The Gateway Configuration
If calls cannot be placed both internal and external to the site, your best and
quickest troubleshooting method is using debug commands in the gateway.We’ll
get into these issues much deeper in the troubleshooting section.
With CCM and the gateway now communicating, we’ll next need to tell
CCM what hardware to use to reach off-net calls. Our earliest example uses the
2621 router with one NM-2V module, and two FXO cards to supply four ports
of analog POTS lines.You’ll need to configure each FXO port in the gateway to
choose the order in which the lines will be used, the type of port, and if the port
is to be used at all.You can activate and deactivate each line as needed should a
port go bad, or perhaps is being tested by the telco office.
In the dial plan section of CCM, we must state how the number strings are
to be treated.We selected the PreAT feature and used the string 9@ to reach an
outside line, while denoting nothing for an inside connection. PreAT means we
must dial a 9 to get an outside line (to use the gateway’s MGCP services), stripping
off the numbers before the @ when the call is completed. In this example,
the only thing to strip off is the 9 to get an outside line, since you’d not want to
transmit the 9 to the local telco as part of the dialing string. Such custom dialing
strings can be used to choose a particular long distance carrier and force long
distance calls to take a specific path as the preferred route.
Next, we need to make sure the DHCP server on the network functions and
is properly configured to support the IP phones. DHCP is one of the few services
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Figure 10.10 The Gateway Configuration
Designing and Implementing Single Site Solutions • Chapter 10 359
CCM operates, but we already have a DHCP server running on the same subnet.
This allows us to provide DHCP services to the client computers and remain
independent of the CCM itself. Also, all CCM servers must have an entry in the
DNS server for this site. One important change to the DHCP configuration,
however, is to specify the usage of a Trivial FTP (TFTP) server for the IP phones
in order to download their firmware configuration.This configuration is stored
on the CCM server who’s IP address is used as the TFTP server in the DHCP
configuration.
With both DHCP and DNS servers properly configured, we next have to
physically install the phones. For the purpose of this discussion, we’ll presume
that the installation is on a small site without VLANs.We’ll also use the Model
7960 IP phone, the most popular business class phone in use today.This model is
actually a three-port Fast Ethernet switch. One port is an internal only switch
port (used by the phone’s electronic controls), the second is the inbound connection
coming from the 3524 switch, and the third port goes to the desktop computer
(as shown in Figure 10.11).