How are phone calls routed and who is responsible for what?[snip]
Who is responsible for this routing and how does one go about protecting
> the route to your phone number.
> The point of this exercise is performance and security.
> 1. Performance
> When we get VOIP service from a supplier, how can we determine
> their ability to perform. On a simple level, we can ping their SIP
> server. Fast, consistent ping may mean good service. However we don't
> know if we just connecting to a sip server that connects to another sip
> server that may or may not have a good connection.
Since the reason for designing ARPANET was to make effective use of unreliable data links, the Internet's design is based on the idea of time-shifting, i.e., that a packet which fails on one route can be retransmitted on another without data loss. In other words, the core protocols rely on the idea of retransmission to make up for errors that occur while data is in transit from one point to another.
For this reason, _there is no specification for minimum transit time_ in the IPV4 protocol: it was designed to transport _data_ and its use for phone calls is (at best) a Kludge, because voice has only a few hundred milliseconds to make the trip from speaker to listener. Voice-over-IP only sort-of-works in an environment where there is a surplus of capacity.
Although VoIP works in most circumstances now, it's not possible to _guarantee_ performance within the IPV4 protocol per se. Users who demand "Common Carrier" grade reliability must make choices about the network (capacity, overhead, redundancy, etc.) that are almost always out of their hands.
> 2. Security
> What if our supplier goes out of business?
You'll have to switch: be careful to make sure that the end-point equipment(s) aren't proprietary to a single company before you sign a contract, or you'll be writing off the devices if the supplier goes belly-up.
How do we get our number?
Do you mean "How does VoIP interface with the PSTN?", or "How do we transfer our phone number to a different supplier?". In the first case, that's handled by the supplier and you shouldn't need to be concerned with it unless you're trying to become an CLEC. In the second, number portability usually allows for transfers of phone numbers.
How long does it take? etc etc.
How long does _what_ take? You're asking very general questions, and unless this is for a homework project, I suggest you hire some competent specialists to advise you.
HTH. YMMV.
William
(Filter noise from my address for direct replies)