Moving from a legacy PABX to a modern IP-PBX offers a number of important advantages. But, when coming to install, commission and phase users across from one system to another, a number of unforeseen problems become apparent. Many people ask how to connect their VoIP gateway to ISDN

Somehow the new system needs to be interfaced to the old so calls can be passed between them. Users on one system will want to communicate with the users on the other, and in-coming/out-going calls are need by both systems. This is typically address in one of two ways:

1. Inter-connect the two systems with a virtual ISDN PRI (if both PRI "sides" of the PRI protocol are supported by the switches), or use a PABX protocol such as DPNSS or QSIG.

This solution has the advantage of inter-connectivity but the disadvantages of:

1.1 Having to add equipment and spend money on the legacy switch which is being replaced (if it will even support the additional card or cards)

1.2 Having to involve and co-ordinate the legacy PABX vendor or maintainer with the new vendor, plan the installation, arrange number-re-routing with both vendors and generally try to co-ordinate users moving with both PBX vendors. This seemingly minor task can actually become a major logistical and costly area, especially as the original vendor/maintainer has little interest in helping a move to another platform/supplier. A large amount of money and heart-ache can be spent in just this one area!

2. Because of the issues raises in the points above, many companies or System Integrators take the simple route or ordering a second PRI for the IP-PBX.

2.1 This is costly as the second PRI is only needed for the transition period

2.2 How do users on one system call users on the other? They have to make a network call ($$$s)

2.3 How can callers contact your users when they will have moved to a completely new number?

3. Moving to a new switch presents opportunities to tidy and re-structure DDI plans, perhaps changing them altogether. Managing the movement of numbers, translating numbers and making sure calls can still contact users can also be a logistic problem.

4. Some IP-PBXs do not handle data calls or non-compressable ISDN calls well. Where perhaps the legacy PABX presented BRIs to local devices such as routers, ISDN faxes etc, the IP-PBX may mean adding dedicated BRI lines from the carrier.

Liberator can help in all of these areas, and more. The low price of the Liberator systems are virtually insignificant compared to cost savings, ease of migration and customer benefits gained from its use.

Locate Liberator on the current PRI as shown below.

Benefits include:

1. Sharing the PRI between both switches
2. Routing in-coming calls to the appropriate device as users move from one to the other
3. No involvement at all required from the legacy PABX vendor maintainer
4. No additional hardware required on the legacy PBX
5. No additional PRIs needed
6. If a new DDI numbering plan is used, Liberator can convert the dialled number before passing it to the IP-PBX. For example, if a user's old DDI number on the legacy PBX was xxx987 and on the new IP-PBX it is to be xxx123, if a caller dials xxx987 Liberator will convert this to xxx123 and tell the IP-PBX it has an in-coming call for that number. This means calls will not be missed or have to be handled via an operator and the migration is seamless for customers and other callers who still have the original DDI number

Liberator can also supply local BRI ports for devices which the IP-PBX does not handle, so it still have an important role once the migration is completed.

Links to Products for this application:

Liberator "S"

• Easy to manage and reconfigure via intuitive graphical interface.
• Supports up to 3 PRIs (in this application typically one to the network, one to the legacy PBX and one to the IP-PBX).
• With or without local BRI "S" interfaces (4, 8, 12 or 16)
• Support for number translation and other features for this application
• Power-failure relay protection from network to either PABX

Liberator "DUO"

• Easy to manage and reconfigure via intuitive graphical interface (click for brief presentation)
• Supports up to 4 PRIs (in this application typically one to the network, one to the legacy PBX and one to the IP-PBX and one other).
• With or without local BRI "S" or "U" interfaces (4, 8, 12 or 16)
• Support for number translation and other features for this application
• Power-failure relay protection from network to either PABX
• Additional redundancy options

The above two products come with up to 16 BRIs plus E1/T1 PRIs. For applications requiring more ports we can either cascade Liberators or look at the DB120 chassis.

Patapsco's new PacketBand products offer a complementary way of transporting voice over IP/MPLS networks.

The PacketBand-ISDN Market Overview document gives a brief explanation and there are a number of applications in the PacketBand-ISDN and PacketBand-TDM areas.

Links to other relevant Liberator applications pages:

PRI conversion

• Convert a PRI network port to multiple BRIs with or without local PRIs

ISDN Simulator or ISDN Emulator

• Simulate BRI and/or PRI for testing, training and demonstrations

T1 to E1 ISDN Conversion

• Convert between T1 ISDN and E1 ISDN

PRI Sharing

• Share a PRI between more than one local PRI, with/without BRIs as well.

See also the drop-down menu at the top left of these pages

All Liberator products are very flexible with the option to use advanced routing, number conversion and scheduling facilities; most are remotely upgradeable via ISDN; relay-protection is available between key interfaces; all are managed by a common, simple and intuitive Manager; all are simple to install and configure.

Thousands of Patapsco products are installed in Carrier and Corporate networks across the world.

In summary, Liberator can make your migration immeasurably smooth for you, your users and callers.

If you would like to know more about this application or to discuss your questions or requirements, please use our on-line help and chat facility in the top banner or contact us.