PSTN, WAN and Cable/Phone company

hendychow

Hi All,

Is there anybody could answer my questions :
1. When I read the CVOICE book, there are 2 connections that are used to make a call, which are
PSTN and WAN.
What's the difference between PSTN and WAN ?
Are they both provided by service provider ? PSTN = Phone company. WAN = ISP Company ?

2. There are some cable companies such as Comcast, Verizon, Time Warner, etc
The examples of the services that they offer are Cable TV + phone +Internet
My question is :
Are those services using Voip Technology or just Digital ?
I am still confused differentiating between Digital and Voip Technology. Please suggest.


Thank you very much


Marius

Deadmaster200

For testing purposes, keep the PSTN and the WAN as two completely separate entities. PSTN is a separate network that was built for the sole purpose of providing telephone service, WAN networks exist to provide data networking services. In reality, yes, it is all one big network. As the book itself says, major service providers have been converged for years, but they didn't really 'converge' as it just developed the way it is naturally.

As far as phone service goes, the difference between analog and digital is simply the method of transmitting human voice over a medium (copper). Analog is the old and original way, like how a microphone works. Your voice is converted into an analog signal and sent over the wire as is. Digital came along to deal with noise, distance limitations, and to enable multiplexing (which if this never happened, the PSTN would never have been able to provide the data services we are familiar with (T1 and so on). Your voice is processed by a computer so that your analog voice can be described with digital bits. That is all digital means and existed LONG before VoIP.

Also, don't get confused about the term VoIP itself. VoIP is just a subset of IP Telephony. VoIP is misused to mean IP Telephony itself. VoIP is the method of taking a traditional PSTN signal and first digitizing it, and then encapsulating that digitized voice into IP packets for use in an IP network. IP Telephony is the concept of an end-to-end packet network providing telephone service. No PSTN-to-IP conversions, no traditional phones. Requires IP phones and other IP telephony versions of PSTN equipment, like gateways, gatekeepers, Cisco Call Manager instead of PBXs and phone switches. However, this only applies to the network under your administrative control. You still have to have VoIP at the edge of the network to communicate with the outside world (at least until IP Telephony completely replaces the PSTN globally which may happen, eventually).