7960 IP Phone Connections
Internet
1601
Router
3524 In-Line
Power Switch
Network Printer
IP Phone Server CallManager
Many network infrastructures today only have one category-5 cable running to
each desktop location.While there are a variety of reasons why two or more cables
are never connected to each desktop, Cisco answered this issue with the release of
the 7960 phone as shown in Figure 10.10.This is also why the previously mentioned
network assessment is so critical to the success of any VoIP project.With
only one cable installed, it must function correctly 100 percent of the time.
Even though this sample installation doesn’t use VLANs, the 3524 switch and
the phone tags each voice packet with the proper Type of Service (TOS) in the
header of each voice packet.This ensures the switch and router properly recognize
and process the packet for what it is, and don’t treat it as a pure data packet. Make
sure you connect the proper cables to the proper ports, each is labeled as such.
Because the phones are powered by the 3524 switch, the phone will try to
initialize and boot up as soon as it is plugged into the network.The bootup operation
is simple, but takes a few minutes to complete. In the first step of the process,
the phone completes the physical connection to the inline power switch.
The switch then sends a low voltage transmission down the wire to the phone,
and the phone responds to the increased voltage by completing the return path
back to the switch.The switch sees this as an acceptance of the increased voltage,
and so ups the voltage again by a small increment.The phone again accepts this
increase, and the process continues until the proper line voltage is present to
power the phone. If this end device were a normal data device, such as a laptop,
the computer’s network adapter would not respond to the initial increase in
voltage, informing the switch that a standard data device was now connected.
The phone attempts to get an IP address via DHCP (which has the pertinent
settings) so the phone knows how to communicate across the network. One of
these settings denotes where to find the TFTP server, which contains the boot
file for the phone. Once the phone downloads its configuration file, which is
stored on the CCM, it now knows how to contact the CCM for the rest of its
configuration settings.Anytime the phone is disconnected and reconnected, the
phone repeats this process.The IP phone is now registered with CCM, and will
show up in the device listing whenever you add a new phone to CCM.
Complete the rest of the physical phone installations, and you’re ready for the
next step: creating the basic dial plan and adding users.
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