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 as a full cone NAT except an external host can send a packet to the internal host only if the internal host had previously sent a packet to the external host IP address.

3. A port restricted cone NAT is like a restricted cone NAT, but the restriction includes port numbers. (extenal host IP address and port number)

4. A symmetric NAT is one where all requests from the same internal IP address and port, to a specific destination IP address and port, are mapped to the same external IP address and port. If the same host sends a packet with the same source address and port, but to a different destination, a different mapping is used. Furthermore, only the external host that receives a packet can send a UDP packet back to the internal host.

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 phone location
3. Proxy notify target SIP phone
4. Target SIP phone replies to Proxy, Proxy to inviting SIP phone
5. Inviting SIP phone ACK target SIP phone (connected)

Key Components:

1. SIP Phone (User agent)
2. SIP Server (registrar, proxy)
3. PSTN gateway
4. App servers (media server, etc)

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)

Voicent provides inbound and outbound development platform for
developers with telephony technology tools to create your
own application based on Voicent SDK.

For outboand applications, you can develop applications by integrate
with BroadcastByPhone and AutoReminder web interface or command line
interface. You may also develop applications directly based on
Voicent Gateway and SDK. For inbound applications, you can use
Voicent IVR studio and Telephony CRM to customize your specific
business needs. Helpful documentation are offered on-line,
within developer’s tutorial, inside the program help menu.
The integration tutorial is available at: http://www.voicent.com/devnet

For learning and experiment purpose, you can download our
free version of Voicent Gateway and all of the applications
including AutoReminder, BroadcastByPhone, Agent Dialer, Telephony CRM
and IVR studio at http://www.voicent.com/download.
You can learn how to develop your own telephony software
with Voicent Gateway technology like VoiceXML, text
to speech and more.

If you would like to purchase Voicent gateway SDK, inbound license
or outbound license, you may do so at http://www.voicent.com/store

We look forward to work with you. We stand behind you in
every step of your development effort to make your
application a successful product.

For complete detailed information,
please visit http://www.voicent.com

>
> As a notification system linked to a Voip platform…would like to speak with
> you we have partner in the health care industry that we maybe able to
> intergrate with a solution for medical staff…

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 http://www.voicent.com/devnet for commandline interface.

> We are looking for a solution to send Alert Emergency messages through our
> Application. We are looking for a hosted solution that we can connect to
> through an API.
> I am wondering how many lines would you have available at any given moment to
> send those messages! And what is the best solution for our alert service.
>

The modem have two RJ-11 phone jacks: One is “LINE” jack. The other is
“PHONE” jack. The “LINE” jack connects to the phone line for outbound call.
The “PHONE” jack connects to a phone as inbound call. For
more information on setup voice modem, see FAQ #6 at http://voicent.com/support

The license is unlimit time. You can transfer the license from computer
to computer. For details on how to transfer license, please see
FAQ #8 at http://voicent.com/support

Also, feel free to download and try the software before you buy
to see how it suites your need at http://www.voicent.com/download

> I have a phone line, goes into my modem, I do not understand where the
> phone comes into play, is my only oppourtunty through a head set through
> my computer or how do I set it up so that I can use it though the phone?
> Finally, if I was to purchase the licencing, and was to change computers
> can I un install the program and licence another machine? How long do I
> have the rights for this licencing, is it unlimited?
>

Yes we do have reseller’s program you can sign up for. To sign up, please
see http://voicent.com/affiliate/reseller.html

> We sell document imaging software to doctors offices amoung other types of
> compaines. I was wondering if you had any reseller discounts as I would be
> interested in reselling your appointment reminder app.
>
>