Page 126 - Asterisk™: The Future of Telephony

The following configuration should get you connected with an Internet Telephony
*
Service Provider (ITSP), although it is impossible to know the unique configurations
each service provider will require from you, and ideally the provider will give you the
configuration required to connect your system with its own. However, not all are going
to support Asterisk, so we’re going to provide you with a generic configuration which
should help you get on your way and, ideally, going in a matter of minutes:

[my_service_provider]
type=peer
host=10.251.55.100
fromuser=my_unique_id
secret=my_special_secret
context=incoming_calls
dtmfmode=rfc2833
disallow=all
allow=gsm
allow=ulaw
deny=0.0.0.0/0
permit=10.251.55.100/32
insecure=invite

Configuring a Local Firewall

If you’re running iptables on the same machine as the Asterisk box, then you can run
the following commands to open port 5060 for SIP signaling, and ports 10,000 through
20,000 for the RTP traffic. You can also narrow the range of RTP ports in the rtp.conf
file located in /etc/asterisk. An excellent book on iptables firewalls is Linux Firewalls by
Steve Suehring and Robert Ziegler (Novell Press).
# iptables -I RH-Firewall-1-INPUT -p udp --dport 5060 -j ACCEPT
# iptables -I RH-Firewall-1-INPUT -p udp --dport 10000:20000 -j ACCEPT
# service iptables save
Be aware that this will allow all UDP traffic from any source access to ports 5060 and
10,000 through 20,000.

Most of the previous configuration may be familiar to you by now, but in case it’s not,
here is a brief rundown.
By defining the type as a peer, we are telling Asterisk not to match on the [my_serv
ice_provider] name, but rather to match on the IP address in the INVITE message
(when the provider is sending us a call). The host parameter is the IP address that we’ll
place our calls to, and the IP address we’ll be matching on when receiving a call from
the provider.

# Be sure to check the policy of any service provider you are looking to connect with, as some of them may not
allow you to use a PBX system with its service.
* Also known as a VoIP Service Provider (VSP).

98 | Chapter 4: Initial Configuration of Asterisk