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After you install CUCM, some initial configuration has to be done before starting to deploy
endpoints. This initial configuration includes the items in Table 5-1.
Network Components
CUCM leverages various IP networking protocols and systems.
Network Time Protocol
Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer
systems over IP networks through use of a hierarchical clock strata organization. A stratum
level 1 timing source device is an extremely precise clock source using the rare earth element
cesium. Cesium clocks used to be very expensive, but most service providers with large
central offices now have local stratum level 1 clocks. Global positioning system (GPS)
satellites provide a stratum level 1 clocking source that provides a cost-effective synchronization
system.
Stratum level 1 clocks are distributed over networks to provide timing information to a large
number of devices. A linear relationship exists between the number of nodes passed and the
degradation of the timing quality.
Stratum level 2 timing sources are based on the rare earth element rubidium. Distribution
of stratum 2 time information becomes inaccurate more quickly than stratum 1 information.
Table 5-1 Publisher Server Required Services
Configuration Item Description
Network settings Basic network settings have already been configured during installation,
but some of them should be revisited (use of external NTP and DNS
servers), and network settings that are not configurable during
installation (for example, enabling DHCP services on CUCM) have
to be addressed before endpoint deployment.
Network and feature services CUCM servers run network services (automatically activated) and
feature services (activated by the administrator). After installation,
network services should be checked, and desired feature services
have to be activated.
Enterprise parameters CUCM has cluster-wide configuration settings called enterprise
parameters. After installation, enterprise parameter default values
should be verified and modified if required.
Service parameters CUCM services have configurable parameters that can usually be set
per CUCM server. After installation and service activation, service
parameter default values should be verified and modified if required.
CUCM Initial Configuration 89
Stratum level 2 timing is not as accurate as stratum level 1, but the timing is accurate enough
to time a large SONET node. SONET nodes are very high-speed networks that are used
by service providers to transport time-division multiplexing (TDM) voice calls through
networks operating at up to OC-192 speeds (almost 10 Gbp/s). T1 and T3 voice interfaces
are provisioned from SONET nodes, such as the Cisco ONS 15454.
Stratum level 3 timing sources are based on the rare earth element quartz, which has become
affordable enough that it is built in to most off-the-shelf wristwatches. Stratum level 3 is
accurate enough to time a SONET node, but it quickly loses accuracy when distributed to
other nodes. Most T3 (44.736 Mb/s) controllers have built-in oscillators with a stratum
level 3 timing source. T3 interfaces multiplex (28) individual T1 interfaces for a total of
672 voice channels.
CUCM has an option to use NTP to obtain time information from a time server. Only
the CUCM publisher will communicate with one or more NTP servers. The timing that the
publisher receives is synchronized to the subscriber servers. If an external NTP server is not
used, CUCM can be manually configured with the date and time. The system time in most
servers is a stratum level 4 timing source and should not be relied on to time a production
network.
Dynamic Host Configuration Protocol
Dynamic Host Configuration Protocol (DHCP) is a protocol that allows IP endpoints to
obtain their IP settings dynamically from a server. The most important settings include the
IP address, subnet mask, default gateway, TFTP server (option 150), and DNS server.
CUCM features a DHCP server that was designed to serve Cisco IP Phones only.
Trivial File Transfer Protocol
Trivial File Transfer Protocol (TFTP) is a simple file transfer protocol used by Cisco IP Phones
to obtain configuration files and their software (binary image load). A CUCM server has to
run the TFTP service on at least one server to be able to support Cisco IP Phones.
Domain Name System
Domain Name System (DNS) is a name-resolution protocol that allows IP applications to
refer to other systems by logical names rather than IP addresses. A CUCM cluster can be
configured to use either DNS or IP addresses.
NOTE More information on SONET, optical networking, and the ONS 15454 is
available in Cisco Self-Study: Building Cisco Metro Optical Networks (METRO), by
Dave Warren and Dennis Hartmann (Cisco Press, 2003).
90 Chapter 5: Initial Configuration Settings
NTP and DHCP Considerations
NTP can be configured during installation of the CUCM product. NTP can also be
configured after the installation procedure using the CUCM Administration web pages.
It is extremely important that all network devices have accurate time information because
the system time of CUCM is relevant in the following situations:
■ Cisco IP Phones display date and time information; this information is obtained from
CUCM unless an NTP reference is assigned to the phone. NTP references can be
configured in date/time groups in CUCM versions 5.x and later. The date/time group is
then added to Cisco IP Phone devices.
■ Call details records (CDR) provide time-stamped call reporting, analysis, and billing
information. Call management records (CMR) contain quality of service (QoS)
information regarding the quality of phone calls, including the number of lost packets
(per direction), average jitter (delay variation), and maximum jitter. CMRs are mapped
to CDRs.
■ Alarms, log files, and trace files include time stamps with millisecond-level accuracy.
One second of processing in a CUCM server can have hundreds of lines of trace output.
Troubleshooting calls that involve multiple servers frequently require the correlation of
alarm, event, and trace information available in different systems. Correlation of these
records is possible only if all devices in the network have the same date and time
information.
■ CUCM includes features that rely on date and time. These features include time-of-day
routing, certificate-based security features, and remote support.
Figure 5-1 displays a master reference clock from which the publisher server is synchronizing
time. The publisher server redistributes the timing information to the subscriber servers.
NOTE Cisco Unified Communications IP Telephony, Part 2 (Cisco Press, 2007)
explains the operation of X.509v3 certificates, certificate trust lists, IPsec, transport layer
security, and Secure Skinny Client Control Protocol (SCCPS).
CUCM Initial Configuration 91
Figure 5-1 Network Time Protocol
CUCM and all network devices should synchronize their time from a stratum level 1 NTP
server. To modify NTP configurations in CUCM, navigate to System > NTP Servers from
the CUCM Administration web pages, as shown in Figure 5-2. NTP servers can be added,
deleted, or modified.