Information Technology Reference
In-Depth Information
devices (such as a CUCM server) to pull date and time information from a Cisco router
using NTP, use the
ntp master <
stratum number
> command from global configuration
mode. For example, entering
ntp master 4
instructs the Cisco router to deliver date and
time information to requesting clients, marking it with a stratum number of 4.
Note:
Example 3-4 illustrates configuring a Cisco router to support NTP. This is neces-
sary if you are supporting a Cisco IP Telephony network using Communication Manager
Express (CME). If you were using a full CUCM solution, you'd configure NTP on the
CUCM server.
Now that the Cisco IP Phone has gone through the complete process, it is ready to register
with the call-management system (CME or CUCM). Before we discuss this final step, keep
in mind what the phone has gone through up to this point:
1.
The phone has received Power over Ethernet (PoE) from the switch.
2.
The phone has received VLAN information from switch via CDP.
3.
The phone has received IP information from the DHCP server (including Option 150).
4.
The phone has downloaded its configuration file from the TFTP server.
The Cisco IP Phone is now looking at a list of up to three call processing servers (depend-
ing on how many you have configured) that it found in the configuration file it retrieved
from the TFTP server. The phone tries to register with the first call processing server. If
that fails, it continues down the list it received from the TFTP server until the phone
makes it through all the listed call processing servers (at which point it reboots if it finds
no servers online).
If the IP phone finds an active server in the list, it goes through the registration process us-
ing either the Skinny Client Control Protocol (SCCP) or Session Initiation Protocol (SIP).
The protocol the phone uses depends on the firmware it is using. Today, most Cisco IP
Phones use the SCCP, which is Cisco proprietary. However, as the SIP protocol matures,
widespread support continues to grow. Because SIP is an industry standard, using it across
your network provides benefits such as vendor neutrality and inter-vendor operation.
Key
To p i c
Note:
The SIP standard is moving so quickly, by the time you read this, SCCP may not
be the most popular protocol for Cisco IP Telephony networks. SCCP will most likely take
its place in the proprietary protocol history topics (which contain other items, such as the
InterSwitch Link [ISL] trunking protocol and the Cisco original inline power method).
Regardless of the protocol used, the registration process is simple: The Cisco IP Phone
contacts the call processing server and identifies itself by its MAC address. The call pro-
cessing server looks at its database and sends the operating configuration to the phone.
The operating configuration is different than the settings found in the configuration XML
file located on the TFTP server. The TFTP server configuration is “base level settings,” in-
cluding items such as device language, firmware version, call processing server IP ad-
dresses, port numbers, and so on. The operating configuration contains items such as
