asterisk users - Mar 2006 - Creating a voip network... use asterisk?

I wish to create a voip phone system used by different people accross 
the internet.
I want certain people dotted around the country to be able to connect 
via voip to our main office.
At first this will be using software phones but could extend to hardware 
based phones if it works well.
I would like to run an asterisk server and connect everybody to this 
server from around the country.
This could then connect to the PSTN network via ISDN in the future but 
initially I just want ourselves using internal calls on the voip network.
Would this concept work?
Is there a better way to do this?
Would SIP be the protocol to use to connect remote users to our VOIP 
asterisk server? Would SER be a better alternative?

            Client
               |
Client---------> The Internet--->----Asterisk Server <------Client
               |                                          |
            Client                                PSTN Network


Any help would be most appreiciated.
Thanks

Mark Hayward wrote:
> I wish to create a voip phone system used by different people accross 
> the internet.
> I want certain people dotted around the country to be able to connect 
> via voip to our main office.
> At first this will be using software phones but could extend to hardware 
> based phones if it works well.
> I would like to run an asterisk server and connect everybody to this 
> server from around the country.
> This could then connect to the PSTN network via ISDN in the future but 
> initially I just want ourselves using internal calls on the voip network.
> Would this concept work?
> Is there a better way to do this?
> Would SIP be the protocol to use to connect remote users to our VOIP 
> asterisk server? Would SER be a better alternative?
> 
>            Client
>               |
> Client---------> The Internet--->----Asterisk Server <------Client
>               |                                          |
>            Client                                PSTN Network
> 
> 
> Any help would be most appreiciated.
> Thanks
> 
>
Yes, this would work, asterisk would do this and more.  I would do it like
this.  Give the roaming users SIP phones.  On the Asterisk server setup
these users profiles in sip.conf with
host=dynamic
since they would be roaming around.  Now, does the Asterisk server have a
static or dynamic ip, or is it behind a nat?  If static ip, then in the
users sip phones put in the ip of Asterisk, and evert time they start up
the phone it will register on asterisk.  If asterisk is behind a nat, put
nat=yes in users profiles in sip.conf, and maybe do port forwarding on the
gateway/firewall.  If dynamic ip like adsl, use no-ip.com.
Then on the Asterisk server you assign extensions to these roaming users,
and also assign numbers that can phone for the guys in the office.  If you
put in a ISDN card, you just put in this route/extension in Asterisk.

Anything I missed?


-- 
thanks,
yusuf