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)

We have customers using Vonage.
With Voicent software, you can set call interval so the dialer will not
continuously using the phone line. This seems to satify some phone
company’s unlimited calling plan.
> I am doing the research and set up for a friend in the home loan business. We
> are intent on trying your dialer software and […]