Part-1
PABX to PABX interface is called Tie. A term Tie line, or it called a tie trunk or a private trunk, is a physical line that connects two or more private phone networks. This connection permits a business or other association to set up a network that makes it single for multiple locations. Tie line makes the multiple locations to virtually one location.
Different types of tie line/tie trunk are applies for PABX to PABX interface depending on PABX system type.
IP PABX to IP PABX is generally interfacing via IP trunk or SIP trunk technology. Usually IP trunk supports in same brand of PABX system. IP trunk is generally uses proprietary signalling and it supports same Brand only.
SIP trunk interface is open for all brands of SIP supported IP PABX system. SIP is a standard protocol that can connect any SIP supported system/devices.
E1/ISDN PRI is digital signalling system which is 30 channel interfaces. E1 have some different signalling system like SS7, R2MFC, CAS, PRI etc. Another type of connection is also uses in EU countries namely T1.T1 is accommodate with 23 channel. In Asian region, mostly use E1/ISDN PRI interface.
Most of the IP PABX brand supports SIP Trunk and Digital trunk interfacing and Digital PABX supports E1/ISDN PRI interface only.
Presently market is growing with IP PABX and lots of existing PABX are digital or analog or hybrid system.
In this situation how can we interface IP PABX to other legacy PABX that have no E1 or ISDN PRI interface option or unavailability of necessary card/modules/licensing.
In PART-2, we will discuss about legacy interfacing solution. By using this solution we can connect any PABX to any type of PABX with code dialling or close number dialling.