I’ve written my last couple of blogs on ISDN vs. SIP and Open Source vs. Proprietary PBX’s. Now I would like to conclude this subject with why Hospitals really should implement the SIP protocol on their PBX rather than remain with their legacy PBX, which could be TDM, or even the earlier signaling protocol H.323.
I would like to go over a couple of problems I have seen in the industry with utilizing these legacy PBX’s. The largest complaint on legacy PBX’s, especially the ones with TDM interfaces, is the lack of bearer channels. Every time you want to increase your capacity, you will need to add another T1 card, which of course only adds 23 more bearer channels, or 24 if you have the capability of running a shared d-channel as in a NFAS configuration. A second common problem is the display name being sent over the TDM trunk via the ISDN protocol. Some ISDN protocols use Information Elements (I.E) in the ISDN Setup Message while others may use Facility Messages to send the Calling Name. Sometimes, if supported at all, this configuration can be cumbersome. A third problem also seen, especially in a Tandem PBX, is the lack of the ability to sometimes send the actual calling number or perform any digit manipulation.
With a SIP PBX, especially Open Source, all of these problems can be easily resolved. There is no 23 bearer channel limitation. If you want the ability to place more calls, you just have to make sure you have the appropriate hardware such as memory and CPU power. As for the Calling Name, it can be taken from the Display Info in the SIP Header. This is pretty much automatic, really little to no configuration. Digit manipulation and the calling number are simple with SIP. The calling number is generally sent in the host part of the SIP from header. The calling number can also be obtained easily from what is referred to as a P-Assert or Remote Party-ID.
As for H.323, it really is an end of life protocol, still used somewhat in the public sector, but not much use in the private sector. Although closer than SIP in relation to ISDN signaling, there is little development being done with it today.
So in conclusion, choose SIP for your hospital.