Information Technology Reference
In-Depth Information
Chapter 8
Although voice signaling and media transport protocols, such as MGCP, H.323, SIP, SCCP, and RTP, are essential, other generic
infrastructure protocols, such as DNS, TFTP, NTP, and Power over Ethernet (PoE), are also required in order for a telephony network
to operate properly.
DNS, TFTP, NTP, and PoE are discussed in this chapter.
DNS
Cisco CUCM, Cisco IP phones, and other devices in a network can use DNS to resolve names to IP addresses. If the DNS server is
down or inaccessible, or if the DNS entry is incorrect, failures can occur. For example, it is possible for Cisco IP phones to use DNS
during registration, but registration will fail if they are unable to resolve the name of the CUCM.
Because DNS servers can be a point of failure in a network, it is a good idea to explicitly configure CUCM servers and other devices
to use IP addresses whenever possible. To use IP addresses instead of DNS in a CUCM cluster, navigate to
System, Server
in Cisco
CUCM Administration.
Although the use of DNS generally is not recommended for use in a Cisco CUCM environment, there are certain exceptions to this
rule. For example, if a NAT device is between Cisco IP phones and the CUCM to which they are registered, DNS is required to
ensure proper communication. Also, DNS can be used to provide disaster recovery for IP telephony in certain situations.
TFTP
Devices such as Cisco IP phones require TFTP to retrieve configuration files and other information.
