TELECOM Digest OnLine - Sorted: Re: Phone Call Routing

Re: Phone Call Routing

William Warren (w_warren_nonoise\
Thu, 08 Mar 2007 17:39:17 -0500

John Schmerold wrote:

> How are phone calls routed and who is responsible for what?
> 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

> 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

> 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.



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