IP-based System vs Traditional PBX

Total cost of Ownership

This depends much on the size of the organization. In small offices most VoIP
systems are little more expensive than a small PBX of key telephone systems (KTS).
In large offices it would be about the same. But adding redundancy in a VoIP
system means addition of surveys and this can make the system much expensive
them a large PBX. However, if one factors in all the additional usable features,
invariably an IP-PBX system comes out more cost effective. Additionally as the
number of users per location increases, the cost advantage dramatically tilts in
favor off IP-PBX as the incremental investments in an IP based infrastructure
are absolutely linear, as opposed to traditional PBX’s where increments are in
exponential steps. Another advantage in favor of IP-PBX, is that it is
completely standards based, and all the various components inter-operate in a
vendor independent manner. Thus not locking the user into any one vendor.

Quality of service

This depends much on the data network. The quality of VoIP voice is as good
if not better than PBX systems if the data network is well designed and not
heavily loaded. Once VoIP or IP telephony solution is installed and optimized,
end users are usually oblivious to whether or not the call is over an IP
infrastructure or over a circuit switched network. In fact, QoS is a concern on
shared networks and not in the case of managed IP networks.

Operational cost

This is where VoIP shines the most. These systems make moves, adds and
changes very simple. You can just pick up a phone and plug in anywhere on the
LAN and it automatically registers with the call servers. The server then sends
all your calls to that phone. In some systems it is possible to log on to the
network from any phone. Moves, adds and changes are one of the largest
operational expenses in a telephone network and VOIP can almost eliminate it.
Also, a converged solution means lower cost as compared to operating two
separate infrastructures.

Efficiency

If addressed from a perspective of increasing user productivity, the IP
approach is definitely more efficient as it enables new generation services like
collaboration, unified messaging, follow me anywhere, et all.

In terms of bandwidth efficiency, in case the voice on the network is
compressed, VOIP can meet, or even beat traditional systems. However, if you do
not compress it, VoIP would use 25-30% more bandwidth due to packed and
signaling overheads.

Ease of administration and manageability

Extremely user friendly and can be handled by any body due to the
availability of GUI-based interfaces for administration and management of a
standard PC platform.