Just thought I ought to add my two cents. I come from a ‘traditional’ European based LEC. Currently we are looking to deploy VoIP in our core networks and exand that to reach the end user.
One of the main hurdles we find is QoS right down to the CPE. People will connect to our IP core network by using DSL technologies and there is no overkill in bandwidth there.
To get back to Krishna’s original question, there are a couple of other, competing technologies there. VoDSL is basicly splitting voice into different frequencies to make better use of copper in the ground (ie. more lines per copperpair), one of the major drawbacks here that this technology does not offer any integration between voice and data. VoATM, in the public networks this could offer some advantages since ATM offers QoS from the start, in the LAN environnement the main problem is that not to many people use ATM based LAN’s.
The other issue we still find is cost of QoS aware CPE to be used with VoIP services. Routers that support multiple queues and other QoS features are still very expensive, especially when the target market is SME companies (10 to 50 users).
To get back to Phone Guy’s original answer. It’s not entirely true that IP does not offer resend capabilities, TCP supports resend. UDP is the protocol used for VoIP and this one does not offer resend. In any case it would not be of any use to use resend in the VoIP application, since late packets cannot be played (imagine this). As for the variable routes that IP uses, there is a solution out there named MPLS (based on Tagswitching by Cisco), that solves this problem.
As for prices. In end-user equipment the prices vary. I’ve seen an interesting German product that starts at USD 1400 for 10 users (this includes software, 5 IP phones and 5 headsets) and just needs a PC to mimmick a PBX. We ourselves sell PBX VoIP boards starting from USD 2300 for 4 ports.
Good luck with your study.