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1.       Plan the Deployment

·         Plan carefully and don’t rush it.  If necessary offer proof of concept testing for critical call flows

·         DDI planning – migration  planning and renumbering of legacy ISDN lines

·         Validate architecture/design

·         Design call flows for inbound, outbound, DR fail-over contingencies,

·         VoIP readiness testing

2.       Design

·         Where possible, use a gateway device rather than connecting directly to the PBX’s Ethernet adapter.  A gateway device is either:

                                                               i.      a Session Border Controller (SBC) or;

                                                             ii.      a SIP to ISDN converter

Some PBX manufacturers insist on connecting via an SBC

As a Rule of Thumb:  if fewer than 20 trunks you may connect directly to the PBX’s Ethernet port.  If more than 20 use either SIP to ISDN converter or SBC.  The SBC provides a cut-out for the PBX and delivers improved:

a.       Security

b.      Demarcation

c.       Session management

d.      Interoperability

·         Resilience:

·         Deploy multiple endpoints on;

·         Multiple bearers

·         Consider load balancing:

·         ITSP end

·         PBX end

·         Bandwidth provision
Where possible avoid transit via the public Internet – use connections that are peered with your ITSP
Be very wary of xDSL connections, even when provided as managed WAN tail circuits.  The poor reliability and consistency of xDSL technology makes it inherently unsuitable for SIP trunks except for very small deployments. 

3.       Design your VoIP deployment for security

·         Firewall

·         Firewall plus SBC/converter

·         Toll Fraud protection

·         SIP port to be used - you do not have to use 5060

·         Access control lists