1. A full cone NAT is one where all requests from the same internal IP address and port are mapped to the same external IP address and port. Any external host can send a packet to the internal host, by sending a packet to the mapped external address.
2. A restricted cone NAT is the same […]

Real time media protocol based on UDP for voice. Separate from SIP.
SIP establish connection and port numbers for RTP. Not necessary using the same path.
Audio Quality depends on codec. ILBC used for google talk and Gizmo, Skype.

When a SIP phone starts, it first register itself with the SIP registrar.
1. SIP phone send HTTP request to SIP registrar
2. SIP registrar send SIP phone info to a location database (ip address etc)
3. ACK SIP phone
Basic call flow:
1. Invite from a SIP phone to SIP registrar (Proxy)
2. Proxy query location database and finds target […]

SIP Express Router: Free GPL-ed SIP server (registrar, proxy, redirect)
http://iptel.org/ser/features
De-facto standard
SER: domains, subscribers
Routing language
extension modules
http://iptel.org/download

INVITE: initiates sessions
ACK
CANCEL
BYE
REGISTER
OPTIONS
SIP extension methods:
SUBSCRIBE/NOTIFY/MESSAGE: instant messaging
REFER: call transfer
PRACK: provisional reliable responses
INFO
UPDATE

SIP Phones (User-Agents)
SIP Servers (Registratar, Proxy, Redirect)
SIP PSTN Gateways
Application Servers (Media Servers)

The number of phone lines is determined by your computer’s PCI slot.
Voicent software can support unlimited phone lines. The restriction is
limited PCI slots on each computer. For large group of phone lines, you
need to consider using mulitple computers with networking. This is
our enterprise edition od BroadcastByPhone.
For your integration, you can check out more developer’s information
at […]

In order to test the product properly, you must have a campatible
voice modem that works with the software. If you can not find on at your
place, you may order one at http://www.voicent.com/store.
We ship voice modem internationally.
>
> Hi We are interested in your Broadcast by Phone as our messaging system for. But I have downloaded […]

Please see deatiled product demo, product brochure
and pricing, feature listing is at
http://voicent.com/appointment-reminder-phone.php
> I would like pricing and capacity information regarding your voice reminder
> package. Interested in using this system to remind customers of past due
> utility bills.
>
>

1. Yes, only professional/enterprise version has interactive feature.
2. Yes, you can upgrade. It is $299 to upgrade later. Upgrade
can be purchased any time at http://voicent.com/store/autodialer_upgrade.php
>
> Two Questions:
> 1. with the standard edition, can a person answering the phone use their
> phone keypad to confirm an appointment and other \’interactive\’ numbers?
> Your […]