for networks with fixed
numbering plans and other en-block network environments like
cellular networks or native SIP clients such as IP-Phones.
However there is a significant challenge when it comes to
interworking with the legacy ISDN or POTS networks. So how
do you solve this problem?
Here�s
where a Patton VoIP gateway comes to your rescue in
interconnecting and interworking these two worlds. One of
the primary functions of a VoIP gateway is handling
PSTN/POTS overlap dialing in a way to properly adapt it to
SIP. Patton VoIP gateways implement this solution in two
ways:
1.
Digit
collection
Through
the most flexible call-router configuration on SmartNodes,
the overlap signaling can be converted into SIP en-block
signaling by using advanced number analysis and timers.
Basically the SmartNode starts a timer after each received
digit. If the timer expires, the SmartNode knows that the
number is complete and sends the call to the SIP network. To
avoid the delay of the timer, a termination character like
the # key can be used. For countries with fix number-plans
like Switzerland, advanced dial-plan patterns can be
configured to determine when the numbers are complete. The
picture below shows an example of the digit- collection
timer approach:
2.
SIP overlap dialing
For
countries with open dial-plans, where number pattern
matching is not possible, the conversion of overlap to
en-bloc signaling sometimes results in unacceptable
(multiple seconds) call setup delays to human users. Or the
users are not willing to accept the use of the termination
characters.
To solve
this problem, SmartWare supports SIP overlap dialing
according to standard RFC3578. Using this feature, it is now
possible to provide end to end overlap signaling as known
from the legacy networks.
The
picture below shows an example of SIP overlap dialing.
Due to
the flexibility of SmartWare, both approaches can be
combined as well. To minimize the overhead on the SIP
network, the SmartNode pattern matcher can first collect
some digits like the city codes before the first SIP invite
is sent out.
The SIP
overlap feature is available on all SmartWare releases of
5.3 and later. It is successfully tested and fully
compatible with the Thomson/Cirpack MultiNode B Soft-Switch
and The Aarenet Aareswitch 3.8.
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