SIP Trunking has many advantages over ISDN, they include:
Lower cost of access
The cost of the access component of SIP Trunking is typically significantly cheaper than the more costly ISDN services. Typically expensive individual ISDN line interfaces can be replaced by a single, (or multiple redundant) IP link (via either copper or fibre). This offers the added benefit of reducing capex and opex, as costs for an Ethernet line is dramatically lower than multiple ISDN lines, while offering significantly higher scalable bandwidth.
Lower call rates
SIP Trunking typically offers slightly lower call rates than ISDN services, on a case-by-case basis.
Convergence of voice, data and video over a common IP network provides economies of scope and scale and reduced network complexity.
Independence of Access Network
SIP Trunking is carried over IP networks, meaning that SIP Trunking is independent of the access network type. SIP Trunking can be carried over copper, fibre, or indeed over wireless access networks. Hence, SIP Trunking becomes the preferred form of carrying voice traffic over fibre networks. Implementation of SIP Trunking positions a business for transition to an all fibre access network.
Flexibility in termination
SIP Trunking enables more cost effective least-cost routing (LCR) and provides a far more effective and flexible disaster recovery option, as all voice SIP traffic can be quickly rerouted to a disaster recovery centre; a practical impossibility with ISDN.
Flexibility in dimensioning
SIP Trunking services can be dimension based on average usage rather than peak
SIP Trunking is scalable and granular on a per channel basis, allowing an increase or decrease in number of lines based on changing requirements. This can be as simple as provisioning or prioritizing a larger allocation of bandwidth to SIP out of the existing Ethernet link. Provisioning additional ISDN services, by comparison, requires change increments of 10 channels at a time, and typically requires new lines and line interfaces installed.
Enables feature-rich UC
UC services can be more efficiently delivered over SIP and can potentially federate with suppliers’ and customers’ communication systems and processes, delivering decreased business process costs.
Ref: corvit training